“IN A SPIN” CORRYVRECKAN EARTHCACHE EarthCache
“IN A SPIN” CORRYVRECKAN EARTHCACHE
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Find out why one of the world's largest whirlpools occurs at this spot.
Between the islands of Scarba and Jura lies a stretch of water that strikes fear in all those who sail the Inner Hebrides for here can be found the largest whirlpool in the British Isles – Corryvreckan - the third or sixth-largest whirlpool in the world according to who you believe. It is said that sometimes the roar of the waters can be heard up to 10 miles away!
Yet some years ago when sailing in the area in a Nicholson 32 out of Kilmelford, we anchored in Port an Tiobairt on the NE coast of Jura and walked north to view the “beast” and were surprised to find a gentle water rotation with canoeists bobbing around at the periphery! Obviously it isn’t always a terrifying whirlpool.
So why does it occur here and why does it vary so much in its ferocity? A combination of strong currents and unusual underwater topography conspire to produce a particularly intense tidal race in the Corryvreckan channel.
The strong currents are caused by the geographical relationship between the islands and mainland of the Argyll coast which creates an area of sea with a very complex tidal system. As the main flood of water flows north passing the Mull of Kintyre it sucks the water out of the Clyde Estuary, resulting in an extraordinary anomaly between the towns of Crinan and Lochgilphead. Although these places are just 6 miles apart, the tide is high at one and low at the other. With a diametrically opposed state of tide, huge volumes of seawater pass through the Gulf of Corryvreckan. As the flood proceeds up the Sound of Jura it is squeezed by the narrowing of the Sound and this increases the flow, so that it passes through the Gulf at speeds of up to 8½ knots (≈16 km/h) on a full spring tide.
Unusually the whirlpool in the Corryvreckan works differently when the tide is ebbing (i.e. going out which means passing from W to E between the islands) from when it is flooding (i.e. coming in or passing to the W from the E through the Gulf of Corryvreckan).
On the flood, water flows up the Sound of Jura and is agitated by the geography of the seabed for there are innumerable humps and holes and reefs in the Sound and these create up-thrusts and eddies all over the place. As some of the fast flood tide passes through the narrow channel between the islands of Scarba and Jura it meets 2 unusual seabed features which combine to create the whirlpool. At the eastern end of the channel is a huge hole which drops down to a depth of 219 metres (670 feet) and further west there is a 130 foot basalt pinnacle which rises sharply to within 29 metres (100 feet) of the surface. The steep east face of the pinnacle forces a massive upthrust of water to surface in pulses which are then swept away westward by the tidal flow and these dissipate into vortices or whirlpools moving west. This is all clearly visible when there is no wind and the turbulent patterns are fascinating to see in mirror calm conditions. However when there is any serious wind strength, particularly from the west, the up-thrusts at the pinnacle fold into the oncoming waves and accentuate them. Thus building, in gale force conditions, standing waves that can be 8, 10 or 15 feet high. A truly awesome sight!
On the ebb, however, water is flowing into the Gulf relatively undisturbed from the open sea and the whirlpool is not very prominent. Likewise, when the wind is from the SE, N or NE, then the Gulf of Corryvreckan is sheltered in the lee of Scarba and the sea tends to be less rough and the whirlpool less impressive. The state of the tide and whether it is springs or neaps will also affect the amount of water flowing and hence turbulence so one can never be entirely sure how the whirlpool will be behaving before one gets there.
To claim this Earthcache you do not have to sail to this spot – just view it from the south coast of Scarba or the north of Jura. To get to both coasts requires a tramp over trackless machair and I recommend that people. DO NOT WEAR SHORTS as my legs (& privates!) were the feeding grounds of several ticks when I made the hike many years ago. When you get a view of the Gulf of Corryvreckan observe the state of the whirlpool. You can post a picture of it or yourself if you like but to log this Earthcache you MUST e-mail me with the following 4 facts:-
1) The time you made your observations, preferably in GMT.
2) Was the tide coming in or out or was it slack water at high or low tide?
3) Was the whirlpool moving clockwise or anticlockwise? and
4) Was the whirlpool swirling gently or was it an angry monster?
The author George Orwell lived on Jura near Corryvreckan while he was writing "1984" and he narrowly survived an encounter with the whirlpool when out in a boat with friends.
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