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Washington’s waterfalls–behind each one is a rock!

Of all the many reasons why waterfalls are great, here’s another: they expose bedrock! And that bedrock tells a story extending back in time long long before the waterfall. This posting describes 9 waterfalls that together paint a partial picture of Washington’s geologic history. The photos and diagrams will all appear in my forthcoming book Roadside Geology of Washington (Mountain Press) that I wrote with Darrel Cowan of the University of Washington.

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Rainbow falls along WA 6 in the Coast Range

And waterfalls in heavily forested areas are especially great because they may give the only view of bedrock for miles around! Take Rainbow Falls, for example–the small waterfall on the left. It’s in Washington’s Coast Range along State Highway 6–a place where a roadside geologist could otherwise fall into total despair for lack of good rock exposure. But this beautiful waterfall exposes a lava flow of the Grande Ronde Basalt, which belongs to the Columbia River Basalt Group. Significant? Yes!

This lava erupted in southeastern Washington and northeastern Oregon between about 16 and 15.6 million years ago and completely flooded the landscape of northern Oregon and southern Washington. We know how extensive these flows are because we can see them–and they cover the whole region. The photo below shows them at Palouse Falls in the eastern part of Washington. Take a look at my earlier blog post about the Columbia River Basalt Group? (includes 15 photos and a map)

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Palouse Falls in eastern Washington drops more than 180 feet over lava flows of the Grande Ronde and Wanapum members of the Columbia River Basalt Group.

You might also notice in the photo above that the waterfall is actually pretty small compared to its amphitheatre. That’s because Palouse Falls is part of another flood story –of the Ice Age Floods, described in rich detail on the Ice Age Floods Institute website. Basically, some 40 or 50 gigantic floods coursed through the area towards the end of the Ice Age, between about 15-18,000 years ago. and among other things, carved this canyon. Lobes of the continental ice sheet repeatedly dammed the Clark Fork River in northern Montana and then failed, repeatedly, after forming Glacial Lake Missoula. Imagine the flow volume in the above photo multiplied more than 100,000 times!

Mount Rainier and the Cascade Volcanoes
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At 14,410 feet above sea level, Mount Rainier is the highest volcano in the Cascade Range –and one of the highest spots in the conterminous United States. The volcano itself consists mostly of andesite flows that date back nearly a half million years.

Beneath those lava flows are older rocks that speak to a history of volcanic activity reaching back 70 times that of Rainier’s oldest lavas –to about 35 million years ago. At Christine Falls, you can inspect granitic rock of the Tatoosh Pluton, which is a crystallized magma chamber that formed beneath some early Cascade volcanoes. It was probably active at different times between 26-14 million years ago. At Narada Falls, you can see where Rainier andesite actually flowed over the top of the granite–which tells us that the granite was exposed at the surface 40,000 years ago when that flow erupted. Both these waterfalls are right along the road that winds its way from Longmire up towards Paradise Meadows.

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Christine Falls (left) cuts through granitic rock of Tatoosh Pluton; Narada Falls (right) flows over Rainier Andesite that itself flowed over Tatoosh granodiorite, exposed on the rocky hillside.

If you go to the south entrance of the national park, you can walk a quarter mile from the highway to Silver Falls and exposures of Rainier’s oldest rocks. The Ohanapecosh Formation, made mostly of tuffs and re-deposited volcanic particles, formed by explosive volcanic activity that stretches back 35 million years. The Ohanapecosh Formation forms cliffs throughout much of the national park –and shows up northward as far as Interstate 90.

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Silver Falls in Mount Rainier National Park, spills over outcrops of Ohanapecosh Formation, the park’s oldest rock.

Finding the oldest volcanic rock in the Cascade Volcanoes is important because this incredibly active volcanic chain is fueled by magma generated through the sinking of oceanic lithosphere at the Cascadia subduction zone –and the oldest rocks allow us to estimate when this process started. They get even older at Snoqualmie Falls, just north of I-90. There, rocks of the Mount Persis Volcanics reach ages of 38 million years. Most geologists agree that for Washington, these rocks mark the first volcanic activity after the formation of the Cascadia subduction zone.

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Snoqualmie Falls drops more than 250′ into a gorge of Mt. Persis Volcanics –rocks that mark the onset of volcanic acitity related to today’s Cascadia subduction zone.


Early Volcanic Roots and Continental Accretion

Here it gets a little complicated, because subduction also drove much of Washington’s geologic history before the Cascade volcanoes started to form. This older subduction also formed volcanic chains and through the process of continental accretion, caused Washington to grow westward.

Intro-8. Accretion series-CS4This diagram, modified from my book Roadside Geology of Oregon, illustrates the process of accretion. Basically, some element of the subducting seafloor is unable to fully sink beneath the continent, probably because it’s topographically high– such as with a series of seamounts. This material jams up the subduction zone and causes the sinking to stop temporarily. Eventually, a new subduction zone forms farther offshore and the thing that jammed up the zone in the first place gets added, or accreted, to the edge of the continent. In Washington and Oregon, the younger Cascadia subduction zone is the one that formed the Cascade Volcanoes and the stuff that jammed the zone was a huge fragment of oceanic lithosphere called “Siletzia”. Siletzia now makes up the bottom of Washington and Oregon’s Coast Range. The older subduction zone that got jammed up is the one that’s responsible for the rocks described below.

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Gorge Creek cuts a slot through orthogneiss (inset) of the Skagit Gneiss Complex along State Highway 20 in Washington’s North Cascades.

Gorge Falls along State Highway 20 in the North Cascades cuts this narrow slot through rocks formed because of that older subduction zone. These rocks started as the granitic roots to volcanoes, much in the same way as the Tatoosh Pluton formed the roots to some Cascade volcanoes. Those roots then got squeezed and reheated to make a metamorphic rock called gneiss. In some places it even partially re-melted.

The inset gives a close-up view of the rock. It’s called “orthogneiss” because it started out as an igneous rock. It forms a big part of the Skagit Gneiss Complex, which makes up the core of the North Cascades.

It’s hard to say if the Skagit Gneiss Complex was actually added to the edge of North America from somewhere else, but a lot of other rocks in Washington were–and those episodes of accretion are what caused much of the metamorphism in the North Cascades.

 

For accreted rock, here’s probably my favorite waterfall: Nooksack Falls, along State Highway 542 between Bellingham and the Mt. Baker ski area. It’s made of conglomerate of the Nooksack Group, which accumulated in a submarine fan somewhere off the coast of North America during the Jurassic and Cretaceous Periods, maybe 140 million years ago.

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Nooksack Falls in the North Cascades. the horizontal lines across the falls mark traces of bedding in the rock that’s inclined directly upstream.

Ancient North America

If you go eastward towards Spokane, you eventually find yourself on the North America that existed before all this accretion. Of course, much of the area is now covered by the Columbia River Basalt, but in the northeast corner of the state, you encounter Paleozoic sedimentary rocks that formed along the continental margin of that older continent. Sweet Creek Falls is one place to see these rocks, right off State Highway 31. There, the beautiful stream spills over ledges of Ledbetter Slate, deposited as shale during the Ordovician Period. In the foreground are cobbles of Addy Quartzite, formed as beach-deposited sandstone in the Cambrian.

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Sweet Creek Falls spills over Ledbetter Slate. Cobbles of Addy Quartzite lie in the foreground.

 

Washington’s Geologic Timeline

The timeline below shows Washington’s main geologic events –and you can see where these 9 waterfalls fit. The red text and red-colored bars represent geologic events represented by individual waterfalls, shown in blue.  Kind of amazing… these 9 waterfalls show many of Washington’s most important elements: the Cascade Volcanoes, the Columbia River Basalt Group, continental accretion, and the old continental margin.

And they’re nice places to hang out!

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Timeline of Washington’s geology. Red text signifies events described in this post and represented by various waterfalls (in blue).

 


For more geology photos, please check out my website–it contains a searchable database of more than 2000 geology photos for free download.

Roadside Geology of Washington should be out and available in August, 2017.

Thanks for reading!

 

 

 

 

 

Oregon’s rocky headlands: geologic recycling through erosion and uplift and erosion…

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Crashing waves at Heceta Head, Oregon

You can’t avoid thinking about erosion while standing on one of Oregon’s rocky headlands. The waves keep coming, one after another, each crashing repeatedly against the same rock. Impossibly, the rock appears unmoved and unchanged. How can it not erode?

The answer, of course, is that headlands do erode, quickly, but on a geologic time scale. We just miss out because we live on the much shorter human time scale. And the erosion belongs to a cycle in which coastal uplift causes eroded and flattened headlands to rise and become headlands once again, all subject to more ongoing erosion and uplift.

Wave energy is most intense at headlands because the incoming wave typically feels the ocean bottom near the headland first, which causes the wave to refract. As shown in the aerial photo below, this refraction focuses the wave energy on the headland.

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Wave refraction causes wave energy to focus on the headland. Arrows are perpendicular to wave fronts.

As you can see in the next few images, headlands don’t erode evenly. They erode irregularly, as the waves exploit any kind of weakness in the rocks such as faults and fractures, or if they’re sedimentary, bedding surfaces. The products of this erosion are as beautiful as they are interesting: sea stacks, sea arches, sea caves… The list goes on and on.

Headland and lighthouse, Heceta Head, Oregon

Aerial view of Heceta Head, Oregon.

From the above photo, you can see that sea stacks are simply the leftover remains of a headland as it retreats from erosion. That’s a critical point, because some sea stacks, especially the one with the arch in the photo below, are a long way from today’s coastline.

Sea stacks and sea arch, southern Oregon

Sea stacks and sea arch, southern Oregon

Those rocks, 1/4 to a 1/2 mile away used to be a part of the coastline? The land used to be way out there? YES!!! For me, that’s one of the very coolest things about sea stacks –they so demonstrate the constant change taking place through erosion.

Taken to its extreme, erosion renders headlands into wave-cut platforms, such as the one below at Sunset Bay. Being in the intertidal zone, these platforms make great places for tide-pooling–and ironically, for people-watching too. Geologically, they form important markers because they’re both flat and form at sea level. When found at higher elevations, they indicate uplift.

Wave-cut bench, Sunset Bay, Oregon

Wave-cut bench at Sunset Bay, Oregon

In fact, looking carefully at the photo above, you can see a flat surface on the other side of the bay. It’s an uplifted wave-cut platform! Called a marine terrace, it’s covered by gravel and sand originally deposited in the intertidal zone. Those deposits rest on bedrock that, at an earlier time, was also flattened by the waves. The photo below shows a better view of this terrace from the other side.

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Breaking wave at Shore Acres State Park, Oregon. Tree-covered flat surface in the background is an uplifted marine terrace.

These uplifted marine terraces can be found up and down Oregon’s coastline. Researchers recognize several different levels, the oldest being those uplifted to highest elevations. The one in the photo above at Shore Acres State Park is called the Whiskey Run Terrace and formed about 80,000 years ago. You can see a similar-aged terrace below as the flat surface beneath the lighthouse at Cape Blanco, Oregon’s westernmost point. An older, higher terrace forms the grass-covered flat area on the right side of the photo.

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Cape Blanco, Oregon looking NE. The flat surface beneath the lighthouse is the ~80,000 year-old Cape Blanco Terrace, probably equivalent to the Whiskey Run Terrace at Shore Acres; the flat area on the right side of the photo is the higher Pioneer Terrace,  formed ~105,000 years ago.

Researchers take the approximate ages of the terraces and their elevations to calculate approximate rates of uplift. In this area, Kelsey (1990) estimated a rate of between 4-12 inches of uplift every 1000 years. That might seem slow, but over hundreds of thousands of years, it can accomplish a great deal.

And look! The uplifted terraces? They’re on headlands! Of course, because they’ve been uplifted! And the headlands are now eroding into sea stacks and then platforms –to be uplifted in the future and preserved as marine terraces that sit on top headlands. And on and on, as long as the coastline continues rising.

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Blowhole near Yachats, Oregon. Incoming wave funnels up a channel eroded along a fracture and explodes upwards on reaching the end.

Some links and references:
Kelsey, H.M., 1990, Late Quaternary deformation of marine terraces of the Cascadia Subduction Zone near Cape Blanco, Oregon: Tectonics, v. 9, p. 983-1014. (Detailed study of Cape Blanco, including uplift rates).

Miller, M., 2014, Roadside Geology of Oregon, Mountain Press, Missoula, 386p. (General reference which details the concepts and includes several of the photos used here).

Earth Science Photographs–free downloads for Instructors or anybody: my webpage!

Scientists, Science, Icicles, and Faith

In January, I started teaching the Introductory Geology course “Environmental Geology and Landform Development” –with two lecture sections of about 200 students each. And this course, populated largely by folks who are fulfilling a science requirement and  otherwise try to avoid science like it was the plague, needed some general statement about science. After all, it’s science that may someday save them from the plague!

So science… what is it? Seems like scientists themselves have a zillion different definitions, so I started with “Scientist. –What’s a scientist?” If you google “scientist” and then look at the images, you see this. As this image is a screenshot of photos that aren’t mine, I intentionally blurred it, but you should get the idea of what’s there.

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Really??? these are the most popular images of scientists and in every picture–save the tiny one in the lower right– is some person in a WHITE LAB COAT and a microscope or a beaker. Ironically, it shows about 50% of the scientists as women. Go figure there too.

Looks like we’ve been fed a misrepresentation of what scientists are. We actually do a wide variety of things. In geology, we do a wide wide range of things. We spend time in the field (see picture below), we write, we draw maps and cross-sections, we look down microscopes (maybe in jeans and t-shirts), we write computer models, we do experiments, and we sometimes wear white lab coats.

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Geologist inspecting a fault zone between the dark-colored Beck Spring Dolomite and the overlying light-brown Noonday Dolomite. Death Valley, California.

All the time, we’re trying to understand something about our world. Our universe. We’re collecting information (data). We’re testing ideas. We’re adding detail to somebody else’s ideas. We’re building a framework of knowledge that’s grounded in our observations and testable ideas. Replace the word “ideas” with “hypotheses” in this paragraph –and you get science.

Ideally, most scientists approach their work using the “scientific method” –which is a highfalutin way of saying they see something they don’t understand (an observation), which causes them to ask a question (like how did this happen?); they come up with ideas (hypotheses) that may explain it, and then they test those hypotheses.

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Icicles?

Which is what we did in class with icicles! The month before–in mid-December–Eugene had this incredible ice storm, which covered everything in ice to make it look like a scene from the movie Frozen. It was beautiful and destructive. And we can all pretty much guess how icicles form: water starts to drip off the branch but freezes before it falls off. Icicles grow straight downward off the branch because water, like everything else, falls vertically with gravity.

As it turned out, some of the icicles seemed to grow straight out from the branches. Look at the photo below! How could this be? We know icicles should grow straight downwards! So as a group, we came up with some hypotheses, shown below next to the picture. I was the proud sponsor of hypothesis #4 and #5.

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Alternate hypotheses to explain near horizontal growth of icicles

As a group (all 200 of us), we could rule out hypothesis #3, that the picture was rotated. I shot the image and promised I didn’t rotate it! We could also rule out hypothesis #4, that the ice somehow grew horizontally towards the branch, because that idea conflicted with all previous observations we’d made on icicles, that they grow away from the branch as ice progressively freezes.

That left hypotheses #1, #2, #5. We figured ways we could test #1, #2. If it were the wind, for example, we’d expect all the icicles to go in one direction in a given place, regardless of the limb angle. If it were #2, we might expect to see some icicles show a curve to indicate progressive tilting of the branch–which you can actually see in the photo above!

Hypothesis #5, that “Some magical force caused it to grow sideways”isn’t testable. It’s NOT TESTABLE. We can’t come up with ways to support it or rule it out. You can believe it if you want to, but it’s not science.

That’s the point. To be scientific, a hypothesis must be testable. Most of us hold various non-scientific beliefs in our hearts that we know to be true –for us. I think that’s a good thing. For many of us, those beliefs lend us qualities like strength or courage or compassion when we need them the most. They’re still not scientific.

And that’s what really gripes me about the “scientific creationists” –as well as today’s Republican Party. The “scientific creationists” say they use science to demonstrate the existence of God, or that Earth is young –when believing either requires a suspension of science and an act of Faith. By claiming they’re being scientific, the “scientific creationists” hamstring their own belief system. They take the wonder out of religion and render it baseless and sterile.

And the Republicans? They’re now all about “alternative facts”. Maybe it’s unfair to group “all Republicans” together –but I see very few standing up to this reckless leader we have. Maybe they just lack integrity.

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this photo was rotated

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