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Mountain in Transition

inside the crater of Mt. St. Helens
(click on images to see them at full size)

Terminus of Crater Glacier, Mt. St. Helens, Washington

There’s a glacier in the crater of Mt. St. Helens—and unlike most other glaciers, it’s growing. Shaded by soaring crater walls and continually replenished by snow avalanches and rockfalls, it oozes forward more than 100 feet per year. At the sound of a loud crack, I look up at its steep front to see a bunch of rocks breaking free of the ice and tumbling downwards to rejoin their compatriots at the bottom. Soon, the ice will advance over them and they’ll be a part of the glacier again.

I’ve long been attracted to these landscapes, practically devoid of organic life but alive just the same. They evoke a sense of timelessness, a connection to Earth’s past, long before mammals and reptiles, let alone humans, colonized its surface. Besides this glacier, near-continuous rock fall and rising dust plumes, there’s a 1000’ tall lava dome that still puts out steam. Younger than many teenagers, the dome formed as sticky silica-rich lava extruded from a vent in the crater floor. It rose to within 800 feet of the highest part of the rim over a period of 5 years, from 2004-2008. It now towers over an older dome, which grew from 1980 until 1986, scarcely middle-aged by human standards.

Crater domes and fumarole emissions. The dark ledge across the bottom of the photo marks the terminus of Crater Glacier.

My group is taking its lunch break. One person’s off shooting photos, a few are talking quietly, another’s inspecting some of the pumice and broken rocks that blanket this part of the crater. Our guides are conferring over our route. I feel lucky to be here, having been invited a few months ago to accompany the group to talk about the geology. The Mt. St. Helens Institute, the non-profit that organized the trip, does so under a special use permit from the Gifford Pinchot National Forest.

Looking northward to Spirit Lake and Johnston Ridge, I see a landscape of somber browns, yellows, and grays, decorated with greens. Most of those colors come from rock, either ancient bedrock or eruptive products from the big eruption in 1980.  The greens though come from vegetation that is rapidly covering the lower elevations. On the way here, we walked over ashy fields spotted with prairie lupine, paintbrush and a host of other wildflowers I couldn’t identify, small stands of juvenile Douglas Fir and through the occasional jungle of alder.

View northward from the crater entrance to Spirit Lake and the eastern edge of Johnston Ridge.

Almost nothing in my view was spared the effects of the 1980 eruption. At 8:32am, May 18, a magnitude 5.1 earthquake caused the bulging north side of the mountain to fail as a gigantic avalanche, releasing pressure on the magma within the volcano, which naturally expanded northwards at supersonic speeds. Entire forests blew over in the scalding hot gas. 10 miles from the crater and forty years later, you can still see many of these trees lying down in formation, just like toothpicks. The failed north side of the mountain, all .67 cubic miles of it, ranks as the world’s largest debris avalanche in recorded history. I can see its path, marked by giant piles of rock called hummocks. Even here in the crater are deposits of the debris avalanche, forming towers of conical pointed hills more than 100 feet high.

Hikers and landslide hummocks in the crater of Mt. St. Helens, Washington.

I stoop down to look at a small plant. It’s all by itself, growing between loose, rounded pieces of pumice and undoubtedly rooted in more of the same. An early colonizer. If the crater floor were to remain undisturbed, more vegetation would creep in and eventually, this place would become lightly forested like other places nearby at this elevation. Of course, that’s unlikely here, with an advancing glacier and all the rocks falling from the rim.

Or more eruptions! Mt. St. Helens is, without question, the most active volcano in the Cascade Range, with more than a dozen smaller eruptions since the big one on May 18. And long before 1980 there were hundreds. The US Geological Survey closely monitors Mt. St. Helens’s ongoing activity as well as its geologic past to understand the volcano’s behavior through time. They define its history in terms of four distinct eruptive “Stages” that stretch back some 275,000 years. The most recent of these, the Spirit Lake Stage, started about 3900 years ago and is further divided into six eruptive “Periods”, each marked by multiple eruptions and separated by times of dormancy. One of these eruptions, between 3500-3300 years ago during the Smith Creek Period, dwarfed the 1980 eruption. And in the early 1480s, two eruptions of comparable size to the one in 1980 occurred just two years apart.

Shading the sun from my eyes, I look southward to the volcano’s rim, and I can see a whitish layer produced by these two eruptions. It’s called the “W Tephra”. More than 250 feet of rock now sits above it –all formed after 1480. And there used to be 1300 feet of rock above that, until it was blasted off in 1980—which means that in 500 years, Mt. St. Helens grew more than a quarter mile in height. Just before its cataclysmic eruption, its summit stood 9,677 feet above sea level.

Dacite domes and Crater Glacier in crater of Mt. St. Helens, Washington. The W Tephra forms the light-colored band at the end of the arrow.

It’s the myriad smaller eruptions that cause a volcano to grow, and in the case of Mt. St. Helens, they mostly produce lava domes instead of lava flows. As a college student, I had the hardest time visualizing a lava dome because the photographs I saw just looked like gigantic piles of broken rock.  But that’s basically what they are, gigantic, dome-shaped, piles of rock. Imagine lava that is so viscous it can hardly flow, oozing out of a volcanic vent, and pushing aside or piling on top of earlier extruded lava, and cooling and breaking up in the process. By its very nature, silica-rich lava like the dacite of Mt. St. Helens is highly viscous. Silica molecules bond with each other to form interconnected networks, so the more silica in a lava, the more viscous it tends to be. Lower silica lavas like andesites contain fewer of those networks so they’re more likely to produce lava flows. Basaltic lavas contain even less silica and flow even easier.

Feeling a gentle breeze, I close my eyes and imagine this place sometime in the future. Two hundred years? Five hundred years? I picture the crater walls, slightly lower now, having steadily eroded through time, their debris gradually filling the crater. A couple large landslides have removed large fractions of one of the walls and piled their debris up against today’s modern domes. During this time, the mountain was largely dormant, but now a pulse of basaltic magma is working its way towards the surface, intruding the gray dacite domes along fracture surfaces as black basaltic dikes. Some of these dikes break through the top of the domes and spill out as basaltic lava flows, which flow a short way down and out of the crater. Mt. St. Helens awakens again, but this time, the lava is basalt so it awakens quietly.

I remind myself that this volcano hasn’t produced much basalt during its 275,000-year history. It doesn’t tend to “awaken quietly”, but more like some grumpy person who you’ve roused with a splash of ice water. Besides the numerous domes, its products typically depict violence: deposits of fallen ash or pumice, or pyroclastic flows, which consist of fast-moving ash, pumice and rock fragments mixed with hot gases. The only basalt lavas from Mt. St. Helens erupted during the end of the Castle Creek Period, which stretched from about 2500 to 1900 years ago. Ape Cave, the lava tube on the volcano’s south side, formed in these lavas, as did the steep rocky slopes we climbed on our hike into the crater. And there, low on the east crater wall, I can see the drama: black Castle Creek dikes slicing through light-colored rock of an older dacite dome. They’re overlain by dark-colored Castle Creek lava flows likely fed by the dikes below, just like my daydream.

Basaltic dikes of the Castle Creek Period cut an older dacite dome. Pyroclastic flow deposits form the layered materials near the bottom of the photo in shadow.

As we start our descent, I reflect on the ongoing Modern eruptive period. Before the first earthquakes on March 16, nearly everyone in the Pacific Northwest viewed Mt. St. Helens as a perfectly symmetrical and docile ice cream cone of a mountain. My college friend Michael longed to return home to Portland for long enough to climb it, partly because it offered such a wonderful glissade after summiting. Then less than two weeks after those first earthquakes, the first steam eruptions began. Then more earthquakes. Bulging of the northern edifice. Steam. Earthquakes. May 18. 

We’ve learned so much since then! We’ve watched the Modern Period unfold with our own eyes as well as with a vast array of ever-evolving instruments. We can see the rich details of the volcano’s behavior to the point that researchers divide the last 40 years into two subperiods, defined by the formation of each lava dome. We’ve watched Crater Glacier evolve from a snowfield to a full-on glacier that itself has experienced major changes in its shape and behavior. We’ve watched the crater rim erode. We’ve watched vegetation recolonize a landscape that was suddenly rendered devoid of nearly all organic life.

Loowit Falls and debris avalanche deposits.

Our group stops for a quick break at Forsyth Spring to absorb the flourishing willows, alders, and sounds of running water. I contemplate the earlier phases of Mt. St. Helens, reaching back to its origin as a series of lava domes 275,000 years ago. Those phases must have been as interesting and diverse as today, but we can experience them only through whatever preserved evidence we can find in the volcano’s deposits. We can’t taste the water or feel the freshness of new growth. Still, we can imagine it.

For this reason, I don’t think of today’s Mt. St. Helens as being “reborn” as it’s so often described. Sure, the vegetation is returning, but I can’t help but see it as incidental to the overall story of a volcano that’s always in transition. The 1980 eruption wasn’t an end point or a beginning –just an event that happened during a long eventful history. We’re experiencing just another moment, another transition, in this volcano’s cycle of life.


All photos freely available from geologypics.com. Click here for more photos of Mt. St. Helens and its geology. Type “Mt. St. Helens” into the search to see them all!

In Transit

This little black pebble, now sitting on my desk, traveled a lot today. After picking it up beneath a cliff face in southwestern Montana, I carried it in my pocket for a few hours and then drove some 20 miles to this college dorm where I’m staying.  It’s the most this pebble has moved for millions of years. 

Some time ago–this morning, a week, a year, 10 years, 100 years—the pebble weathered out of a much larger rock and fell to the ground. Its worn, rounded edges tell me that before it became part of that larger rock, it traveled down a stream bed –and its size tells me that its source probably wasn’t too far away. As is typical of stream gravel, its movement was irregular, marked by short bursts of movements during floods separated by longer periods of rest on a gravel bar or in the channel itself. Somewhere along the line, the pebble became buried by more sediment, probably because the land subsided or the river channel switched to another position. Eventually, the pebble and the rest of its surrounding sediment turned into rock.

Read more…

Grand Canyon Unconformities –and a Cambrian Island

A prominent ledge punctuates the landscape towards the bottom of the Grand Canyon. It’s the Tapeats Sandstone, deposited during the Cambrian Period about 520 million years ago, when the ocean was beginning to encroach on the North American continent, an event called the Cambrian Transgression. Above the ledge, you can see more than 3000 feet of near-horizontal sedimentary rocks, eroded into cliffs and slopes depending on their ability to withstand weathering and erosion. These rocks, deposited during the rest of the Paleozoic Era, are often used to demonstrate the vastness of geologic time–some 300 million years of it.

View of the Grand Canyon from the South Rim trail. Arrows point to the Cambrian Tapeats Sandstone.

View of the Grand Canyon from the South Rim trail. Arrows point to the Tapeats Sandstone.

But the razor-thin surface between the Tapeats and the underlying Proterozoic-age rock reflects the passage of far more geologic time  –about 600 million years where the Tapeats sits on top of the sedimentary rocks of the Grand Canyon Supergroup. Those rocks are easy to spot on the photo above because they contain the bright red rock called the Hakatai Shale. Even more time passed across the surface where the Tapeats sits on top of the 1.7 billion year old metamorphic basement rock. You can put your thumb on the basement and a finger on the Tapeats –and your hand will span 1.2 billion years! Read more…

Cove Palisades, Oregon: a tidy short story in the vastness of time

If I were a water skier, I’d go to Lake Billy Chinook at Cove Palisades where I could ski and see amazing geology at the same time. On the other hand, I’d probably keep crashing because the geology is so dramatic! Maybe a canoe would be better.

Lake Billy Chinook, Oregon

View across the Crooked River Arm of Lake Billy Chinook to some of the 1.2 million year old canyon-filling basalt (right) and Deschutes Fm (left). The cliff on the far left of the photo is also part of the 1.2 million year basalt.

The lake itself fills canyons of the Crooked, Deschutes and Metolius Rivers. It backs up behind Round Butte Dam, which blocks the river channel just down from where the rivers merge. The rocks here tell a story of earlier river canyons that occupied the same places as today’s Crooked and Deschutes Rivers. These older canyons were filled by basaltic lava flows that now line some of the walls of today’s canyons.

CovePalisades2From the geologic map, modified from Bishop and Smith, 1990, you can see how the brown-colored canyon-filling basalt, (called the “Intracanyon Basalt”) forms narrow outcrops within today’s Crooked and Deschutes canyon areas. It erupted about 1.2 million years ago and flowed from a vent about 60 miles to the south. You can also see that most of the bedrock (in shades of green) consists of the Deschutes Formation, and that there are a lot of landslides along the canyon sides.

The cross-section at the bottom of the map shows the view along a west-to-east line. Multiple flows of the intracanyon basalt filled the canyon 1.2 million years ago –and since then the river has re-established its channel pretty much in the old canyon. While the map and cross-section views suggest the flows moved down narrow valleys or canyons, you can actually see the canyon edges, several of which are visible right from the road.

Read more…

Geologypics.com– A new (and free) resource for geological photographs

What better way to kick off my new website than to write about it on my blog? To see it, you just need to click on the word “home” in the space above. Or you can click the link: geologypics.com.

Here’s part of the front page:
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As it says, the site offers free downloads for instructors –and for anybody who’s craving a good geology photograph. It’s my way of contributing to geology education –showing off some of our landscape’s amazing stories and providing resources for other folks who want to do the same.

I think the best part of the whole site is that red button in the middle of the home page. It says “Image Search by Keyword”.

Right now, there are more than 2200 images you can search for — all of which are downloadable at resolutions that generally work for powerpoint. If you search for “sea stack” for example, you’ll get 38 hits –and the page will look like this:

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First page of sea stacks when you search on the term.

 

Notice that ALL the photos are presented as squares–which works for most photos, but not all. To help mitigate that, the photos with vertical or panorama formats say so in their title, so you know to click on them to see the whole image. Take the photo in the upper center, for example –it’s got a  vertical format. Here it is:vertial image

 

A more detailed caption below the photo, along with its ID number appears at the bottom of the pic. This particular image is the chapter opener to the Coast Range in my new book “Roadside Geology of Washington“, which I wrote with Darrel Cowan of University of Washington.

There are also galleries –a chance to browse a variety of images without having to think of keywords. Similar to the search, they’re presented as squares so you need to click on the photo to see the whole thing.

 

Here’s what the photo gallery page looks like (on the left), followed by part of the “glaciation” page you’d see if you clicked on “glaciation”.  Woohoo!

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part of Galleries page (left) and part of Glacial page (right)

 

Then there’s the “About” page, which gives some information about me and details my policies regarding use of the images (basically, you can download freely for your personal, non-commercial use if you give me credit; if you want to use the image in a commercial publication you need to contact me to negotiate fees). There’s also a “News” page, that gives updates on the website. There’s a contact page from which you can send me emails. And the blog? It goes right back to here!

And finally, if you’re looking for a great web designer? Try Kathleen Istudor at Wildwood SEO –she created the site and spent hours coaching me on how to manage it.

Enjoy the site!

 

Summarizing Washington State’s Geology –in 19 photo out-takes

Washington State displays such an incredible array of geologic processes and features that it makes me gasp –which is one reason why writing “Roadside Geology of Washington” was such a wonderful experience. I also got to do it with my long-time friend and colleague (and former thesis advisor at the University of Washington) Darrel Cowan. The book should be on bookshelves in mid-September –and I can’t think of a better way to celebrate than by summarizing Washington’s amazing geology with a bunch of out-take photos –ones that didn’t made it into the book or even to my editor. Like the photo below:

Mount Baker, Washington (150916-4)

Mt. Baker, a glaciated stratovolcano in northern Washington State.

Mount Baker’s a stratovolcano that erupted its way through the metamorphic rock of the North Cascades. I took the photo from the parking lot at a spot called Artist’s Point –at the end of WA 542 –and my editor nixed it because I already had enough snow-capped volcanoes in the book.

On the cross-section below–which includes elements of Oregon as well as Washington, Mt. Baker is represented by the pink volcano-shaped thing labelled “High Cascades”. The following 15 or so photos illustrate most of the other features on the cross-section –so together, they illustrate much of the geology and geologic history of the state!

Cross-section across PNW

Generalized cross-section across Washington and Oregon.

Washington State and geologic provinces

Washington State and geologic provinces.

A quick note about organization: I’m separating the images according to their  physiographic province. There are six in Washington: Coast Range, Puget Lowland, North Cascades, South Cascades, Okanogan Highlands, and Columbia Basin.

 

Coast Range:
As you can see in the cross-section, the Coast Range borders the Cascadia Subduction Zone and consists of three main elements: the Hoh Accretion Assemblage in yellow, Siletzia (called the “Crescent Formation” in Washington) in purple, and the post-accretion sedimentary rock in brown. Siletzia is the oldest. It was thrust over the Hoh Accretion Assemblage, which is still being accreted at the subduction zone. The post-Accretion sedimentary rocks were deposited over the top of Siletzia after it was accreted about 50 million years ago.

And here are some photos! Siletzia formed as an oceanic plateau and so is characterized Read more…

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).

Read more…

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.

Cape Blanco, Oregon

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!

Landscape and Rock–4 favorite photos from 2015

Landscape and bedrock… seems we seldom connect the two. We all like beautiful landscapes, but most of us don’t ask how they formed –and even fewer of us think about the story told by the rocks that lie beneath it all. Those make two time scales, the faster one of landscape evolution and the much slower one of the rock record. Considering that we live in our present-day human time scale, it’s no wonder there’s a disconnect!

Take this photo of Mt. Shuksan in northern Washington. My daughter Meg and I drove up to the parking lot at Heather Meadows and went for a quick hike to stretch our legs and take some pictures just before sunset.We had about a half hour before the light faded –and all I could think about was taking a photo of this amazing mountain. But the geology? What??

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1. Mt. Shuksan and moonrise, northern Washington Cascades.

Thankfully, I’d been there in September scoping out a possible field project with a new grad student, and had the time to reflect… on time. From the ridge we hiked, shown as the dark area in the lower left corner of the left-hand photo below, we could almost feel Shuksan’s glaciers sculpting the mountain into its present shape. Certainly, that process is imperceptibly slow by human standards.

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Mt. Shuksan: its glaciated NW side, summit, and outcrop of the Bell Pass Melange.

But the glaciers are sculpting bedrock –and that bedrock reveals its own story, grounded in a much longer time scale.

It turns out that the rock of Mt. Shuksan formed over tens of millions of years on three separate fragments of Earth’s lithosphere, called terranes. These terranes came together along faults that were then accreted to North America sometime during the Cretaceous. At the top of the peak you can find rock of the Easton Terrane. The Easton Terrane contains blueschist, a metamorphic rock that forms under conditions of high pressures and relatively low temperatures, such as deep in a subduction zone. Below that lies the Bell Pass Melange (right photo) –unmetamorphosed rock that is wonderfully messed up. And below that lies volcanic and sedimentary rock of the Chilliwack Group.

Here’s another of my favorites from 2015: the Keystone Thrust! It’s an easy picture to take –you just need to fly into the Las Vegas airport from the north or south, and you fly right over it. It’s the contact between the gray ledgey (ledgy? ledgeee?) rock on the left and the tan cliffs that go up the middle of the photo.

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2. Keystone Thrust fault, Nevada–gray Cambrian ridges over tan Jurassic cliffs.

The gray rock is part of the Cambrian Bonanza King Formation, which is mostly limestone, and the tan cliffs consist of  Jurassic Aztec Sandstone. Cambrian, being the time period from about 540-485 million years, is a lot older than the Jurassic, which spanned the time 200-145 million years ago. Older rock over younger rock like that requires a thrust fault.

Talk about geologic history… the thrust fault formed during a period of mountain building during the Cretaceous Period, some 100-70 million years ago, long before the present mountains. And the rocks? The limestone formed in a shallow marine environment and the sandstone in a sand “sea” of the same scale as today’s Sahara Desert. We know it was that large because the Aztec Sandstone is the same rock as the Navajo Sandstone in Zion and Arches national parks.

Cambrian-Jurassic

left: Limestone of the Cambrian Bonanza King Formation near Death Valley; right: Cross-bedded sandstone of the Jurassic Navajo Sandstone in Zion NP, Utah.

So… the photo shows cliffs and ledges made of rocks that tell a story of different landscapes that spans 100s of millions of years. But today’s cliffs and ledges are young, having formed by erosion of the much older rock.  Then I flew over it in about 30 seconds.

At Beach 2 near Shi Shi Beach in Washington State are some incredible sea stacks, left standing (temporarily) as the sea erodes the headlands. The sea stack and arch in the photo below illustrates the continuous nature of this erosion. Once the arch fails, the seaward side of the headland will be isolated as another sea stack, larger, but really no different than the sea stack to its left. And so it goes.

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3. Sea arch and headland at Beach 2, Olympic Coast, Washington.

And of course, the headland’s made of rock that tells its own story –of  deposition offshore and getting scrunched up while getting added to the edge of the continent.

ShiShi

Bedrock at Beach 2 consists mostly of sandstone and breccia. The white fragment is limestone mixed with sandstone fragments.

And finally, my last “favorite”. It’s of an unnamed glacial valley in SE Alaska. My daughter and I flew by it in a small plane en route to Haines, Alaska to visit my cousin and his wife. More amazing landscape–carved by glaciers a long time ago. But as you can expect, the rock that makes it up is even older and tells it’s own story.

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4. Glacial Valley cutting into Chilkat Mountains, SE Alaska.

Of course, this message of three time scales, the human, the landscape, and the rock-record time scale applies everywhere we go. Ironically, we’re usually in a hurry. I wish I kept it in mind more often, as it might slow me down a little.

Here’s to 2015 –and to 2016.

To see or download these four images at higher resolutions, please visit my webpage: favorite 10 geology photos of 2015.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Conglomerate!

A trip to Death Valley over Thanksgiving two weeks ago reignited all sorts of things in my brain, one of which being my love of conglomerate. Honestly, conglomerate HAS to be the coolest rock!

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Tilted conglomerate in Furnace Creek Wash, Death Valley.

Just look at this stuff! Just like any good clastic sedimentary rock, it consists of particles of older rock–but with conglomerate, you can easily see those particles. Each of those particles opens a different door to experiencing deep geologic time.

As an example, look at the conglomerate below, from the Kootenai Formation of SW Montana. It contains many different cobbles of light gray and dark gray quartzite and pebbles of black chert. The quartzite came the Quadrant Formation and chert from the Phosphoria Formation. So just at first glance, you can see that this conglomerate in the Kootenai contains actual pieces of two other older rock units.

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Conglomerate of the Kootenai Formation, SW Montana.

But consider this: The Quadrant formed as coastal sand dunes during the Pennsylvanian Period, between about 320-300 million years ago and the Phosphoria chert accumulated in a deep marine environment during the Permian, from about 300-250 million years ago. The Kootenai formed as river deposits during the early part of the Cretaceous Period, about 120 million years ago. All those are now together as one.

Similar to the modern river below (except for the glaciers), the Kootenai rivers transported gravel away from highlands –the highlands being made of much older rock that was uplifted and exposed to erosion. That older rock speaks to long gone periods of Earth history while the gravel speaks to the day it’s deposited.

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Athabasca River in Jasper National Park, Alberta

But this is where my head starts to spin: the modern gravel is made of rounded fragments of old rock –so when you look at a conglomerate, you glimpse at least two time periods at once: you see the conglomerate, which reflects a river or alluvial fan –or any environment near a bedrock source– and you also see the particles, which formed in even older environments.

And it gets worse –or better. What happens when you see a conglomerate eroding? The conglomerate is breaking up into modern sediment, which consists of pieces of older sediment –that at one time was modern sediment that used to be older sediment?  Look at the pebbles below. I keep them in a rusty metal camping cup on a table in my office.

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“Recycled” pebbles of the Kootenai Formation.

These stream pebbles eroded out of the Kootenai conglomerate. So… they’re simultaneously modern stream pebbles and ancient ones –AND… they originated as the Quadrant and Phosphoria Formations. Four periods of time, spanning 300 million years, all come together at once.

And if that’s not enough, those conglomerates in Death Valley? They  contain particles of… conglomerate! Look! The arrow in the left photo points to the boulder of conglomerate on the right. If you click on the photos, you can see them enlarged.

All those particles, which are now eroding and becoming modern sediment, were yesterday’s sediment. And the conglomerate boulder? It too is becoming “modern sediment” and it too was “yesterday’s sediment” when it was deposited on an alluvial fan with the rest of the material. However, it goes a step further: its pebbles and cobbles were both “modern” and “yesterday’s” sediment at a still older time. And before that? Those pebbles and cobbles eroded from even older rock units, some of which date from the Cambrian, about 500 million years ago.

For fun, here’s a photo of another conglomerate boulder.

Conglomerate clast in conglomerate

Conglomerate boulder in conglomerate of the Furnace Creek Formation, Death Valley, CA.

 

I can’t help but wonder how Young Earth Creationists would deal with these rocks. Given their story of the Grand Canyon, in which the Paleozoic section was deposited during early stages of “The Flood” and the canyon was carved during the later stages (they really do say that too!), they’d probably roll out that same blanket answer: The Flood. End of discussion. No questioning, no wondering.

In my opinion, one of the beautiful things about geology is that we’re always questioning and wondering.

 

 

for more geology photos, please visit my website.

 

 

 

 

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