DEGLACIATION HISTORY OF LATVIA

Latvia occurs at the inner margin of the depositional zone of the of the Scandinavian ice sheet where the main features of glacial topography were created by subglacial processes. During the last glaciation it was affected by the Baltic, Rîga and Peipsijärv ice streams. The ice streams terminated in lobes and tongues separated by interlobate zones. The insular uplands and interlobate ridges represent zones of collision of ice lobes and glacier tongues moving in different directions and through separate neighbouring lowlands. The formation and location of ice lobes and glacier tongues, and their dynamics were originally controlled by subglacial bedrock, but during the last glaciation mainly by the pre-Weichselian topography. The influence of the subglacial topography increased particularly during deglaciation, as ice thickness decreased. A very complex lobate structure, with many small glacier tongues and sub-tongues, existed at the onset of ice-sheet decay. During final phases of deglaciation the ice dynamics were simplified and only the largest radial ice lobes and glacier tongues remained active in the lowlands. This reactivation of the lowland ice lobes and glacier tongues was induced not only by climatic and environmental changes but was also caused by the melting and stagnation of the glacier in the adjacent uplands that improved ice mass balance in the lowlands. As a result of deglaciation of stagnant ice, a complex of superimposed glacial landforms in upland areas formed simultaneously with the glacial landforms continuum created by active ice fluctuations in lowlands. Later, related to melting of stagnant ice sedimentation and landform processes occurred in lowlands. The deglaciation of Latvia was controlled by different glacial geological processes interacting both spatially and temporally. Our recent investigations suggest that only four phases of the deglaciation can be reliably recognised in Latvia. In order of decreasing age, they are the Pomeranian, South Lithuanian, Middle Lithuanian, North Lithuanian and North Latvian phases. The ice sheet finally retreated from Latvia during the Late Weichselian Late-glacial Interstadial, about 14-12 ka BP, but periglacial conditions persisted until the beginning of the Holocene.