MAP OF LATE WEICHSELIAN DIRECTIONAL ICE-FLOW FEATURES OF LATVIA

The map of Late Weichselian directional ice-flow features of Latvia is an integral part of the INQUA project Ice flow directions in the Peribaltic area during the Weichselian Glaciation. Directional ice-flow features in the Latvian database and on the map were classified according to the legend worked out for the map of the entire Central and Eastern European area. The Latvian map and database were constructed using the ArcInfo system during the period of 1999-2003. The map is supported by a supplementary map showing the lobate structure of the peripheral cover of the Scandinavian ice sheet with major interlobate zones in Latvia and patterns of drift lineations in glaciated lowlands. Directional ice features were digitized from 1:50,000 (or 1:75,000) topographic maps, derived from the interpretation of satellite images and digital maps and from papers, unpublished reports and personal communications. The geographic base was compiled from the satellite map of Latvia on scale 1:50,000 and consists of multiple coverages that include basic geography. The main directional ice-flow features were formed during the Late Weichselian. Streamlined landforms are strongest and constant directional indicators of ice flow. Only when the till fabric, striations and deformational features were formed under the extensional flow regime of rapidly advancing glacial tongues they indicate the final local direction of glacial movement. In other cases they reflect directions of local stress or older ice movements. Superimposed sets of radial and transverse glacial topographic lineations formed beneath the margin of the retreating ice lobes and indirect features complicate the ice-flow mosaic. However, near parallel mega-scale lineations with latest cross-cutting features are common in macro-depressions with longitudinal extensional or compressional ice flow. The diverging pattern of ice-flow appears in glacial lowlands widening downglacier, while converging lineations occur in lowlands narrowing downglacier or along the sides of the largest interlobate uplands. Furthermore, in upland areas also transverse and isometric topographic features dominate, and the reconstruction of ice flow direction should be based mainly upon indirect features and fabric lineations.