The Loch Lomond Stadial

What is the Loch Lomond Stadial?

The final stage of the British-Irish Ice Sheet is known as the Loch Lomond Stadial, the Loch Lomond Readvance or Younger Dryas Stadial¹. In Ireland, it is known as the Nahanagan Stadial.

The Loch Lomond Stadial was a period of glacial readvance during the overall shrinking of the British-Irish Ice Sheet. By the end of the Loch Lomond Stadial, all the ice fields and glaciers in Britain had entirely receded, and all the ice had gone.

Coire Ardair, north of Loch Laggan, was occupied by a valley glacier during the Loch Lomond Stadial. Its maximum extent is constrained by the moraines in the valley bottom. Photo: B. Davies.

When was the Loch Lomond Stadial?

The Loch Lomond Stadial came right at the end of the British-Irish Ice Sheet, during the Late Pleistocene. After a period known as the Windermere Interstadial, around 14,000 years ago, where the temperature was warmer, ice had retreated to ice caps mountainous regions. It is likely that some small ice caps survived the Windermere Interstadial².

A sudden cooling of the atmosphere in the Northern Hemisphere happened around 12,900 years ago, called the Younger Dryas, which caused the ice caps to expand and form the Loch Lomond Stadial ice masses shown in the map below³. A sudden warming at 11,700 years ago caused these ice masses to recede rapidly and melt entirely^1,3,4.

The limits of the Loch Lomond Stadial ice. Data from Bickerdike et al., 2018⁸.
Bathymetry data are from the GEBCO 2018 dataset (https://www.gebco.net/data_and_products/gridded_bathymetry_data/) and land elevation from the European Environment Agency EU-DEM (https://www.eea.europa.eu/data-and-maps/data/eu-dem)

There has been some recent controversy about the timing of deglaciation at the end of the Loch Lomond Stadial. Some researchers favour an early deglaciation around 12,500 years ago⁵. But more recent work to date the timing of retreat has upheld the traditional view that the Loch Lomond Stadial ice masses lasted until the at least the end of the Younger Dryas, with some ice lasting into the beginning of the Holocene^1,6.

Cosmogenic nuclide dating of boulders on Rannoch Moor to determine the age of deglaciation. Photograph courtesy of David Small.

Where was the ice during the Loch Lomond Stadial?

The map above shows the maximum extent of the readvance of ice during the Loch Lomond Stadial. We call this stage the Loch Lomond Stadial because of the large moraines that formed close to the shores of today’s Loch Lomond⁷. The main mass of ice, the West Highland Glacier Complex, was centred around Rannoch Moor and Fort William⁸. But there were smaller ice fields located in mountainous regions of Scotland, England and Wales.

The terminal moraines of the Loch Lomond Stadial at Loch Lomond, and Glacial Lake Blane. Data from Bickerdike et al., 2016¹⁵; 2018⁸.
Elevation data: OS Terrain 5 (https://www.ordnancesurvey.co.uk/business-government/products/terrain-5)

The Loch Lomond Stadial in Scotland

The West Highland Glacier Complex was the largest ice mass in the UK during the Loch Lomond Stadial. It grew on the west side of the country because of the higher rainfall brought in from the Atlantic by the prevailing winds. It extended from Ullapool in the north to Loch Lomond in the south⁸.

Plateau ice fields existed in the Monadhliath, the Cairngorms, and the Northwest Highlands at Assynt, as well as on Skye and Mull, with smaller cirque and valley glaciers on Harris and Arran. There was also a large plateau ice field in the Tweedsmuir Hills⁹.

Drift limits showing the maximum extent of the Loch Lomond Stadial glacier in the Lomond Lobe at Conic Hill, above the eastern shore of Loch Lomond. Photograph from Bickerdike et al., 2018⁸.

The Loch Lomond Stadial in Wales

In Wales, the Loch Lomond Stadial was mostly restricted to cirque glaciation in the mountains of Snowdonia. This area is covered in great detail in this article that explains the landforms associated with cirque glaciers.

There were also some small cirque glaciers in the Brecon Beacons⁸. These glaciers were the farthest-south glaciers to exist in Britain during the Loch Lomond Stadial.

The Loch Lomond Stadial glacial landsystem of Cwm Idwal. Photo: J. Bendle

The Loch Lomond Stadial in England

In England, there were Loch Lomond Stadial ice fields, cirque and valley glaciers in the Lake District¹⁰, and smaller cirque glaciers in the north Pennines and the Cheviots⁸. In the Lake District, a plateau ice field has been suggested, which covered High Street and the surrounding area, but the evidence from geomorphology and dating is weak⁸.

Six cirque glaciers in the north Pennines and one cirque glacier in the Cheviots have been identified, and would have formed by accumulation of snow blown from large plateau areas⁸.

The ice extent in the Lake District during the Loch Lomond Stadial. Data from Bickerdike et al., 2018⁸. Lake outlines from the Environment Agency shapefile database.
Elevation data: OS Terrain 5 (https://www.ordnancesurvey.co.uk/business-government/products/terrain-5)

Ice-dammed lakes during the Loch Lomond Stadial

In 1805, English geologist George Bellas Greenough visited the already-famous Parallel Roads of Glen Roy, and noted them to be similar to shorelines of a lake. He then interpreted the parallel roads to be the shorelines of a former lake, although he and later geologists could not agree on the dam that would allow the lakes to form¹¹.

In 1840, comparing Scotland to the present-day Alps, Louis Agassiz interpreted the parallel roads to be shorelines of ice-dammed lakes, using this evidence to announce there had once been glaciers in Scotland¹¹.

The three Parallel Roads of Glen Roy. Original photo by Richard Crowest – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6823829

Three parallel roads, one at 350 m, one at 325 m, and one at 260 m, mark different elevations of the lake surface, and three different stages of ice-dammed lake¹². The first lake shoreline to form was when the ice was at its greatest extent, forming the 350 m shoreline. Then, as ice began to retreat, the 325 m shoreline formed, followed by the 260 m lake¹².

The lake finally drained at the end of the Loch Lomond Stadial, in a catastrophic event known as a glacial lake outburst flood, or jökulhlaup, which drained the water away into the Great Glen¹³.

The Parallel Roads of Glen Roy with proglacial lake fan sediments in the foreground. a large landslide has covered the parallel roads on the hillside, therefore we know the landslide must have happened afterwards, during the Holocene. Photo: B. Davies

Other ice-dammed lakes existed during the Loch Lomond Stadial too⁸. A large proglacial lake fomed at the terminus of the Loch Lomond glacier, called Glacial Lake Blane⁴. Smaller lakes existed in Glen Doe, Glen Garry, and at Achnasheen⁸.

Why is the Loch Lomond Stadial so important?

The Younger Dryas cold period was a time when the climate changed rapidly, first a rapid cooling at the start of the Younger Dryas, then a rapid warming at the end³. Because of this rapid change over tens to hundreds of years, we study the Younger Dryas as it may hold clues to future rapid change.

We need to understand what drives ice-sheet retreat to forecast what may happen to future glaciers and ice sheets, and the Younger Dryas glaciation is perfect for this. Because it is the most recent phase of glaciation, evidence for the Loch Lomond Stadial is well-preserved, and can tell us about how glaciers and ice fields reacted to sudden warming¹⁴.

References

1. Lowe, J. et al. On the timing of retreat of the Loch Lomond (‘Younger Dryas’) Readvance icefield in the SW Scottish Highlands and its wider significance. Quat. Sci. Rev. 219, 171–186 (2019).

2. Bradwell, T. et al. Ice caps existed throughout the Lateglacial Interstadial in northern Scotland. J. Quat. Sci. 23, 401–407 (2008).

3. Anderson, D. E. Implications for Understanding Abrupt Climatic Change. Prog. Phys. Geogr. 21, 230–249 (1997).

4. MacLeod, A. et al. Timing of glacier response to Younger Dryas climatic cooling in Scotland. Glob. Planet. Change 79, 264–274 (2011).

5. Bromley, G. R. M. et al. Younger Dryas deglaciation of Scotland driven by warming summers. Proc. Natl. Acad. Sci. U. S. A. 111, 6215–6219 (2014).

6. Small, D. & Fabel, D. Was Scotland deglaciated during the Younger Dryas? Quat. Sci. Rev. 145, 259–263 (2016).

7. Rose, J. Glasgow region field guide. (Quaternary Research Association, 1980).

8. Bickerdike, H. L., Evans, D. J. A., Stokes, C. R. & Ó Cofaigh, C. The glacial geomorphology of the Loch Lomond (Younger Dryas) Stadial in Britain: a review. J. Quat. Sci. 33, 1–54 (2018).

9. Pearce, D., Rea, B. R., Bradwell, T. & McDougall, D. Glacial geomorphology of the Tweedsmuir Hills, Central Southern Uplands, Scotland. J. Maps 10, 457–465 (2014).

10. Sissons, J. B. The loch lomond stadial in the British Isles. Nature 280, 199–203 (1979).

11. Brazier, V. et al. The Parallel Roads of Glen Roy, Scotland: geoconservation history and challenges. Proc. Geol. Assoc. 128, 151–162 (2017).

12. Sissons, J. B. The lateglacial lakes of Glens Roy, Spean and vicinity (Lochaber district, Scottish Highlands). Proc. Geol. Assoc. 128, 32–41 (2017).

13. Sissons, J. B. Lateglacial marine erosion and a jokulhlaup deposit in the Beauly Firth. Scottish J. Geol. 17, 7–19 (1981).

14. Boston, C. M., Lukas, S. & Carr, S. J. A Younger Dryas plateau icefield in the Monadhliath, Scotland, and implications for regional palaeoclimate. Quat. Sci. Rev. 108, 139–162 (2015).

15. Bickerdike, H. L., Evans, D. J. A., Ó Cofaigh, C. & Stokes, C. R. The glacial geomorphology of the Loch Lomond Stadial in Britain: a map and geographic information system resource of published evidence. J. Maps 12, 1178–1186 (2016).