AN ASSESSMENT OF ROCK GLACIER SLIDING USING 17 YEARS OF VELOCITY DATE- NAUTARDALUR ROCK GLACIER, NORTH ICELAND

Velocity measurements on three transverse lines across the surface of the 400-m-long Nautardalur rock glacier in the Trollaskagi peninsula, North Iceland, were started in 1977. Readings have been continued at v arious intervals since then and provide over 17 yr of data. Individual ly observed points indicate slow movement with little apparent variati on over the time period. Center-line velocities are of the order of 0. 25 m yr(-1) on the uppermost line nearest a corrie glacier, 0.2 m yr(- 1) on the middle profile and 0.25 m yr(-1) on the lowest profile near the snout of the rock glacier. Substantial differences in velocity exi st between the virtually stagnant and stable lateral margins (<0.05 m yr(-1)) and the more rapid central section (max. 0.31 m yr(-1)). No ev idence for rock glacier sliding over this period has been found. Compa rison of aerial photographs from 1946 to 1985 and direct measurements suggest that the snout position has moved forward (<1 m) over this per iod.