Doubt Cast on Cairngorm Glacier

by Dan Bailey - UKHillwalking.com Jan/2014
This news story has been read 4,418 times

Tuesday's story on the existence of a glacier in Scotland's comparatively recent past stirred up a lot of interest, but (perhaps inevitably) it hasn't taken long for an opposing academic view to surface. Cairngorms expert Dr Adam Watson has cast doubt on the claims of glaciation a mere 400 years ago.

 

+Dr Adam Watson, 195 kbDr Adam Watson

A biologist, ecologist, author, mountaineer and campaigner, Dr Watson has spent his life in scientific study of the Cairngorms, and in celebrating and defending them. Dubbed 'Mr Cairngorms', he is widely acknowledged as Scotland's pre-eminent authority on the range, and has written extensively about the area. 

Dr Watson is not convinced by the research carried out by Dr Kirkbride at Coire an Lochain, nor by a parallel study by Dr Stephan Harrison and Dr Anne Rowan which used a numerical model to simulate the climate in the Cairngorms over the period in question.

'Moraines are ruled out because of their descriptions of the sharp-angled pink, lichen-free boulders in a matrix of coarse sand and grit' he told us.

'Debris flows are the most likely explanation, with intense rainstorms gouging gravel and boulders down the gullies, starting at the cliff top. I have seen such ridges formed in that corrie and Coire an t-Sneachda overnight from a thunderstorm rainfall.'

'The papers are typical studies of geomorphologists who fail to dig a single soil pit and ignore fundamental principles of soil science' says Dr. Watson. 

 

'This failure includes Sugden, who made the original proposal of glaciers in several corries of the Cairngorms in the 1700s and one in Garbh Choire Mor in the early 1800s. '

'The claim in Kirkbride about moraines in Coire an Lochain of Cairn Gorm is particularly unlikely' Dr Watson thinks. 

'A snow patch survives till winter during very few years in that corrie, whereas in Garbh Choire Mor [Braeriach] the patches almost always survive till winter, and hence this is the most likely site for a glacier in Scotland.'

'As I wrote in my book A Snow Book, Northern Scotland, the evidence at Garbh Choire Mor, the snowiest site in the Cairngorms, is that the supposed moraine ridge is a protalus rampart, fed annually by boulders, soil, vegetation and other debris coming down in avalanches. Other gravel etc comes down in flash floods down the gullies.' 

However at Coire an Lochain the hypothesis for a protalus rampart can be ruled out, Dr Watson believes, 'because [Dr Kirkbride's] descriptions of the sand and grit immediately below the surface show too little organic material. A moraine can be ruled out because the soil had no organic or other horizons to judge from his brief description. I think debris flows during intense rainstorms, bringing masses of boulders and gravel down the gullies, are a likely explanation.'

+Scottish Glacier, 221 kbScottish Glacier
© Dave Kerr, Apr 2010


To help explain all this Dr Adam Watson has allowed us to reproduce this chapter from his book A Snow Book, Northern Scotland. It specifically covers Braeriach's Garbh Choire Mor, though the principles can be applied more widely.

Chapter 6. Cairngorms glaciers in the 18th and 19th centuries highly unlikely

Historical evidence on snowier conditions in the 1700s and 1800s during the Little Ice Age can be compared with recent research on the time that has elapsed since the ground became free of ice or perennial snow. The lichen Rhizocarpon geographicum grows on cliffs and boulders, in the form of roughly circular patches that increase in diameter year by year as the lichen grows, and the growth rate has been measured in several countries. Sugden (1974, 1977) measured the diameter of the biggest patches of this lichen in seven corries in the Cairngorms, and compared this with other workers’ measurements of the growth rate. He and his student Sheila Rapson found that the diameter on the downhill side of the outermost moraine exceeded that on the uphill side of the innermost moraine. He inferred that the biggest (i.e. oldest) of the lichen patches on the uphill side of the innermost moraine had started to grow between 1644 and 1725, and much more recently about 1800 on an innermost ridge much nearer the present Garbh Choire Mor snow-bed. Though postulating (1977, Conclusion) that glaciers occurred there prior to these years, he referred several times in his main text to ‘snow or ice’. Lamb (1977) recounts Manley’s suggestion to him ‘that it may have been firn rather than having attained the density of ice’. This fits observations of no lichen on bedrock and boulders beside firn, as well as beside glaciers.

Because no lichens grow on boulders, bedrock or subsoil at today’s two most persistent snow patches at Garbh Choire Mor (above), one need not even postulate firn. Long-lying snow would suffice. No rock lichens grow today on boulders at snow patches of far less persistence than the two at Garbh Choire Mor, e.g. at Ciste Mhearad and Garbh Uisge Beag. However, it follows from Sugden’s study that long-lying snow must have covered a far bigger area than in recent decades. In 1943–2010, no snow survived immediately behind the inner moraines in any of his seven corries apart from Garbh Choire Mor, and none immediately behind inner moraines in any other corrie in the Cairngorms.

Later research by radiocarbon dating and pollen analysis shows that the moraines formed more than 6000 years ago, not in recent centuries (Rapson 1990). Noting that ‘A quick glance at the area immediately surrounding the semipermanent snowpatch in Garbh Choire Mor today clearly shows the ability of snow to kill lichens’, Rapson suggested that extra snow inside the moraines during the Little Ice Age would have killed rock lichens, thus explaining their current smaller diameter inside the moraines than outside them. However, she wrote that the inner moraine at Garbh Choire Mor may be an exception. Although it lacked enough organic material for tests by radiocarbon dating and pollen analysis, she commented on the moraine’s current fresh appearance, with hardly any vegetation and with boulders angular and unweathered. She suggested that a glacier in the Little Ice Age may have formed the inner moraine.

An alternative and far more likely explanation is that the ridge is not a moraine but a protalus rampart. Each year, boulders and soil becoming loose and falling from the cliffs, or being torn out by snow avalanches, slide down the steep surface of the snowfield immediately below the crags. They then pile up far below, adding to the ridge. On several days from October through to early summer of different years I have watched this happening, and the signs of it are clearly evident on many days in every summer. Although Berry (1967) did refer to the moraine lip of the upper corrie, he then added, ‘This is probably a type of avalanche boulder tongue, built up by the accumulation of avalanche debris and by the rocks released from the walls of the corrie by frost shatter’. I agree with his suggestion in the last quoted sentence.

The angular boulders mentioned by Rapson would be unlikely to have resulted from deposition in the form of a moraine, because glacial action would have rounded them. Hence I suggest the hypothesis that the ridge is a protalus rampart. If boulders below the surface are angular and the soil contains little clay or silt, this would tend towards refuting the hypothesis of the ridge being a moraine, and support its being a protalus rampart. This can be put to the test by detailed inspection of boulders, soils and vegetation, using the well-tested methods of soil survey, It seems suprising that this was  omitted by geomorphologists..

The mound lies in the corrie’s centre below the long-lying snow, south of 943 980, with a slight hollow on its west side. Sugden did not inspect the type of rocks and soil on the mound. If it is a moraine, rocks would be rounded due to grinding by ice, and all exposed faces of surface rocks would carry some lichen unless there was a long-lying snow patch nearby. By contrast, a protalus rampart consists largely of angular or sharp-edged rocks that have fallen due to frost-shattering of cliffs. Only the outer surface of a cliff has rock-lichen. If a piece breaks off, only its outer face has rock-lichen. If a piece has come from inside the cliff after an outer surface comes off, it will have no lichen on any face. So, if any rock on the mound has a face with no lichen, this freshness indicates a protalus rampart.

From a distance the mound seems to consist of nothing but boulders, but if no soil is visible on the surface it would be worth looking under a few of the topmost boulders to see if they are lying on soil. If there is any, it is likely to be dark topsoil that has been torn from the cliffs in avalanches.

The almost fluorescent yellow-green of Rhizocarpon geographicum imparts a unique hue to the cliffs of Garbh Choire Mor, greater than any other Scottish cliff. It likes snow, but too much snow deters it and other rock-lichen, so the cliff immediately above the longest-lying snow patches shows the pink colour of the local granite.

When the snow patches are tiny or have vanished, it would be useful to record by photos how far the vegetation-free zone extends on boulders and soil around the Sphinx and Pinnacles patches. Lichens, moss and other plants would begin to extend on to this zone if the average duration of snow declines. Photos showing the edge of the zone would be valuable, along with a note showing where the photograph was taken so that the location can be revisited. GPS would be a useful additional tool for this.

On 23 September 2010, Attila Kish visited the snow patches further up the corrie in truly awful weather, and on the way to them he inspected the ridge or mound after I had sent him the background information and suggestions about the best aims on a brief visit. He noted that the western part of the mound, facing the upper corrie, consisted of boulders, but the eastern section had a surface with some soil mixed with boulders. On that eastern section he used a trowel to dig a soil pit about 15–20 m downhill from the crest, and took photographs of the pit, using the trowel to give scale. The weather was bad and the light poor, but his preliminary reconnaissance proved useful.

The upper soil horizons comprised '12–15 inches of organic soil before getting to a lighter, what looked like mixed organic/mineral layer. The overlying vegetation was crowberry/Rhacomitrium with alpine club moss and stiff sedge. My memory of soil types is vague, but it certainly wasn’t what I think of as classic moraine type soil i.e. a thin layer of organic before getting into the mineral clay/gravel mix. I’m just thinking of ‘borrow pits’ dug by estates or path contractors in moraine country, where they’re getting very quickly through to the material they want for surfacing'.

His photographs confirm his general description above. The thickness of the upper soil horizons above the mineral horizons goes against the hypothesis of a moraine, especially given the exposure and short plant growth at that altitude and location. During avalanches, the larger boulders tend to pile up on the western side of the mound and the finer soil particles and bits of vegetation move further downhill, tending to concentrate on the more sheltered eastern side of the mound. This helps explain the remarkable thickness of the upper horizons. At such an exposed site, an upper horizon of less than an inch would be expected, far less 12–15 inches. Attila Kish intends to revisit the mound in better weather and dig another pit, as well as make observations on the angularity and weathering of the boulders and on whether recently deposited boulders and pieces of rock from the cliff as a result of the previous winter’s avalanches are lying on top of boulders with rock lichen or on top of vegetation.

References

Rapson, S.C. (1990). The age of the Cairngorm coire moraines. Scottish Mountaineering Club Journal 34, 457–463.

Sugden, D. E. (1974). Deglaciation of the Cairngorms and its wider implications. Problems of the deglaciation of Scotland (ed. by C.J. Casseldine & W.A. Mirtchell), 17–28. STAG Special Publication 1. Geography Department, University of St Andrews.

Sugden, D. (1977). Did glaciers form in the Cairngorms in the 17th–19th centuries? Cairngorm Club Journal 97, 189–201.

 

 

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