Tuktoyaktuk's west shore is retreating by an average of 0.3 to 3 meters per year, and during large storms can retreat by up to 5 meters over a few days. At this pace, the northern-most area of the community will be inaccessible by road by the year 2050.

Erosion mechanisms

Erosion on permafrost coasts is both thermal (thawing frozen ground releases the sediments) and mechanical (wave action physically removing the sediments from the shore) [1],[2]. Ice-rich sediments are subject to relatively rapid erosion; quick-thawing ice adds water and makes it easier for the sediments to move downslope, and only a portion of the volume eroded from the coast goes onto the beach or nearshore sediment budget (the ice portion becomes water).

There are three main types of shoreline erosion in Tuktoyaktuk: longshore transport, offshore transport, and thermal action [3].

• Longshore transport - Waves arriving at an angle to the shore gradually move sediments along the length of the coast.

  Sediments moving down the shore can accumulate and form spits, which can tell us about the primary drift direction. Tuktoyaktuk has gravel spits at the north and south of the peninsula, telling us that sometimes currents move towards the north, and sometimes they move towards the south.

• Offshore transport - The rapid removal of sediments away from the coast due to changing water levels and wave conditions during storms.

• Thermal action - Gradual consolidation and transportation of sediments by the outflow of melted ice.

Measuring erosion

Erosion is usually described as a rate of change in meters per year. Knowing the annual average shoreline retreat is useful to determine the long-term safety of a building or road, and to see if the speed of erosion has changed over time.

Aerial photographs can be used to determine the shoreline position at a given time. To measure shoreline change, first we take photos from several years and trace the shoreline on each one. The shorelines are all put together in the same map, in order to measure the distance it moved from one year to the next.

To measure the rate of change, we measure the distance between shorelines, and then divide by the length of time between them. These measurements are taken at many places along the coast, in order to see both how fast erosion is happening and where it is the most extreme.

Past and recent shoreline erosion rates

In the past, aerial photos were only taken every several years, so the measured rates of erosion are averages over long periods of time. In recent years, it has become easier to take aerial photos with small unmanned aerial vehicles (UAVs, or drones), so we have a better idea of the amount of erosion occurring in a single year.

Between 1950 and 1970, the average annual recession rate along Tuktoyaktuk’s west shoreline were between 0.6 meters per year (north of the cemetery) and 3 meters per year (along the gravel beach south of Pokiak Lake) [6]. Engineering consulting reports from 1972 to 1994 used a generalized average rate of 1.8 meters per year for the west shore to estimate future shoreline locations and identify infrastructure most at-risk [7,8]. Based on these average annual erosion rates, UMA Engineering Ltd. concluded in 1994 that the peninsula would be inaccessible by road by the year 2040, if no action was taken to protect the shoreline.

Since 1970-1985, slower rates of shoreline erosion have been observed at Tuk Island and on the community’s shoreline from Flagpole Point to the southern reach of Pokiak Lake. In some sectors, shoreline protection structures have slowed erosion. A period of reduced storminess from 1996 to 2015 likely also contributed to the slower erosion rates seen even in unprotected areas [6]. The gravel beaches along Pokiak Lake and the spit to the south are capable of both erosion and accretion, unlike the purely eroding banks to the north and along Tuk Island [6].

The average rates give a general idea of the magnitude of erosion around the community. However, erosion in Tuktoyaktuk usually isn't a slow, continuous process - most shoreline retreat occurs during storm events, with periods of relative stability in between. Single storm events have been known to produce up to 7 meters of shoreline retreat in areas where ground ice is exposed [8]. More often, however, storms cause shoreline retreat on the order of 3 meters in the span of two or three days [3].