The River Spey brings pebbles to the coast, where there is superb visible evidence of uplift of the land after the ice melted
The lower reaches of the River Spey gives a classic example of a mature braided river system. Vast quantities of stones are washed downstream when the river is in spate. As the river widens, the force of the water is dissipated and the stones are dumped, forming shingle bars and islands between the ever-shifting channels of the river. To the west of the mouth of the river is the ‘Sea of Stones’, one of the most extensive shingle systems in Britain.
The coast here is sheltered from the south and west, but is fully exposed to the north-east, from which the strongest winter storms come. This, plus the effects of the tide, result in longshore drift; that is, the effect of wind and tide moving stones and sand westwards along the coast. At the same time, the sea is encroaching on the land. Pillboxes built during the 1939-1945 war to watch for enemy vessels approaching no longer have a view of the sea because of the banks of stones that have been building up over the decades since then. The line of tank traps along the coast is being engulfed by the stones at its western end, before being once again exposed and then destroyed by the sea.
Inland from the tank traps are parallel ridges of stones that tell a fascinating story. During the last glacial period, Scotland was covered by a huge ice cap, probably several kilometres thick. The enormous weight of the ice pushed the Earth’s crust down into the mantle of the Earth. After the ice melted about 15,000 years ago, Scotland began to rise, very slowly, and it continues to do so today as the land seeks to reach equilibrium without the weight of the ice. You can imitate this process by floating a block of wood in a bucket of water, and placing a stone on top. When it settles, note how much of the wood is submerged in the water. Then remove the stone, and when the block of wood reaches equilibrium again, note how the wood has risen relative to the water level.
Each of the ridges in the Sea of Stones is a storm beach left high and dry as the land rose relative to the sea. 10,000 years ago, the sea reached the foot of the Binn Hill; now it is almost 700 metres away, and the former shore is about 15 metres higher than the present shore. So, you can work out that the land has risen 15 metres in 10,000 years, an average of 1.5 millimetres a year.
Text contributed by Anne Burgess
Find out more
Scottish Wildlife Trust Reserve: https://scottishwildlifetrust.org.uk/reserve/spey-bay/
Hansom, J.D. (2003) Spey Bay, Moray. In: May, V.J. & Hansom, J.D. Coastal Geomorphology of Great Britain. Geological Conservation Review Series No. 28. Joint Nature Conservation Committee, Peterborough, 290-296.
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