At last, the long-awaited continuation of our series on Oregon geology! If you were breathless with anticipation, you can breathe now.
In Parte the First, we made it to Astoria, and caught a fleeting glimpse of Tillamook Head. We learned that the Columbia River Basalt flows are responsible for a lot of the outstanding features of the area, but didn’t get to see much of them because of all the damned trees in the way. Well, trees have a hard time growing on cliffs whilst pounded by salt water, so the bastards are in retreat, and we finally get to see ourselves some rocks. We also get more than a distant, misty glimpse of Tillamook Head, and learn why it is called “massive.” Follow me after the jump for a look at why earth, air, fire and water were the original elements.
We’ve made it to Ecola State Park, my darlings. You may be thinking, “What a silly name! Sounds like ebola without the b.” But you won’t be thinking it for long, because you’ll be distracted by nature’s artistic genius:
Take a moment to enlarge that photo and absorb it a bit. Here’s the words of one of my characters to help along your appreciation:
“Do you realize, Alex, that however many millions of years ago, all of this was a burning mass of superheated rock? None of this existed until good Mother Earth vented her rage and spilled this land from her belly. Outstanding. It almost lies beyond comprehension.”
Key word: almost. We can comprehend it, although it took centuries of effort by geologists to piece together its story. That effort began with Nicolas Steno, who emphasized the importance of strata, and continued with Dr. James Hutton, who got us thinking in terms of millions upon millions of years rather than a paltry handful of thousands. Charles Lyell carried the revolution forward by applying the processes of today to the past, which helped us understand how geological features are formed. Studies of wave erosion, along with studies of faults and such, revealed how nature carves such beautiful scenery out of dark black basalt. Advances in chemistry and the study of the Columbia River Basalts showed us that a lot of the land here came from back east, rather than forming right along the coast as some thought. And then came the plate tectonics boys and girls to finish this chapter of the story. There are still things we don’t understand about how this land formed, but we’ve got the big picture fairly well figured out.
When you look at that picture, you’re looking at a lot more than just pretty land, sea and mountains. You’re looking at an epic tale.
Let’s get storytelling. And we’ll start as all good stories do, in media res, with something sure to catch the reader’s attention: Tillamook Head.
That would not have been a good place to be 15.6 million years ago, when the basalts erupting from fissures in eastern Oregon flooded the landscape all the way to the sea. Granted, you would have had nice, comfy mudstone under your feet – our old friend the Grande Ronde Basalt flow intruded that mudstone along bedding planes, forming a sill, rather than just pouring out on top of the land just there. But it probably would’ve been uncomfortably warm. That sill is 250 feet thick. Imagine having 250 feet of molten rock flowing under a thin skin of mudstone. Brings a whole new meaning to the word hotfoot, doesn’t it just?
Here’s a wonderful example of a thinner sill to give you an idea of what the Grande Ronde was up to amidst the mudstones:
Don’t turn your nose up at it. That’s a perfectly good mineral sandwich, that is, even though the filling’s not 250 feet thick.
The Grande Ronde flow headed west along the continental shelf, following bedding planes until it was more than 600 feet under the sea. And it wasn’t just calmly flowing through the middle of its mudstone sandwich. In fact, had you been there, you might have seen quite the sight about a mile offshore as a portion of the Grande Ronde found a weak spot and headed for the surface, erupting up through the sedimentary stone and making its own private island, which we now know as Tillamook Rock:
Some rock, right? I mean, it’s big enough to fit a lighthouse on. And at one time, it probably looked a lot like this:
All that basalt is Tillamook Head’s raison d’etre, but if the sill had intruded just a bit higher or lower, it wouldn’t exist. It’s on account of the mudstone, you see. Mudstone is easier for the ocean to erode than basalt, and that nice, thick sill right at sea level keeps the head from getting cut away by waves. Had it been located any differently, water would have done its work, eroded the mudstones away, and the basalt sill would’ve gone plop into the sea. Little bits of interest would have still been there, though, because some of those Eocene seafloor basalts we discussed in the last episode ended up jammed onto the Head. Not that I managed to find them this trip. But it’s nice to know it’s not all just mudstone and modern basalt up there – if you search, you’ll find bits of submarine volcanoes and seamounts.
Someday, though, despite its basalt bulwark, Tillamook Head will succumb to the persistence of water, and shall end up looking much like this:
Those little sea stacks mark the previous position of the headland. A few thousand years ago, the heads were much bigger. All that’s left of all that land now is a few stubborn chunks of basalt. This next image will help us see what’s going on:
Oh, the waves are nice and polite now, but consider a few things: all that pretty, soft sand between the rocks is carried in by the waves, which wields it like sandpaper. When they get a little more vigorous, they toss in some gravel. And when they get really worked up during storms, they toss boulders around with abandon – the lighthouse can attest to that, as it’s been assaulted by bouncing boulders more than a few times in its history. The basalt can stand up to the abuse better than the mudstone – you see how the mudstone to the left is all soft and crumbly, while the basalt looks rather more stolid. But pound on it long enough with all that grit, and it too wears away. Basalt becomes sand, silt and gravel, mixed with mudstone remnants, and will someday be reborn as mud and sandstones laid down in layers on the continental shelf. Due to the vagaries of plate tectonics, it could eventually find itself hoisted up to form new sea cliffs. If it’s really fortunate (and we’re not), it might even find itself intruded by new flood basalts, offering it protection from the erosive action of the sea, and thus a reprise as a magnificent headland. Immortality of a sort. If rocks had religion, they’d probably be Buddhist or Hindu, knowing they have an endless round of reincarnations awaiting them.
We’ll get back to destruction in a moment, but first let’s talk about creation. More than one Columbia River Basalt group found its way to the sea here at Ecola. Along with our old friend the Grande Ronde, the younger Frenchman Springs member decided to go for a swim. It piled on top of the Grande Ronde basalts and dived right on in:
The Oregon coastline is famous for its sea stacks. We have some fine examples here, just off shore:
And they look solid as, well, rock, but they won’t be there forever. The dikes and sills are destined to get chopped into ever-smaller pieces, and this is where our four elements combine to make some rather awesome geology.
Fire, y’see, became earth. The molten rock cooled and solidified, creating new land, and immediately started getting itself bashed by water. Water seems all calm and serene until you soak a sink full of encrusted dishes and realize the stuff just took a few hours to soften up a crust it would’ve taken a chisel to get rid of earlier. Get water moving, and its erosive power increases: any kid who’s carved canyons into the poor defenseless front yard with a garden hose can tell you that. Add sand to the mix, and it gets downright abrasive. But then, you might ask, why isn’t the coastline sanded smooth? Why isolated sea stacks? Why big chunks ripped out?
This is where air comes in. Yes, air. Denizens of dry country, as I used to be, don’t realize that water pushes a lot of air around, but it does. And the results can be rather spectacular:
Those miniature sea caves there are full of air. When the breakers pound into them, air’s compressed and driven into fractures in the rock. Eventually, between the beating those rocks take from air and water, big chunks of rock get loosened and knocked out. Given enough time and wave action, and highly-fractured rock gets carved right out, leaving the less-fractured stuff standing (for the moment). Hence, sea caves and arches. Gravity provides an assist in pulling undermined things down. And we end up with boulder-strewn beaches which themselves are ground down to help provide all that lovely sand we love to build castles in.
Headlands take a hell of a thrashing. They’re out there in front, with nothing to shield them from the onslaught of the surf. Here’s the concept in miniature:
See how the waves are all curving around to converge on the projecting tip of rock? They get squashed as they converge, and all their energy gets squashed with them. That allows them to concentrate their force in a much smaller area – it’s not all spread out. Thus, the headland bears the brunt, and the waves work on making all the crooked bits straight and smooth. The echinoderms and other assorted sea creatures that call that tide pool home will have to look for other accommodations. And so, if you built your house on a headland, will you.
It’s not just waves that have sculpted Ecola, though – gravity’s got its heavy hand in, and even though the trees try to cover for it, they give it away:
Note the crazy angles of the tree trunks in the background. The area’s riddled with shallow faults, which have triggered landslides. The land’s so steep here that it doesn’t take much encouragement for those soft mudstones to go slip-sliding away. One of the books I consulted, In Search of Ancient Oregon, has a photo of one of the fences tilting from the slump of the land. That fence has since been rebuilt, because it was standing straight and proud when I arrived. Won’t be long, though, before it’s tilting like several drunken sailors again.
That mudstone weathers away to nice, rounded tops overlying the stiff basalts:
Sharp eyes will have caught a glimpse of the pillow basalts in the sea caves, but for those who wanted more clarity shall have it:
Fractured and pillowed basalts tell us there was a big hoo-ha here long ago, when lava flowing over (and through) land hit the water and cooled rapidly. The neatest thing about this, to me, is the fact that even if the sea had retreated long before we got here, we’d still know there was an ocean present when these rocks were laid down. The story is contained within the mudstones and the pillow basalts. The earth testifies about its accomplices of air, fire and water, even when we’re not witnesses to the commission of the – well, one could hardly call astounding geological processes a crime. So think of it like this: we’ve come late to an amazing display. We’re only seeing it torn down, but the land’s more than happy to tell us about what it was like when it was built and in its heyday, long ago when good mother Earth split open and spilled forth sheets of fire to meet air and water, and give us a gorgeous place to stand while we contemplate her power.
And in our next installment, we’ll get to stand right inside that power. But for now, I leave you with a wonderful waterfall – because it’s not just the sea working to carve this land: