The Cause of Explosive Growth, Widening of N. Oregon Coast Beaches Last Century

Published 08/22/21 at 6:42 AM PDT
By Oregon Coast Beach Connection staff

(Seaside, Oregon) – Most people don't know this about the north Oregon coast: Seaside was once a much different landscape. Instead of all sandy and soft, it was rather rubbly and rocky, and had a fairly steep slope down to the water.

Yet out of the people that do know that, even fewer know that miles and miles of the north Oregon coast did not exist before about 100 years ago. Seaside's beach was around 700 feet shorter, and parts of Fort Stevens had nearly a mile added onto it around the beginning of the 20th.

The curious culprit of all this is the building of the jetties on the Columbia, along with the introduction of invasive dune grass species to stabilize the sands. Construction started in the 1890s and finished up about the early ‘20s, causing a massive shift in the beachscape in far less than 30 years.

Seaside then

Building the jetties greatly increased the rate that sand flowed and then was deposited in the area, and it also can – ironically – cause erosion in other places.

Seaside and Gearhart were affected immensely as well. All those fat, puffy dunes and that long walk to Gearhart's sands were not there back around 1900. Local geologist Tom Horning told Oregon Coast Beach Connection back in 2010 that as much as 2000 feet worth of dunes from east to west was created by those moving sands, and they've gotten as high as 45 feet.

Dune growth rates more than doubled after the turn of the century. Soon, according to Horning, dunes each year grew by around 35 feet and up to three feet vertically.

Scotch Broom was introduced to the area in the early century to stabilize dunes, and that helped dunes grow eastward as well, actually destroying grazing land on the north Oregon coast.

In Seaside, the difference in how the beach looked between 1900 and about 20 years later is remarkable. There was about 100 to 200 feet of it back then, and it had a lot of rounded stones. Now, it's sometimes over 1,000 feet from the Prom to the ocean and it's all soft sands.

Interestingly enough, Seaside would have that wild and untamed dune look of Gearhart if it didn't shave off a few layers of sand every year.

According to Horning, the tides are likely turning on all that collecting of sand, however. Erosion is happening more and more in these areas and it's possible the dune-building may stop and go the other direction.

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