A new report by the US Geological Survey claims that the 1,000-mile Alaskan coastline is eroding at an average rate of 1.4 metres per year. The geology of the North Slopes makes them particularly susceptible to erosion as well as the behaviour of continuous permafrost. In the areas that are seeing the most recession, the coast is composed of fine grained sand and silt held together by ice and frozen sediment.
With summer, the ice thaws and material slumps and slides, to be further battered by waves. ‘Because the material is so fine grained,’ says Ann Gibbs, one of the authors of the report, ‘it’s quickly removed from the beach and doesn’t provide protection from future wave attack. At locations where grain sizes are larger, beaches tend to be wider and therefore erosion is slower.’
Because the North Slopes are so far north, the USGS only has coastal data from the 1940s. This can make it difficult to observe change or confidently say whether the erosion is increasing with climate change.
‘Observed and projected increases in air and sea temperatures, along with increases in the length of sea-ice free condition, do suggest that the North Slope coast will become increasingly vulnerable to erosion in the future,’ says Gibbs.
Because the northern coast is relatively uninhabited, accelerated erosion is not an immediate threat to human habitation, however there are huge tracts of US federal lands, decommissioned Early Warning Radar systems and oil and gas-related infrastructure that could be damaged. This is as well as habitat for a variety of wildlife species, many of which are threatened and endangered. ‘Where there is existing coastal development,’ says Gibbs, ‘structures may need to be removed and lands remediated or protected. It is also important to consider the possibility that these carbon-rich bluffs might add to the carbon budget. This is known as organic carbon contribution and may influence ocean acidity.’
This article was published in the September 2015 edition of Geographical Magazine