PORTLAND, Ore. (KOIN) — The pair of massive sinkholes that continue to swallow up the popular lookout at Cape Kiwanda State Natural Area may one day form a new sea stack, a report recently completed by the Oregon Department of Geology and Mineral Industries shows.

According to the report, Cape Kiwanda Lookout is undergoing drastic geological changes that may one day cause a “catastrophic” collapse of the lookout’s underlying sea cave. Oregon State Parks spokesperson Chris Havel told KOIN 6 News that the parks department has permanently moved the lookout fence back more than 50 feet following DOGAMI’s recommendations.

“The coast is beautiful and ever-changing,” Havel said. “The fact that we can see this up close from the park is a special experience, and we invite people to come take a look from the safer side of the fence.”

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    Sand slides into one of the sinkholes at Cape Kiwanda lookout. (Photos by Jimi Mckillip)
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  • An aerial view of the Cape Kiwanda lookout formation. (DOGAMI)
  • A diagram showing the underlying cave system. (DOGAMI)
  • Cape Kiwanda’s changing landscape throughout the years. (DOGAMI)
  • The cave system beneath the sinkholes. (DOGAMI)

In its report, DOGAMI concludes that the two sinkholes that formed in January and May of 2023 were caused by a circulation of ponding groundwater that slowly dissolved an underlying rock formation. Although a cave system exists beneath the sinkholes, DOGAMI said that there is no clear, vertical chamber leading from the sinkholes to the sea cave at this time. Scientists say that the existing sinkholes could persist until all support gives out and a hole forms in the lookout.

“In time, we suspect that this part of Cape Kiwanda may eventually form a small sea stack as the western sea cave collapses, while a wave-cut channel could eventually form along the main east-west cave system, similar to the existing wave-cut channel located immediately north of the developing cave system.”

Drone photos and video taken by viewer Jimi Mckillip on Oct. 15 show that the newer of the two sinkholes remains especially dangerous, with a steep drop into a large hole of shifting sand. Cape Kiwanda’s geology consists of 15-million-year-old sandstone and siltstone formed during the middle Miocene period when the Pacific Ocean enveloped much of Western Oregon.