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So What’s a Coastal Bluff Got To Do With Mount St. Helens?

The views expressed are those of the author and are not necessarily those of Scientific American.


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Ah. Very glad you asked. You see, I’d like to introduce you to one of my favorite geologic spots in the known universe. Let me show you my first sight of it:

South Bluff, Discovery Park, June 2000

South Bluff, Discovery Park, June 2000

That was my first glimpse of a coastal bluff made of glacial sediments. I didn’t know that at the time. It was more, “Wow, cool bluff!” and off to get distracted by the baby seal at the lighthouse.

Baby seal near lighthouse at Discovery Park.

Baby seal near lighthouse at Discovery Park.

Yeah, you know you wanted to see the baby seal. What an experience that day was! A walk through a forest greener than any I’d ever seen, across a sandy trail with signs saying “UNSTABLE BLUFF” all over the place, and then down and down and down until beach and sea and seal. Hundreds of clear jellyfish washed ashore gleamed like diamonds on that stony beach. And this amazing bluff, which would, nearly a decade later, put a match to the kindling laid by my physical geography professor and the great state of Arizona.

So. Seven years spent trying to get back there, and then a glorious May day, and a discovery at Discovery: this bluff was like nothing I’d ever seen.

South Bluff, Discovery Park, May 2007

South Bluff, Discovery Park, May 2007

I knew there was a story in those sediments. I thought it was sandstone, and went to touch it – missing sandstone, which I’d grown up with – but it wasn’t stone at all. Just very, very solid sand, silt and clay, packed layer upon layer and polished by the Sound. I’d never known compact mud could form cliffs. This didn’t happen in my experience. I walked along it, patting, listening to the solid sound of my palm against something that seemed solid and forever and yet shouldn’t have lasted a day.

This may be where it began, that urge to understand. Not just comprehend the broad strokes needed to paint a convincing story world, but the fine detail: what was the biography of this place, this near-stone; how could it possibly come to be?

It drew me back. Again. Again. Again.

South Bluff, Discovery Park, June 2009

South Bluff, Discovery Park, June 2009

Our Oregon trip poured fuel on the flame. My geology interest went from curiosity to obsession. I had a better camera, and a book of Washington geology hikes, and there was my park, my beautiful Discovery, in there.

South Bluff, Discovery Park, October 2010.

South Bluff, Discovery Park, October 2010

Now I knew. The near-stone I’d run my hands over, trying to read with touch, had been laid down tens of thousands of years before; then the ice arrived and built the rest of my bluff. It carved my Sound. Now this began to make sense. Knowing it better, understanding it more, deepened my love for this place. It’s amazing to see a slice of geologic history so cleanly cut and displayed. And it seemed like forever. Nothing lasts, eternal, but this felt like it wouldn’t change in my lifetime. It would always be there, with it’s richly colored pre-ice sediments, its gray clay, its lovely tan sand.

And then I brought my geologist friend Ryan down. Yes, he studies meteorites, mostly, but his blog’s name is Glacial Till, and so it seemed appropriate somehow. I’d show him that magnificent bluff with its clean-cut display andohmygodthere’salandslide!

South Bluff, Discovery Park, September 2012

South Bluff, Discovery Park, September 2012

Bluffs don’t behave themselves, y’see. But we geologists, we often love it when the scenery misbehaves. What a marvelous opportunity to see geologic processes at work!

South Bluff, Discovery Park, June 2013

South Bluff, Discovery Park, June 2013

It’s all still there: remnants of landslides, the wonderful stratigraphy, the geologic-lab-inna-park. Summer makes me long for the sea, so we’ll spend a little while here. Discovery Park’s South Bluff has stories to tell. It will teach us about Seattle’s Pleistocene history. It will demonstrate some soft sediment deformation, and discuss the carving of Puget Sound. It will demonstrate why it’s not wise to build your house perched up high with an uninterrupted view of the Sound. And it will tell us what it has to do with Mount St. Helens.

This bluff, our bluff, spent some of the 60s with our own Donal Mullineaux and Rocky Crandell – two of the USGS geologists who would later do such thorough work teasing out Mount St. Helens’s eruptive past that they predicted she could erupt within the century. Mullineaux used South Bluff as the type section for both the Lawton Clay and the Esperance Sand, giving us a much clearer picture of the past thirty thousand years here. Crandell built on his work to change our understanding of how Puget Sound formed. We might even see some other familiar names as we go along – Pacific Northwest geologists seem to be intrigued by anything and everything, and you never know where you might run in to an old friend.

By the time we’re done, you’ll know this grand old bluff so intimately that you’ll greet it as someone you’ve always known when you meet it for the very first time. You’ll be able to lead people on your very own geotour when you come visit. You’ll be able to hold your own in conversations about Puget Sounds engineering woes. And you’ll know why Mullineaux and Crandell found South Bluff so fascinating, despite the fact nothing’s exploded here for a very long time.

Not bad for a place that’s basically a pile of compressed sediment that’s barely a blip on the geologic time scale, eh?

(And yes, I promise, we’ll have much more Mount St. Helens after we get done dabbling our toes in the sea. Not to worry!)

Dana Hunter About the Author: Dana Hunter is a science blogger, SF writer, and geology addict whose home away from SciAm is En Tequila Es Verdad. Follow her on Twitter: @dhunterauthor. Follow on Twitter @dhunterauthor.

The views expressed are those of the author and are not necessarily those of Scientific American.





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