Helena Alexanderson

Several ice-dammed lakes formed between the Younger Dryas moraines and the Tana River valley during the retreat of the Fennoscandian Ice Sheet over northeast Norway. Drainage of these lakes left an indelible scar on the landscape; the Gaccetávži ravine, a feature over 10 km long and up to 120 m deep. Here, we use LiDAR-derived digital terrain models, alongside field investigations and novel remote sensing techniques, to propose a model for the formation, evolution, and eventual drainage of the lakes that led to the ravine's formation. Initially, four smaller lakes were established at the margin immediately after the Younger Dryas (YD), separated by ice overlying areas of higher relief. With marginal retreat, three lakes coalesced before breaking through an ice-dam to join with the fourth lake and form one large lake. At its greatest extent, the lake covered 59 km2 and held 1.7 km3 of water. The first breakthrough triggered an outburst flood and initiated the formation of the ravine. Subsequent periods of lake drainage occurred with ice-front oscillation and the opening of new spillways and outlet channels. This pattern is recorded in a succession of glaciofluvial terraces and erosional features around the ravine and south towards the Tana River.