Isle of Skye: The Braes tombolo EarthCache
Hidden : 5/21/2010
Difficulty:
2 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

The Braes Tombolo

 A spit, a bar, but nothing to do with bingo; tombolos are unusual, and, on Skye, quite unique landscape features...and a chance to visit GC282WX, too.

The coast of northern and western Skye bears witness to the relentless attrition by the sea over thousands of years. These 'wave-cut platforms' are a reminder that the sea was once as much as 30 metres higher than today. The platforms were created at various times over the past 500,000 years, during glacial periods when the earth's crust sagged under the enormous weight of ice sheets. During these periods the sea level rose in Scotland, even though the world's oceans were partly locked up in great continental ice sheets and sea level at the equator was at least 100 metres lower than today.

Two distinct sets of raised beaches occur on Skye. Those lying 15 to 30 metres above sea level formed as Scotland's last major ice sheet decayed, about 15,000 years ago. The other set of raised beaches formed between 8,000 and 6,500 years ago during a period of rapid rise in world sea level caused by the melting of ice sheets in North America and Scandinavia and before Scotland had completely recovered from the unloading of its former ice cover.

These raised beached occur up to 10 metres above present sea level; some are associated with long abandoned caves, geos and sea stacks and at Braes, south of Portree, the coast is linked to an island by an unusual gravel spit (a 'raised tombolo'). An Aird, the ‘island’ is a splendid location with a fine view of the landslip formation of Ben Tianavaig to the north.

A tombolo (Italian, from Latin tumulus – mound) is a deposition landform in which an island is attached to the mainland by a narrow piece of land such as a spit or bar. Once attached, the island is then known as a tied island.

True tombolos are formed by wave refraction. As waves near an island they are slowed down by the shallow water surrounding it. These waves then refract or “bend” around the island to the opposite side as they approached. The wave pattern created by this water movement causes a convergence of longshore drifting on the opposite side of the island. The waves sweep sediment together from both sides. Eventually, when enough sediment has built up the beach shoreline, known as a spit, will connect with an island and form a tombolo.

To log this EarthCache, email countrymatters with answers to the following questions, before you log your visit. I will respond promptly:

(a) What is your estimate of the width of the tombolo at its narrowest point, i.e. the grassy bit;
(b) By how much do you calculate the sea level would have to rise to cover the tombolo?

Additional Hints (No hints available.)



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