Erosion
Rock erosion can happen in different ways. Erosion is Weathering (the breaking down of the rock) and then the Transportation of the material away. The rate of erosion varies depending upon the type of rock, ie. hard rocks will erode at a slower rate than softer rocks.
Lets look at some forms of erosion :-
Weathering
Weathering is classified into 2 groups:
Chemical. eg Slightly acidic water. Chemicals produced by plants and animals. Probably not so relevant at this site but still a cause.
Physical. An external force is required. eg Attrition (banging stones together), Abrasion (liquid sand papering), Hydraulic Action (usually air pressure release, as it is more sudden). All can be caused by the tide. Freeze Thaw action - number of times this happens is critical, hence this is less important in UK with our present climate. This is obviously quicker in a permeable rock layer (as would chemical weathering be).
**Wind**
This will transport the material away once the rock has been broken down into small units. The wind can also blow small rock particles around causing a sand blasting effect (abrasion). (Even in deserts this effect tends to be over estimated.)
**Water**
This is important as a method of transportation. Waves and running water can also cause weathering by hydraulic action, abrasion and attrition. Important on coasts and in rivers.
**Water Permeation**
This is weathering and not transport. Water gets into a permeable rock. This can lead to freeze thaw (hydraulic) action if the temperature regularly goes through freezing point. Or chemical weathering (eg acidic water flowing through limestone).
**Wave Action**
This both breaks up rocks (Abrasion, Attrition and Hydraulic Action) and transports the weathered material away. Higher energy waves will do more weathering and transportation.
**Human Action**
Often seen in soft rock areas where human action is frequent. Shallow gullys can be seen on footpaths where many people have walked over time. The frictional action of walking boots or shoes upon the rock loosens grains and these are carried away either on shoes or by any of the other actions listed above.
This EarthCache covers two sites just a few metres apart.
Site A. You should be standing in front of an archway.Please answer the following questions.
A1. Which of the above processes do you think created this arch ?
A2. To the left of the arch how many different colours of rock can be seen and what type of rock is this ?
A3. Please stand inside the arch and tell me how high the top of the arch is above sand level
A4. Do you think this type of rock is hard or soft ?
A5. To prove your visit please tell me what man made item is just to the left of the archway.
Site B. Please move to the cliff face approx 25m downstream at N 53 22.647 W 003 13.155
B1. Looking at the face, which of the above processes do you think have eroded the face ?
B2. Estimate the height of the rock face at this point.
B3. Describe in your own words what features you can see in the rock face.
In order to claim this EarthCache please submit your answers via the message system as this allows a photo to be added. A photo would be nice (not a requirement) please avoid putting photos containing answers to the questions on the cache page. Pictures with answers shown will be deleted.