Friday, July 10, 2015

Wave-cut Terraces at Semiahmoo Peninsula

On a trip out to Semiahmoo Peninsula I noted the step-wise slope up a road on the peninsula. I knew from previous work in the area as well as LiDAR imagery that the area had been submerged below sea level during the late stages of the last glacial period as the ice mass retreated from the area. The mass of glacial ice, as much as 6,000 feet thick in this area, had pressed the local land surface downward hundreds of feet. As the land surface rebounded from the mass of ice and emerged from below the sea surface. Wave action on the emerging land surface left faint wave cut terraces on the landscape. For the most part these features are very hard to see. But the road view below appeared to be a nice example.   

Step-like slope of wave cut terraces
Selder Road, Birch Bay
The wave worked soils  also show up in aerial views as subtle differences in the soils. The soils in the area are dominantly silt/clay drift, but where thin beach deposits of gravel have been left, the drainage difference is reflected in the plant growth depending on the time of year. 

I've put up a few posts on wave cut terraces in the San Juan Islands with LiDAR imagery:

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