On chemical denudation caused by ground water in central Finnish Lapland

In the study an estimate was made of the chemical denudation caused by ground water discharged from surficial deposits, on the basis of the dissolved inorganic matter, during the late and postglacial period of approximately 10 000 years. The calculations are based on the premise that in only a gently sloping, till-mantled tract the infiltration coefficient of the ground water varies between 0.20 and 0.40, and in level tracts covered with sand and gravel between 0.40 and 0.60. Further, the amount of annual precipitation taken into account in the calculations varies from 450 to 500 mm, and the dry unit weights of the till and the stratified drift amount to 1.60 and 1.70 t per cu. m. The assumption was made that the postglacial fluctuations in climatic conditions in one and another direction cancel each other out to the extent that they do not significantly affect the calculations. The appreciable amounts of matter brought down out of the atmosphere by the rain have been taken into account. The chemical denudation caused by ground water percolating through till in areas of silicic bedrock corresponds to the elimination of a soil layer of between 2.0 and 4.5 cm in thickness, the corresponding value in areas of subsilicic bedrock being 5.5 to 11.0 cm. In silicic bedrock areas the chemical denudation is slightly more intensive in stratified drift than in till deposits. Not taking into account the composition of the surficial deposits and the bedrock, the average rate of chemical denudation in the whole study area was found to be from 2.4 to 5.8 cm. This finding is in agreement with the calculations made on the basis of brook and river waters