Mull is covered in ice

The Pleistocene:

The last episode of Britain’s and Mull’s geological history is associated with world-wide general worsening of climate. At the end of the Tertiary temperatures everywhere had become lower and snow and ice accumulated in polar and mountain regions.  Accumulation of snow happens gradually but has a knock-on effect for an ice age to start. All that is needed is for winter snow on mountain summits not to melt the following or subsequent summers in order for snow to build up, gradually become converted into ice and eventually move out from accumulation hollows to flow as glaciers downslope. Summer air temperatures over these snow capped mountains remain cool, not warm enough to melt the previous year’s accumulate. Once the process has begun it is self perpetuating. The great Ice Age began and ice sheets built up, before  inexorably spreading over millions of square miles of northern:- Europe, Siberia and North America. The effects of the Ice Age are so noticeable that although this geological timespan is very short (only 1 million years) it has been accorded its own Period, the Pleistocene, and a new ‘era’ was created - the Quaternary.

In the past 2.5 MY cold polar waters have advanced southwards more than 20 times and ice sheets have built up on adjacent land masses. During these advances the Gulf Stream was deflected eastward towards Spain, and Britain was subjected instead to cold polar currents from Greenland. In Britain there were several glacial periods of Arctic cold interspersed with Temperate periods like today. In these glacial periods the average annual temperature lay between -6 to -9 degrees centigrade and all Britain’s mountainous areas became centres of glacier growth. Mull had its own corrie glaciers which gradually built up and flowed out down the old river valleys as valley glaciers, whilst on the mainland other glaciers were growing too. As arctic conditions deepened the mountain glaciers coalesced into something akin to the Greenland ice-cap and ice-sheets spread out over lowland Britain.  There were three main glacial phases each lasting several thousand years. The first and most extensive was the Anglian, this was followed by the Wolstonian, and finally the Devensian which was the least extensive.  Ice sheets more than 1000 metres thick reached as far south as North London.  A vast ice-sheet from Scandinavia flowed across the swampy depression of what is now the North Sea and entered eastern England.  Another ice sheet advanced up the Channel from the west.

 Ice sheets flowing out from the Western Highlands flowed across to Mull, whilst on its central higher ground  (on the harder rocks of the old Central Igneous Complex) Mull’s own valley glaciers were dominant. Ben More would possibly have had its peak visible just above the ice at its maximum, forming a nunatak. Some of the best glaciated valleys are to be seen from its summit, Glen Clachaig, Glen Cannel and Glen Forsa. Glacial sediments, till, outwash sands and gravels can be seen widely in Mull especially in the Glen More and Loch Don areas.

Mountains of Mull seen from the top of Ben More.