Corryvreckan
Watched a fascinating "Equinox" on Ch4 last night about whirlpools.
Unsurprisingly Corryvreckan was featured (as it is the closest to home).
The programme charted an expedition by a group of divers who took a dive
to investigate the depths of the maelstrom. They didn't actually dive to
the bottom as it turns out that the whirlpool is over 200 metres deep (!)
but they did dive on the spike of rock that contributes to the ferocity
of the waters around the area, which is only 30 metres down. They found
rocks scoured by the action of the whirlpool, including hollows carved out
of solid rock by other rocks and the extreme forces of the water (imagine
a washing machine filled with granite boulders and you'll get the picture).
They were diving in a short period between the tides when it was relatively
calm but once the tide turned they explained it was like standing under
a waterfall (and remember, this is 30 metres down). The only way they could
get back to the surface was to launch their rescue buoys and haul themselves
up on the hawser that connected them to the buoy.
When the tide turns the water rushes through the channel and over the spike
of rock they were diving on - the water is effectively flowing downhill
at this point as the incoming tidal surge is 1 metre higher than the water
on the other side of the spike, and this creates eddies of water which turn
into whirlpools, which typically only last for a few minutes before they
are consumed by other whirlpools and eddies. As such, therefore, Corryvreckan
isn't really a permanent whirlpool but more of stretch of incredibly strong
currents (running at over 20 knots) - a giant washing machine which mixes
millions of tons of water together every hour.
Current research indicates whirlpools are absolutely vital to life on Earth.
As with many things in nature they are based around the concept of fractals
- the further away from the water you are the bigger the whirlpool appears
(the famous one of Norse mythology in the North Sea is several kilometers
across). When you look from space you see whirlpools several thousand miles
across, particularly in the Pacific. They perform the essential task of
mixing warm and cold seawater together - if this didn't happen the temperature
of the oceans would fall to freezing within 3000 years, totally changing
the climate and potentially making Earth uninhabitable.
By the way, the best time to go and see Corryvreckan (or any whirlpool)
is at the spring and autumn equinoxes, as the tides are highest at that
time, and therefore the tidal surge is as well. At this time the surface
of the sea at Corryvreckan actually bulges upwards, apparently quite noticeable
to the naked eye...
alan
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