geologictimepics

Geology and Geologic Time through Photographs

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.

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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

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.

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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.

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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.

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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.

 

 

 

 

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!

Rockin’ countertops–geologic time in our kitchens and bathrooms!

I stopped by a “granite” supplier yesterday –the kind of place that sells “granite” and “marble” slabs for countertops.  Besides the fact that almost none of the slabs were actually granite or marble, they were spectacular rocks that showed wonderful wonderful detail. I nearly gushed at the idea of taking a geology field trip there.  It’s local, and you seldom find exposures like this anywhere else!

slabs of polished rock at a "granite" warehouse --not sure if any of this is actually granite, but it all reflects geologic time.

slabs of polished rock at a “granite” warehouse –most of it’s not actually granite, but it all reflects geologic time.

Generally speaking, “granite” in countertop language means “igneous” or “metamorphic” –crystalline rocks that form miles beneath Earth’s surface and so require great lengths of time to reach the surface where they can be quarried.  When I first started this blog, geologic time with respect to igneous and metamorphic rocks were some of the first things I wrote about –it’s such pervasive and important stuff.

So the main point is that your friend’s kitchen with “granite” countertops surrounds you with geologic time every time you walk in there!

But check out that green polka-dotted rock on the right side of the photo.  Full of rounded cobbles –it’s a conglomerate, originating by sedimentary processes on Earth’s surface. Does it indicate great lengths of geologic time? A Young Earth Creationist might say it were a deposit of “the Flood” and end-of-story.

Here’s a closer look:

Polished conglomerate --individual cobbles are metamorphic rocks. The green color comes from the mineral chlorite.

Polished conglomerate –individual cobbles are metamorphic rocks. The green color of the background material comes from the mineral chlorite. That’s a penny (on the left) for scale.

The conglomerate is made of beautifully rounded cobbles and small boulders that are almost entirely metamorphic in origin.  Most of them are gneisses, which form at especially high grades of metamorphism, typical of depths greater than 8 or 10 miles!  After a (long) period of uplift and erosion, the rock was exposed to erosion, gradually breaking into fragments, which eventually became these rounded cobbles, and ended up in the bottom of a big stream channel or on a gravel bar somewhere.

But that’s not the end of the story, because this deposit of rounded cobbles itself became metamorphosed –so it had to get buried again. We know that because the rock is pervaded by the mineral chlorite, which gives the rock its green color.  Chlorite requires metamorphism to form.  Granted, the rock isn’t highly metamorphosed –there’s no metamorphic layering and chlorite forms at low metamorphic temperatures– but it’s metamorphic nonetheless, typical of depths of a few miles beneath the surface.

And if you look even closer, you can see some of the effects of the reburial pressures: the edges of some of the cobbles poke into some of the other ones. This impingement is a result of the stress concentrations that naturally occur along points of contact.  The high stress causes the less soluble rocks to slowly dissolve into the other, more soluble rock.

cobbles, impinging into each other. Stars on right photo show locations.

cobbles, impinging into each other. Stars on right photo show locations.

I’m already jealous of the person who’s going to buy this slab of rock. It tells a story that begins with 1) metamorphic rock forming deep in the crust, then 2) a long period of uplift and erosion to expose the rocks, then 3) erosion, rounding, and deposition of the metamorphic cobbles, 4) reburial to the somewhat shallow depths of a mile or two–maybe more, 5) more uplift and erosion to expose the meta-sedimentary deposit, 6) Erosion by human beings.

And me? Personally, I’d like to make a shower stall or a bathtub out of this rock –can you imagine???


Some links you might like:
a blog I like that’s about science and creationism
another blog about an ancient Earth and deep time
my original song “Don’t take it for Granite“. (adds some levity?)
Geology photos for free download.

 

 

 

Columbia River Basalt Group–outrageous!

I can’t stop thinking about the Columbia River Basalt Group–the series of basalt flows that blanketed so much of my state of Oregon about 15 million years ago. Abbreviated as “CRBG”, it covers a lot of Washington too, as well as parts of western Idaho and northern Nevada. If you’re driving across those parts, you’ll likely travel miles and miles and miles over basalt basalt basalt –and that causes some people to say (mistakenly) that it’s boring. Some geologists even get grumpy about it because it covers up all the older rock.  Outrageous!

Lava flows of the CRBG in northern Oregon and Mt. Adams of southern Washington.  With views like this, how can you say the CRBG is boring? (Location "F" on map below.)

Lava flows of the CRBG in northern Oregon and Mt. Adams of southern Washington. With views like this, how can you say the CRBG is boring? (Photo “F” on map below.)

But of course, the CRBG is outrageous for a whole host of other reasons. For one thing, it really is huge: it covers an area of more than 77,000 square miles with a volume of more than 52,000 cubic miles –that’s more than 50x the volume of air between the north and south rims of the Grand Canyon! Really—the National Park Service estimated the volume of “Grand Canyon Air” to be about 1,000 cubic miles. It also erupted over a fairly short period of time: from about 17 million years ago to 6 million –but 96% of it erupted between 17 and 14.5 million years ago.

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And… most of it erupted from fissures in eastern Oregon and Washington –the roots of which are now preserved as dikes. And… many of the lavas made it all the way to the Pacific Ocean. And… (here’s the outrageous part), on reaching the Pacific, many of the flows re-intruded into the existing sediments and sedimentary rocks along the coastline to form their own magma chambers, some of which were thousands of feet thick! AND… some basaltic magma from those chambers then re-intruded the country rock to form dikes –and some even re-erupted on the seafloor!

All these outrageous details. Now think about them for a moment. They really happened. That’s what I find so wonderful and amazing about geology. We learn all these things and we put them in some part of our consciousness that doesn’t really let them soak in –but once in awhile they do.

Finally, the CRBG is beautiful and forms beautiful landscapes! Below are some photos to illustrate it, from feeder dikes in eastern Oregon to sea stacks eroded from a giant sill on the coast.

And I’ll save my snarky comments about young earth creationism for another post.

–and at the bottom, I’m adding a short glossary to explain some of the terms.

Ok… the photos!

 

Photo A. Steens Mountain and Alvord Desert.  The CRBG started with eruption of the Steens Basalt about 16.7 million years ago, which makes up the upper 3000′ or so of Steens Mountain, shown here.  Steens Mountain is one of our state treasures –it’s a fault-block mountain, uplifted by Basin-Range extension along a normal fault along its eastern side.

Fault-bounded east front of Steens Mountain and Alvord Desert.

Fault-bounded east front of Steens Mountain; mudcracked playa of Alvord Desert in foreground.

 

Photo B. Steens Basalt at Abert Rim. Like most of the CRBG, The Steens basalt covered outrageously huge areas.  It also makes up the cliffs above Lake Abert about 75 miles to the east.  Called Abert Rim, the cliffs are also uplifted by a big normal fault.  Lake Abert occupies the downdropped basin.  And much of the Steens basalt consists of this really distinctive porphyry with outrageously big plagioclase crystals!

Photo B.  Steens Basalt at Lake Abert; Abert Rim in background.

Photo B. Steens Basalt at Lake Abert; Abert Rim in background.

 

Photos C-1, C-2. CRBG dikes.  One reason we know that the CRBG erupted from fissures is that we can see their roots, as dikes cutting through older rock.  C-1 shows a dike cutting through previously erupted basalt flows in Grande Ronde Canyon, Washington; C-2 shows some narrow little dikes cutting accreted rock of the Triassic Martin Bridge Limestone. Photos 5 and 6 of my last post shows some aerial photos and describes this area in more detail.C. Feeder dikes

 

Photo D. Imnaha Canyon. The next major unit of the CRBG is the Imnaha Basalt, followed by the Grande Ronde Basalt.  Both these units erupted from sites in northeastern Oregon and southeastern Washington.  This view of Imnaha Canyon in Oregon shows the Imnaha Basalt near the bottom and the Grande Ronde Basalt at the top.

Photo D.  Imnaha Canyon, Oregon.

Photo D. Imnaha Canyon, Oregon.

 

Photo E. Picture Gorge Basalt at the Painted Hills.  And the next youngest unit of the CRBG was the Picture Gorge Basalt, shown capping the ridge in the background. Unlike most of the CRBG, the Picture Gorge Basalt originated in central Oregon, not too far from here–there’s a whole swarm of dikes near the town of Monument, Oregon.

The colorful hills in the foreground make up the Painted Hills of John Day Fossil Beds National Monument, another of our state treasures.  I like this photo because it gives a sense of what lies beneath the CRBG –and the John Day Fossil Beds are outrageous in their own way–but save that for another time.

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Photo F. Lava Flows of the CRBG and Mt. Adams, a modern volcano of the High Cascades in Washington.  See the first picture at the top of the post!

 

Photo G. Wanapum Basalt near The Dalles. This exposure of the Wanapum Basalt, which overlies the Picture Gorge Basalt, tells the story of the CRBG as it flowed into and filled a lake along the Columbia River some 15 million years ago. At the bottom of the flow, pillow basalt formed as the lava poured into the lake, while the upper part of the flow shows the columnar jointing typical of basalt that flows across land.  What’s more, this exposure lies less than a mile off I-84 in The Dalles, Oregon.  See page 251 of the new Roadside Geology of Oregon for another photo and more description!

Photo G. Single flow of Wanapum Basalt near The Dalles, Oregon.

Photo G. Single flow of Wanapum Basalt near The Dalles, Oregon.

 

Photo H.  Upper North Falls, Silver Falls State Park, Oregon.  This wonderful state park hosts about a zillion waterfalls that spill over cliffs of CRBG, 14 of which lie in the main river channels of the north and south forks of Silver Creek.  The falls depicted in this photo are 136 feet high!

Upper North Falls at Silver Falls State Park, OR.  The roof of the alcove consists of Wanapum Basalt, the bedrock near the river channel consists of Grande Ronde Basalt.

Upper North Falls at Silver Falls State Park. The roof of the alcove consists of Wanapum Basalt, the bedrock near the river consists of Grande Ronde Basalt.

Notice that the picture’s taken from behind the water. The trail goes into a big alcove, so it’s easy and safe.  The alcove formed because this particular waterfall crosses the contact between the Wanapum Basalt and the underlying Grande Ronde Basalt –and there is a 10-20′ thick, easily eroded, sedimentary unit between the two.  Remember the Grande Ronde Basalt –from Photo D in northeastern Oregon? Here it is, just east of Salem!

 

Photo I.  Saddle Mountain, northern Coast Range.  Here starts the truly outrageous part of the CRBG story.  Saddle Mountain, the highest point in the northern Coast Ranges, consists almost entirely of the rock on the right: brecciated pillow basalt, full of the alteration mineral palagonite. Apparently, the basalt started to flow into the ocean at about here, formed pillows and fragmented like crazy in the water-lava explosions. I. Saddle Mtn

But!  These flows were likely confined too –such as in a submarine canyon–which allowed them to develop enough of a pressure gradient to intrude downward into bedding surfaces, faults, and fractures of the Astoria Formation.  The diagram below illustrates the process in cross-section.  The diagram also give a context for photos I-L.  intrusive CRBG diagram4

 

Photo J.  Sea stacks of intrusive Columbia River Basalt Group at Ecola State Park.  Some of the magma chambers were several thousand feet thick and are now exposed as gigantic sills along the coast.  One such sill is Tillamook Head, of which Ecola State Park is a part –and it’s eroding into the sea stacks you can see in the distance.J.130120-11lrs

 

Photo K.  Haystack Rock at Cannon Beach, OR.  Go figure, one of our iconic state landmarks is an undersea volcano?  You can actually walk out to this thing at low tide and see lots of pillow basalt and dikes intruding the Astoria Formation.  The smaller sea stacks are part of the same complex.K.130121-12

 

Photo L. Seal Rock, Oregon.  Seal Rock is the southernmost exposure of CRBG on the coast –and it too, is intrusive.  It’s a big dike that trends NNW for about a quarter mile out to sea.  And along its edges, there are smaller dikes that you can see intruding the Astoria Formation, such as in the smaller photo.  The arrow points to where you can see the small intrusion, at low to medium tides.

L. Seal Rock


Some Terms:
dike: a tabular-shaped intrusion that cuts across layering in the surrounding rock.  Imagine magma flowing along a crack and eventually cooling down and crystallizing.  That would form a dike.  A feeder dike is a dike that fed lava flows at the surface.

normal fault: a type of fault along which younger rocks from above slide down against older rocks below.  They typically form when the crust is being extended.

porphyry: an igneous rock with larger, easily visible crystals floating around in a matrix of much smaller ones.

sill: an intrusion that runs parallel to layering in the surrounding rock.


 

Some references:

Reidel, S.P., Camp, V.E., Tolan, T.L., Martin, B.S. 2013. The Columbia River flood basalt province: stratigraphy, areal extent, volume, and physical volcanology. In The Columbia River Basalt Province, Geological Society of America Special Paper 497, eds. S.P. Reidel, V.E. Camp, M.E. Ross, J.A. Wolff, B.S. Martin, T.L. Tolan, and R.E. Wells, p. 1-44.

Wells, R.E., Niem, A.R., Evarts, R.C., and Hagstrum, J.T. 2009. The Columbia River Basalt Group—From the gorge to the sea. In Volcanoes to Vineyards: Geologic Field Trips through the Dynamic Landscape of the Pacific Northwest, Geological Society of America Field Guide 15, eds. J.E. O’Connor, R.J. Dorsey, and I.P. Madin, p. 737-774.


Some links:

Roadside Geology of Oregon
Geology pictures for free download
Geologic map of Oregon

Aerial photos: Yellowstone Lake to Portland, Oregon at 30,000 feet

What a start to the new year!  January 1, I flew home to Oregon with a north-facing window seat on a spectacularly clear day.  So much incredible landscape!  So much incredible geology!  Here are nine photos I shot out the plane window, keyed to the geologic map below.

Yel-PDX + US map

Photo 1.  Absaroka Range, northern Wyoming and southern Montana.  You can see that these mountains consist of layered rocks (see bottom of photo especially)–but they’re not sedimentary.  They are basaltic to dacitic lava flows and pyroclastic rocks of the Absaroka Volcanic Field,  erupted from about 53-43 million years ago.  Much of the present topography is the result of glacial erosion during the Pleistocene.

Absaroka Range, east edge of Yellowstone Lake on left.

Absaroka Range, east edge of Yellowstone Lake on left.

 

Photo 2.  Yellowstone Lake.  As you can see on the map, Yellowstone Lake fills only a fraction of the caldera created by Yellowstone’s Lava Creek Eruption, 600,000 years ago.  Since then, rhyolite lavas, shown in pink, filled in the caldera.  Notice the oval-shaped bay at the end of the lake’s western arm.  It’s called West Thumb, and is a younger caldera that erupted about 150,000 years ago.  It’s a caldera within a caldera!  It’s pretty big too– almost identical in size to Crater Lake in Oregon –but compared to the main caldera, it’s tiny.

Photo and geologic map of Yellowstone National Park

Photo and geologic map of Yellowstone National Park. The dashed red line marks the caldera edge.

 

Photo 3. Recent faulting of the Basin and Range Province. In this photo, the Pahsimeroi River flows northwestward to its confluence with the Salmon River, near the left side of the photo –and the Salmon continues flowing northward for about 100 miles before it turns westward and eventually joins the Snake River.

Recent faulting along western edge of Lemhi Range, Idaho.

Recent faulting along eastern edge of Pahsimeroi Valley, Idaho–and western front of Lemhi Range.

But what I think is so cool about this photo is that it so clearly shows the abrupt western edge of the Lemhi Range, which runs diagonally from the right (east) side of the photo to just above the center.  The range literally rises right out of the ground.  That abruptness is caused by faulting that takes place recently and frequently enough that erosion doesn’t keep up with it.  The fault is a normal fault, caused by crustal extension.  Notice the linear nature of the ranges to the northeast (upper right) –More normal faulting!  This is a northern expression of the Basin and Range Province.  Woohoo!

 

Photo 4. Mountains of the Idaho Batholith.  Granitic rock of the Idaho Batholith underlies a huge area of Idaho, some 14,000 square miles of it. On the geologic map, it’s the big green area.  The rock intruded as a series of plutons during the Late Cretaceous, from about 100 – 65 million years ago.  Similar in age and composition to the Sierra Nevada Batholith, the Idaho Batholith was fed by magma created during subduction along the west coast of North America.

Mountains of the Idaho Batholith

Mountains of the Idaho Batholith

 

Photo 5. Hell’s Canyon.  Not only does the north-flowing Snake River in Hell’s Canyon form the boundary between Idaho and Oregon (Yay, we made it to Oregon!), and not only is it the deepest canyon in the conterminous United States, but it’s also incredibly important from a geologic-history-of-western-North-America point-of-view.

Notice the flat areas above the canyon–they’re especially visible on the west (left) side, but you can also see them on the east.  Those places are flat because they’re made of flat-lying basalt of the Columbia River Basalt Group. These basalts erupted mostly between 17-14.5 million years ago, but kept erupting off and on until about 6 million years ago –and they cover ALL of northern Oregon and ALL of southeastern Washington State.  In fact, they flowed all the way to the Pacific Ocean.

Hell's Canyon and the Snake River.

Hell’s Canyon and the Snake River. The Imnaha River forms the next deep canyon to the left (west).

Those basalt flows overlie rock of the Wallowa accreted terrane: mostly volcanic and sedimentary rock that formed in an island arc setting, far offshore from North America.  It was added (accreted) to the North American continent during the Mesozoic –probably some 150 million years ago.

 

Photo 6. Wallowa Mountains, Oregon. Just west of Hell’s Canyon are the Wallowa Mountains, Oregon’s premier alpine country outside of the Cascades.  Like Hell’s Canyon, the Wallowas contain the accreted Wallowa terrane overlain by Columbia River Basalt –but the Wallowas also host the Wallowa Batholith, a Jurassic-Cretaceous granitic “stitching pluton”.  It’s called a stitching pluton because it intrudes across accreted terranes and “stitched” them together.

Glacial valleys and frontal fault zone on the north side of the Wallowa Mountains, Oregon.

Glacial valleys and frontal fault zone on the north side of the Wallowa Mountains, Oregon.

You can see a bunch of other things in this photo though.  First off, the mountains end suddenly in a line: a recently active fault zone that has uplifted them more than 5000′ relative to the valley floor. Also, you can see how glaciers carved the landscape.  Notice the deep U-shaped valleys, cirques, and knife-edged ridges called aretes.  And see the lake in the upper right corner of the photo?  It’s Wallowa Lake, dammed by a glacial moraine!

(at this point, the folks in the seats next to me wanted to throw me out of the airplane)

 

Photo 7. View of Washington High Cascades over The Dalles.  That’s Mt. St. Helens on the left (west), Mt. Adams in the middle, and Mt. Rainier in the far distant right.  Mt. Rainier is 90 miles away!

Looking north over the Dalles to Mts. St Helens, Rainier, and Adams.

Looking north over the Dalles to Mts. St Helens, Rainier, and Adams.

These volcanoes are dormant –which means that they’re …sleeping?  And they can awaken at any time.  I remember a college friend of mine wanted to climb Mt. St. Helens in 1979.  It was dormant then, and nobody worried about it.  Then in May, 1980 it erupted violently, blowing off its top 2000′.  Both St. Helens and Mt. Rainier have erupted many times in the past several thousand years; Mt. Adams though, erupted only twice in that period.

 

Photo 8.  Columbia Gorge, the Washington High Cascades, and the Bonneville Landslide.  From left (west) to right, the volcanoes are Mt. St. Helens, Mt. Rainier, and Mt. Adams.  You can see the Bonneville Landslide along the river on the right side of the photo, directly below the left base of Mt. Adams.  It detached from the cliffs directly behind it about 1450 A.D. and slid right into the river –and it pushed the river about a mile to the south! Just downriver from the landslide, you can seevthe Cascade Locks zig-zagging across the river.

View northward over the Columbia River Gorge to the Washington High Cascades.

View northward over the Columbia River Gorge to the Washington High Cascades.

The ridges at the bottom of the photo lead up to Mt. Hood, another dormant stratovolcano and Oregon’s highest peak.  Apparently, the view out the south side of the plane was even more ridiculously cool.

 

Photo 9. Columbia River, just below Portland.  Right near Portland, the Columbia River turns northward for about 40 miles before it heads west again out towards the Pacific–and it drops only 10 feet in elevation for the whole distance.  The northward deflection of the river is probably the result of uplift of the Portland Hills, which likely began as long as 16 million years ago (they also deflect 16 million year old lava flows of the Columbia River Basalt). That town along the river in the background is St. Helens, Oregon.

View northward, down the Columbia River.

View northward, down the Columbia River, Washington on the right, Oregon on the left.


See more geologic photos of Oregon by typing “Oregon” into the geology search engine on my website –or type “Oregon, aerial” if you want to see aerial shots!  And if you’re suddenly really excited about Oregon geology, please check out the new edition of Roadside Geology of Oregon!

 

 

 

“Crazy Modern Period” -a vanishingly thin sliver of Earth History

I’m in Florida, visiting my mother. There’s a beach, waves, shorebirds… And it’s warm! Late last week, my youngest daughter and I boarded a plane in Portland, Oregon, flew to Chicago –and then on to Fort Myers, Florida –across the continent for a distance of nearly 3000 miles. Being the holidays, the airports were packed, with people going in all directions, all over the planet. And like most people, we arrived at our destination the same day we departed.

Above the clouds --somewhere over eastern Oregon.

Above the clouds –somewhere over eastern Oregon.

Of course, just about everybody agrees that us human-types do pretty amazing things, like fly across the continent in a day and communicate instantly with family, friends, and colleagues on the other side of the planet. Oh for goodness sake… human beings have traveled to the moon and sent spacecraft to Mars!

In the context of geologic time, however, humanity and its accomplishments are positively mind-boggling. Homo sapiens dates back some 100,000 years, a miniscule period of time given that Earth is 4.55 billion years old. But it wasn’t until 1933, less than 100 years ago, that humans entered the “crazy-modern period” –when we flew the first airline flight across the US with no overnight stops. At that point, all parts of our planet became readily accessible to the public.

Divide 100 years by 4.55 billion? Our “crazy-modern period” is one 45.5 millionth of Earth history. What a unique moment in Earth history we’ve created! No other species has come close to anything like this –ever— in 4.55 billion years.

Sanibel Island and the Florida Gulf Coast --while descending into Fort Myers

Sanibel Island and the Florida Gulf Coast –while descending into Fort Myers

I won’t try to speculate how long our resources and (relatively) clean environment will last, but if we don’t figure out a way to live sustainably, these amazing times will soon disappear no matter how smart we are. Our sliver of Earth history will remain vanishingly small. Earth will heal, of course –but humans don’t have the same luxury of geologic time.

Regardless of whether or not we survive our successes, all of us share this unprecedented time. Here’s to another solstice passing –and to another calendar year. _MG_3784

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