Glacial trough, Bealach na Baa

A ‘glacial trough’ is a long U-shaped valley. Some of the most striking glaciated valleys in the British Isles are near the west coast of northern Scotland. Bealach na Baa (‘Cattle Pass’ in Gaelic) is one of the most dramatic. A small river runs down it now; but the enormous gash that towers 700 m above it was made by ice.

The glacier that occupied this valley until 10,000 years ago was one of the last to survive in the UK at the end of the Ice Age. In geological time, therefore, the ice was very recent; and the clues in the landscape are still fresh: plenty of erratics, and halfway up the valley a ledge of glacially smoothed rock with striations.

When the Bealach na Baa glacier and others in the area were in a ‘surge’ condition, they could move as fast as 10 km a year. A surge must have occurred part-way along the valley as the steep downhill run from the 900-metre summit down to sea level gave the glacier a huge amount of power to grind away at the land.

Erosion in valley glaciers was produced by two forces: firstly by the ice itself; and secondly by boulders, rocks and stones — the ground moraine — caught up in the base of the glacier. When the ice retreated from Bealach na Baa, glacial erosion had straightened and widened the valley, leaving a U-shaped trough in the landscape.

Lowland glaciation — outwash zones

Glacial outwash

The effects of glaciation outside highland areas are less dramatic, but still widespread. The edges of ice caps and glaciers are rather ‘messy’, as these are the regions in which they’re starting to release all the different bits of material they’ve picked up along their path, including huge boulders.

In Iceland, at the end of winter, at the edge of the ice, water takes over from ice as the main driving force: an event that occurred millions of times during our glacial period. Like a river, this glacial meltwater starts to move objects downstream, away from where the ice has come to rest. As the ice melts, a huge range of material — boulders, stones, gravel, and whatever the ice has captured — is carried away.

The landscapes created by the ice itself may be spectacular. But those formed just beyond the glacial limit are vast in scale. There are many different types of glacial deposit, of which one example is the ‘outwash plain’ found in Iceland.

Most of the time, the outwash plains support very little vegetation. Here, material is constantly being moved around by the streams on the outwash plain, so vegetation does not have time to take root. Much of it is so fine that it is easily whipped up by the wind. Much further south, in Europe, this dust contributed to one of the most fertile soils on the continent, called ‘loess’.

A long time ago in Britain, ice, water and wind worked together in similar ways. At its maximum extent, the ice came as far south as the River Thames. Glacial deposits left beneath the ice still cover this much of the country, and water and wind deposited material beyond the ice, even further south. Four-fifths of the landscape of the country was shaped by glaciation in the last ice age.

Ice from all directions

Wood Lane Quarry, Shropshire

At Wood Lane Quarry in Shropshire, glacial deposits have been revealed consisting of fragments of rock brought in by three different ice sheets, from three different directions, and from hundreds of kilometres away. Among these it is easy to find granite from Cumbria, limestone from north Wales, and sandstone from Ireland.

In this quarry local Triassic sandstone which has been ground up by the ice is also found. This is processed and sold to the building and construction industries.