Active temperate glacier landsystem

Temperate glaciers reach the pressure-melting point throughout, for at least for part of the year. Today, temperate glaciers are found in mild maritime climates such as southern Iceland, western Norway, New Zealand, and southern Chile, where both winter snowfall and summer melt rates are high.

Temperate glaciers are often very sensitive to changes in climate and will periodically advance (e.g. during the winter) even when in overall recession. This type of glacier is defined as active.

The lake-terminating ice margin of the active temperate Fjallsjökull glacier, Iceland. Photo: Wojciech Strzelecki

The active temperate glacier landsystem reflects the wet-based thermal regime of temperate glaciers, and their tendency to oscillate in response to seasonal temperature. The landforms created by lowland temperate glaciers (such as those in southern Iceland) fall into three groups: ice marginal landforms, subglacial landforms, and glaciofluvial and glaciolacustrine landforms.

Landform assemblages of active temperate glaciers

Ice-marginal landforms

One of the most characteristic features of the active temperate glacier landsystem are the sharp, low relief moraine ridges found on their forelands1,2. These moraines are typically <10 m high and mimic the shape of the glacier snout when deposited, often taking on a saw-tooth pattern that reflects the pattern of ice-margin crevasses3.

Sawtooth push moraines on the foreland of Skaftafellsjökull, southern Iceland. Photo: Chensiyuan

These moraines are formed by a combination of ice pushing and the dumping of sediment from the snout. Some sediment may also be squeezed out from beneath an advancing snout (either during winter advance, or during the summer when sediment beneath the snout can become saturated with water and more mobile).

Because active temperate glaciers often advance during winter and retreat during summer, a series of annual push moraines can form during deglaciation4-6.

Annual push moraines formed at the retreating terminus of Skálafellsjökull, Iceland (see ref. #3). The moraines display a sawtooth planform that closely mimics the shape of the ice margin. Image: Google Earth.

Subglacial landforms

The beds of former active temperate glaciers are characterised by landforms of both erosion and deposition1,2.

Where exposed at the land surface, bedrock is polished, moulded and striated. The bedrock may also be shaped into roches moutonnées, indicating that both abrasion and quarrying occur at active temperate glacier beds.

Streamlined subglacial landforms, such as flutes and drumlins, are also common on temperate glacier forelands1,7. These features form in large groups at right angles to push moraines (i.e. in the direction of former glacier flow) by some combination of subglacial deformation8,9 and the ploughing (erosion) of soft sediments by the overriding glacier10.

The foreland of Svínafellsjökull, Iceland, showing flutes and debris stripes aligned at right angles to push moraines in the direction of former ice flow (Evans et al., 2019). Image: Google Earth.

Temperate glacier forelands sometimes contain overridden moraines1,2, which are more subdued than push moraines and have flutes across their surfaces. These serve as evidence for ice-overriding during a glacier advance.

Glaciofluvial and glaciolacustrine landforms

While not unique to the active temperate glacier landsystem, glaciofluvial and glaciolacustrine landforms are common owing to the high volumes of meltwater released by temperate glaciers during the spring and summer months1,2.

Proglacial streams that flow away from the snout produce outwash (also referred to as sandur) fans11, whereas meltwater draining around the sides of the glacier form kame terraces and narrow outwash corridors1,2.

As sandur fans form in contact with the snout, they often develop ‘pitted’ surfaces where glacial ice is buried and later melts out, leaving small lakes at the outwash surface1,2.

Outwash (sandur) deposits around the margin of Skeiðarárjökull, southern Iceland. The many pits and pockmarks that break up the outwash surface form by the melting of buried ice over time. Image: Google Earth.

Some temperate glacier forelands also contain eskers, which are narrow, often sinuous ridges of glaciofluvial sand and gravel that form in subglacial, englacial and supraglacial (all ice-walled) channels, which give some indication of the patterns of meltwater drainage in former glaciers12.

Sinuous esker ridges on the foreland of the Breiðamerkurjökull glacier, southern Iceland. (see ref. #12). Image: Google Earth.

Ice-dammed or proglacial lakes are commonly found around the margins of receding temperate glaciers. These lakes interrupt the path of sediment-containing meltwater streams, allowing thick sequences of sediment to accumulate at the lake bottom1,2. Lake shorelines and deltas also form around glacial lake margins and often remain clear in the landscape after a lake has drained1.2.

Proglacial lake developing around the Skaftafellsjökull ice front (Iceland). Photo: Óðinn

The active temperate glacier landsystem

The active temperate glacier landsystem1,2 serves as a clear and detailed signature of past glacial activity, particularly of ice-front oscillations and meltwater drainage patterns.

Research has shown that active temperate glaciers existed in a wide range of formerly glaciated regions. For example, some Ice Age (around 20,000 years ago) glaciers of the Laurentide13 and Patagonian ice sheets14 and the New Zealand mountain ice cap15 produced landform assemblages typical of active temperate glacier activity.

Because the behaviour (e.g. seasonal advance and retreat patterns) of active temperate glaciers is closely tied to climate, identifying their landsystem in formerly glaciated areas can serve as a record of past climate.

In summary, the active temperate glacier landsystem1,2 usually contains: large areas of low amplitude push, dump and squeeze moraines (that mark out former glacier positions), which often record active annual recession; flutes, drumlins, and ice-moulded bedrock between moraine ridges; and extensive glaciofluvial (outwash, eskers, kame terraces) and glaciolacustrine (shorelines) features that provide evidence of abundant meltwater around the glacier snout.

References

[1] Evans, D.J.A. and Twigg, D.R., 2002. The active temperate glacial landsystem: a model based on Breiðamerkurjökull and Fjallsjökull, Iceland. Quaternary Science Seviews21, 2143-2177.

[2] Evans, D.J.A., 2003. Ice-marginal terrestrial landsystems: active temperate glacier margins. In Evans, D.J.A. (Ed.) Glacial Landsystems. Hodder–Arnold, London.

[3] Evans, D.J.A., Ewertowski, M. and Orton, C., 2016. Fláajökull (north lobe), Iceland: active temperate piedmont lobe glacial landsystem. Journal of Maps12, 777-789.

[4] Bradwell, T., 2004. Annual moraines and summer temperatures at Lambatungnajökull, Iceland. Arctic, Antarctic, and Alpine Research36, 502-508.

[5] Beedle, M.J., Menounos, B., Luckman, B.H. and Wheate, R., 2009. Annual push moraines as climate proxy. Geophysical Research Letters36.

[6] Chandler, B.M., Evans, D.J.A. and Roberts, D.H., 2016. Characteristics of recessional moraines at a temperate glacier in SE Iceland: Insights into patterns, rates and drivers of glacier retreat. Quaternary Science Reviews135, 171-205.

[7] Evans, D.J.A., Nelson, C.D. and Webb, C., 2010. An assessment of fluting and “till esker” formation on the foreland of Sandfellsjökull, Iceland. Geomorphology114, 453-465.

[8] Boulton, G.S., 1976. The origin of glacially fluted surfaces-observations and theory. Journal of Glaciology17, 287-309.

[9] Benn, D.I., 1994. Fluted moraine formation and till genesis below a temperate valley glacier: Slettmarkbreen, Jotunheimen, southern Norway. Sedimentology41, 279-292.

[10] Tulaczyk, S.M., Scherer, R.P. and Clark, C.D., 2001. A ploughing model for the origin of weak tills beneath ice streams: a qualitative treatment. Quaternary International86, 59-70.

[11] Evans, D.J.A. and Orton, C., 2015. Heinabergsjökull and Skalafellsjökull, Iceland: active temperate piedmont lobe and outwash head glacial landsystem. Journal of Maps11, 415-431.

[12] Storrar, R.D., Evans, D.J.A., Stokes, C.R. and 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.

[13] Evans, D.J., Lemmen, D.S. and Rea, B.R., 1999. Glacial landsystems of the southwest Laurentide Ice Sheet: modern Icelandic analogues. Journal of Quaternary Science14, 673-691.

[14] Darvill, C.M., Stokes, C.R., Bentley, M.J., Evans, D.J.A. and Lovell, H., 2017. Dynamics of former ice lobes of the southernmost Patagonian Ice Sheet based on a glacial landsystems approach. Journal of Quaternary Science32, 857-876.

[15] Sutherland, J.L., Carrivick, J.L., Evans, D.J.A., Shulmeister, J. and Quincey, D.J., 2019. The Tekapo Glacier, New Zealand, during the Last Glacial Maximum: An active temperate glacier influenced by intermittent surge activity. Geomorphology343, 183-210.

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