The project aims to determine how variation in the basal hydrology system influence the glacier velocity and strain rates on Holtedahlfonna. By using high precision measurements from two or more permanent GNSS-stations on the glacier, together with meteorological data and a melt model, we not only want to analyze the seasonal speed-up during the summer of 2015, but also look at smaller short-term variation within this period. The field work will be divided in two periods, one trip during spring and one in autumn.