PATICE interactive map

In this interactive map, you can explore all the glacial landforms and chronologies that were used to generate the new reconstructions of the last Patagonian Ice Sheet from 35,000 years ago to the present day.

Click the PATICE logo below to launch the online interactive webmap.

The GIF below shows the extent of the ice sheet in 5000 year timeslices. The colours around the margin show where we have high, medium and low confidence in where we have placed the margin.

The image below shows the evidence used to create the reconstruction. You can explore this data yourself using our interactive map that uses ArcGIS Online.

Using the PATICE interactive map

To open the interactive map, click here.

To zoom into a specific area, press shift and draw a box with your mouse. You can also scroll with your mouse, and use the zoom in/out buttons in the top left corner.

The icons in the top left allow you to interact with the map. You can view the legend and the layer list, and zoom in and out. The left/right arrows go to the previous or next extent (the spatial extent of the map viewed).

ArcGIS Online Tools

In the Layer List, you can toggle visibility of layers on and off, view the attribute information, and view the metadata (click on the three dots to the right of each layer).

Clicking on a feature will bring up a popup with the attribute information and some explanatory information.

Click on a feature to bring up a popup with more information.

You may also be interested in our interactive map of the glacial landforms of Britain during the Younger Dryas!

PATICE

PATICE: The Patagonian Ice Sheet from 35,000 years ago to the present day

PATICE logo

This page provides a brand-new reconstruction of the Patagonian Ice Sheet from 35,000 years ago to the present day (called PATICE).

PATICE is a new compilation of published ages and geomorphology, ranked and assessed and recalibrated, which we use to generate new empirical reconstructions of the ice sheet and its ice-dammed palaeolakes.

Citation: Davies et al., 2020. The Evolution of the Patagonian Ice Sheet from 35 ka to the Present Day (PATICE). Earth-Science Reviews. 

You can explore the PATICE data in the ArcGIS online interactive online map (no ArcGIS licence needed).

Resources

All the data used in the new PATICE reconstruction has been made available fully open-access, and the paper is available as gold open access.

Below, there is more information about our map and database.

PATICE reconstruction

The Patagonian Ice Sheet formed during the last glaciation along the Andean mountain chain. It blocked the drainage of rivers to the Pacific, so large lakes formed in front of the ice margin as it receded. You can watch the ice sheet separate out into its different parts and the lakes draining and changing through time in the GIF below.

PATICE reconstruction, 35,000 years ago to the present day

The Patagonian Icefields

Patagonia, in southernmost South America, is a region with accelerating glacier recession1,2. Glaciers here are shrinking rapidly, which is enlarging glacial lakes, increasing flood risk3 and causing sea level rise4.

The Southern Andes region lost 1,208 billion tonnes of glacier ice from 1961 to 20165, contributing 0.92 ± 039 mm per year to global sea level rise (27 mm from 1961 to 2016).

Today, there are four main icefields. The Northern Patagonian Icefield (46.4°S to 47.5°S), the Southern Patagonian Icefield (48.3°S to 52°S), the Gran Campo Nevado (52.8°S) and the Cordilleran Darwin Icefield (54.5°S)6.

The glaciers and icefields of Patagonia. Copyright J. Bendle

The region also has numerous small glaciers and icefields, often centred on volcanoes. The lowest latitude Southern Hemisphere glacier that reaches the ocean is found in the Northern Patagonian Icefield (Glaciar San Rafael).

In total, the present-day icefields and glaciers cover a total area of 22,718 km2, equating to a sea level equivalent of 15.1 mm7. These glaciers are all rapidly receding, as you can see in the GIF below.

Recession of the North Patagonian Icefield, AD 1870 (Little Ice Age) to 2011.

Reconstructing past glacier change in Patagonia

We can use the past record of ice sheet behavior to understand how these glaciers interact with climate, and to better predict how they might behave in the future.

Patagonia has a rich record of glacial geomorphology that can help us to understand how glaciers might behave in the future8. In this study, we created a new GIS database of published glacial geomorphology and published ages to reconstruct the extent of the ice sheet from 35,000 years ago to the present day, in 5000-year time slices.

Patagonian piedmont lobes in the Chilean Lake District. Moraine geomorphology by Glasser and Jansson (2008) and PATICE.

We also reconstructed the evolution of ice-dammed lakes. As the glacier ice shrank back, large and deep lakes formed in front of the ice margin. These lakes existed until the glacier ice shrank back past a col or spillway, allowing the lake to drain. These lakes may have been a key influence on the glaciers, as deep water would have encouraged the calving of icebergs.

Ice dammed lakes form when the normal drainage is blocked by glaciers.

The past behavior of the Patagonian Ice Sheet during different climate states and during rapid climate transitions could shed insights into ways in which the region is sensitive to changes and how it could respond to future change. The southern mid-latitudes are a particularly data-sparse region of the globe, and reconstructions of the Patagonian Ice Sheet provides a unique insight into the past terrestrial glacial and climatic change.

Last Glacial Maximum

The Patagonian Ice Sheet was centred on the central mountain chain of the Andes, and stretched from 38° to 56°S. During glacial maxima, the icefields coalesced to form a single large ice mass9,10.

Its eastern margin comprised fast-flowing lobes of ice that extended out into the Argentinian steppe landscape, the largest fastest of which were ice streams. The western margin reached the continental shelf in the Pacific Ocean.

The Local Last Glacial Maximum occurred at 33,000 to 28,000 years ago from 38°S to 48°S, and earlier, at around 47,000 years ago from 48°S southwards.

PATICE Reconstruction of the Patagonian Ice Sheet at the Local Last Glacial Maximum (35,000 years ago)

At its maximum extent, the Patagonian Ice Sheet covered 492,600 km2, with a sea level equivalent of 1,496 mm (the sea level amount locked up in the ice sheet). It was 350 km long and 2090 km wide.

It was comparable in size to the Antarctic Peninsula Ice Sheet today. For comparison, Sweden is 450,295 km2 and the UK is 242,495 km2.

Comparison of the Patagonian Ice Sheet at 35,000 years ago and the Antarctic Peninsula Ice Sheet today. Both maps are to the same scale.

After the Last Glacial Maximum

The Patagonian Ice Sheet began to retreat and shrink by 25,000 years ago. The ice sheet stabilized and formed large moraines during the period 21,000 to 18,000 years ago, which was then followed by rapid deglaciation, especially between 18,000 and 15,000 years.

By 15,000 years ago, the Patagonian Ice Sheet had separated into several disparate ice masses, draining into large ice-dammed lakes along its eastern margin. These lakes probably encouraged the calving of icebergs, and facilitated rapid melting.

Glacial readvances or stabilisations occurred at least at 14,000 to 13,000 years ago, 11,000 years ago, 6000 to 5000 years ago, 2000 to 1000 years ago, and 500 to 200 years ago.

Glacier lakes

On the eastern side of the Andes, the moraines from these glacier outlet lobes often mark the present-day continental watershed drainage divide. Today, many of the glacial lakes of Patagonia drain westwards, into the Pacific Ocean. The Patagonian Ice Sheet dammed this drainage route, forcing higher lake levels and drainage to the Atlantic Ocean.

During glacier recession, a series of large proglacial lakes formed along the eastern margin, dammed between the ice sheet and higher ground or moraines11–15. As the ice sheet receded, continental scale drainage reversals occurred14,16,17.

In the GIF above, you can see the glacial lakes forming as the ice sheet retreats back towards the high ground of the Andes. By about 10,000 years ago, most lakes have either drained completely or dropped to their current levels.

Evolution of glaciers and lakes from 16,000 years ago to 5,000 years ago around the Northern Patagonian Icefield. The glacier lakes (pink) change as the ice dams recede past particular cols or spillways.

This figure shows how the ice dammed glacial lakes evolved as the glacier ice receded. As the glaciers shrank, new cols and spillways became available, resulting in the lakes dropping to a new level.

Rates of recession

The Patagonian Ice Sheet was relatively stable from 35,000 to 30,000 years ago. Recession from the Local Last Glacial Maximum began by 25,000 years ago, predating the global Last Glacial Maximum. This may be because the Patagonian Ice Sheet was smaller and more dynamic than the larger global ice sheets.

Very rapid recession and widespread deglaciation began after 18,000 years ago, during a period of rapid warming highlighted in the Antarctic ice cores18 and rapid global sea level rise. It may also have been driven by a southwards shift in the Southern Westerly Winds.

The Patagonian Ice Sheet probably contributed ~615 mm to global sea level rise between 20,000 and 15,000 years ago, when it shrank from 359,600 to 121,800 km2.

Glaciers stabilized or re-advanced during the Antarctic Cold Reversal, but the Patagonian Ice Sheet was much smaller at this time (116,700 km2).

Accelerating rates of glacier recession

Rates of recession of the Patagonian Ice Sheet form 35,000 years ago to the present day

Rates of recession were slow through the Holocene until the last few decades (with the caveat that some time periods are highly uncertain). Absolute recession rates (km2 per year; km2 a-1) over recent decades rival those seem between 20,000 and 15,000 years ago for an ice sheet that was more than two orders of magnitude larger.

Relative rates of recession (percentage change per year; % a-1) are higher between 200 years ago and 2011 AD than at any time observed in our reconstruction. It is likely that there were periods of time with especially rapid recession during the last glacial-interglacial transition, when many outlet lobes were calving into large, ice-dammed lakes, but our compilation is unable to capture this.

There are fewer degrees of freedom for ice extent and volume changes during the Holocene (last 10,000 years). Ice margins stabilized not far from present-day positions by the Early Holocene, and dated moraines suggest that readvances were similar to the advance at 200 years ago in size.

Thus we can argue that average rates of ice-marginal recession are currently faster than at any time observed in the Holocene, in line with the recent temperature changes observed in Antarctica and Patagonia, following a sustained period of relative stability, and when glacial lake area remains fairly constant.

Since observations indicate that rates of recession have accelerated in Patagonia over recent decades, from 34.2 km2 a-1 (0.14 % a-1) for 1986 to 2001 AD to 51.2 km2 a-1 (0.22 % a-1) for 2001-2011 AD6, this is especially concerning.

Ice-dammed palaeolakes

Glacial lake area peaked at 13,000 years ago, with an estimated area of 13,999 km2. These large lakes would have accelerated glacial recession at this time by encouraging the outlet glacial lobes to calve icebergs.

Glacial lake area minimum was reached by about 10,000 years ago. Rapid recession from 13,000 to 10,000 years ago led to many cols and spillways opening, and the lakes reached their current spatial extent and volume by about 10,000 years ago.

As the ice dams receded, this cold, fresh water may have been released suddenly into the Pacific Ocean, possibly affecting regional climate14,16.

The remaining lake water today, from lakes that were in the footprint of the palaeolakes, is 6,824 km2. Overall, between the maximum lake extent at 13,000 years ago and today, there has been a reduction in lake area of 7,176 km2.

Area of glacial lakes for each time slice (ka: thousands of years ago)

How was the reconstruction made?

There is a large volume of published ages and glacial geomorphology that help us to reconstruct the past ice sheet extent and dynamics in Patagonia. The geomorphological data provide information on former ice sheet margins, ice-dammed palaeolake evolution, and ice-flow direction. Our new GIS database includes 58,823 landforms and 1,669 published ages.

Published ages and geomorphology used in PATICE

Glacial Geomorphology

Landforms were mapped from satellite images and digital elevation models, most commonly LANDSAT 7 and LANDSAT 8 images, as well as high resolution satellite imagery available in Google Earth.

Our compilation includes moraines, trimlines, glacial lineations (bedrock and sedimentary drumlins or flutes), meltwater palaeochannels, outwash plains, shorelines, deltas and cirques. Our compiled maps also show related topographic landforms such as rivers, lakes and volcanoes.

Numbers of different landforms used in PATICE

In total, we mapped 58,823 landforms, including 25,009 moraines, 2,507 shorelines, 3,926 lineations, 4,309 empty cirques and 4,536 palaeochannels.

Moraines and trimlines give us information about former ice sheet margins, whilst lineations and the pattern of moraines tells us about ice-flow direction. Cirques tell us about regions that were previously glaciated, but now are ice-free. Palaeochannels, outwash plains, shorelines and deltas give us information on ice-dammed palaeolakes.

There is more information on Patagonian Glacial Geomorphology here.  In the view below, you can use Google Earth to explore Patagonian moraines around the North Patagonian Icefield. The arcuate ridges denote the position of the former ice margin.

In general, there are four distinct temperate glacial landsystems in Patagonia.

  1. An upland glacier landsystem, with an assemblage of cirques, lateral and terminal moraines, mountain glaciers and snow patches, flutes, and lakes;
  2. In the lowlands, a land-terminating glacial landsystem, with moraine arcs, outwash plains, meltwater channels, drumlins, and hummocky moraine;
  3. A lowlands glaciolacustrine landsystem, with deltas and shorelines, and ice-contact glaciofluvial landforms;
  4. An offshore glaciomarine landsystem, with fjords, offshore moraine ridges, drumlins, raised fluvial deltas and slope failures, and turbidity current channels.

Chronology

There are many ways to fix in time particular glacial landforms. Each technique dates something slightly differently, which makes them hard to compare directly. Our GIS database includes 1,669 ages relevant to the timing of deglaciation. Each age is scrupulously checked and recalibrated according to the latest protocols.

Number of ages used in each different dating technique

Our database includes cosmogenic nuclide exposure-age dating of boulders, ideally situated on moraines to give a time of formation for that moraine, radiocarbon dating of organic material, tephrochronology (dating of volcanic ash layers), lichenometry (measuring the size of specific species of lichens to derive an exposure age), dendrochronology (tree-ring dating), historical sources (archival maps and photographs), varve ages (annually laminated lake sediments), and optically stimulated luminescence.

Bethan Davies sampling a boulder for cosmogenic nuclide exposure age dating in Patagonia.

Each age is assessed according to our protocols and given a reliability assessment. The most reliable cosmogenic nuclide ages are used to give an average age for moraine formation.

Reconstructing the ice extent

We used the moraines, dated by various methods, to reconstruct the ice margin. At places where we were confident of the age of the moraines, we could draw short, isolated isochrones.

Secondly, we interpolated between the isochrones to reconstruct overall ice-sheet limits, using moraines and topography.

Thirdly, we provided an assessment of our degree of confidence in each ice margin, from high confidence to medium confidence and low confidence. High confidence ice limits have both well defined glacial geomorphology and a well constrained chronology.

Medium confidence ice limits are defined by geomorphology and are near to published ages, but are less well constrained.

Low confidence limits have no well-defined geomorphology, lie far from published ages, and are first interpretations that require further investigation.

Mapping ice margins and assigning levels of uncertainty. Example from the Southern Patagonian Icefield.

The PATICE Team

Authors are in alphabetical order.

Bethan J. Davies, Christopher M. Darvill, Harold Lovell, Jacob M. Bendle, Julian A. Dowdeswell, Derek Fabel, Juan-Luis García, Alessa Geiger, Neil F. Glasser, Delia M. Gheorghiu, Stephan Harrison, Andrew S. Hein, Michael R. Kaplan, Julian R.V. Martin, Monika Mendelova, Adrian Palmer, Mauri Pelto, Ángel Rodés, Esteban A. Sagredo, Rachel Smedley, John L. Smellie, Varyl R. Thorndycraft. 

References


1. Braun, M. H. et al. Constraining glacier elevation and mass changes in South America. Nat. Clim. Chang. 1 (2019).

2. Meier, W. J.-H., Grießinger, J., Hochreuther, P. & Braun, M. H. An updated multi-temporal glacier inventory for the Patagonian Andes with changes between the Little Ice Age and 2016. Front. Earth Sci. 6, 1–21 (2018).

3. Wilson, R. et al. Glacial lakes of the Central and Patagonian Andes. Glob. Planet. Change 162, 275–291 (2018).

4. Malz, P. et al. Elevation and mass changes of the Southern Patagonia Icefield derived from TanDEM-X and SRTM data. Remote Sens. 10, 188 (2018).

5. Zemp, M. et al. Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016. Nature
568, 382–386 (2019).

6.Davies, B. J. & Glasser, N. F. Accelerating shrinkage of Patagonian glaciers from the Little Ice Age (AD 1870) to 2011. J. Glaciol. 58, (2012).

7. Carrivick, J. L., Davies, B. J., James, W. H. M., Quincey, D. J. & Glasser, N. F. Distributed ice thickness and glacier volume in southern South America. Glob. Planet. Change 146, (2016).

8. Coronato, A. & Rabassa, J. Chapter 51 – Pleistocene Glaciations in Southern Patagonia and Tierra del Fuego. in Developments
in Quaternary Sciences
(eds. Jürgen Ehlers, P. L. G. & Philip, D. H.) Volume 15, 715–727 (Elsevier, 2011).

9. Caldenius, C. C. Las glaciaciones cuaternarias en la Patagonia y Tierra del Fuego. Geogr. Ann. 14, 1–164 (1932).

10. Mercer, J. H. Variations of some Patagonian glaciers since the Late-Glacial. Am. J. Sci. 266, 91–109 (1968).

11. García, J.-L., Strelin, J. A., Vega, R. M., Hall, B. L. & Stern, C. R. Deglacial ice-marginal glaciolacustrine environments and structural moraine building in Torres del Paine, Chilean southern Patagonia. Andean Geol. 42, 190–212 (2015).

12. García, J.-L., Hall, B. L., Kaplan, M. R., Vega, R. M. & Strelin, J. A. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history. Geomorphology 204, 599–616 (2014).

13. Turner, K. J., Fogwill, C. J., McCulloch, R. D. & Sugden, D. E. Deglaciation of the eastern flank of the North Patagonian Icefield and associated continental-scale lake diversions. Geogr. Ann. Ser. A, Phys. Geogr. 87, 363–374 (2005).

14. Thorndycraft, V. R. et al. Glacial lake evolution and Atlantic-Pacific drainage reversals during deglaciation of the Patagonian Ice Sheet. Quat. Sci. Rev. 203, 102–127 (2019).

15. Davies, B. J., Thorndycraft, V. R., Fabel, D. & Martin, J. R. V. Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia. Quat. Sci. Rev. 200, (2018).

16. Glasser, N. F. et al. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Sci. Rep. 6, 21064 (2016).

17. García, J.-L. et al. Early deglaciation and paleolake history of Río Cisnes Glacier, Patagonian Ice Sheet (44 S). Quat. Res. 91, 194–217 (2019).

18. Cuffey, K. M. et al. Deglacial temperature history of West Antarctica. Proc. Natl. Acad. Sci. 113, 14249–14254 (2016).

Glaciolacustrine Landforms in Patagonia, Chile

Monte San Lorenzo, the source of Calluqueo Glacier

This article summarises a recent publication by the AntarcticGlaciers.org author Bethan Davies and colleagues on glaciolacustrine sediment-landform assemblages in Chilean Patagonia:

Davies, B. J., Thorndycraft, V. R., Fabel, D. & Martin, J. R. V. Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia. Quaternary Science Reviews 200, 287-312, (2018).

Ice-dammed lakes in Patagonia | Glacial geomorphology | Glaciolacustrine landforms | Glacial landforms | Glaciolacustrine landsystems | Further reading | References | Comments |

Ice-dammed lakes in Patagonia

Following the Last Glacial Maximum in Patagonia, outlet glaciers from the Patagonian Ice Sheet (see figure below) receded1, resulting in the formation of large ice-dammed lakes that drained across Argentina to the Atlantic Ocean2,3.

The Patagonian Ice Sheet at the Last Glacial Maximum (LGM; 21,000–19,000 years ago), with extent of contemporary glaciers shown in blue. Study area is highlighted. Map by Jacob Bendle.

These ice-dammed lakes grew as the glaciers receded, and this may have affected ice-sheet dynamics by influencing calving.  These “glaciolacustrine” environments have a number of distinctive landforms, including morainal banks, deltas4, shorelines5 and push moraines.

We conducted a detailed study of the glaciolacustrine landforms near Cochrane in Chile (see Davies et al., 2018)6, using both glacial geomorphological mapping and cosmogenic nuclide dating to analyse glacial landforms and establish the manner and timing of their formation.

Physiography of the study area. Our research focused on the Salto Valley and Monte San Lorenzo ice cap, Chile. From Davies et al., 2018.

You can inspect the study area yourself, using Google Maps:

Glacial geomorphology

The Río Baker valley preserves a number of detailed glacial and glaciolacustrine landforms relating to outlet glaciers from the North Patagonian Icefield and Monte San Lorenzo.

During the last glaciation, these outlet lobes coalesced to form part of the Lago Cochrane outlet lobe at the Last Glacial Maximum. These landforms were formed later, in association with a large ice-dammed lake that occupied the Baker Valley. This ice-dammed lake had several different levels that related to different drainage pathways as glaciers receded and new cols opened up.

Our glacial geomorphological map shows the detailed landform assemblage in the area around Cochrane.

Glacial geomorphological map of the region around Cochrane, Chile. From Davies et al., 2018.

Glaciolacustrine landforms

Glacier lake shorelines

The level that had the highest geomorphic imprint in the Cochrane area is the 350 m lake. This ice-dammed lake can be traced throughout the Baker Valley, around Lago Cochrane/Pueyrredón, and into the Lago General Carrera/Buenos Aires valley. It probably drained through a 350 m col above Río Bayo, draining around the northern margin of the Northern Patagonian Icefield and into the Pacific Ocean7.  We call this lake “Lago Chalenko”.

This lake resulted in the formation of shorelines, which are eroded into glacial sediments on valley sides at a consistent elevation; 460 m north of Cochrane, and 340-350 m around Valle Grande, around the Juncal Massif and around Lago Esmeralda. The shorelines are gently valley-dipping platforms, with a flat long-profile and often with exotic and local boulders.

Sediments associated with the glacier lake include well sorted laminated silts and clays, with dropstones indicating iceberg rafting.

Varyl Thorndycraft inspecting some glaciolacustrine sediments near Cochrane.

Deltas

There are a series of perched flat-topped delta terraces (350 – 460 m) at the foot of Río Estero Elva, which currently drains into Lago Cochrane/Pueyrredón. Gilbert-type deltas such as these form when streams enter lakes 4,8-10, and form in stepped sequences upstream of modern lake deltas.

Perched deltas above the present-day lake. They have been incised by the present-day stream, with new deltas forming as the lake level lowers.

Morainal banks

Adjacent to the Esmeralda Moraines, is an asymmetric moraine closely associated with the 350 m shoreline. The moraines have a wedge shape, with a shallow ice-proximal slope and a steep ice-distal slope. The moraines reach 330 m in height, and are below the 350 m shoreline.

The Salto Moraines are at the edge of a hanging valley, perched above Valle Grande. The Salto Moraines reach heights of 350 m above sea level, and are closely associated with the 350 m shoreline, which is cut into the top of the moraines around the Juncal Massif.

The Salto Moraines. Google Earth Pro.

The Salto Moraines have a gentle ice-proximal slope, which is interrupted with numerous small recessional moraines, and a steep ice-distal slope. The steep ice-distal slope of the Salto Moraines is imprinted with shorelines and deltas, indicating lower lakes persisted in Valle Grande after Lago Chalenko drained.

The Esmeralda and Salto Moraines. From Davies et al. 2018.

These asymmetrical moraines are interpreted as ‘Morainal Banks’ formed at the grounding line of a valley glacier that terminated in Lago Chalenko.

You can view these moraines yourself, and compare the morainal bank with the Esmeralda push moraines, in Google Maps above.

Ice-contact fans

On the eastern flank of the “Juncal Massif” there is an accumulation of sediments that dips towards the valley floor.  This is interpreted as an ice-contact fan, which formed subaqueously at the grounding line of the glacier that terminated in Lago Chalenko as it receded.

Glacial landforms

Push moraines

The Esmeralda Moraines (see geomorphological map above) are classical push moraines, formed above the level of the lake. They are arcuate, sharp-crested, cross-valley ridges with a ridge crest at 360-366 m. The narrow ridge crest is only 3 m wide, and the moraine ridges are 60 m high, with symmetrical, steeply sloping sides. Inside the main moraine crest are numerous smaller moraines, interpreted as recessional moraines.

These moraines represent an advanced position of Calluqueo Glacier from Monte San Lorenzo. South of the Esmeralda Moraines are a set of recessional moraines, called the “Moraine Mounds”11, which represent a stillstand during the recession of Calluqueo Glacier.

A shoreline is cut into glacial sediments around Lago Esmeralda below the height of the Esmeralda Moraines, suggesting that the 350 m glacial lake (Lago Chalenko) flooded the valley upon recession of Calluequeo Glacier from this position.

Esmeralda Moraines and Lago Esmeralda. Left is the asymmetric morainal bank, right is the sharp-crested subaerial push moraine. From Google Earth Pro.

Lateral moraines

Numerous lateral moraines are perched on the hillsides of the Salto Valley. One moraine, field-checked at 510 m, is contiguous with the terminal Esmeralda Moraines. These moraines are sharp-crested, sloping, and wrap around the hillsides. The moraines photographed below are all above Lago Esmeralda.

Kame terraces

Directly opposite the Juncal Fan, against the other side of the Salto Valley, is an accumulation of sediments with a flat topped surface. This is interpreted as a kame terrace that formed in the gap between the glacier and the valley side, with meltwater streams washing in sediments.  The flat flop surface is equivalent to the ice surface.

Ice-scoured bedrock

Patches of ice-scoured bedrock crop out in the valley floor and on the valley sides regionally. They form well-developed bedrock lineations that are aligned along the valley long-axis. These lineations are interpreted as roche moutonnées. They form by a process of glacial abrasion and polishing as the glacier ice flows over the bedrock.

Ice sculpted bedrock around Lago Juncal. From Google Earth Pro.

Glaciolacustrine landsystems

The Cochrane region bears a distinctive assemblage of landforms, with valley glaciers terminating in a glaciolacustrine environment, forming sub-aqueous, asymmetric morainal banks and sharp-crested, terminal push moraines.

Glaciolacustrine landforms in this landsystem include deltas, palaeoshorelines and subaqueous fans. The morainal banks formed before large drops in the altitude of the valley floor, indicating that calving and lake depth were some of the main controls on glacier terminus position.

Sediments were deposited on the lake floor by turbidity currents and underflows emanating from the glacier margin in front of the morainal bank. Glaciolacustrine deposition is likely to be strongly influenced by underflows into a sediment-stratified proglacial lake. Freshwater buoyant plumes emanating from the ice margin are usually more important in glaciomarine environments.

The confined environment has led to a great diversity in sediments and landforms, with asymmetric morainal banks forming during periods of stability and ice-contact fans forming along the valley sides during periods of recession. These landforms are indicative of abundant meltwater and a high sediment flux.

Glaciolacustrine landsystem for the sediments and landforms near Cochrane. From Davies et al., 2018.

Further Reading

There are several pages on this website on the Patagonian Ice Sheet:

See also our webpages on Glacial Lakes.

References

1              Martínez, O., Coronato, A. & Rabassa, J. in Developments in Quaternary Sciences Vol. Volume 15  (eds Philip L. Gibbard Jürgen Ehlers & D. Hughes Philip)  729-734 (Elsevier, 2011).

2              Bendle, J. M., Palmer, A. P., Thorndycraft, V. R. & Matthews, I. P. High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling. Quaternary Science Reviews 177, 314-339, (2017).

3              Bendle, J. M., Thorndycraft, V. R. & Palmer, A. P. The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia. Journal of Maps 13, 654-673, (2017).

4              Bell, C. M. Quaternary lacustrine braid deltas on Lake General Carrera in southern Chile. Andean geology 36, 51-65, (2009).

5              García, J.-L., Hall, B. L., Kaplan, M. R., Vega, R. M. & Strelin, J. A. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history. Geomorphology 204, 599-616, (2014).

6              Davies, B. J., Thorndycraft, V. R., Fabel, D. & Martin, J. R. V. Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia. Quaternary Science Reviews 200, 287-312, (2018).

7              Glasser, N. F. et al. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Scientific Reports 6, 21064, (2016).

8              Longhitano, S. G. Sedimentary facies and sequence stratigraphy of coarse-grained Gilbert-type deltas within the Pliocene thrust-top Potenza Basin (Southern Apennines, Italy). Sedimentary Geology 210, 87-110, (2008).

9              Ashley, G. M. in Modern and Past Glacial Environments   (ed John Menzies)  335-359 (Butterworth-Heinemann, 2002).

10           Bell, C. Punctuated drainage of an ice-dammed Quaternary lake in Southern South America. Geografiska Annaler: Series A, Physical Geography 90, 1-17, (2008).

11           Glasser, N. F., Harrison, S., Schnabel, C., Fabel, D. & Jansson, K. N. Younger Dryas and early Holocene age glacier advances in Patagonia. Quaternary Science Reviews 58, 7-17, (2012).

Glacial geomorphology of the Patagonian Ice Sheet

This page is based largely on Bendle et al. (2017) and summarises the glacial geomorphology of the North Patagonian Icefield region (46–48°S).

Glaciers and the Patagonian landscape

The Patagonian Ice Sheet has expanded and contracted at least five times during the last million years1. During glacial periods, large outlet glaciers discharged along major valleys (see map below), moving mass from the ice-sheet interior to its margins2. These glaciers also eroded, entrained, transported, and deposited rock and sediment, moulding the landscape and creating glacial landforms.

The Patagonian Ice Sheet at the Last Glacial Maximum (LGM; 21,000–19,000 years ago) with extent of contemporary glaciers shown in blue. Copyright: J. Bendle.

Why study glacial landforms?

The sediments and landforms left behind by glaciers are window into the evolution of the Patagonian Ice Sheet through time. For example, ice-marginal landforms, such as moraines, tell us about the extent or thickness of former glaciers. Other landforms provide us with information about the conditions at glacier beds or margins. Glacial erosional landforms, for instance, give us clues about the bed temperature, hydrology, and flow behaviours of former glaciers, and hence glacier thermal regime. When combined with methods of dating glacial deposits, glacial geomorphology allows us to reconstruct former glacier behaviour.

How are glacial landforms mapped?

From ‘remotely sensed’ data

When at its maximum extent, the Patagonian Ice Sheet was very large2, with outlet glaciers of similar size to those draining the Greenland Ice Sheet today. Therefore, it would be almost impossible to map its glacial geomorphology solely on foot. To get around this problem, we use ‘remotely sensed’ imagery (i.e. information about Earth’s surface obtained from aircraft or satellite).

Glacial geomorphology of the Lago Buenos Aires basin, based on satellite image interpretation (Bendle et al., 2017). Copyright: J. Bendle.

Satellite images are useful because they cover large areas, making it possible to assess regional landform distribution quickly and efficiently (see image above)2,3,4. Digital Terrain Models are also valuable in areas of steep or undulating relief, as they provide 3D representations of Earth’s surface that may give clues about the origin of landforms. For example, while a moraine typically has a crest with two sloping sides, a lake shoreline has a flat upper surface with a single sloping side (see image below).

Hillshade model with draped Digital Elevation Model (DEM), showing moraine complexes and glacial lake shorelines (note shading on one side of feature only).

‘Virtual globe’ software, such as GoogleEarth, is also useful in landform mapping as it allows the mapper to view the landscape in 3D, and customise the angle of viewing (see image below)4. With GoogleEarth it is also possible to measure the size (e.g. length, width, area) and elevation of features very quickly and simply, which may help an accurate landform interpretation be made.

Oblique view generated using GoogleEarth software, and enabling the mapping of moraine ridges. Image: GoogleEarth. Compiled by J. Bendle.

On foot, in the field

Field mapping is used to check whether features mapped from satellite images have been correctly identified, and to identify additional landforms that are not easily recognised in satellite datasets, such as small-scale or low-relief features, or landforms that may be hidden beneath vegetation or clouds in satellite imagery3,4.

Field mapping of glacial landforms in the Lago General Carrera–Buenos Aires valley. Photo credit: V. Thorndycraft.

Ice-marginal landforms

Ice-marginal landforms were produced in abundance at the snout and sides of former Patagonian glaciers2,3,4,5, due to the dumping of debris from the ice surface, the pushing and squeezing of debris at the snout, or by the flow of meltwater.

Latero-frontal moraines

On the forelands of former glaciers, moraine ridges mark out former ice limits. In central Patagonia, these ridges reach 50 m relief and can run continuously for tens of kilometres in latero-frontal arcs (see image below)2,3,4. The overall distribution of moraines can be used to reconstruct the pattern of ice retreat (see image below)6.

Latero-frontal moraine arc marking the former limit of the Lago General Carrera–Buenos Aires outlet glacier during the Last Glacial Maximum (~21,000-19,000 years ago). Photo credit: J. Bendle.

Trimlines

Sharp lines on valley sides, known as trimlines, are common closer to the contemporary North Patagonian Icefield7. Trimlines mark the boundary between terrain that has been recently covered by ice, and terrain that has been ice free for a longer period of time. Therefore, trimlines provide information about glacier thickness change.

Valley side trimlines (labelled with white arrows) marking the former thickness of the Callequeo Glacier, Monte San Lorenzo. Note moraine ridges in the foreground. Photo credit: J. Martin.

Meltwater channels

Meltwater channels come in many varieties. Most commonly they follow the lateral margins of former glaciers3,4,8, and can be straight, sinuous, or meandering (see image below). They start and end abruptly, and rarely contain rivers in the present day. Like moraines, meltwater channels are useful for reconstructing former glacier extent.

Meltwater channels cut into the surface of outwash deposits, and dissecting moraine ridges (right). Image from: GoogleEarth.

Outwash plains

Outwash plains are surfaces of glaciofluvial sand and gravel that build up in front of a stable ice margin. They may slope gently away from a former ice margin to form an expansive plain (see image below), or can accumulate in topographic lows between moraine ridges (see image above)3,4. The vast outwash plains of Patagonia2 tell us that meltwater streams carrying high sediment loads were common around former ice margins3,4.

Outwash plain grading away from moraine ridges in the Lago Cochrane–Pueyrredón valley. Photo credit: J. Bendle.

Subglacial landforms

Subglacial landforms are produced at the bed of former glaciers and commonly relate to patterns of former ice or meltwater flow.

Eskers

Eskers are straight to sinuous ridges of glaciofluvial sand and gravel, which are formed in subglacial, englacial, or supraglacial channels. They can form single ridges (as shown in the image below) or consist of a braided network. Eskers give an indication of meltwater flow patterns within or beneath former glaciers9, which is important for ice dynamics (e.g. motion).

A sinuous esker ridge, and several smaller eskers (all shown in green), mapped from satellite imagery in the Lago Cochrane-Pueyrredón valley. Copyright: J. Bendle.

Ice-moulded bedrock

In the major valleys, the bedrock has been widely scoured or smoothed by subglacial erosion processes (see image below)4. This suggests that the outlet glaciers that once overrode this terrain were (at least sometimes) warm-based, fast-flowing, and carrying a significant basal debris load10.

Glacially-smoothed bedrock outcrops in the Ibañez valley, Chile. Photo credit: J. Bendle.

In some areas, the bedrock has been moulded into very long, linear ridges called glacial lineations (see image below). When mapped at a regional-scale, these landforms reveal the flow pathways of former outlet glaciers (see map below)4.

Glacial lineations formed in bedrock south of the Lago Cochrane-Pueyrredón. Image: GoogleEarth. Compiled by J. Bendle.

Map of glacial lineations (red lines) formed at the bed of the Lago General Carrera-Buenos Aires and Lago Cochrane-Pueyrredón outlet glaciers. Interpretation of glacier flow direction is shown by dashed lines. Copyright: J. Bendle.

Drumlins

Drumlins are streamlined hills formed under moving glacier ice11. They are elongated in the direction of ice flow. Like glacial lineations, therefore, they can be used to reconstruct glacier dynamics. Their length may also be related to ice velocity12, with more elongated drumlins formed under faster flowing ice. While not that common around the Northern Patagonian Icefield (see image below), drumlin swarms occur more widely around the Southern Patagonian Icefield, and across Tierra del Fuego3,13.

Drumlin swarm in the Lago Cochrane-Pueyrredón valley. Ice flow from left to right. Image from: GoogleEarth.

Glaciolacustrine landforms

These landform types are produced in association with glacial lakes, which were common around the Patagonian Ice Sheet margin14,15.

Glacial lake shorelines

Shorelines are long, continuous terraces with flat surfaces that mark the level of a former glacial lake. Around Lago General Carrera–Buenos Aires, extensive ‘flights’ of shorelines are seen (see image below) and reflect changing lake level through time4,14,15.

Top: Relict glacial lake shorelines above the present-day Lago General Carrera-Buenos Aires, marking the level of a former glacial lake. Photo credit: J. Bendle. Bottom: GoogleEarth image showing a flight of former lake shorelines.

Raised deltas

Raised deltas are flat-topped accumulations of sand, gravel, and cobbles (see image below). They mark the point at which rivers entered former glacial lakes and deposited their sediment load. Like shorelines, therefore, they provide an indication of glacial lake level14.

Raised lacustrine delta approximately 100 m above the modern Lago General Carrera-Buenos Aires, marking the level of a former glacial lake. Photo credit: J. Bendle.

What does the pattern of landforms tell us?

The geomorphology of the North Patagonian Icefield region indicates that (1) when outlet glaciers reached their maximum extent they remained stable on flat plains, forming large moraines and outwash plains. Subglacial landforms (e.g. glacial lineations) suggest that (2) the glaciers were (at least sometimes) fast-flowing and warm-based. The presence of shorelines and raised deltas show that (3) large proglacial lakes developed around the retreating ice margins during deglaciation.

References

[1] Coronato, A. & Rabassa, J. 2011. Pleistocene glaciations in Southern Patagonia and Tierra del Fuego. In Ehlers, L., Gibbard, P.L., Hughes, P.D. (Eds.) Developments in Quaternary Sciences, 15, Elsevier. pp. 715–727.

[2] Glasser, N.F., Jansson, K.N., Harrison, S. & Kleman, J. 2008. The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S. Quaternary Science Reviews, 27, 365–390.

[3] Darvill, C.M., Stokes, C.R., Bentley, M.J. & Lovell, H. 2014. A glacial geomorphological map of the southernmost ice lobes of Patagonia: the Bahía Inútil–San Sebastián, Magellan, Otway, Skyring and Río Gallegos lobes. Journal of Maps, 10, 500–520.

[4] Bendle, J.M., Thorndycraft, V.T. & Palmer, A.P., 2017. The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia. Journal of Maps, 13, 654–673.

[5] García, J.L., Hall, B.L., Kaplan, M.R., Vega, R.M. & Strelin, J.A. 2014. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history. Geomorphology, 204, 599–616.

[6] Darvill, C.M., Stokes, C.R., Bentley, M.J., Evans, D.J. & Lovell, H., 2017. Dynamics of former ice lobes of the southernmost Patagonian Ice Sheet based on a glacial landsystems approach. Journal of Quaternary Science, 32, 857–876.

[7] Glasser, N.F., Harrison, S. & Jansson, K.N., 2009. Topographic controls on glacier sediment–landform associations around the temperate North Patagonian Icefield. Quaternary Science Reviews, 28, 2817–2832.

[8] Bentley, M.J., Sugden, D.E., Hulton, N.R. and McCulloch, R.D., 2005. The landforms and pattern of deglaciation in the Strait of Magellan and Bahía Inútil, southernmost South America. Geografiska Annaler: Series A, Physical Geography, 87, 313–333.

[9] Storrar, R.D., Evans, D.J., Stokes, C.R. & Ewertowski, M., 2015. Controls on the location, morphology and evolution of complex esker systems at decadal timescales, Breiðamerkurjökull, southeast Iceland. Earth Surface Processes and Landforms, 40, 1421–1438.

[10] Glasser, N.F. & Jansson, K.N. 2005. Fast-flowing outlet glaciers of the last glacial maximum Patagonian Icefield. Quaternary Research, 63, 206–211.

[11] Stokes, C.R., Spagnolo, M. and Clark, C.D., 2011. The composition and internal structure of drumlins: complexity, commonality, and implications for a unifying theory of their formation. Earth-Science Reviews, 107, 398-422.

[12] Stokes, C.R. & Clark, C.D., 2002. Are long subglacial bedforms indicative of fast ice flow?. Boreas, 31, 239-249.

[13] Lovell, H., Stokes, C.R., Bentley, M.J. & Benn, D.I. 2012. Evidence for rapid ice flow and proglacial lake evolution around the central Strait of Magellan region, southernmost Patagonia. Journal of Quaternary Science, 27, 625–638.

[14] Glasser, N.F., Jansson, K.N., Duller, G.A., Singarayer, J., Holloway, M. & Harrison, S. 2016. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Scientific Reports, 6. 21064.

[15] Bendle, J.M., Palmer, A.P., Thorndycraft, V.R. and Matthews, I.P., 2017. High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling. Quaternary Science Reviews, 177, 314–339.

The Patagonian Icefields today

Geographic setting

Patagonia, between ~40°S to 56°S, is the most southerly part of the South American continent. The landscape of this region is one of contrasts. Dense temperate rainforests cover the western coast, whereas the eastern plains are flat, vast, and arid. Perhaps most striking, however, are the high, Patagonian Andes, which rise steeply (up to around 4000 m asl) above deeply carved glacial fjords and valleys, and are home to the Patagonian Icefields.

The rugged, and densely vegetated west coast of Patagonia (Pacific fjords in distance). The high, ice-covered Andes are shown in the foreground. Photo: Miguel Vieira Wikimedia Commons.

Climate of Patagonia

Patagonia is one of the windiest and wettest places on Earth. The region has a temperate maritime climate, with a strong west-east precipitation gradient as a result of the year-round passage of westerly winds over the Patagonian Andes(1,2). On the west coast, annual precipitation reaches up to 7,500 mm year, whereas less than 1,500 mm a year falls east of the icefields(3,4). The snowfall brought by the westerly winds are the main source of accumulation for the glaciers of this region.

Windswept Nothofagus Antarctica tree, Ushuaia, Tierra del Fuego, Patagonia, Argentina. Photo: Leonardo Pallotta, Wikimedia Commons.

The Patagonian Icefields

While the Patagonian Andes are home to hundreds of small caps and valley glaciers(5,6,7,8), most ice is locked up in three large icefields, called the North, South, and Cordillera Darwin Icefields (see map below). Together, these icefields contain around 5,500 gigatons of ice, enough to raise global sea level by around 15 mm if completely melted(9).

The three major Patagonian Icefields, which occur south of ~46°S, are the largest expanse of ice in the Southern Hemisphere outside Antarctica(10). While large, today’s icefields are the remnants of a much larger Patagonian Ice Sheet, which formed during the global LGM around 21,000 years ago.

The icefields and glaciers of Patagonia. Major outlet glaciers are labelled. Glacier outlines from Pfeffer et al. (2014). Copyright J. Bendle

Dynamic outlet glaciers

Outlet glaciers of the Patagonian Icefields are fed by heavy snowfall (up to 10,000 mm per year) in the accumulation area, and have high melt rates at lower elevations. As a result, they have high mass balance gradients and are very dynamic(10), especially on the western coast snowfall is highest(11).

Heavy cloud cover and snowfall over Monte San Valentín (4058 m asl) in the accumulation zone of the North Patagonian Icefield. Photo: Murray Foubister Wikimedia Commons.

North Patagonian Icefield

Size, elevation, and structure

The North Patagonian Icefield (NPI) stretches over 100 km from 46°30’S to 47°30’S (see map above). Its current size is estimated at ~3,700 km2(8,12).

The NPI is drained by 29 main outlet glaciers (>10 km2), with glacial tongues that terminate in different settings(7). 11 (38%) outlet glaciers terminate on land, 17 (59%) terminate in lakes (e.g. Glacier Exploradores), and only one (3%), Glacier San Rafael, terminates in the sea.

The average elevation of NPI glaciers is around 400 m lower on the western side of the icefield (1240 m asl) than on the east (1640 m asl), reflecting the higher rates of snowfall in the west(8).

The North Patagonian Icefield seen from space. Image: NASA.

Glacier Flow speeds

The fastest-flowing glacier of the NPI is Glacier San Rafael (NASA Fig). This glacier is flowing at 7.6 km per year (around 20 metres per day11). In total, three NPI glaciers flow faster than 1 km per year (San Rafael, San Quintín, and Colonia11).

Outlet glacier flow speeds calculated from satellite imagery. The fastest-moving glaciers (shown by green and yellow colours) terminate in the Pacific Ocean fjords and embayments, or in large glacial lakes (e.g. Glacier Upsala). Image: NASA (based on data from Mouginot and Rignot, 2015)

South Patagonian Icefield

Size, elevation, and structure

The South Patagonian Icefield (SPI) is the largest of the South American icefields. It stretches over 350 km from 48°20’S to 51°30’S, and its current size is estimated at ~12,200 km2 (around three times larger than the NPI8).

The SPI is drained by 53 main outlet glaciers (>10 km2) that are generally larger than those of the NPI. The SPI has a similar amount of lake-terminating glaciers (59%), but more (17 or 32%) marine-terminating glaciers(7).

The South Patagonian Icefield seen from space. Image: NASA

Glacier Flow speeds

The SPI also has some of the fastest flowing glaciers in the world (see glacier flow speed diagram above). Of the ten fastest SPI outlet glaciers, which all move faster than 2.5 km per year, eight flow out into Pacific Ocean fjords (e.g. the Jorge Montt glacier shown below) and two into large glacial lakes (e.g. Glacier Upsala). The fastest, Glacier Penguin, flows at 10.3 km per year (around 28 metres per day11). These data suggest that ocean heat plays an important role in melting at glacier fronts, and rapidly drawing down ice from the SPI interior.

The Jorge Montt outlet glacier of the Southern Patagonian Icefield, flowing out into a Pacific Ocean fjord that is choked with icebergs. Image: NASA.

The Upsala outlet glacier of the Southern Patagonian Icefield, flowing into a iceberg filled proglacial lake (Lago Argentino). Image: NASA

Cordillera Darwin Icefield

Size, elevation, and structure

The Cordillera Darwin Icefield (CDI) is the smallest (~2600 km2), and southernmost of Patagonia’s icefields(13), existing between 54°40’S to 55°00’S. It is also the least studied. Most CDI glaciers descend to sea level, and many flow into the Pacific Ocean(8).

Glacier Flow speeds

Most CDI outlet glaciers have flow speeds of between 1 and 3 metres per day(13). However, the marine-terminating Marinelli Glacier (the largest and fastest moving of the CDI glaciers) and Darwin Glacier, flow much faster, at around 8-10 metres per day(13).

The Cordillera Darwin Icefield seen from space. Image: NASA

Glacier change

Most glaciers of the Patagonian Icefields are experiencing negative mass balance, as a result of glacier thinning and the widespread retreat of ice-fronts(5,11,14). Only Glacier Pío XI (the largest glacier in South America) from the South Patagonian Icefield has grown in recent years(15,16). The overall pattern of ice loss make the Patagonian Icefields one of the largest current sources of global sea level rise (they contribute ~10% of that from all glaciers and ice caps worldwide17,18).

Since the Little Ice Age

Since the end of the Little Ice Age at around 1870 AD, over 90% of Patagonian outlet glaciers have shrunk(5,8,19) (see GIF below). Reconstructions of Little Ice Age glacier extents(19) show that the North Patagonian Icefield has lost around 103 ± 20.7 km3 of ice, and the South Patagonian Icefield around 503 ± 101.1 km3. This gradual melting of the icefields has contributed around 0.0018 mm to global seal level rise per year (or 0.27 mm in total) since 1870 AD(19).

Retreat of the North Patagonian Icefield between 1870 AD (the end of the Little Ice Age) to 2011.

Over the 21st century

During the last 40-50 years, however, the rate of Patagonian ice loss has sped up substantially. Between 1975 and 2000, the North and South Patagonian Icefields have lost a combined 15.0 ± 0.7 gigatons of ice per year(17). Between 2000 and 2011, the rate of ice loss increased further to 24.4 ± 1.4 gigatons per year(20,21), and has since remained similar (between 2011 and 2017 the icefields lost 21.29 ± 1.98 gigatons per year16).

Retreat of the HPS-12 outlet glacier of the Southern Patagonian Icefield between 1985 and 2017. The glacier terminus has retreated approximately 13 km in the last 30 years. Images from NASA. Compiled by: J. Bendle

Contribution to rising sea level

The current contribution of the Patagonian Icefields to global sea level rise is around 0.067 ± 0.004 mm per year(21), over one order of magnitude greater than the long-term contribution since the Little Ice Age(19). The rate of glacier melting is expected to continue, and maybe even increase, in coming decades(22).

Causes of icefield retreat: a warming atmosphere

The rapid melting of the Patagonian Icefields during the 21st century has several possible causes. For example, a warming atmosphere has resulted in a greater number of warm ‘summer’ days each year, and more melting at the glacier surface(23). At 50°S, for example, a warming of 0.5°C between 1960 to 1999 has resulted in a 0.5 m water equivalent increase in annual glacier melt in the ablation area(24).

Less snowfall, more rainfall

The amount of snowfall falling over the Patagonian Icefields decreased by around 5% between 1960 and 1999, whereas the amount of rainfall increased, both as a result of warmer air temperatures(24). Alongside faster surface melting, therefore, the amount of annual accumulation is getting smaller, preventing glacier growth.

Continued warming in Patagonia, therefore, will have a major impact on glacier accumulation and ablation trends(25), and will ultimately dictate the fate of the Patagonian Icefields.

References

[1] Garreaud, R.D., Vuille, M., Compagnucci, R. and Marengo, J., 2009. Present-day South American climate. Palaeogeography, Palaeoclimatology, Palaeoecology281, 180-195.

[2] Garreaud, R., Lopez, P., Minvielle, M. and Rojas, M., 2013. Large-scale control on the Patagonian climate. Journal of Climate26, 215-230.

[3] Carrasco, J.F., Casassa, G. and Rivera, A., 2002. Meteorological and climatological aspects of the Southern Patagonia Icefield. In The Patagonian Icefields (pp. 29-41). Springer, Boston, MA.

[4] Schneider, C., Glaser, M., Kilian, R., Santana, A., Butorovic, N. and Casassa, G., 2003. Weather observations across the southern Andes at 53°S. Physical Geography2, 97-119.

[5] Davies, B.J. and Glasser, N.F., 2012. Accelerating shrinkage of Patagonian glaciers from the Little Ice Age (~AD 1870) to 2011. Journal of Glaciology58, 1063-1084.

[6] Falaschi, D., Bravo, C., Masiokas, M., Villalba, R. and Rivera, A., 2013. First glacier inventory and recent changes in glacier area in the Monte San Lorenzo Region (47 S), Southern Patagonian Andes, South America. Arctic, Antarctic, and Alpine Research45, 19-28.

[7] Pfeffer, W.T., Arendt, A.A., Bliss, A., Bolch, T., Cogley, J.G., Gardner, A.S., Hagen, J.O., Hock, R., Kaser, G., Kienholz, C. and Miles, E.S., 2014. The Randolph Glacier Inventory: a globally complete inventory of glaciers. Journal of Glaciology60, 537-552.

[8] Meier, W.J-H., Grießinger, J., Hochreuther, P. and Braun, M.H., 2018. An updated multi-temporal glacier inventory for the Patagonian Andes with changes between the Little Ice Age and 2016. Frontiers in Earth Science, 6, 62.

[9] Carrivick, J.L., Davies, B.J., James, W.H., Quincey, D.J. and Glasser, N.F., 2016. Distributed ice thickness and glacier volume in southern South America. Global and Planetary Change146, 122-132.

[10] Warren, C.R. and Sugden, D.E., 1993. The Patagonian icefields: a glaciological review. Arctic and Alpine Research25, 316-331.

[11] Mouginot, J. and Rignot, E., 2015. Ice motion of the Patagonian icefields of South America: 1984–2014. Geophysical Research Letters42, 441-1449.

[12] Dussaillant, I., Berthier, E. and Brun, F., 2018. Geodetic Mass Balance of the Northern Patagonian Icefield from 2000 to 2012 using two independent methods. Frontiers in Earth Science6, 8.

[13] Melkonian, A.K., Willis, M.J., Pritchard, M.E., Rivera, A., Bown, F. and Bernstein, S.A., 2013. Satellite-derived volume loss rates and glacier speeds for the Cordillera Darwin Icefield, Chile. The Cryosphere7, 823-839.

[14] Rivera, A., Benham, T., Casassa, G., Bamber, J. and Dowdeswell, J.A., 2007. Ice elevation and areal changes of glaciers from the Northern Patagonia Icefield, Chile. Global and Planetary Change59, 126-137.

[15] Schaefer, M., Machguth, H., Falvey, M., Casassa, G. and Rignot, E., 2015. Quantifying mass balance processes on the Southern Patagonia Icefield. The Cryosphere, 9, 25-35.

[16] Foresta, L., Gourmelen, N., Weissgerber, F., Nienow, P., Williams, J.J., Shepherd, A., Drinkwater, M.R. and Plummer, S., 2018. Heterogeneous and rapid ice loss over the Patagonian Ice Fields revealed by CryoSat-2 swath radar altimetry. Remote Sensing of Environment211, 441-455.

[17] Rignot, E., Rivera, A. and Casassa, G., 2003. Contribution of the Patagonia Icefields of South America to sea level rise. Science302, 434-437.

[18] Gardner, A.S., Moholdt, G., Cogley, J.G., Wouters, B., Arendt, A.A., Wahr, J., Berthier, E., Hock, R., Pfeffer, W.T., Kaser, G. and Ligtenberg, S.R., 2013. A reconciled estimate of glacier contributions to sea level rise: 2003 to 2009. Science340, 852-857.

[19] Glasser, N.F., Harrison, S., Jansson, K.N., Anderson, K. and Cowley, A., 2011. Global sea-level contribution from the Patagonian Icefields since the Little Ice Age maximum. Nature Geoscience4, 303-307.

[20] Willis, M.J., Melkonian, A.K., Pritchard, M.E. and Ramage, J.M., 2012. Ice loss rates at the Northern Patagonian Icefield derived using a decade of satellite remote sensing. Remote Sensing of Environment117, 184-198.

[21] Willis, M.J., Melkonian, A.K., Pritchard, M.E. and Rivera, A., 2012. Ice loss from the Southern Patagonian ice field, South America, between 2000 and 2012. Geophysical Research Letters39. L17501.

[22] IPCC, 2013. The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, UK.

[23] Monahan, P.A. and Ramage, J., 2010. AMSR-E melt patterns on the Southern Patagonia Icefield. Journal of Glaciology56, 699-708.

[24] Rasmussen, L.A., Conway, H. and Raymond, C.F., 2007. Influence of upper air conditions on the Patagonia icefields. Global and Planetary Change59, 203-216.

[25] Schaefer, M., Machguth, H., Falvey, M. and Casassa, G., 2013. Modelling past and future surface mass balance of the Northern Patagonia Icefield. Journal of Geophysical Research: Earth Surface118, 571-588.

The westerly winds and the Patagonian Ice Sheet

The moisture-bearing Southern Westerly Winds

The Patagonian Ice Sheet, which formed during the Last Glacial Maximum (LGM) around 21,000 years ago, was strongly influenced by the Southern Westerly Winds. These winds blow around the Southern Hemisphere in the mid-latitudes (see map below) and deliver snow and rain to the western coast of southern South America[1], sustaining glaciers.

These strong winds also control the location of major ocean fronts (the boundary between water masses of different temperature) in the Southern Ocean and, as a result, the temperature of waters at the ocean surface[2,3].

Windswept Nothofagus antarctica tree, Ushuaia, Tierra del Fuego, Patagonia, Argentina. By Leonardo Pallotta, Wikimedia Commons.

Reconstructing past changes in the southern westerlies

As Patagonia covers a large latitudinal transect, extending from 40°S to 56°S, it is a critical region for investigating how the Southern Westerly Winds, and other climate systems, have changed over the last 21,000 years, and how these changes affected Patagonian glaciers.

Map of the Southern Hemisphere showing the Southern Westerly Wind belt (SWW) and Subtropical Front (STF) in the present day. The westerlies bring rain and snowfall to the west coast of Patagonia. The Subtropical Front sits at the northern limit of the westerly wind belt. Figure copyright Jacob Bendle.

Southward wind shifts driving glacier recession

Following the end of the Last Glacial Maximum (LGM) the Southern Westerly Winds abruptly shifted southward towards Antarctica[4,5], and pulled the warm Subtropical Front with them[2,3] (see left-hand side of diagram below). Records of former glacier extent show that the Patagonian Ice Sheet began to rapidly retreat and thin at about the same time (~18,000 years ago[6,7,8]), suggesting that as the winds moved south, the amount of snowfall feeding the ice sheet decreased.

The wind-driven shift of the Subtropical Front caused the coastal waters around Patagonia to warm[2]. With less accumulation (snowfall) and warmer temperatures, the Patagonian Ice Sheet started to retreat.

Diagram showing how the location of the Southern Westerly Winds (SWW) and Subtropical Front (STF) impact the mid-latitudes. Left: When the westerly winds and Subtropical Front contract (move south) cool, moist air stops flowing over Patagonia, and warm waters enter the mid-latitude oceans. This favours glacier retreat. Right: When the westerly winds and Subtropical Front expand (move north) strong winds bring precipitation to Patagonia, and cold Southern Ocean waters cool the mid-latitude oceans. This favours glacier advance. Figure copyright Jacob Bendle.

Northward wind shifts driving glacier advance

Whereas the southward shift of the Southern Westerly Winds triggered Patagonian Ice Sheet retreat at ~18,000 years ago, a northward wind shift between ~14,500 and 12,800 years ago, in the Antarctic Cold Reversal (a cool period recorded in Antarctic ice cores), revived glacier activity[9,10,11,12].

As the westerly winds moved north over Patagonia (see right-hand side of diagram above), increased snowfall led to glacier growth. Because the winds also pulled cool Southern Ocean waters into the mid-latitudes, ocean and air temperatures around Patagonia cooled, leading to less ice sheet melting. The combination of increased accumulation (snowfall) and decreased ablation (melting) led to glacier readvance.

Hemisphere-wide glacier response

Glaciers in the Southern Alps of New Zealand also readvanced in the Antarctic Cold Reversal, at the same time as glaciers in Patagonia[13]. This suggests that the shift in the position of the the westerly winds and ocean fronts were a major driver of climate and ice sheet behaviour across the entire mid-latitude belt below ~40°S.

SWW controls on climate

The Southern Westerly Wind system controls the climate of the Southern Hemisphere in other ways, and these are important for modern and past glaciers.

For example, when the westerlies move towards Antarctica, the warm waters they drag southwards causes the sea-ice around Antarctica to break up and retreat[14]. This causes the ocean around Antarctica to warm, and releases heat to the atmosphere.

Also, when the westerly winds are positioned over the Southern Ocean, they cause relatively warm water that is trapped at depth to rise to the ocean surface. This releases heat and CO2 from the ocean, and causes atmospheric warming[15].

Further reading

References

1. Garreaud, R.D., Vuille, M., Compagnucci, R. & Marengo, J. 2009. Present-day South American climate. Palaeogeography, Palaeoclimatology, Palaeoecology, 281, 180–195.

2. Lamy, F., Kaiser, J., Arz, H.W., Hebbeln, D., Ninnemann, U., Timm, O., Timmermann, A. & Toggweiler, J.R. 2007. Modulation of the bipolar seesaw in the Southeast Pacific during Termination 1. Earth and Planetary Science Letters, 259, 400–413.

3. Barker, S., Diz, P., Vautravers, M.J., Pike, J., Knorr, G., Hall, I.R. & Broecker, W.S. 2009. Interhemispheric Atlantic seesaw response during the last deglaciation. Nature, 457, 1097–1102.

4. Denton, G.H., Anderson, R.F., Toggweiler, J.R., Edwards, R.L., Schaefer, J.M. & Putnam, A.E. 2010. The last glacial termination. Science, 328, 1652–1656.

5. Moreno, P.I., Villa-Martínez, R., Cárdenas, M.L.& Sagredo, E.A. 2012. Deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from SW Patagonia (52°S). Quaternary Science Reviews, 41, 1–21.

6. Boex, J., Fogwill, C., Harrison, S., Glasser, N., Hein, A., Schnabel, C. & Xu, S. 2013. Rapid thinning of the Late Pleistocene Patagonian Ice Sheet followed migration of the Southern Westerlies. Scientific Reports 3, 2118.

7. Moreno, P.I., Denton, G.H., Moreno, H., Lowell, T.V., Putnam, A.E. & Kaplan, M.R. 2015. Radiocarbon chronology of the last glacial maximum and its termination in northwestern Patagonia. Quaternary Science Reviews, 122, 233–249.

8. Bendle, J.M., Palmer, A.P., Thorndycraft, V.R. and Matthews, I.P., 2019. Phased Patagonian Ice Sheet response to Southern Hemisphere atmospheric and oceanic warming between 18 and 17 ka. Scientific Reports, 9,.

9.  Moreno, P.I., Kaplan, M.R., François, J.P., Villa-Martínez, R., Moy, C.M., Stern, C.R. and Kubik, P.W., 2009. Renewed glacial activity during the Antarctic cold reversal and persistence of cold conditions until 11.5 ka in southwestern Patagonia. Geology, 37(4), 375-378.

10. García, J.L., Kaplan, M.R., Hall, B.L., Schaefer, J.M., Vega, R.M., Schwartz, R. and Finkel, R., 2012. Glacier expansion in southern Patagonia throughout the Antarctic cold reversal. Geology, 40, 859-862.

11.  Sagredo, E.A., Kaplan, M.R., Araya, P.S., Lowell, T.V., Aravena, J.C., Moreno, P.I., Kelly, M.A. and Schaefer, J.M., 2018. Trans-pacific glacial response to the Antarctic Cold Reversal in the southern mid-latitudes. Quaternary Science Reviews, 188, 160-166.

12. Davies, B.J., Thorndycraft, V.R., Fabel, D. and Martin, J.R.V., 2018. Asynchronous glacier dynamics during the Antarctic Cold Reversal in central Patagonia. Quaternary Science Reviews, 200, 287-312.

13. Putnam, A.E., Denton, G.H., Schaefer, J.M., Barrell, D.J., Andersen, B.G., Finkel, R.C., Schwartz, R., Doughty, A.M., Kaplan, M.R. and Schlüchter, C., 2010. Glacier advance in southern middle-latitudes during the Antarctic Cold Reversal. Nature Geoscience, 3, 700-704.

14. Pedro, J.B., Jochum, M., Buizert, C., He, F., Barker, S. and Rasmussen, S.O., 2018. Beyond the bipolar seesaw: Toward a process understanding of interhemispheric coupling. Quaternary Science Reviews, 192, 27-46.

15. Toggweiler, J.R., Russell, J.L. and Carson, S.R., 2006. Midlatitude westerlies, atmospheric CO2, and climate change during the ice ages. Paleoceanography, 21(2).

Patagonian Ice Sheet at the LGM

What was the former Patagonian Ice Sheet?

The Patagonian Ice Sheet was a large, elongated mountain ice mass that developed over the Andes mountains of southern South America during cold periods[1]. The Patagonian Ice Sheet has advanced and retreated at least 5 times in the last million years[2] in response to changes in global climate (i.e. cooling and warming).

What evidence is there for this former mountain ice sheet?

The evidence for past glaciations of the Patagonian Ice Sheet is preserved in the landscape in the form of landforms (such as moraines) and sediments (such as fine-grained lake sediments and coarse, poorly sorted glacial sediments). The great quantity and variety of glacial landforms in Patagonia[3] make the record of Patagonian Ice Sheet activity one of the longest and most complete anywhere in the world[4].

Map of the Patagonian Ice Sheet at the Last Glacial Maximum around 21,000 years ago. The modern North (NPI), South (SPI), and Cordillera Darwin (CDI) Icefields, and other smaller mountain glaciers, are shown in light blue for comparison.

Last Glacial Maximum (21,000 years ago)

During the global Last Glacial Maximum (LGM) around 21,000 years ago, the Patagonian Ice Sheet almost completely submerged the Patagonian Andes between around 38 to 56°S[1]. In length, the distance between the most northern and southern tips of the ice sheet was around 2000 km (see map above).

How big was the Patagonian Ice Sheet?

Computer simulations estimate that, when at its largest, the Patagonian Ice Sheet had a volume of ~525,000 km3[5]. However, as climate warmed after the LGM, the Patagonian Ice Sheet rapidly thinned and retreated[6,7,8,9]. In all, the ice sheet shrank by ~500,000 km3 in ~8-9000 years, and contributed ~1.2 m to global sea level[5].

Ice sheets at the Last Glacial Maximum worldwide, around 27,000 to 21,000 years ago

What is left of the Patagonian Ice Sheet?

Today, small remnants of the Patagonian Ice Sheet exist in the form of three main mountain icefields, these are: the Northern Patagonian Icefield (NPI; shown in the GIF below), Southern Patagonian Icefield (SPI), and the Cordillera Darwin Icefield (CDI). These ice masses are currently rapidly retreating under the influence of global warming.

Recession of the North Patagonian Icefield, AD 1870 (Little Ice Age) to 2011.

The structure of the former Patagonian Ice Sheet

The Patagonian Ice Sheet was divided into two main parts: a western part and an eastern part that spread out from a central ice-divide along the Andean mountains (see map at top of page). The Patagonian Ice Sheet was drained by at least 66 major outlet glaciers[1]. These outlet glaciers transported ice from the interior parts of the ice sheet to the margins and, in doing so, they controlled the overall form of the ice sheet[1].

But rather than simply flowing east or west from the main ice-divide, these outlet glaciers were strongly influenced by topography (see the arrows showing former ice flow directions in the diagram below), being funnelled through a complicated network of bedrock valleys[10,11].

Outlet glacier flow pathways around the NPI at the Last Glacial Maximum (red line). Glaciers flowed along bedrock valleys (dashed lines) and fed into large, fast-flowing outlet glaciers (solid lines) that filled the widest and deepest troughs.

Pacific Ocean fjords

On the west side of the ice sheet, most outlet glaciers flowed into Pacific Ocean fjords (see the present-day example in the satellite image below). We cannot currently be sure how far these outlet glaciers advanced, because the seafloor has not yet been explored for glacial landforms.

However, computer simulations suggest that most outlet glaciers would have reached the continental shelf edge at the LGM[5]. These simulations also show that, on the west side of the ice sheet, glaciers were fast-flowing, with ice velocities of up to 400 m per year due to plentiful snowfall over the Andean mountains.

 

A glacier of the modern South Patagonian Icefield (top right) flowing into a deep valley filled with sea water, known as a fjord (bottom left). Image from NASA.

Piedmont lobes

In the northern parts of the former Patagonian Ice Sheet, such as the Chilean Lake District (see map below), west-flowing glaciers did not extend to the Pacific Ocean, but instead formed large piedmont lobes that remained on land[8,12].

The geomorphological map below shows moraines (red lines) that delimit the maximum extent of former outlet glaciers in the Chilean Lake District. Note the piedmont lobe glaciers that spilled out on to flat coastal plains, with their source areas high in the mountains.

Patagonian piedmont lobes in the Chilean Lake District. Moraines mapped by Glasser and Jansson (2008) (ref. 3)

Below is an example of a present-day piedmont lobe glacier in Alaska.

The Agassiz (left) and Malaspina (right) piedmont glaciers spilling out from the Alaskan mountains on to flat coastal plains. Former outlet glaciers in the Chilean Lake District would have looked something like this. Image from NASA.

Moraines and glacial lakes

On the eastern side of the ice sheet, outlet glaciers flowed along large valleys that emerged on the flat Argentinian plains. At the LGM, the largest outlet glaciers advanced more than 150 km east of the modern icefield limits[13]. When they moved on to the flat plains they stabilised, and constructed arcuate terminal moraines[14,15,16,17,18], such as those shown in the photograph below.

During periods of Patagonian Ice Sheet retreat (such as after the LGM) many valleys were flooded with glacial lakes (see the shorelines photographed below, which provide evidence for these former lakes) as meltwater was trapped between terminal moraines and the receding glacier margins[15,19,20,21]. These lakes, which in some valleys were more than 500 m deep[21], had an important role on ice dynamics, likely increasing the rate of glacier retreat through the calving of icebergs[22].

Arcuate terminal moraine (crestline marked by arrows) formed by a major outlet glacier in central Patagonia. The moraine ridge is made up of unconsolidated glacial sediment (that either fell from the glacier surface, or was pushed out from beneath the ice margin), and marks the terminal (or end) point reached by the glacier. Image: J. Bendle.

Top: glacial lake shorelines (marked by white arrows) cut into a terminal moraine. Bottom: a raised lake delta (a landform created when a river enters a lake and deposits sediment) and beach. These landforms can be used to work out the depth of former glacial lakes. Image: J. Bendle.

Why is it important to study the Patagonian Ice Sheet?

Ice sheets are sensitive to changes in the temperature and circulation patterns of the atmosphere and oceans. This means that, firstly, the reconstruction and dating of former ice sheet activity can be used to better understand ice sheet-climate interactions[23]. Such information may be critical in understanding how modern ice sheets will respond to continued global warming[24].

Secondly, in the Southern Hemisphere, which is dominated by oceans, Patagonia is one of only a few areas of land from which scientists can develop records of past environmental change. Such records, which include records of long-term glacial change, allow us to more fully understand how the Southern Hemisphere climate system works, and how it may interact with climate changes happening at the global scale[25].

References

[1] Glasser, N.F., Jansson, K.N., Harrison, S. & Kleman, J. 2008. The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S. Quaternary Science Reviews, 27, 365–390.

[2] Coronato, A. & Rabassa, J. 2011. Pleistocene glaciations in Southern Patagonia and Tierra del Fuego. In Ehlers, L., Gibbard, P.L., Hughes, P.D. (Eds.) Developments in Quaternary Sciences, 15, Elsevier. pp. 715–727.

[3] Glasser, N.F. & Jansson, K. 2008. The glacial map of southern South America. Journal of Maps, 4, 175–196.

[4] Rabassa, J. & Clapperton, C.M., 1990. Quaternary glaciations of the southern Andes Quaternary Science Reviews, 9, 153–174.

[5] Hulton, N.R., Purves, R.S., McCulloch, R.D., Sugden, D.E. & Bentley, M.J. 2002. The last glacial maximum and deglaciation in southern South America. Quaternary Science Reviews, 21, 233–241.

[6] Hein, A.S., Hulton, N.R., Dunai, T.J., Sugden, D.E., Kaplan, M.R. & Xu, S. 2010. The chronology of the Last Glacial Maximum and deglacial events in central Argentine Patagonia. Quaternary Science Reviews, 29, 1212–1227.

[7] Boex, J., Fogwill, C., Harrison, S., Glasser, N., Hein, A., Schnabel, C. & Xu, S. 2013. Rapid thinning of the Late Pleistocene Patagonian Ice Sheet followed migration of the Southern Westerlies. Scientific Reports 3, 2118.

[8] Moreno, P.I., Denton, G.H., Moreno, H., Lowell, T.V., Putnam, A.E. & Kaplan, M.R. 2015. Radiocarbon chronology of the last glacial maximum and its termination in northwestern Patagonia. Quaternary Science Reviews, 122, 233–249.

[9] Hall, B.L., Porter, C.T., Denton, G.H., Lowell, T.V. & Bromley, G.R. 2013. Extensive recession of Cordillera Darwin glaciers in southernmost South America during Heinrich stadial 1. Quaternary Science Reviews, 62, 49–55.

[10] Glasser, N.F. & Jansson, K.N. 2005. Fast-flowing outlet glaciers of the last glacial maximum Patagonian Icefield. Quaternary Research, 63, 206–211.

[11] Glasser, N.F. & Ghiglione, M.C. 2009. Structural, tectonic and glaciological controls on the evolution of fjord landscapes. Geomorphology, 105, 291–302.

[12] Denton, G.H., Heusser, C.J., Lowel, T.V., Moreno, P.I., Andersen, B.G., Heusser, L.E., Schlühter, C. & Marchant, D.R. 1999. Interhemispheric linkage of paleoclimate during the last glaciation. Geografiska Annaler: Series A Physical Geography, 81, 107–153.

[13] Caldenius, C.C. 1932. Las glaciaciones cuaternarios en la Patagonia y Tierra del Fuego. Geografiska Annaler, 14, 1–164.

[14] Kaplan, M.R., Ackert, R.P., Singer, B.S., Douglass, D.C. & Kurz, M.D. 2004. Cosmogenic nuclide chronology of millennial-scale glacial advances during O-isotope stage 2 in Patagonia. Geological Society of America Bulletin, 116, 308–321.

[15] Sagredo, E.A., Moreno, P.I., Villa-Martínez, R., Kaplan, M.R., Kubik, P.W. & Stern, C.R. 2011. Fluctuations of the Última Esperanza ice lobe (52°S), Chilean Patagonia, during the last glacial maximum and termination 1. Geomorphology, 125, 92–108.

[16] Darvill, C.M., Stokes, C.R., Bentley, M.J. & Lovell, H. 2014. A glacial geomorphological map of the southernmost ice lobes of Patagonia: the Bahía Inútil–San Sebastián, Magellan, Otway, Skyring and Río Gallegos lobes. Journal of Maps, 10, 500–520.

[17] García, J.L., Hall, B.L., Kaplan, M.R., Vega, R.M. & Strelin, J.A. 2014. Glacial geomorphology of the Torres del Paine region (southern Patagonia): Implications for glaciation, deglaciation and paleolake history. Geomorphology, 204, 599–616.

[18] Bendle, J.M., Thorndycraft, V.T. & Palmer, A.P., 2017. The glacial geomorphology of the Lago Buenos Aires and Lago Pueyrredón ice lobes of central Patagonia. Journal of Maps, 13, 654–673.

[19] McCulloch, R.D., Bentley, M.J., Tipping, R.M. & Clapperton, C.M., 2005. Evidence for late glacial ice dammed lakes in the central Strait of Magellan and Bahía Inútil, southernmost South America. Geografiska Annaler: Series A Physical Geography 87, 335–362.

[20] Lovell, H., Stokes, C.R., Bentley, M.J. & Benn, D.I. 2012. Evidence for rapid ice flow and proglacial lake evolution around the central Strait of Magellan region, southernmost Patagonia. Journal of Quaternary Science, 27, 625–638.

[21] Glasser, N.F., Jansson, K.N., Duller, G.A., Singarayer, J., Holloway, M. & Harrison, S. 2016. Glacial lake drainage in Patagonia (13-8 kyr) and response of the adjacent Pacific Ocean. Scientific Reports, 6. 21064.

[22] Carrivick, J.L. & Tweed, F.S. 2013. Proglacial lakes: character, behaviour and geological importance. Quaternary Science Reviews, 78, 34–52.

[23] Kaplan, M.R., Fogwill, C.J., Sugden, D.E., Hulton, N.R.J., Kubik, P.W. & Freeman, S.P.H.T. 2008. Southern Patagonian glacial chronology for the Last Glacial period and implications for Southern Ocean climate. Quaternary Science Reviews, 27, 284–294.

[24] IPCC, 2013. The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, UK. doi:10.1017/CBO9781107415324.

[25] Killan, R. & Lamy, F. 2012. A review of glacial and Holocene paleoclimate records from southernmost Patagonia (49-55°S). Quaternary Science Reviews, 1–23.

Patagonian Ice Sheet

This page summarises some of our recent research on the dynamics of Patagonian outlet glaciers during the Last Glacial Maximum and following deglaciation. Pages on glacial landforms are especially relevant to the Geography A-Level curriculum.

Here, you can watch a seminar I gave about the Patagonian Ice Sheet:

 

Further reading:

Drumlins

Drumlins around Lago Viedma

Although the Patagonian Icefields aren’t generally associated with drumlins (Glasser et al., 2008), there are some around Lago Viedma in the South Patagonian Icefield. They have been described in detail (Ponce et al., 2013) but they show up beautifully in the Landsat map below. The mapping below is by me (Bethan Davies) and Glasser and Jansson (2008). Drumlins are probably rare in Patagonia as the temperate ice masses release large amounts of meltwater, which may destroy any bedforms.

Drumlins around Lago Viedma, South Patagonian Icefield. The background image is Landsat 7 ETM+ from 2001. Panels C and D are to the same scale.

Drumlins around the world

Drumlins have been observed at the beds of former palaeo ice-sheets across the world. They are found across the Pennines of Britain, in Anglesey, and in the Lake District (Livingstone et al., 2008; Hughes et al., 2010, 2014). In the photo below there is a drumlin on Anglesey. The farmer has helpfully put a stone wall along the long-axis of the drumlin.

Drumlin in Anglesey. Photograph: Bethan Davies

The most ubiquitous subglacial landforms

Drumlins are therefore one of the most ubiquitous landforms formed underneath ice sheets (Clark et al., 2009).  They are typically oval-shaped hills, with a long-axis parallel to ice flow. The up-ice (stoss) face is typically steeper than the down-ice (lee) face (Stokes et al., 2011). They are typically between 250 – 1000 m long, 120-300 m wide, and 1.7 to 4.1 times as long as they are wide (Clark et al., 2009). They also generally occur in clusters, or swarms, as can be seen in the images from around Lago Viedma above.

Drumlins. Top: cross-profile, Second: view from above. Third: a swarm of drumlins. Adapted from work on Wikimedia Commons.

Drumlins in palaeo-ice sheet reconstruction

Glacial geologists frequently use these swarms of drumlins in palaeo-ice sheet reconstruction, because they can be directly related to the direction of former ice flow. They can therefore be used to reconstruct the dynamic behaviour of former ice sheets (Livingstone et al., 2010; Livingstone et al., 2012).  Their length may be related to ice velocities, with a tendency to become more elongated under fast ice-flow conditions. At their longest, they grade into Mega-Scale Glacial Lineations, typically found under former ice-streams.

The mystery of how drumlins are made

Although drumlins have a typical morphology, they can be made up of lots of different kinds of internal sediments, ranging from mainly bedrock, to mainly till, to mainly sorted sediments (Stokes et al., 2011). A diagnostic process for their formation is therefore challenging to deduce.

Cross-section through a drumlin on Anglesey. This one is mostly made of glacial till. Photo: Bethan Davies

One theory growing in popularity is the ‘instability theory’, which states that small perturbations in the bed of the ice sheet grow under a positive-feedback mechanism into the large landforms we see on land (e.g., in Britain and in Patagonia) today (Stokes et al., 2013). Such instabilities tend to grow exponentially, with a rate dependent on wavelength.  Essentially, the process amplifies the relief at the ice-bed interface and results in the formation of bedforms like drumlins in recognisable patterns.

Further reading

References

Clark, C.D., Hughes, A.L.C., Greenwood, S.L., Spagnolo, M., Ng, F.S.L., 2009. Size and shape characteristics of drumlins, derived from a large sample, and associated scaling laws. Quaternary Science Reviews 28, 677-692.

Glasser, N., Jansson, K., 2008. The Glacial Map of southern South America. Journal of Maps 4, 175-196.

Glasser, N.F., Jansson, K.N., Harrison, S., Kleman, J., 2008. The glacial geomorphology and Pleistocene history of South America between 38°S and 56°S. Quaternary Science Reviews 27, 365-390.

Hughes, A.L.C., Clark, C.D., Jordan, C.J., 2010. Subglacial bedforms of the last British Ice Sheet. Journal of Maps 6, 543-563.

Hughes, A.L.C., Clark, C.D., Jordan, C.J., 2014. Flow-pattern evolution of the last British Ice Sheet. Quaternary Science Reviews 89, 148-168.

Livingstone, S.J., Evans, D.J.A., Ó Cofaigh, C., Davies, B.J., Merritt, J.W., Huddart, D., Mitchell, W.A., Roberts, D.H., Yorke, L., 2012. Glaciodynamics of the central sector of the last British–Irish Ice Sheet in Northern England. Earth-Science Reviews 111, 25-55.

Livingstone, S.J., Ó Cofaigh, C., Evans, D.J.A., 2008. Glacial geomorphology of the central sector of the last British-Irish Ice Sheet. Journal of Maps 2008, 358-377.

Livingstone, S.J., Ó Cofaigh, C., Evans, D.J.A., 2010. A major ice drainage outlet of the last British-Irish Ice Sheet: the Tyne Gap, northern England. Journal of Quaternary Science 25, 354-370.

Ponce, J.F., Rabassa, J., Serrat, D., Martínez, O.A., 2013. El campo de drumlins, flutes y megaflutes de lago Viedma, Pleistoceno Tardío, provincia de Santa Cruz. Revista de la Asociación Geológica Argentina 70, 115-127.

Stokes, C.R., Fowler, A.C., Clark, C.D., Hindmarsh, R.C.A., Spagnolo, M., 2013. The instability theory of drumlin formation and its explanation of their varied composition and internal structure. Quaternary Science Reviews 62, 77-96.

Stokes, C.R., Spagnolo, M., Clark, C.D., 2011. The composition and internal structure of drumlins: Complexity, commonality, and implications for a unifying theory of their formation. Earth-Science Reviews 107, 398-422.

Patagonian Ice Sheet thinning during a changing climate

J.Boex, C. Fogwill, S. Harrison, N.F. Glasser, A. Hein, C. Schnabel and S. Xu.  Rapid thinning of the Late Pleistocene Patagonian Ice Sheet followed migration of the Southern Westerlies. Scientific Reports 3: 2118, p. 1-6

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The Patagonian Ice Sheet

Patagonian mountains east of the North Patagonian Icefield. Credit: Stephen Harrison

Patagonian mountains east of the North Patagonian Icefield. Credit: Stephan Harrison

This recent open-access paper in the new journal Science Communications, which is part of the Nature group, has demonstrated that the during the deglacial period (~19,000 years ago), the Patagonian Ice Sheet in South America responded rapidly in response to changing precipitation patterns and warming during the last deglaciation. The fact that the Patagonian Ice Sheet responded so quickly to changes in precipitation and temperature has vivid implications for the current, and future, behaviour of the current North Patagonian Icefield  and South Patagonian Icefield. We already know that the shrinkage of the North and South Patagonian ice fields was faster over the last decade or so than at any point in the last couple of centuries. Understanding on a broader scale how these sensitive, high-latitude ice masses are dependent on small changes in atmospheric circulation means that we will better be able to predict the future behaviour of these ice sheets. Reconstructing rates of ice-sheet decay since the Last Glacial Maximum means that we can better assess the mechanisms of climate change (including changing wind patterns) during a major climate transition. Continue reading