The formation of natural arches
A natural arch is a rock formation where a rock arch forms, with an opening underneath. Most form where cliffs are subject to erosion by the sea, rivers or weathering. This natural arch is an example of coastal erosion.
Natural arches start as caves. Caves occur when waves force their way into cracks in the cliff face. This water will contain sand and other materials which erode the rock. In addition, air may become trapped in joints or cracks in the rock. When waves break, this trapped air is compressed which weakens the rock. Both these methods causes caves to form.
When the erosion breaks through to the other side, this forms an arch.
In time, arches will become bigger so that the top is no longer supported. When the arch collapses, this will leave the headland on one side and a stack on the other.
The stack will be eroded at the base and eventually collapse to form a stump.
Logging requirements
The coordinates will take you to where you can see one of the natural arches along this coastline.
Please send your answers to the following questions in a separate message:
- This natural arch is formed of two types of rock. Name the rock types of the upper and lower halves of the arch. Please also describe the look and feel of the two different types of rocks.
- The uneven surface separating these two rock types is known as unconformity. What does this mean?
- Please estimate the height of the space under the natural arch.
OPTIONAL: Please also post a picture in your log of you or your GPS with the natural arch.
Please note, you do not need to walk down to the arch although you may find this easier to answer the questions. However, please take care if you do choose to go down.