This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Hug Point State Park in Oregon could use a hug. Pioneers certainly weren't very affectionate with it: they blew bits of it up. Millions of years before that, massive amounts of flood basalt intruded a nice, calm delta, which also made things pretty explosive. Despite that rather hazardous history, it's a super-lovely place that is eminently hugable, so that's where we're going on this national day of hugging people¹ and things².
Oh, yes, that is a waterfall on the beach! You'll find a little bit of just about everything here: luscious golden sandstones, sea cliffs of pale sedimentary and dark igneous rock, sea caves, sea stacks, peaceful coves with sandy beaches, and the fault that Fall Creek flows down. Everything weaves together with the sea, and makes for one of the most magical places on Earth, a little pocket of paradise - especially if you go as gaga for geology as I do.
Hug Point is not merely gorgeous, it's a great place to go if you want to immerse yourself in both human and geological history. Plan your visit for low tide so that you can see it all! It's nearly impossible and quite dangerous to maneuver around the headlands during high tide. You know how major freeways get during rush hour? The beach here was basically a highway between Astoria and Tillamook in pioneer times, but it could only be used during low tide, so it became even less passable than our roads for many hours every day. Late in the 19th century, they tried to improve matters by blasting a statecoach route through one of the sea cliffs, but you still had to hug the cliff pretty tight to get round it, and it was still precarious. This is why it got named Hug Point.
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People have been hugging the geology there for centuries! But we didn't unravel it's epic story until recently.
Maybe some of the folks who worked on that road wondered about the fantastic interweaving of pastel sandstone and rugged dark basalt. I imagine they spent plenty of time cursing the latter as they blew a road through it. If they'd looked closely, they may have seen signs that some of this basalt had been blown up before. Geologists up until the last quarter of the 20th century thought the basalt was local. They saw things like dikes and sills of basalt intruding the sandstones, and it surely looked like there had been a whole lot of local volcanism going on in the past. But when they studied the chemical composition of the basalts, they matched the signature of the Columbia River Basalt Group, which consisted of continental flood basalts that had erupted hundreds of miles away. And when they did gravity studies, they found out the flows were rootless. If they'd erupted from somewhere beneath the coast, the dikes should have extended thousands of feet down. But after a few hundred feet, these just vanished!
Weird.
A lot of hard work eventually pieced together the remarkable story. Dig your toes into the sand, face the cliffs and the cove, and travel back in time with me to around sixteen million years ago. See that great big river emptying into the sea? It's flowing all the way from eastern Washington and Oregon, then draining through the Western Cascades volcanic arc, bringing down cobbles and pebbles of all sorts of igneous and metamorphic rocks like granite, pumice and schist you wouldn't ordinarily find over here. This is a possible channel of the ancestral Columbia River, which has flowed even further south in the past. There isn't a Coast Range yet. The sediments of the delta this river's depositing will become the sedimentary Astoria Formation. Pretty fabulous, eh?
It looks peaceful, except when the river floods, but flood basalts have been erupting to the east for nearly two million years. Round about 15.6 million years ago, Grande Ronde flows of the Columbia River Flood Basalts erupted several hundred miles away, near the present Idaho border. They coursed through river valleys and canyons, finding their way to the coast. This molten rock was still extremely hot when it arrived. It invaded the sandstones, creating thick sills, and sank into the sands and mud of the shores, forming pseudo-dikes that pinched out a few hundred feet below the surface. In places, the basalts and sediments mixed. The sediments deformed as they were invaded; steam explosions from the water within them disrupted their former orderly layers.
Cold seawater boiled against the hot molten rock, oxidizing it to a deep reddish hue. Where the water flashed to steam, it blew the flows apart, leaving them fractured. Broken pieces solidified into breccias as they cooled.
The river had to find another course. Thick basalt flows cooled into solid rock and set up housekeeping with the sandstones. The Coast Range continued rising, and lifted those sandstones and basalts high, letting them create the sea cliffs of today. Faults made pathways for creeks like Fall Creek. Landslides happened, and if you explore around the Hug Point area, you'll see the hummocky terrain that tells you one happened here, too.
Today, this is a beautiful and peaceful spot. The only explosions in millions of years have been caused by pioneer dynamite, not the violent interaction of steaming hot basalt and the ocean. Erosion carves the stone headlands into fantastic shapes. The most excitement you get is the occasional landslide, the intermittent earthquakes, and the pounding fury of storm waves. But this is still an active landscape, and who knows what excitement subducting plates have in store for us? Hug your lovely peaceful geology while it lasts!
1. Always get permission, first! Only give hugs to them as wants 'em.
2. Avoid hugging things that could result in serious injury, like cacti or aa basalt flows.
References:
Beeson, Marvin H. (1987): Columbia River Gorge: The geologic evolution of the Columbia River in northwestern Oregon and southwestern Washington. In Cordilleran Section of the Geological Society of America: Decade of North American Geology, Centennial Field Guide Volume 1. Boulder, CO: Geological Society of America.
Bishop, Ellen Morris (2004): Hiking Oregon's Geology. Seattle, WA: The Mountaineers Books.
Bishop, Ellen Morris (2003): In Search of Ancient Oregon. Portland, OR: Timber Press.
Mueller, Marge and Ted (1997): Fire, Faults, & Floods: A Road & Trail Guide Exploring the Origins of the Columbia River Basin. Caldwell, ID: University of Idaho Press.
Wells et al (2009): The Columbia River Basalt Group - From the gorge to the sea. In Volcanoes to Vineyards: Geologic Field Trips Through the Dynamic Landscape of the Pacific Northwest. Boulder, CO: Geological Society of America.