Inside Heceta Head / Cliffs Near Florence: All Come from Oregon Coast Volcano

Published 05/18/22 at 3:25 PM PST
By Oregon Coast Beach Connection staff

(Florence, Oregon) – At one point in time, long, long ago, the area between Yachats and Florence was one big mass of molten lava. Actually, at various points in time this was so. A sizable volcano dominated the future central Oregon coast for miles in either direction. If you look at the new lava flows going on in Hawaii right now you get an idea. From the northern edges of Yachats down to those soaring cliffs just north of Florence was one big inferno; or it was that black, super hot stuff you see now in Hawaii, what lava looks like just after it cools down a bit. (All photos Oregon Coast Beach Connection)

All this took place about 37 million years ago. The bulk of the western state was still under the ocean, like Salem and Silverton, etc. But just offshore, there was apparently a small island chain about where Yachats is, and at one end was the volcano that would later get the name Cape Perpetua.

That's right, Cape Perpetua was a volcano, and a mighty one. Its lava spread for miles, much of it underwater still, and created the black basalts we now see at Yachats, spreading all the way down to Heceta Head and those cliffs that include the Sea Lion Caves.

They are called the Yachats Basalts, according to Oregon coast geologists like Tom Horning in Seaside or University of Oregon's Marli Miller. But there's more than just frozen lava in the mix sometimes, and that pops up as different colored rock.

Oregon Coast Beach Connection has looked into the Perpetua volcano before, and discovered plenty of eye-popping things it did from Yachats down through spots like Bob Creek or Strawberry Hill. Yet we were still left with the question: what about those bubbly, rolling cliffs near Florence and Heceta Head?

Horning and Miller answered yes, these were part of the same basaltic complex. 37 million years ago was part of the Eocene era, about where the volcano was at its most active. The Perpetua volcano created all the lava, making for basalt sometimes hundreds of feet down, and as the area slowly rose above the ocean over those millions of years most of it was eroded away. Thus, you get the intriguing shapes and rock oddities you find now around Yachats and Heceta Head, like the basalt rocks that mysteriously look like steps.

Photos of those cliffs north of Florence show some different colors and layers as the cliffs descend into the sea. And sometimes Heceta Head will show some surprising colors as well.

“The basalt does vary somewhat, but it's mostly a series of basaltic lava flows, which might be why it's stratified in the photo,” Miller said. “In some places though, there's basaltic sandstone and conglomerate from erosion of the volcanoes during the same time period --there's a great exposure of the basaltic conglomerate at Heceta Head - and that can give it a prominent layering too.”

A lot of examples of this can be found in Miller's latest book, Oregon Rocks!.

Then, at the last chunk of cliffs that looms above Florence's Baker Beach, you'll notice a massive blob that's clearly been separated from the main cliff (apparently it's called Cox Rock). Miller said that is now a sea stack.

“The headland used to extend out and include that rock, but the waves eroded the headland back irregularly and left it as a remnant,” she said. “Soon enough, it will erode too. It's just like the sea stacks at Heceta Head, or Bandon. In many cases, the last connection between the sea stack and the coast is an arch, which eventually fails.”

Even though the material is that very sturdy basalt, it can erode away in front of us. Case in point: an arch in Oceanside on the north Oregon coast disappeared in 2004, leaving two sea stacks.

Sea stacks at Heceta Head

About the same time Perpetua was going, another infamous volcano was erupting under the ocean: Cascade Head at Lincoln City. These two, Horning said, have a lot in common.

“These two lava piles erupted simultaneously in the ocean and built oceanic seamounts just off the late Eocene coast of Oregon, about 36 million years ago,” he said. “The lavas have chemical and isotopic features that indicate they erupted in a rift environment.”

Here's where it gets insanely complex and involves a few different theories as to what fueled them. Some think it was cracks and faults that developed far under the ocean floor because of the ways Oregon and Washington were squished between two other moving plates. Others think it could be the giant hole at Yellowstone. The curious thing there is that Yellowstone's massive fracture doesn't move: the continental places move over it, like a conveyor belt. At 37 million years ago it may have been just under the future Oregon coast, and then later, at 14 million years ago, it was known to be about the Idaho border. There, it created a massive set of lava flows that seared across the proto Oregon territory and created wonders like the Columbia Gorge, Tillamook Head, Cape Meares, and as far south as Seal Rock.

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