Environmental Engineering Reference
In-Depth Information
theterminalmoraine,acontinuouslineofdebrisleftbytheglacierthatoccupiedtheLoughorvalley.This
glacier greatlymodifiedthelandscape byprovidinganabundantsupplyofsilts,clays,sandsandboulders
that have been reworked during the subsequent rise in sea level to form the basis of the marshes today. It
is also likely that ice reached the coastal cliffs on the north shore, clearing frost-shattered debris and soli-
fluction material. Ice sheets and glaciers also brought many large rocks into the peninsula, the most obvi-
ous of which is Arthur's Stone. Utilised in the Neolithic period to form a chambered tomb, the 24-tonne
conglomerate capstone contains brown clay-ironstone, coal fragments and traces of fossil plants, which
do not occur in the Devonian conglomerates elsewhere in the peninsula. This confirms that the capstone
was derived from the northern outcrop of the Millstone Grit and carried to Gower by the ice.
FIG
20.
Solifluction bench below Rhossili Down and Rhossili Rectory, now a holiday cottage owned by the National
Trust. (Harold Grenfell)
David Painter for Figures
After the glaciations the sea level rose again and at its maximum extent low cliffs were cut in Oxwich
and Swansea bays. Since then sediments accumulating in front of these low cliffs has isolated them from
the sea and sand dunes have formed. Present marine activity is restricted to a limited zone at the foot of
the soft cliffs. In contrast the limestone cliffs were largely shaped in the Pleistocene when sea levels were
high. The north Gower cliffs, which are now some distance from the sea, are in the main 'fossil' cliffs,
while those on the south coast are best described as 'relict' because although they were largely shaped at
the same period as those of north Gower in places they are still subject to erosion by the sea. Periglacial
conditions were also present immediately following the last glaciation, but the retreat of the ice was rapid
and much of the peninsula is thought to have been ice-free by 14,000 to 15,000 years ago. There is no
reason to believe, however, that the ice will not return. Despite global warming, the present conditions
represent only a brief respite in a predominantly glacial age.
At the end of the Pleistocene period, 10,000 years ago, sea levels were well below the present, prob-
ably at least 22.5 metres lower. Early in the postglacial period the area of the present-day Bristol Channel
would have been occupied by a large river in the middle of a wide plain of birch tundra. From the end of
the last glaciation to the early Neolithic, about 5,700 years ago, sea levels in Britain rose steadily as the
