Jean Bjornson

Abstract

Mountain-top detritus characterizes the two high summits of the Gaspésie Mountains,eastern Canada. It is suggested that these angular rock-rubble accumulations developed from thedisintegration of coarse-grained igneous bedrock exposed to thermal stress and ice segregationduring prolonged episodes of permafrost formation in the cold periods of the Pleistocene. Frostwedging and frost heaving (‘jacking’) were the primary mechanisms. Today, climatic conditionson the summits permit only thin and marginal permafrost bodies. Stone nets and stripes aredeveloped where a residual bedrock-derived debris mantle is present. They reflect frost-inducedmovements within the active layer. The latest of these movements probably occurred during thecold period following the LGM and persisted into the mid-Holocene. The transition from nets tostripes relates to slope angle.

Keywords: mechanical weathering, permafrost, blockfields, patterned ground, Gaspésie Mountains, Québec, Canada.