Loch Maree from Glen Docherty
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Despite the millennia of geology involved in the formation of Scotland most of the current regions owe their appearance to the last Ice Age which occurred between 20,000 and 10,000 years ago. During that time the planet went through a prolonged cold period causing the Arctic ice to extend from the North Pole and to cover Europe. Scotland was covered by an ice sheet and little of the land below would have been visible with only the very highest peaks above the level of the ice.
The movement of the expanding ice sheets, its tremendous weight while it covered the land and the movement as it retreated must have had a massive impact on the land below. Of course, this can only be surmised from the evidence visible today as it's impossible to determine exactly how the land looked prior to the last Ice Age.
Volcanic activity in this region ceased about 50 million years ago, after which the landscape was shaped by glaciation from about 1.8 million years ago to the end of the Great Ice Age about 10,000 years ago. The shape of Glen Docherty is typical of a glen formed by the action of glaciers. Glaciers tend to follow the pre - existing drainage. They take the V-shaped valleys that flowing waters carve and widen out the bottom of the valley into a U. The glacial ice puts the most erosion on the lower portion of the valley sides, so it widens out the V shape into a U. Additionally, the flowing ice erodes the insides of meanders, straightening out once sinuous river channels. Unlike water where the inertia of the water causes erosion on the outside of a curve as the water collides with the bank in order to change direction flowing ice moves slow enough that the same inertial forces are not at play. The erosion of flowing ice is greatest where the ice moves fastest, and that is where the slope of the valley is greatest. The inside of the bends is where the topography drops faster than the outside of a bend. The end result is the straightening and widening of the valley.
A valley is an extended depression in the Earth's surface that is usually bounded by hills or mountains and is normally occupied by a river or stream. Because valleys are usually occupied by a river, they can also slope down to an outlet which can be another river, a lake or the ocean.
Valleys are one of the most common landforms on the Earth and they are formed through erosion or the gradual wearing down of the land by wind and water. In river valleys for example, the river acts as an erosion agent by grinding down the rock or soil and creating a valley. The shape of valleys varies but they are typically steep-sided canyons or broad plains, however their form depends on what is eroding it, the slope of the land, the type of rock or soil and the amount of time the land has been eroded.
There are three common types of valleys which include V-shaped valleys, U-shaped valleys and flat floored
V-Shaped Valley
A V-shaped valley, sometimes called a river valley, is a narrow valley with steeply sloped sides that appear similar to the letter "V" from a cross-section. They are formed by strong streams, which over time have cut down into the rock through a process called downcutting. These valleys form in mountainous and/or highland areas with streams in their young stage. At this stage, streams flow rapidly down steep slopes.
U-Shaped Valley
A U-shaped valley is a valley with a profile similar to the letter "U." They are identified by steep sides that curve in at the base of the valley wall. They also have broad, flat valley floors. U-shaped valleys are formed by glacial erosion as massive glaciers moved slowly along. U-shaped valleys are found in areas with high elevation and in high latitudes, where the most glaciation has occurred. Due to their large size and weight, glaciers are able to completely alter topography, but it is the alpine glaciers that formed most of the world's U-shaped valleys. This is because they flowed down pre-existing river or V-shaped valleys during the last glaciation and caused the bottom of the "V" to level out into a "U" shape as the ice eroded the valley walls, resulting in a wider, deeper valley. For this reason, U-shaped valleys are sometimes referred to as glacial troughs.
Flat-Floored Valley
The third type of valley is called a flat-floored valley and is the most common type in the world. These valleys, like V-shaped valleys, are formed by streams, but they are in their mature stage. The valley floor gets wider. Because the stream gradient is moderate or low, the river begins to erode the bank of its channel instead of valley walls. This eventually leads to a meandering stream across a valley floor. Over time, the stream continues to meander and erode the valley's soil, widening it further. With flood events, the material that is eroded and carried in the stream is deposited which builds up the floodplain and the valley. During this process, the shape of the valley changes from a V or U shaped valley into one with a broad flat valley
Ice-carved landscapes
Under the right conditions, glaciers can be very effective agents of erosion. In the uplands, powerful ice streams carved deep glacial troughs from the existing valleys (e.g. Glen Clova and Glen Docherty) and sometimes formed deep rock basins on their floors (e.g. Loch Ness and Loch Monar). Elsewhere, they breached watersheds, cutting new glens that now form important transport routes (e.g. Glencoe and Glen Shiel). By far the greatest impact was in the West and Northwest Highlands, illustrated by the fact that 90% of the corries and more than 90% of the rock basins are in westerly flowing river catchments. There, snowfall was greater, the ice thicker and the glaciers steeper and faster flowing and hence capable of more effective erosion. Each successive glaciation not only helped to shape the landscape, but also removed most of the deposits of earlier glaciations. Therefore much of the evidence we see today dates from the time of the last major glacial period. This last period began around 33,000 years ago and peaked about 22,000 year ago, when a large ice sheet covered all of Scotland and extended southwards to the Midlands of England.
To claim this earthcache, please send the answers to the questions below to us by email - do not post in your online log.Your log may be deleted if this criteria is not met. Educational guidelines for Earthcaches are set by Geocaching.com and GeoSociety.org (Earthcache) and have to be adhered to.
1 Would you describe the shape of the valley you see before as a V,U or flat floored valley ? Give reasons
2 How thick was the piled up sand and gravel which went on to become the Torridon sandstone ? Info board may help
3 Looking at the valley sides and tops,estimate the height of the valley sides, are both sides the same height, is the vegetation, rocks etc the same on both sides ? Describe what you see and can you give reasons for any differences ?
4 Can you see any evidence of glacier remains on the left hand side of the valley here today ? Describe what you see and where would it have been found in the glacier ?
While not compulsory, it is always nice to see a photo from your visit ~ enjoy the view !
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