High and Dry
The isle of Rum has witnessed a complicated history of sea-level rise and fall over the last million years or so. This is reflected in the geomorphology of the island's rugged, spectacular coastline.
Where the land presently meets the sea has been the coastline on Rum for only a few thousand years. High above the waves, 30 to 40 m in fact, is a rock platform that encircles almost the entire island. This represents Rum's oldest coastline and was cut by waves around 1000,000 years ago (before the last glacial period), when the sea level was much higher than it is now.
At the time of the last major glacial period, sea level across the inner Hebrides was still higher than today. As the Scottish ice sheet thinned and the glaciers rapidly retreated, a great weight of ice was removed from the land and so the Earth's crust locally began to rise.
Rebounding of the land caused the relative sea level on Rum to fall, even though the actual volume of water in the ocean had increased due to the melting ice. The raised beaches and abandoned shorelines left high and dry are the legacy of these once higher sea levels. The raised beach at Harris on the west coast of Rum is 30 m above the present-day tidemark. Similar but smaller abandoned beach fragments are found at Kilmory Bay in the north and at Loch Scresort in the east of the island.
Once the rate of crustal uplift had slowed almost to a halt, sea level around Rum began to rise. Evidence of this is seen at Harris, Kilmory and Guirdil bays where a second set of raised beaches are set back from the present-day storm beach. These post-glacial beaches, at 5 to 6 m above the high-tide mark, formed around 6000 years ago. Although not noticeable, the sea level on Rum is still falling slowly as the island gradually rises!