Cryoplanation Terraces: Periglacial Cirque Analogs

ABSTRACT

The altitudinal frequency distributions of cryoplanation terraces in four areas of Alaska approximate normal probability curves, reflecting an elevation-controlled climatic zone that is optimal for terrace development. The elevational coincidence of cryoplanation terraces and glacial cirques in central and western Alaska indicates that development of cryoplanation terraces requires altitudinal proximity to the climatic snowline in mountainous regions with continental climatic conditions, reinforcing the nivation hypothesis of terrace development. Because criteria used to define “lower limits” in traditional regionalizations of alpine periglacial phenomena are inherently unstable, it is preferable to base definitions of altitudinal zones on statistical measures of central tendency.