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Geology and Geologic Time through Photographs

Archive for the category “national parks”

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.

Shuksan combo

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Death Valley National Park– Geology Overload!

Death Valley… I can’t wait! Tomorrow this time, I’ll be walking on the salt pan with my structural geology students, gawking at the incredible mountain front –and soon after that, we’ll be immersed in fault zones, fractures, and fabrics!

Death Valley salt pan at sunrise.

Death Valley salt pan at sunrise.

Death Valley presents incredible opportunities for all sorts of geology, especially geologic time; you can look just about anywhere to see and feel it.  Take the salt pan.  It really is salt –you can sprinkle it on your sandwich if you want.  It’s there because the valley floor periodically floods with rainwater.  As the rainwater evaporates, dissolved salt in the water precipitates.  And some 10,000 years ago, Death Valley was filled by a 600′ deep lake, which evaporated, leaving behind more salt. Before that, more shallow flooding and more lakes.

Aerial view of faulted front of the Black Mountains.

Aerial view of faulted front of the Black Mountains.

But the basin is more than 4 miles deep in some places! It’s not all salt, because there are a lot of gravel and sand deposits, but a lot of it is salt.  That depth speaks to geologically fast accumulation rates, because it all had to accumulate since Death Valley formed –probably in the last 2 or 3 million years.  But still, 2 or 3 million years is way past our realm of experience.

Hiker in the Funeral Mountains of Death Valley.

Hiker in the Funeral Mountains of Death Valley.

To really go back in geologic time though, you need to look at the mountains. Most of the mountains contain Upper Precambrian through Paleozoic sedimentary rock, most of which accumulated in shallow marine environments.  There’s a thickness of more than 30,000 feet of sedimentary rock exposed in Death Valley! Deposited layer after layer, you can only imagine how long that took.

We can measure the thickness of the rock because it’s no longer in its original horizontal position.  The ones in the photo above were tilted by faulting –which occurred during the period of crustal extension that formed Death Valley today.  The rocks in the photo below were folded –by a period of crustal shortening that took place long before the modern extension.  The folding occurred during the Mesozoic Era –more than 65 million years ago.

Aerial view of Titus Canyon Anticline.

Aerial view of Titus Canyon Anticline.

Above the Upper Precambrian to Paleozoic rock are thousands of feet of volcanic and sedimentary rock, tilted and faulted, but not folded. They reveal many of the details of the crustal extension that eventually formed today’s landscape.  For example, the photo below shows Ryan Mesa in upper Furnace Creek Wash.  In this place, the main period of extensional faulting predates the formation of modern Death Valley.  Look at the photo to see that faulting must have stopped before eruption of the dark-colored basalt flows.  Notice that there has to be a fault underneath the talus cones that separates the Artist Dr. Formation on the left from the Furnace Creek Formation on the right.  Because the fault does not cut the basalt though, it has to be older.  Those basalts are 4 million years old, older than modern Death Valley.  –And that’s the old mining camp of Ryan perched on the talus.

Angular unconformity at Ryan Mesa: 4 Ma basalt flows overlying faulted Artist Drive (left) and Furnace Creek (right) formations.

Angular unconformity at Ryan Mesa: 4 Ma basalt flows overlying faulted Artist Drive (left) and Furnace Creek (right) formations.

And beneath it all? Still older rock!  There’s some 5,000 feet of even older Precambrian sedimentary rock, called the “Pahrump Group” beneath the 30,000 feet of Upper Precambrian and Paleozoic rock–and below that, Precambrian metamorphic rock.  It’s called the “basement complex” because it’s the lowest stuff.  Here’s a photo.

pegmatite dike and sill intruding mylonitic gneiss

pegmatite dike and sill intruding gneiss

The pegmatite (the light-colored intrusive rock) is actually quite young–I think our U-Pb age was 55 Ma –but the gneiss is much older, with a U-Pb age of 1.7 billion years.  Billion!  Forget about the U-Pb age though.  These rocks form miles beneath Earth’s surface –and here they are, at the surface for us to see. Without knowing their age, you’re looking at deep geologic time because of the long period of uplift and erosion required to bring them to the surface.  And it happened before all those other events that described earlier.

THIS is why, when visiting Death Valley, you need to explore the canyons and mountains –not to mention the incredible views, silence, stillness…


Some links:
Geologic map of Death Valley for free download
Slideshow of Death Valley geology photos

–or better yet, type “Death Valley” into the geology photo search function on my website!

Just scratching the surface. A geologic cross-section of Oregon speaks to unimaginable events.

The cross-section below runs from the Cascadia subduction zone across Oregon and into eastern Idaho.  It outlines Oregon’s geologic history, beginning with accretion of terranes, intrusion of granitic “stitching plutons”, and deposition of first North American-derived sedimentary rocks, and ending with High Cascades Volcanic activity and glaciation.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

Schematic geologic cross-section across Oregon, from the Cascadia Subduction zone into western Idaho.

The cross-section barely scratches the surface of things. Moreover, it boils everything down to a list, which is kind of sterile. But the cross-section also provides a platform for your imagination because each one of these events really happened and reflects an entirely different set of landscapes than what we see today.

Think of the CRBG about 15 million years ago. The basalt flows completely covered the landscape of northern Oregon and southern Washington. Or the Clarno volcanoes –only a part of the green layer called “Clarno/John Day”. They were stratovolcanoes in central Oregon –when the climate was tropical! Or try to wrap your mind around the accreted terranes, some of which, like the Wallowa Terrane, contain fossils from the western Pacific.

To emphasize this point, here’s Crater Lake. Crater Lake formed because Mt. Mazama, one of the Cascades’ stratovolcanoes, erupted about 7700 years ago in an eruption so large and violent that it collapsed in on itself to form a caldera. It’s now a national park, with a whole landscape of its own. And if you visit Crater Lake, you’ll see evidence that Mt. Mazama had its own history –which dates back more than 400,000 years. But Crater Lake and Mt. Mazama make up just a tiny part of the Cascades, which are represented on this diagram by just this tiny area that’s shaped like a mountain.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

Crater Lake occupies the caldera of Mt. Mazama, which erupted catastrophically some 7700 years ago.

So the cross-section is kind of sterile and just scratches the surface. But what makes geology so incredible is that we’re always learning new things and digging deeper –and we know we’re just scratching the surface –that there will always —always— be something  to learn.


click here and type “Oregon” into the search for photos of Oregon Geology.
click here for information about the new Roadside Geology of Oregon book.

Crater Lake caldera, Oregon –some things happen quickly!

Crater Lake never ceases to amaze me.  It’s huge –some 6 miles (10 km) across, deep –some 1700 feet deep in parts –the deepest lake in the United States and 7th deepest on the planet– incredibly clear, and really really blue.  And for volcano buffs, one of the best places ever!

Crater Lake as seen from The Watchman.  Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake as seen from The Watchman. Wizard Island, which formed after the caldera collapse, occupies the center of the photo.

Crater Lake is a caldera, formed when ancient Mt. Mazama erupted so catastrophically that it emptied its magma chamber sufficiently for the overlying part of the mountain to collapse downward into the empty space.  That was about 7700 years ago.  Soon afterwards, Wizard Island formed, along with some other volcanic features that are now hidden beneath the lake–and then over the years, the lake filled to its present depth.  It’s unlikely to rise any higher because there is a permeable zone of rock at lake level that acts as a drain.

Here’s one of the coolest things about the cataclysmic eruption: Not only was it really big, but it happened really fast.  We know it was big because we can see pumice, exploded out of the volcano, blanketing the landscape for 100s of square miles to the north of the volcano –and we can see the caldera.  We can tell it happened quickly because the base of the pumice is welded onto a rhyolite flow that erupted at the beginning stages of the collapse; the rhyolite was still HOT when the pumice landed on it!  You can see the welded pumice on top the Cleetwood Flow along the road at Cleetwood Cove.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove.  Note how the base of the pumice is red from oxidation --and forms a ledge because it's so hard.

pumice welded onto top of Cleetwood rhyolite flow at Cleetwood Cove. Note how the base of the pumice is red from oxidation –and forms a ledge because it’s so hard.  Pumice blankets the landscape all around Crater Lake.

Crater Lake though, is so much more than a caldera –it’s the exposed inside of a big stratovolcano!  Where else can you see, exposed in beautiful natural cross-sections, lava flow after lava flow, each of which erupted long before the caldera collapse and built the original volcano? Within the caldera itself, these flows go back 400,000 years–the oldest ones being those that make up Phantom Ship –the cool little island (some 50′ tall) in Crater Lake’s southeast corner.

Phantom Ship, in Crater Lake's southeast corner, is made of the caldera's oldest known rock, at 400,000 years old.

Phantom Ship, in Crater Lake’s southeast corner, is made of the caldera’s oldest known rock, at 400,000 years old.

I can’t resist.  The caldera formed about 7700 years ago, incredibly recent in Earth history–incredibly recent in just the history of Mt. Mazama!  To a young earth creationist though, that’s 1700 years before Earth formed.  Now THAT’S amazing!


Click here if you want to see a Geologic map of Crater Lake.
Or… for more pictures of Crater Lake, type its name into the Geology Search Engine.  Or… check out the new Roadside Geology of Oregon book!

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