The Geography Department

8-1 Coasts   

 5   Cliff failure and protection

Geog123   book 2

pages 16-17   1.7 Cliff collapse!

In January 2003 this section of the cliff at Walton-on-the-Naze has slipped, a movement called a rotational slump.

Barton-on-Sea, showing the cliff-top shops above layers of sand. Below the sand is the clay which, when saturated, causes the cliff to fail in a slump. Near the sea the slope is reinforced with rocks.

 

 

Why cliffs collapse

 

Not all cliffs are of hard rock, many are made up of quite soft deposits, of sand and clay. Most cliffs in the east of England are soft, from Walton-in-the-Naze to Dunwich, to Happisburgh in Norfolk and on up to the cliffs of Holderness (next section Coasts 6).

 

Geology- is all-important in determining how a cliff collapses (it will always collapse, sooner or later) . A chalk cliff will simply collapse over its full height, pile up rock debris at its base .. which is eroded by the waves, before they cut a notch and the process repeats. Cliffs of clay, or clay and sandstone, can slide, quite rapidly, towards the coast.

 

 

 

Rotational slump - occurs when a column of the cliff breaks away and slips down the cliff. The break is in the shape of a curve, and the block of cliff follows this curve.

 

 

 

Mudflow- occurs when the cliff become so saturated with rainwater that the cliff collapses and is mobile enough to flow quite quickly on to the beach.

 

Barton-on-Sea in Hampshire is a famous location for cliff failures. The reason for the cliff being so weak lies in its geology, with sands lying on top of clays. When heavy rains fall they make the sands heavy, but the water also goes through the permeable sands to wet the clay and the clays become slippery. The cliffs above the clays slide down and are removed by the waves on the coast.

 

 Video G215 tells the story.

The case of Holbeck Hall

insurers IPDury's account of Holbeck Hall's collapse.

pages 16-17 answer questions 2,3 and 5.

This is a photograph of the landslip that destroyed the hotel of Holbeck Hall in the town of Scarborough in Yorkshire.

Geological Society information booklet on landslides

Coastal defences    Below are a selection of the methods used to protect our coasts.

Revetments and steel piling at Overstrand, North Norfolk

Revetments, steel piling, rip rap and wooden retaining posts at Overstrand, North Norfolk

Rip rap and recurved sea walls at Withernsea on the Holderness coast, Yorkshire

Gabions of stones, in this case they look like flint, at Overstrand. They are retained behind timber works, a concrete esplanade and steel piling!

A stepped sea wall, and concrete/stone groynes at Walton-on-the-Naze.

A stone groyne at Mapplelton, Holderness, in Yorkshire. Rip rap protects the cliff in the foreground. a small beach has built up to the north of the groyne.

Preventing more damage

1. sheet 1E No more landslips! Homework

2. construct a table describing how each of the above coastal defence measures works. Which do you think might be the most effective at Walton-on-the Naze (opposite)?

 

	revetments
	steel piling
	rip rap
	sea wall
	gabions
	beach
	groynes

^Rip rap and the northern end of the concrete seal wall at Walton-on-the-Naze.

Coasts 1 Coastal environments

Coasts 2 Cliff and headland erosion

Coasts 3 Longshore drift

Coasts 4 Purbeck case study

Coasts 5 Cliff failure

Coasts 6 Holderness

Coasts 7 Rising sea levels

Year 8 work

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