Physical weathering of pre-existing rock ultimately leads to the formation of sedimentary rocks, as well as development of many desert landforms. In the 19th century geologists proposed that periodic daily solar heating and cooling could cause the breakdown of exposed rocks, however, laboratory studies in the 1930s cast doubt on “diurnal solar insolation” as a cause of physical weathering. Recent research has restored the key role the sun plays in physical weathering.

Les McFadden is a professor emeritus in the UNM Earth & Planetary Sciences (E&PS) Department. He received an MS & PhD in geosciences from the University of Arizona after earning a BA in anthropology from Stanford University. He served as chair of the E&PS Department (1999-2007) and is a fellow of the Geological Society of America (GSA). In 2017 he received the Kirk Bryan Award for Excellence from the Council of the GSA.