Geoscience Reference
In-Depth Information
Fig. 7.14
Fluted stacks about
4 m high on the beach at Cullen,
Scotland. Although weathered,
each stack still preserves
numerous cavettos on its flanks.
The flutes align towards the
headwall of the Storegga Slide
high-velocity flow or even wave breaking over the back of
the headland generates such erosional forms. Large storms
can be ruled out as a mechanism for molding these bed-
rock-sculptured features. Although North Sea storms can
generate 15 m high waves superimposed on a 2 m high
storm surge, such waves are short in wavelength and break
offshore of headlands. Both fluted terrain and the chiseled
headland at Logie Head require sustained, high-velocity,
unidirectional flow that only a catastrophic tsunami result-
ing from a mega-slide or asteroid impact into the sea could
produce.
It might also be conceivable to attribute such features to
glacial activity or to sub-glacial flow. After all, the features
Hall described were later attributed to just such a process.
Indeed, the orientation of flutes along the Grampian coast-
line corresponds to flow lines for the Late Devensian ice
sheet that covered this region. However, the fluted features
at St. Andrews (and east of Edinburgh at Dunbar), which
also point in the same general direction as those along the
Grampian coast, are not aligned with the direction of ice
sheet movement. Finally, if the flutes are the products of
glaciation or catastrophic sub-glacial water flow, then the
features should not be limited just to the immediate coast-
line. Their similarity to features in southeastern Australia,
which at no time has been affected by glacial ice during the
Pleistocene, implies a common mechanism for both local-
ities. It is only fitting that after 150 years, evidence can be
found in eastern Scotland for Hall's (
1812
) hypothesis for
bedrock sculpturing by catastrophic tsunami—albeit on a
smaller scale than he envisaged.
7.6
Bristol Channel, United Kingdom,
January 30, 1607
In northwestern Europe, the Storegga slides are not unique.
The 1,000 m bathymetric contour is the site of at least 15
other slides on the continental slope between west Ireland
and northern Norway (Kenyon
1987
). The largest of these is
equivalent in size to the smallest Storegga slide. At least
seven of these slides exist along the coast of Ireland within a
few hundred kilometers of the coast. Remnant slides also
exist on underwater platforms between the British Isles and
Iceland with a debris flow, again as large as the smaller
