Last week, a 10-foot-wide sinkhole appeared at Cape Kiwanda on Oregon’s north coast. This is the second sinkhole to appear at the cape this year, just inches away from the one that emerged in January.
A sinkhole is a depression in the ground that has no external drainage. So, when it rains the water stays inside, ponds up and then drains down into the subsurface.
Lauren Gabel is a geologist with the Oregon Department of Geology and Mineral Industries. She says that there are many reasons for a sinkhole to happen but typically, they appear when a cavity or cave develops underneath the surface of the ground. Sinkholes can pose dangers when these cavities don’t stop growing.
“If that cavity becomes too large to support its roof, that roof may collapse,” Gabel said. “It rapidly, or even slowly, starts to sink because there is no support.”
According to Gabel, the Oregon coast is composed of a very strong rock known as basalt. But at Cape Kiwanda, it is made of sandstone which is constantly being eroded by waves from the Pacific Ocean.
Using drone footage, geologists suspect that the interaction between land and sea is to blame for the recent changes on the coast.
“The wave action is preferentially eroding these weaknesses in the rock,” Gabel said. “We actually see a sea cave that’s forming just seaward of these two sinkholes.”
Gabel said because of the constantly shifting dynamic of coastal environments, little can be done at these locations.
In a statement, Oregon Parks and Recreation said:
“While any natural area carries risk, enjoying Cape Kiwanda safely requires visitors to pay special attention and to always respect the safety barriers throughout the park and all state parks. The sinkholes could change at any moment, and others could appear. If you see something that concerns you, leave the area and report it to Cape Lookout State Park staff at 503-842-4981. In an emergency, call 911.”
Lauren Gable joined OPB’s Think Out Loud to discuss sinkholes. You can listen to the full conversation here: