Evidence of Forest Erosion by Sea Level Rise

The northwest and west shoreline of Cormorant Island, British Columbia appears to have eroded due to sea level rise during the last few decades.

Observation by Tom Okey:

I went hiking on the trails on the northwest and west sides of Cormorant Island on the afternoon of 10 April 2020, and I ended up walking along the northwest-facing beaches. I noticed that the forest along this whole shoreline, including some relatively large trees and forest soils, appears to have been undercut and eroded by the ocean.

It appears that the roots of some of these trees had been undercut over a period of time such that some of them had individually adapted with growth responding to this undercutting, many of them were leaning toward the ocean the way coconut palms do on the eroding coastlines of tropical islands. In some places, 'bulkheading' was provided by logs that had either washed onto the beach some time ago, or they were older forest logs. I made these observations just after 4 pm, which was during a high tide of 4.65 m (at 4:14 pm).

Environmental Reporting BC has reported that sea level has been rising at an average rate of "13.3 cm per century at Prince Rupert, 6.6 cm per century at Victoria and 3.7 cm per century at Vancouver, while average sea level fell at Tofino at the rate of 12.4 cm per century." Observed variations in sea level rise among locations reflects differences in vertical geological movement in different locations. It should also be noted that these are historical rate estimates, and that future rates may be considerably higher given that rate of sea level rise is accelerating globally. The alternate explanation for this erosion is increases in the magnitude or intensity of storms during recent decades, but there is less evidence that this has occurred in this region (Okey et al. 2014).

It is my assumption that Cormorant Island is comprised largely of soft sediment; I am tempted to think of the island as a terminal moraine or as sediment otherwise deposited by the historical glacier that carved the Nimpkish River watershed to the south. However, I have not found any good descriptions of the geology of Cormorant Island. In any case, the Northwest coastline of Cormorant Island is low-lying and comprised of soft sediment, and this coastline is projected by the Climate Central's Surging Seas tool to undergo pronounced inundation and erosion during coming decades.

Literature cited

Okey, T.A., Alidina, H.M., Lo, V., Jessen, S. 2014. Effects of climate change on Canada's Pacific marine ecosystems: a summary of scientific knowledge. Rev. Fish. Biol. Fish. 24 (2):519-559.