Virtual Cabinet of Curiosities
14. Glacial striations, Dr David Graham
These basalt rocks were collected from Mýrdalsjökull, an ice cap on the Katla volcano in southern Iceland. They nicely illustrate the processes operating to modify and transport sediment within and beneath temperate glaciers. Both show clear evidence of abrasion at the glacier bed, in the form of striations associated with interactions between larger grains and polishing by fine grains. The angular rock was quarried from the bedrock and shows very limited evidence of subsequent modification. The superimposition of striations on the rounded rock is highly unusual. The shape provides evidence of prolonged high-energy fluvial transport, possibly during a jökulhlaup (flood associated with a volcanic eruption). The rock has subsequently been entrained by the glacier and transported at its bed.