The sea cliffs here are one of the classic sites for seeing first-hand the scale of deformation which can be caused by glaciers and ice sheets.
To log this cache you will need to send me the answers to the following questions:
1a. From observation how thick, to the nearest 10 metres, do you estimate the chalk table to be?
1b. Based on your estimate and the data in the Description, how many thousands of years did this block of chalk take to form?
2. What is the mineral in chalk?
3. The original bedding is preserved by bands of what?
4. As an option, but to preserve a record and to show you were there please take a photo of yourself or your Geocaching name beside the curved brickwork on the shoreline
The large scale deformation here - known as “glacitectonism” - was formed during the Anglian glaciation about 450 thousand years ago by a major ice sheet flowing from the North.
As it advanced towards this location the ice detached a number of large, slab-like blocks - known as “glacial rafts” composed of chalk and the overlying shallow marine sands and gravels and transported them before stacking them into the glacial sediments being laid down at its margin.
The main glacial raft at Overstrand is over 100 m in length, and dips at between 20° to 30° towards the North. Although deformed by the ice, the original bedding within the chalk is clearly preserved by bands of nodular flint. Towards the southern end of the raft, this bedding is folded by an open, asymmetrical monocline which formed as the chalk was being pushed southwards by the ice. It is worth walking to the defined waypoint to observe this.
The spectacular glacial rafts at Overstrand form part of a complex, variably deformed sequence of glacial sediments exposed along the North Norfolk coast which record the repeated inundation of this part of eastern England by ice during the Middle Pleistocene Anglian glaciation.
Now reflect for a moment on the chalk deposit that has 'arrived' here. Chalk is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton and marine organisms that had settled on the sea floor. Studies have shown that chalk deposits develop very slowly, at a rate of about 1 to 6 centimeters per thousand years. For the purpose of the question assume that this block developed at its original location at a rate of 4 centimetres per thousand years.
SAFETY NOTICE:
Take careful note of the Parking suggestion and the Trailhead. There is a track at this point which gives access to the beach. Be wary of taking 'shortcuts' away from the path:grass is slippery when wet. You must take account of the state of the tide as there is a risk of tidal cutoff and risk of drowning, This is particularly the case if you approach directly from Overstrand. Furthermore, the walk along the foreshore includes pebble, rocks and large boulders some of which are covered in seaweed and natural foreshore materials. Take care of your footing and route.
If you get in trouble, call 999 as soon as you can and ask for the Coastguard, telling them Place (where you are - use the GPS coordinates), Problem and People (how many of you they are).
This cache has been placed with the kind permission of North Norfolk District Council ( who also advise that the phone signal here can be poor - so downloading for offline use might be worthwhile) and in consultation with the Crown Estate and Natural England.
On a personal note I want to acknowledge the courtesy and efficiency of the Public Servants who assisted in securing permission to proceed with this EarthCache.