Short-term geomorphic dynamics of the Yukon and Herschel Island coasts based on LIDAR DEMs from 2012 and 2013

Arctic permafrost coasts, especially when they are unconsolidated and ground ice rich, are extremely vulnerable to climate change. Rising temperatures of air and seawater, lengthening of the open-water season and increase in storm events are likely to prompt higher rates of coastal erosion and consequently increase the rate of land loss and material transport to the near-shore zone. Many studies have addressed this issue by compiling rates of shoreline erosion over the past fifty to sixty years to find trends, yet few investigations have attempted to look at it in three dimensions and at annual time scales, although erosion of Arctic coasts is known to be very complex and nonlinear. This study focuses on high resolution short-term (one year) erosion rates and geomorphic change. It is based on DEMs that were obtained from LIDAR surveys of the Yukon Coast and Herschel Island during the AIRMETH campaigns in 2012 and 2013. The DEMs were processed to obtain a horizontal resolution of 1 meter and serve as an elevation source from which the comparison was made. The elevations from the 2012 DEM were then deducted from elevations in 2013 to obtain erosion and accumulation values for each pixel. Preliminary results show that coastal retreat encompasses a range of processes acting at different temporal and spatial scales. They can be divided into denudation and abrasion processes. Denudation is the various types of mass wasting, such as translational slides, active layer detachments or retrogressive thaw slumps. The material delivered from these abrupt events is made available for abrasion, which is transferring the material to the shoreface at longer time scales. The accumulated material temporarily protects cliffs from incident wave energy and abrasion is reactivated when the material is removed. The erosion from gullies and thermo-erosional valleys is another form of material delivery to coast. Shoreline retreats from 2 to 5 meters were recorded on the most exposed parts of the coast, while vertical changes of cliffs account locally for more than 10 meters and extend up to 20 meters laterally. Locations where these high numbers are observed are often characterised by the adjacent accumulation of material on the beach. This study shows that the pathways for the transfer of material from the coast to the sea are very diverse and are often limited by the ability of abrasion to remove material delivered by the mass wasting of coastal bluffs