Scottish Islands Explorer - November-December 2016

40 SCOTTISH ISLANDS EXPLORERNOVEMBER / DECEMBER 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 investiga-

tive 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 aer

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