Information Page: ArcticCoastalErosion2010
Grade level: Middle (6-8), High (9-12), Under graduate (13-16), Graduate / Professional
Statement: melt of a permafrost coastal bluff
Abstract: one can watch a month of coastal melting in one minute. This movie is a time-lapse of 15 min shots taken at Drew Point along the Beaufort Sea. Drew Point is about halfway between Point Barrow and Prudhoe Bay on the North Slope of Alaska.This particular movie was taken in August 13th-September 11th, 2010.
The coastal bluffs you see in the ovie are about 4 m high, the blocks that erode away were measured to be 10.5m long. A large volume of the permafrost is just ice (uto 70%), the rest is fine sediment and peat as well as grass that grows in the upper 35 cm (the active layer).
There are polar bears passing by!
Erosion rates along permafrost coastlines of Alaska’s North Slope have been increasing over the past few decades (from 1953 onwards). The coast around Drew Point, roughly between Point Barrow and Prudhoe Bay along the Beaufort Sea, consists of ice-rich bluffs of about 3-5m high.
Thermal energy accounts for most of the erosion potential along these ice-rich permafrost coastlines, so predictive models of coastal erosion require an understanding of how sea-ice and sea surface temperatures evolve, both through the summer ice-free season and interannually.
To describe patterns of nearshore SST in the Beaufort Sea a team of USGS, INSTAAR and the Naval Postgraduate School deployed wave and ocean temperature sensors offshore from the National Petroleum Reserve in Alaska (NPR-A) during the summer of 2009. These sensors were placed in a shore-normal array between 0.2 and 10 km offshore, in water depths ranging from ~1m to 7m. Second, data is available from meteorological stations on the Alaskan North Slope to summarize the regional weather patterns that drive observed changes in ocean waves and temperatures over this time period. And lastly, we use satellite data to summarize sea ice position and sea surface temperatures over the past decade.
As long as the sea ice is still hugging the coast, which can be upto Halfway July, erosion is very limited. Subsequently, early in the summer when sea ice remains near the coast, the nearshore open water area is sheltered from mixing and warms to its highest temperatures of the summer. Water nearshore can become very warm, up to 10 degrees C, and consequently high thermal erosion occurs along the coast. As the sea ice margin retreats in mid-summer, summertime storsm homogenizes the temperatures offshore, collapsing the offshore temperature gradient to less than 0.5 degrees C per km and dropping the nearshore temperatures by almost 5 degrees C. Thermal erosion potential is consequently reduced later in the summer.
In the Fall season the sea surface water temperature drops to about 2 to -1 degrees C and there may be less potential for erosion.