Movie:Arctic Coastal Erosion Discussion


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Discussion of Arctic Coastal Erosion

Key Attributes

Domain: terrestrial, coastal, environmental controls
Keywords: permafrost
Keywords: sea ice
Keywords: warming ocean
Model name: Animation model name
Name: Irina, Overeem/Daily Camera
Where: Alaskan Coast
When: 2008-2009

Short Description

Grade level: Middle (6-8), High (9-12), Under graduate (13-16)

Statement: Prof. Bob Anderson explains about Coastal Erosion

Abstract: This clip is an interview with Prof. Bob Anderson, University of Colorado, it was posted in the Daily Camera, the Boulder newspaper.

Prof Anderson talks about a study on the northern coastline of Alaska midway between Point Barrow and Prudhoe Bay where the coast is eroding by 15m annually because of declining sea ice, warming seawater and increased wave activity.

A warmer Arctic with a longer sea-ice free season have led to the steady retreat of 15m average and 25m maximum a year of the 4m high bluffs -- frozen blocks of silt and peat containing 50 to 80 percent ice --. These blocks then topple into the Beaufort Sea during the summer months by a combination of large waves pounding the shoreline and warm seawater melting the base of the bluffs.


In Arctic landscapes, recent warming has significantly altered geomorphic process rates. Along the Beaufort Sea coastline bounding Alaska’s North Slope, the mean annual coastal erosion rate has doubled from ~7 m/yr for 1955-1979 to ~14 m/yr for 2002-2007 (Mars and Houseknecht, 2007). Locally the erosion rate can reach 30 m/yr. We aim to understanding the processes that influence coastal erosion rates; since we want to predict the response of the coast and its adjacent landscape to a rapidly changing climate, with implications for sediment and carbon fluxes, oilfield infrastructure, and animal habitat.

The evolution of the permafrost bluffs on the North Slope is controlled by three conditions: length of the sea ice free season, warming sea water and wave and storm surge. During the sea ice-free season, relatively warm waters melt a notch into the ice-rich silt that comprises the 4-m tall bluffs. The bluffs ultimately fail by toppling of polygonal blocks bounded by mechanically weak ice-wedges that are spaced roughly 10-20 m apart. The toppled blocks then temporarily armor the coast against further attack.

The annual coastal retreat rate is controlled by the length of the sea ice-free season, water and air temperatures, and the wave history. Honoring the high ice content of the bluff materials, it is thought that subaerial melt plays a minor role, and that the notching of the base of the bluff acts as an melting dirty ice berg. In quantitative iceberg melting models the local instantaneous melt rate goes as the product of the temperature difference between seawater and bluff material, and the wave height. Calculated instantaneous melt rate can be adjusted to account for the ambient temperature of the permafrost and the presence of non-ice material in the bluffs. Once a block is sufficiently undercut to become unstable it will fail and topple. The latter process can be described as a torque balance.



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