Rainfall thresholds for landsliding in the Himalayas of Nepal

Landsliding of the hillslope regolith is an important source of sediment to the fluvial network in the unglaciated portions of the Himalayas of Nepal. These landslides can produce abrupt increases of up to three orders of magnitude in the fluvial sediment load in less than a day. An analysis of 3 years of daily sediment load and daily rainfall data defines a relationship between monsoonal rainfall and the triggering of landslides in the Annapurna region of Nepal. Two distinct rainfall thresholds, a seasonal accumulation and a daily total, must be overcome before landslides are initiated. To explore the geomorphological controls on these thresholds, we develop a slope stability model, driven by daily rainfall data, which accounts for changes in regolith moisture. The pattern of rainfall thresholds predicted by the model is similar to the field data, including the decrease in the daily rainfall threshold as the seasonal rainfall accumulation increases. Results from the model suggest that, for a given hillslope, regolith thickness determines the seasonal rainfall necessary for failure, whereas slope angle controls the daily rainfall required for failure.     

Genauigkeitserwartung photographischer Sternpositionen bei geschlossener Blockausgleichung

The theoretical accuracy of photographically determined star positions is studied, based on the assumption that the whole sphere is covered by a net of fields, 4 plates each, and that all the plates are adjusted simultaneously in a closed block. The influence of the number of fields on the accuracy is estimated by computing schematized spheric blocks containing only a few reference stars. If the plates are taken with a focal length of 2 meters, the block will consist of 2500 fields, and a mean accuracy of star position of 0.1 can be expected.