The slump in Overstrand, earthcache
Overstrand is between Cromer and Trimingham, where the north east Norfolk Cliffs reach their greatest height and the Cromer ridge meets the coast.
The cliffs at Overstrand are formed of Pleistocene materials including glacial tills, sands, gravels and laminated clays which form the main cliff profile and overlie the Marly chalk. The deposits are highly contorted and rapidly varying in nature including the presence of huge chalk erratics (blocks). These deposits are unconsolidated and have been disturbed by subsequent glacial action and settlement as the ice melted.
The erosion at Overstrand is stated to be 0.75m per annum with an estimated loss of 750 000 cubic metres of material (Cambers, 1973), but the full extent to which cliff retreat has occurred is unknown. A major event in January 1994 resulted in 20m of recession at the cliff top with debris run out across the beach. Three failures since May 1990 have resulted in cumulative cliff top recession of approximately 90m.
The process of erosion at this point is slumping, leaving bowl-shaped hollows high upon the cliff face, below which the slumped material turns into a flow, which carries it down to the beach. Once on the beach the mud flow spreads out to form a 'toe' which is gradually removed by the sea at high tide. At Overstrand most of the cliff retreat happens as a result of slumping followed by flow. About 85% of landslips relate to heavy rain and storm events. Rain falling on the immediate coastal hinterland is absorbed by infiltration and seeps towards the cliffs where the additional weight overcomes the resistance to shearing and the slope falls.
This bracing walk takes you past an interesting stretch of beach and geological section which is important for research into many aspects of Pleistocene and Cretaceous geology in the UK. Some of the youngest chalk in the UK is exposed in the cliff immediately above the east end of the Overstrand promenade.
To log this cache.
To log this cache you will have to visit and answer the questions which are related to the coordinates given.
When the answers are collected, send them to me via my profile. You can log immediately.
Logs without answers will be deleted.
Please do not include pictures in your log that may answer the questions.
To log this Earthcache you are required to comply with 5 requirements
1, at N52 54.963, E001 20.917
note and describe what you can see. (see Q4)
2, from here, at N52 54.954, E001 20.980
describe what can you see to prevent erosion. (look sea-ward)
3, at N52 54.969, E001 20.959,
describe the cliff face and what is running through it. (see Q5)
4, at N52 54.986, E001 20.949,
describe what is here and how it relates to Q1. What is the difference in height.
5, at N52 55.006, E001 20.937,
looking west towards the cliff, why is this similar to Q3 but different
6, optional, at N52 55.051, E001 20.881,
take a picture of the cliff (to see how it changes in time), yourself and / or GPSr
carry on walking and it brings you to a concrete path back up to the cliff top.
Note:
You don't need to climb any of the cliffs, and you shouldn't as they are very unstable. Any answers can be found from the footpath. The top footpath requires a bit more care as this has suffered from the slippage.
Cache placed with the kind permission of North Norfolk District Council