Cryoplanation surfaces in the central andes at latitude 35º S

Abstract

Abstract A survey of cryoplanation surfaces in the Andean mountain range near latitude 35º south, and longitude 70º west shows cryoplanation surfaces are present on plutonic, volcanic, sedimentary and metamorphic rocks. Gypsum mountains above the lower limit of permafrost do not show cryoplanation. Most cryoplanation terraces are in areas with mean annual air temperature below −1ºC, (i.e. above the lowest limit of sporadic permafrost at 2800 m). The largest cryoplanation surfaces are observed on sedimentary rocks and located in areas where mean annual air temperatures are near 0ºC. Possibly, these surfaces are inactive under the present climate and were formed in a colder, past cryogenic episode. The largest cryoplanation surfaces are formed in sedimentary rocks, followed by volcanic, metamorphic and intrusive rocks. Gypsum rocks of low frost susceptibility (non‐porous) do not produce cryoplanation terraces. Cryoplanation is thought to be the result of frost shattering, frost heave and gelifluction of frost‐susceptible (porous) rocks in a climate with numerous freeze‐thaw cycles.