Geological history of Lake Võrtsjärv

Abstract

. Lake Võrtsjärv, with a surface area of 270 km 2 , has a very complicated geological history. Proglacial lakes of different shape and size were formed in the Võrtsjärv Lowland. Due to the tectonic uplift outflows to the west closed in the Early Holocene. At the beginning of the Middle Holocene, about 7500 BP, an outflow to the east developed and little by little the lake acquired its present contours. Like many lakes in Europe, Võrtsjärv has an open eastern (leeward) and a more swampy and overgrown western (windward) bank. The bottom sediments consist mostly of sapropel (gyttja), fine sand and silt. The sediments are thicker in the southern part of the elongated lake basin where the up to 9 m thick layer of sapropel is usually underlain by 8 m of lacustrine lime. Gradual rise of water level in the southern portion of the basin is caused by land uplift, the rate of which increases towards the northwest.