Moraine‐ridge formation along a stationary ice front in Iceland

At present the north margin of the temperate ice‐cap Myrdalsjökull is stationary: the ice edge retreats slowly during summer and readvances during winter to much the same position as the previous winter. Although the ice margin in this way has been stationary since around 1984. a frontal moraine ridge. 1.5‐2.5 m high. was under formation in 1986. and in 1989 it was 3–4 m high. The interior of the ridge appeared as imbricately stacked slabs of frozen, clast‐paved lodgement till dipping up‐glacier. At least five to seven slabs were identified in the 1989 ridge. The most proximal one was frozen to the up‐arched glacier sole and dipped beneath the glacier at about 30. In 1989 the volume of lodgement till sediments within the ridge represented a horizontal shortening of the ground moraine of roughly 60–90 m. On the other hand. between 1984 and 1989 the lateral displacement of the ridge toe amounted to only 10 m. It is concluded that the frontal ridge is formed progressively. not like conventional push moraines by thrusting of contemporaneous proglacial or ice‐contact sediments. but chiefly by a combination of basal freezing beneath the thin. clast‐loaded glacier toe each winter and recurrent superposition of frozen lodgement till slabs during small winter readvances.