Chatter mark

{{Short description|Mark left by rocks within moving glaciers}} {{For|chatter marks made in machining|Chatter (machining)}} [[File:Lac Beauchamp chatter marks.jpg|alt=Brown crescent-shaped chatter marks on a formation of gray sandstone.|thumb|Chatter marks on sandstone south of Lac Beauchamp, in Gatineau, Quebec, Canada]] In glacial geology, a '''chatter mark''' is a wedge-shaped mark (usually of a series of such marks) left by chipping of a bedrock surface by rock fragments carried in the base of a glacier (glacial plucking). Marks tend to be crescent-shaped and oriented at right angles to the direction of ice movement.<ref name = EG>Marshak, Stephen, 2009, Essentials of Geology, W. W. Norton & Company, 3rd ed. {{ISBN|978-0393196566}}</ref><ref> Dictionary of Geological Terms, Third Edition (1984). [http://www.agiweb.org/pubs/pubdetail.html?item=300260 American Geological Institute Publications]. Robert L. Bates and Julia A. Jackson, Editors</ref>

There are three main types of chatter marks. A crescentic gouge is an upstream-facing concave mark created when a piece of rock is removed. A crescentic fracture is a downstream-facing concave mark that also results from rock removal. In contrast, a lunate fracture is likewise downstream-facing but forms without the removal of rock material.<ref>[http://www.britannica.com/EBchecked/topic/107979/chatter-mark Encyclopædia Britannica]</ref>

==See also== *Glacial polish *Glacial striation

== References == {{reflist}} {{Commons category}} Category:Glaciology