Undersøkelser av alder, volum og utbredelse av Gloppedalsura, Bjerkreim og Gjesdal kommuner, i Rogaland

This master thesis examines the age, volume and extent of Gloppedalsura in Bjerkreim and Gjesdal communities in Rogaland county. The Schmidt Hammer is used for estimating age. This method is widely used as a relative dating method. In recent years, the Schmidt Hammer has also been used to estimate surface exposure ages by using the relationship between age and R-value to establish a calibration curve. In this thesis, a calibration curve was created by using the age and R-value on new and old rock surfaces that have a “known age”. Based on the calibration curve, the age of Gloppedalsura was estimated. Although there is a high grade of uncertainty, the results strongly indicate that Gloppedalsura was formed by one single rock avalanche event. The estimated age of this event is calculated to be 12 300 ± 480 years ago, which means that the rock avalanche event happened shortly after the area became ice-free. The terraces around 235 m a.s.l in Byrkjedal (Gjesdal community) have presumably been formed by an ice-dammed lake. Most likely, there is an end moraine under the avalanche that was deposited when the ice retreated. At one point in time, the end moraine functioned as a pass-point at 235 m a.s.l, while the valleys to the northwest and northeast of Byrkjedal must have been dammed by glaciers in order to form this lake. The volume of Gloppedalsura has been difficult to estimate due to a high degree of uncertainty in the assumptions for the calculation. The volume is estimated to be at least 8,44 million m^3. However, due to the high degree of uncertainty, the volume might be as much as 30-40 million m^3, a volume that has previously been estimated by NGI (Norwegian Geotechnical Institute). The calculation of run-out distance with the alpha-beta method did not match the observations. There may be several sources of error causing this mismatch, but first and foremost this method is not suitable for avalanches in valleys that do not have a free run-out. The estimated height/length ratios were more precise