Frost Mounds: Active and Relict Forms

Abstract

Frost mounds are ice-cored mounds or hills found in present-day environments characterized by permafrost or seasonally frozen ground. The formation of these landforms during Quaternary cold periods has been inferred from the presence of circular or ovate depressions surrounded by raised rampart-like rims (‘ramparted depressions’) in now-temperate mid-latitude environments. Such landforms were at one time almost universally interpreted as the remains of pingos. Many smaller ground-ice phenomena (i.e., lithalsas, palsas, and seasonal ground-ice mounds) also exist, however, and greater understanding of these smaller ground-ice mounds has driven the reinterpretation of many ramparted depressions as lithalsa remnants. This article reviews the nature, origin, and geomorphic evolution (growth and decay) of all types of frost mound, evaluating the long-term preservation potential for each type. In addition, it highlights nonperiglacial processes (e.g., the melt of buried glacier ice) which can also lead to the development of ramparted depressions, hindering simple interpretation of such landforms.