The Detection of High Altitude Permafrost in Jotunheimen, Norway Using Seismic Refraction Techniques: An Assessment

Abstract

The detection of permafrost and determination of active layer thickness using single channel hammer seismic refraction equipment is described and assessed. Four sites between 1810 and 2200 m asl in Veodalen, Jotunheimen, southern Norway, were surveyed. At these sites the substrate consisted of a heterogeneous diamicton in which sorted circles were well developed At all sites a shallow refracting surface was detected, and excavation at the two higher sites showed this to be permafrost. The permafrost table was shallowest at the highest site (average depth 0.95 m) and deepest at the lowest site (average depth 1.37 m). At many sites a second, deeper refractor, probably bedrock, may have been indicated by field data. Seismic velocities of 0.34 to 0.46 km s⁻¹ were measured in the active layer, and 2.30 to 3.60 km s⁻¹ for permafrost. At one site a velocity of 1.90 km s⁻¹ for the first refracting surface was interpreted as indicating partially frozen sediment close to 0°C, which contained a significant proportion of unfrozen pore water. It is confirmed that large areas of Jotunheimen are underlain by permafrost and that seismic refraction surveys provide an efficient and reliable method of detecting and mapping such high-altitude permafrost.