Scottish Islands Explorer 40: Nov / Dec 2016

The Corryvreckan
Confusion of Flows
With so many opposing forces converging upon one
another, there is a confusion of flows. Essentially, the tidal
flow is disturbed, allowing a rising tide to evolve before the
flow has ebbed. The established consensus attributes the
cause of the Corryvreckan’s movement to strong currents
hitting the pinnacle of rock, but marine research conducted
in 2012 poses a new theory.
Oceanographers from the Scottish Association for Marine
Science (SAMS) mapped the seabed beneath the whirlpool
using high-resolution multi-beam echo-sounder technology.
Perplexingly, they found no evidence of a pinnacle. Having
mapped the steep-sided buttress of rock sticking out from the
Scarba shoreline, they concluded this to be the main driver
of the turbulence.
e research found that strong currents surging between
Jura and Scarba had scoured the ocean floor clean, removing
all sand and mud. Regardless of the cause, its hazardous
nature has never been in question. e primary and investigative
explorer, Martin Martin (c.1660-1719), once wrote of
the phenomenon:
‘It yields an impetuous current, not to be matched
anywhere. e sea begins to boil and ferment with the tide
of the flood, and resembles the boiling of a pot; and then
increases gradually until it appears in many whirlpools, which
form themselves in sort of pyramids, and immediately aer
spout up as high as the mast of a little vessel, and at the same
time make a loud report.’
Topographical Studies
is is from Martin’s seminal book of 1703, A Description
of the Western Isles of Scotland, which was the first published
account of life in the Hebrides as well as being an important
contribution to topographical studies in Scotland at that
time.
e whirlpool phenomenon is rare, with only seven known
in the world that rival or exceed the Corryvreckan in size or
strength. Other noteworthy sites include the Moskstraumen
on the Norwegian coast. It consists of multiple vortices which
interact with one another between the Lofoten Islands and
is globally second strongest - with currents reaching speeds
of 17 knots.
Unusually, it forms in the open sea owing to factors
including strong semi-daily tides and the abnormal seabed
40 SCOTTISH ISLANDS EXPLORER NOVEMBER / DECEMBER 2016