Gorges cut by rivers under ice

A group of researchers has been able to shed new light on the rate of erosion by rivers under ice sheets in parts of the world likely to be covered by future ice sheets that might be considered as potential deep repositories for nuclear waste. The international team, led by the University of Glasgow's School of Geographical and Earth Sciences, found that deep gorges, cut like notches in broad glacial valleys in northern Sweden, had been eroded in only a matter of centuries by rivers of pressurised meltwater flowing beneath ice sheets during a period of ice sheet decay. It suggests that a shift in thinking is required about how landscapes evolve under ice sheets. The research team is an international collaboration of 10 scientists from Australia, Germany, Sweden, Switzerland, UK and the USA, and consists of geomorphologists who specialize in understanding how rivers and glaciers work. It also includes geochemists and physicists who measure cosmogenic radionuclides, such as beryllium-10, in an accelerator mass spectrometer — a machine that counts atoms in order to assess the age of rock surfaces. The team measured cosmogenically-produced beryllium-10 in bedrock surfaces within seven gorges in northern Sweden, a region covered by the continental-scale Fennoscandian ice sheet during the last ice age. Their results show that the gorges emerged fully formed from under the retreating ice 10,000 years ago.