Ice, Wind & Water

Overlying the rocks are deposits that have come from the action of ice, wind and water during the geological period called the Holocene.
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Directly above rocks is a veneer of glacial till. This is an accumulation of unsorted, unstratified mixture of clay, sand, gravel and boulders. There are one of two types of till in east Sutherland and Caithness. The first is a shelly till that contains evidence that it was sourced from the floor of the ancient Moray Firth. The second contains no shells, is brown and contains igneous and metamorphic rocks. It is this second till that covers much of the floor of the Strathy valley. Regionally this glacial till extends as far east as Watten in Caithness. There are other deposits related to glaciation that can be found in the area. It is thought that during the ice age there was over 1km of glaciers above the land surface. This ice sheet is thought to have disappeared around 15,000 years ago.
Deposits related to the meltwater and the bulldozing action of the glacier can be found at the margins of the strath. Better examples of these lateral moraines can be found of the eastern side of the Strath of Halladale.
Boulders transported by the glacier and deposited away from their parent lithologies are called erratics. Those that are placed on top of moraines and rock hills are called perched blocks. Many geologists have examined these to try and understand the pattern of glacial movement in a regional context. Examples of these occur on the hills between Reay and Armadale, including the hills above Strathy.
All of these help us to decipher what happened during the last period of glaciation to hit our strath. At that time we can imagine an environment much like Greenland today. Water melts from the glacier and washes through clay, silt, sand, gravel and boulders carrying these further down stream. Larger boulders can be placed upon deposits as the glacier recedes.
As the glaciers receded the weight of the glacier was removed from the landmass. This in turn resulted in the land rising relative to the sea level. The rise in sea level from the melt water was less than the rate at which the land rose - giving the false impression of sea level drop during the Holocene.
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Evidence of this land rise can be seen in Strathy too. Just to the west of the mouth of the Strathy river a horizontal, linear feature can be seen on the hill side. This feature is called a raised beach and represents the sea-shore during and just after the last glaciation. This fossil beach is duplicated all along the coastline between Durness and Reay.
As temperatures rose at the start of the Holocene (11,000 year to present) there were significant changes in vegetation. Previously vegetation during the glacial period was limited to Arctic-alpine species and afterwards these moved to higher altitudes. Replacing the alpines were juniper, birch, heather and crowberry. Birch was replaced, based on pollen analysis, by heather at around 6200 years before present.
Throughout the last 11,000 years peat has gradually been accumulating as exemplified along the road from Forsinard to Melvich. Generally the climate has been wet and warm enough to encourage the growth of bog forming plants, yet cool enough to supress decomposition. Of course Sphagnum moss is the main constituent of peat bogs; it holds water, produces organic acids that help preserve organic remains and is able to absorb nutrients from water.
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At the mouth of the Strathy river there is evidence of coastal deposition and erosion. Deposition isrepresented by the wide long beach that is enjoyed by many people. The shape or outline of the beach is constantly changing in response to the sea state, seasons and wind direction. The wind has also blown the sand into the dune system that we can see today. This too is constantly adapting to the changes in the environment.
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Geology represents the main control on the coastal erosion of Strathy Bay. The breaks in the rock, called joints, allow air at high pressure to be compressed by waves into these small gaps. Through time these further split the rocks and create the scenery that we recognise now; gloups, geos and caves.
Above the cliffs the soil clings to the edge. In places horizontal ridges can be seen. These do not represent sheep tracks but slow, gradual soil creep related to soil slope failure.