crescentic fracture
Quick Summary
In geology, a crescentic fracture is a type of chatter mark, which are small, curved fractures found on rock surfaces that have been glaciated. These fractures are formed by the pressure and impact of boulders moved by a glacier.1
Chatter marks are commonly 1–5 cm long but can be much larger. They are typically found on hard, brittle rocks like granite. The orientation of these fractures is often at a right angle to the direction of glacial movement.1
There are three main types of chatter marks:
* Crescentic gouge: Concave upstream, formed by the removal of a rock chip.1
* Crescentic fracture: Concave downstream, also formed by rock removal.1
* Lunate fracture: Concave downstream, but without rock removal.1
These features are important indicators of the direction of past ice movement.2
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