Initial stages of weathering and soil formation in the Morteratsch proglacial area (Upper Engadine, Switzerland)

Abstract Investigations in Alpine soils indicate that mineral weathering is much faster in ‘young’ soils ( 87 Sr/ 86 Sr). Furthermore, the accumulation of organic matter within the time sequence and physical soil properties were measured. Decreasing grain size with time shows active physical weathering processes. Soil organic matter has been accumulated during 150 yr at very high rates. Special emphasis has been given to chemical weathering and to the formation and transformation mechanisms of minerals. Of special interest were biotite, chlorite, epidote, plagioclase and calcite. Biotite has been continuously transformed into illite-like components. Within 150 yr, the concentration of epidote significantly decreased. The high Ca/Sr as well as 87 Sr/ 86 Sr ratios in the stream and spring waters confirmed that Ca bearing minerals are weathering and transforming at very high rates in the proglacial area. Also in cryic, ice-free environments, chemical weathering rates are high leading to the formation and transformation of minerals. Disseminated calcite in granitoid rocks, not confined to sedimentary carbonate rocks, also plays a role in subglacial environments. It is, however, not known for how long such an influence is significant and measurable. The high Ca/Na and Ca/Sr ratio in the stream and tributary waters showed that calcite contributes to the supply of soluble Ca, although the ion activity product calculations clearly demonstrated that the waters were undersaturated with respect to this mineral.