2nd Sinkhole on Top of Cape Kiwanda Spells Bigger Dangers, Says Oregon Coast Geologist

Published 05/09/23 at 11:24 PM
By Oregon Coast Beach Connection staff

(Pacific City, Oregon) – The north Oregon coast's Cape Kiwanda manages to step into the spotlight again, as a second deadly sinkhole opens up next to the first one that came about in January. Now, according to Oregon State Parks and Recreation (OPRD), the new one is about 10 inches away from the initial one, and it's 10 feet across and 30 feet deep. (Photo OPRD)

This time, you can see the bottom of the sea cave which one Oregon coast geologist said was the cause. It's gone beyond a sinkhole into a very hazardous chasm.

In the initial incident, Oregon Coast Beach Connection talked to geologist Tom Horning, and he predicted this would happen. It is enlarging slowly, and Horning said the worst or at least more dramatic is yet to come.

“This one worries me,” he told Oregon Coast Beach Connection Tuesday.

OPRD said this new hole developed right inside the safety fencing that was already there, and it's putting park rangers on alert. Staff first learned about it via a social media post, then spent part of Tuesday expanding the safety fencing. It opened up sometime between 10 a.m. Monday and 7:30 p.m. Rangers had just checked in on the sinkhole in the morning, and the photo that alerted them was posted on social media that night.

They, like Horning, aren't sure what it's going to do next. But it's clearly on a trajectory of getting wider and more dangerous. See Cape Kiwanda geology.

Park Ranger Supervisor Travis Korbe everyone should stay clear of this area and keep dogs on leashes on this famed Oregon coast headland .

Photo OPRD

“And [keep] children away from the edges,” he said. “We are monitoring the site daily, but it’s a dynamic environment. The soft sandstone cliffs can give way without warning, which is why it’s important to respect safety fences everywhere in the park.”

Just as in the initial interview, Horning said Tuesday it's a sea cave below that has suddenly collapsed, leaving it to fall inward - which you can now see.

That first sinkhole still measures about 15 feet but seems to have expanded its width slightly to 25 feet.

“The soil appears to be falling into large, unstable voids beneath the cliff caused by strong ocean waves,” OPRD said.

The initial sinkhole, OPRD

This echoes what Horning said, a Seaside-based geologist who has studied Cape Kiwanda himself and even led geology tours there. Both he and OPRD noted the Oregon coast landmark is made of sandstone – not basalt, such as Cape Lookout or Tillamook Head farther north. Sandstone is much less hearty and falls apart easily. OPRD said it's prone to sudden changes.

“Cape Kiwanda is continuing to be eroded this way, washing out sand that blew in a long time ago and filled the cave,” Horning said. “ And so I think that it's going to be pretty hard to stop this thing from finding its own equilibrium. My advice is to keep pushing the fences back – the thing just grows. Just let it do its thing.” [See Complete Guide: Cape Kiwanda State Natural Area]

Horning said filling it up with more rocks won't work, either.

He said it's even entirely possible this part of the headland will give way altogether. People should just steer clear of that area, as more is ready to collapse and you won't know when.

“There's no coming back out, I suspect, if you go in,” Horning said.

What remains of that cave below can likely get 12 feet of water in it or more, he said, depending on tides.

Cape Kiwanda seems slightly more unstable in the last decade, losing more features at a higher rate, such as at the very northwestern edge at the canyon-like area where ocean water careens between taller island-like structures. Part of those islands have come apart more often since 2010. See Just What is Cape Kiwanda on Oregon's Coast? And Why It's Falling Apart

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Andre' GW Hagestedt is editor, owner and primary photographer / videographer of Oregon Coast Beach Connection, an online publication that sees over 1 million pageviews per month. He is also author of several books about the coast.

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