Figure 12. Chatter marks. This image shows two rows of crescent-shaped gouges in granite, roughly aligned from right to left. Geologists refer to these as chatter marks, and they form when cobbles in the base of the glacier bear down in one location, causing the underlying rock to fracture in this characteristic shape. They are important because their shape shows that the glacier moved from right to left.
Last updated on January 6, 2012