Holocene glacier fluctuations of Grovabreen and Holocene snow-avalanche activity reconstructed from lake sediments in Grningstlsvatnet,western Norway

On the southern side of Grovabreen, a plateau glacier in inner Sunnfjord, western Norway, sedimentological analyses of two lake-sediment cores from Groningstolsvatnet have been made in order to reconstruct the Holocene history of Grovabreen and of local snow-avalanche activity. The lake catchment was deglaciated about 9470 cal. BP and glaciers were absent from the catchment between 9470 and 4700 cal. BP, except for a glacier episode, correlated with the 8200 cal. BP Finse event, between 8420 and 7880 cal. BP. The glacier has existed continuously from 4700 cal. BP to the present, reaching its maximum extension around AD 1840 according to lichenometric dates. Single minerogenic particles >1 mm in the sediments retrieved from Groningstolsvatnet are interpreted as dropstones from dirty snow-avalanches eroding the valley sides and deposited on the frozen lake. A local snow-avalanche chronology has been constructed for the last 10000 calendar years, based on the distribution of dropstones in the cores, with pronounced snow-avalanche activity peaking around 10 100 and 8600 cal. BP. This was at a minimum during the period when there were no glaciers in the lake catchment between-7800 and 4700 cal. BP, but increased somewhat around 7100 and 7400 cal. BP. Other marked snow-avalanche episodes occurred around 4000, 3000, 1900 and 1300 cal. BP, and during the recent decades. The snow-avalanche record is largely in accordance with similar records from western Norway and also with a winter-precipitation curve reconstructed from the Jostedalsbreen region.