GLACIOTECTONIC MAP OF LATVIA

The glaciotectonic map of Latvia is an integral part of the INQUA GAGE Working Group project Glaciotectonic GIS Database and Map of Central Europe. The map and database were constructed using the ArcInfo system during the period of 1997-2001. Twenty-nine individuals have contributed information or assisted in preparation of the database. Glaciotectonic features were digitized from 1:50,000 (or 1:75,000) topographic maps and derived from interpretation of aerial photographs, papers, unpublished reports and personal communications. The glaciotectonic map is supported by a supplementary map of the lobate structure of the Scandinavian ice sheet in Latvia and three-dimensional visualizations of the pre-Weichselian and modern surface of Latvia. Most glaciotectonic features were formed during the Late Weichselian. Because Latvia occurs at the transitional zone between the areas of predominate glacial erosion and the inner margin of the depositional belt, mainly subglacial processes created the glaciotectonic features. As a result of deglaciation and subsequent geologic processes these structures and land systems were altered to some extent, and glaciotectonic, other glacial and non-glacial features were superimposed. Glaciotectonic ridges with crests parallel to ice movement direction occur mostly in glacial lowlands, while composite hills and ridges, as well as isometric glaciotectonic hills predominate in the interlobate areas. Transverse features are most common on the peripheries of glacial uplands or on lowland areas with hard bedrock. Large rafts of pre-Quaternary bedrock expressed in topography borders of lowlands and uplands. Buried deformed Pleistocene sediments and bedrock appear on plains but glaciotectonic hills capped by glaciolacustrine sediments are common in the central part of the largest interlobate uplands. The map displays the spatial image of how the development of glaciotectonic structures caused change in the original thickness of glacial, interstadial and interglacial deposits and disruptions in the continuous cover of till.