CONTEMPORARY TERMINAL-MORAINE RIDGE FORMATION AT A TEMPERATE GLACIER - STYGGEDALSBREEN, JOTUNHEIMEN, SOUTHERN NORWAY

Terminal-moraine ridges up to 6 m high have been forming at the snout of Styggedalsbreen for two decades. Based on intermittent observations during this period, combined with a detailed study of ridge morpholog y, sedimentary structures and composition during the 1993 field season , a model of terminal-moraine formation that involves the interaction of glacial and glacio-fluvial processes at a seasonally oscillating ic e margin is presented. In winter, subglacial debris is frozen-on to th e glacier sole; in summer, ice-marginal and supraglacial streams depos it sediments on the wasting ice tongue. The ice tongue overrides an em bryonic moraine ridge during a late-winter advance and a double layer of sediment (diamicton overlain by sorted sands and gravels) is added to the moraine ridge during the subsequent ablation season. Particular ridges grow incrementally over many years and exert positive feedback by enhancing snout up-arching during the winter advance and constrain ing the course of summer meltwater streams close to the ice margin. Th e double-layer annual-meltout model is related to moraine formation by the stacking of subglacial frozen-on sediment slabs (Kruger 1993). Mo raine ridges of this type have a complex origin, are not push moraines , and may be characteristic of dynamic high-latitude and high-altitude temperate glaciers.