Beach

Query: History of the pebbles

Query
I was recently laughed at by friends by suggesting the pebbles had been brought along the coast intentionally and built up (like at Seaford) to ward off sea damage to the coastline developments. If they're natural, I also don't understand why they stop at the tideline? I'd really appreciate it if anyone can explain either the history, or if natural, how such a significant difference can be seen in photographs over just 80 years?
Quietly Curious, 01-08-2003

Response
The pebbles on the south coast are the remnant of the chalk debris (which includes flints) which was eroded from the chalk landscapes of southern Britain by snow meltwater flows at various times in the past two million years. The last time this occured was about 10,000 years ago.

The chalk was deeply frozen and in the short summer defrosts the surface layer of snow and partly defrosted chalk would slump under gravity to lower levels. As the glaciers went into retreat from the English Midlands, and as more snow water was released, rivers, and then sea level rose. The Channel formed (as we know it) about 9,000 - 8,000 years ago and Britain was separated from European mainland. Marine activity swirled away the chalky muds of the channel area and left the flint debris behind.

Currents and wave activity gradually rounded the flints into sub-angular pebbles. Currents and storm conditions drove some of this ashore as a fringe to wave activity, leaving a large quantity in the deep channel. It is this deposit that is being pumped up for 'marine aggregate' (concrete.roads etc) and is pumped ashore for coastal defence measures as at Seaford.

The pebbles are separate from the shore platform that underlies them and the highly mobile shingle is moved in a largely easterly direction for 20/24 hours of the day. It does not move either side of high water. It all ends up at Dungeness eventually.

There is a worrying finding by Sussex University geographers which has become apparent recently, and that is the fact that the shingle is a decreasing resource and that rising sea levels on the south coast, linked to increased storm activity, and dwindling shingle, means a bleak time ahead for coastal dwellers.
Geoffrey Mead, sent to website mailing-list, 05-08-03