Geoscience Reference
In-Depth Information
the present-day Isle of Wight marks the stump of this Chalk belt left by wave erosion
today. West of the present Isle, the wave erosion eventually broke through what must
have been a continuous line of Chalk hills (Fig. 124), exposing the softer Tertiary rocks
to the north to intense wave erosion and creating the broad concave coastline around
Bournemouth. All that remains of the Chalk ridge today are the headlands of Ballard
Point with Old Harry on the Isle of Purbeck, and the Chalk Downs stretching from the
Needles to Culver Cliff on the Isle of Wight.
We can visualise further the effect of this 120 m sea-level change by considering
the present Isle of Wight and its surroundings. At the time of low sea level 20,000 years
ago, the area now occupied by the Isle of Wight was simply an area of higher ground
surrounded on all sides by lower land. To the north, a large Solent River flowed east-
wards along a valley where the Solent seaway is today (Fig. 124). The river transported
water and sediment from much of Dorset and all the main rivers of Hampshire, as well
as from the south, where the higher ground of the present Isle of Wight was continuous
with Chalk hills now covered by the waters of the English Channel, as described above.
The rivers of Southern England and northern France drained into this plain, eventually
flowing into the Atlantic west of Cornwall (Fig. 21). This involved a change in direc-
tion from eastwards to westwards for the waters of the Solent river as it negotiated the
topography and bedrock contrasts generated by the fold and fault movements of the
Purbeck-Isle of Wight stepfold.
Some 20,000 years ago the view shown in Figure 125 would have looked across
the open valley of the Solent river, with no sea visible. The Flandrian sea-level rise has
flooded a large valley, creating the present Solent and making the distant Chalk hills
into the Isle of Wight. In the foreground, the rising sea has also flooded the mouth of
the Lymington tributary of the former Solent river, and storms and tides have mobil-
ised sediment to produce the pattern of river-mouth islands.
