Pronival ("Protalus") Ramparts in the Romsdalsalpane, Southern Norway: Forms, Terms, Subnival Processes, and Alternative Mechanisms of Formation

Abstract

Morphological characteristics and modes of formation of 10 (protalus) ramparts are examined. The landforms are vegetated but active, and comprise arcuate and sinuous ridges and ramps at the downslope margins of semipermanent snowbeds. They are characterized by single, double, and even multiple, sharpcrested lateral ridges and terminal ramp-like frontal sections, and they are composed partly of matrix-supported sediments containing less angular clasts than current-season rockfall and avalanche debris. Alternative modes of formation are considered in explaining the observed morphological and sedimentological characteristics. The conventional supranival debris supply route, involving rockfall, debris flow, and avalanches, is thought to be supplemented by subnival debris supply, including debris flows (observed in a subnival position), fluvial action, and solifluction. The term protalus rampart is misleading in describing the Romsdalsalpane features; protalus is clearly a misnomer as none of the features occurs in a talus-foot position. Hence, the term pronival is suggested as a widely applicable descriptor suitable for any debris accumulations forming ramps or ridges at the downslope margins of snowbeds irrespective of location in relation to slope position.