09 March, 2011

Oregon Geology Parte the Ninth: Taking the Plunge

We've certainly had quite the adventure, haven't we?  Been through Astoria, Ecola State Park, Hug Point north and south; we've enjoyed the world's shortest river, Cape Kiwanda, and Cape Meares, and at last have made it here to the Columbia River Gorge.  Now, and try not to be too shocked here, we're going to go see ourselves more basalt.

Well, that and some waterfalls.

Nothing too spectacular, mind.  I mean, we're only going to see the second highest waterfall in the United States.  It just plunges 620 feet over sheer cliffs of Columbia River Basalts.  It's just sort of, y'know, kinda like ZOMG WTF holy haleakala Batman!

Multnomah Falls
Okay.  Yeah.  That's pretty bloody spectacular, that is.  Let's just stand here silently for a moment and stare.

Stared enough?  Okay.  Let's talk geology, then.

Over the course of 400,000 years, flow after flow of Columbia River Basalts laminated the landscape in thick black basalt.  You can see quite a few of them in the cliff Multnomah Falls cascades down.  Up by the lip there, you can see a wee colonnade, followed by a black band of pillow lava.  I want to pause at pillow lava for a moment, because that tells us something fascinating about the history of this place.  A casual glance at this enormous, solid cliff gives the impression that it was all basalt all the time back then, but the pillows say, "No, wait - it wasn't always flow after flow of blazing hot lava round here.  Look, there was even a pond, or maybe a little lake, right here.  Well, until the next wave of molten rock came through, anyway."

That picturesque pond of water formed on top of a rather thicker previous flow, which you can see as an entabulature and colonnade.  Those three flows pretty much take up the whole of this photo.

Top o' Multnomah
That's a damned lot of basalt.  But wait!  There's more!

Multnomah Falls - Upper Falls
A little over halfway down the cliff, you'll see the falls hit a ledge and fan out.  It's striking the fourth flow, and hiding the fifth: two entabulatures and a small colonnade.  If there wasn't so much hydrology and biology in the way, you'd be able to see more of the geology, but that other stuff's pretty so we won't complain.  Much.

Let's have a look into the plunge pool, shall we?

Multnomah Falls Plunge Pool
Here lies the boundary between the fifth and sixth flows, but the more interesting feature in this photo is the enormous boulder.  It's hard to tell in these photos - all the flows look pretty welded and solid.  But in between flows, erosion happened, and soil horizons formed, and those are more easily attacked by falling water.  It gets cold in the winter, too, and frost works its wedge in.  Eventually, big chunks of cliff fall down and go boom.  Some of them are gargantuan - up to and including the size of a bus.

While you're wandering the trail at Multnomah, don't forget to have fun away from the falls.  There's some delicious geology, including a nice, cozy cave.

The Cave and I
Here's another view, sans moi:

You can see it's in the entabulature, and it is awesome.  Not sure how it was formed, though, so you're on your own there.

And a nice, close view of basalt here:

Not many vesicles, as you can see.  It's pretty solid stuff - aside from all the cracks and fractures.  Not quite so solid as it looks, that.  But absolutely lovely.

Multnomah Falls has carved itself a respectable ampitheatre over the years.  The view from beside it is utterly spectacular:

Isn't that outstanding?

So, you've seen the second tallest waterfall in the United States and gotten really intimate with the Columbia River Basalts.  You may think nothing else can live up to that and your adventures are over, but what you need to do is drive down Samuel C. Lancaster's delightful historic highway.  The scenery is spectacular and the geology even more so.  Check this out:

Basalt Mushroom!
Is that not one of the greatest entabulature-and-colonnades you've ever seen?  Here's a nice closeup:

Boundary Between Colonnade and Entabulature
Drive on, stop at Latourell Falls, and you'll find something even more interesting:

Ooo, Platy!
I think - and mind you, I'm not sure, but I think - this is the lovely gray outcrop of Oligocene Skamania volcanics Ellen Morris Bishop mentioned in Hiking Oregon's Geology.  And if so, that means that these are far older than the Columbia River Basalts - at somewhere between 25 and 30 million years.  They stood there while the flood basalts flowed around them, and still stand today.  Beautiful!

Or I'm wrong and they're just a fine example of platy basalt.  Either way, I love them.  So much, in fact, that I think they deserve another look:

Lovely Little Outcrop

Things get even more interesting on down the trail.  Latourell Falls takes a 250 foot dive over three separate flows of the Columbia River Basalts - our old friends the Grande Ronde (lowest and oldest), the Frenchman Springs, and the Priest Rapids.  Check this out:

Latourell Falls
Look, just look, at the entabulature and colonnade on that thing!

And what's even better is that you can walk right along the side of Latourell Creek and enjoy everything up close, personal, and powerful.  Standing on the edge of a plunge pool is teh awesome.

Hooman for Scale
It's hard to imagine, looking at this, that it began as glowing fountains of molten rock spilling from vents over three hundred miles to the east, over hundreds of thousands of years, wave after wave, paving the earth in deep black basalt.  Let a little erosion happen, a catastrophic flood or several dozen, bung in some plants and streams, and you have something that fair takes the breath away.

Isn't geology wonderful?

Ye olde indispensable volumes of reference as the author was trying to make sense of it all:

Fires, Faults and Floods - one of the best roadside guides to the Columbia River Basin evah.

In Search of Ancient Oregon - simply the most beautiful book written about Oregon's natural history.
Hiking Oregon's Geology - chock full o' adventurous goodness sure to help you get your rocks on.

Northwest Exposures - tying the whole shebang together in one easy-to-follow narrative.

Cataclysms on the Columbia - the book that truly helped me comprehend the incomprehensible.

The Restless Northwest - short, sweet, and yet comprehensive guide to Northwest geological shenanigans.

Roadside Geology of Oregon and Roadside Geology of Washington - indispensable references and inspirations.

Glacial Lake Missoula and its Humongous Floods - not only an informative guide to the discovery and history of the Floods, but an apt title, too!


Suzanne said...

wow wow and did i say wow. eye candy and brain candy!

thanks dana

KLR said...

Hey, have been reading your posts on OR geology - fantastic stuff. Don't stop! Am just an avid layman - have everything on your recommending reading list.

The Skamanias are exposed in the road along I84, Alt points that out in his Roadside book. Forget what else shows up there pre-CRBG. The Troutdale Formation crops up at Crown Point - the idea of gravel from a Pliocene Columbia River channel being uplifted that far is pretty hard to wrap one's head around!

Have you covered Rooster Rock yet? Cool that something like that fell off the cliff face.

Silver Fox said...

Nice post on one of my favorite places!