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

* Jotunheimen Research Expeditions, Contribution No. 118.

Abstract

Morphological characteristics and modes of formation of 10 pronival (“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, sharp-crested 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.