geologictimepics

Geology and Geologic Time through Photographs

Archive for the tag “geology pictures”

04 Jan 2020
10 Comments

Aerial geology photos– favorites from commercial flights of 2019

I always try for window seats when flying and I always try to shoot photos out the window –with varying results! So often, the window’s badly scratched, there are clouds, it’s hazy, the sun angle’s wrong –there are myriad factors that can make good photography almost impossible from a commercial jet. Last year though, I had a few amazing flights with clear skies and a great window seat –and I’ve now loaded nearly 100 images onto my website for free download. Here are 10 of my favorites, in no particular order. You can click on them to see them at a larger size. They’re even bigger on my website.

Mt. Shasta at sunset. Volumetrically, the biggest of the Cascade Volcanoes, Mt. Shasta last erupted between 2-300 years ago –and it’s spawned over 70 mudflows in the past 1000 years. From the photo, you can see how the volcano’s actually a combination of at least 3 volcanoes, including Shastina, which erupted about 11,000 years ago.

Mt. Shasta at sunset, California

Aerial view of Mt. Shasta, a Cascades stratovolcano in northern California.

If you want to see more aerials of Mt. Shasta (shot during the day) –and from a small plane, go to the search page on my website and type in “Shasta”.

 

Meteor Crater, Arizona.  Wow –I’ve ALWAYS wanted to get a photo of Meteor Crater from the air –and suddenly, on a flight from Phoenix to Denver, there it was!

Meteor Crater, Arizona

Aerial view of Meteor Crater, Arizona

Meteor Crater, also called Barringer Crater, formed by the impact of a meteorite some 50,000 years ago. It measures 3900 feet in diameter and about 560 feet deep. The meteorite, called the Canyon Diablo Meteorite, was about 50 meters across.

 

Dakota Hogback and Colorado Front Range, near Morrison, Colorado. Same flight as Meteor Crater –and another photo I’d longed to take. It really isn’t the prettiest photo, BUT, it shows the Cretaceous Dakota Hogback angling from the bottom left of the photo northwards along the range and Red Rocks Amphitheater in the center –then everything behind Red Rocks, including the peaks of Rocky Mountain National Park in the background, consist of Proterozoic basement rock.

Hogback and Colorado Front Range

Aerial view of hogback of Cretaceous Dakota Formation and Colorado Front Range.

 

Distributary channels on delta, Texas Gulf Coast. I just thought this one was really pretty. Geologically, it shows how rivers divide into many distributary channels when they encounter the super low gradients of deltas. And whoever thought that flying into Houston could be so exciting!

Distributary channels on delta, Texas Gulf Coast

Distributary channels on delta, Texas Gulf Coast

 


Meander bends on the Mississippi River. My mother lives in Florida, so I always fly over the Mississippi River when I go visit –but I was never able to take a decent photo until my return trip last October, when the air was clear, and our flight path passed just north of New Orleans. Those sweeping arms of each meander are about 5 miles long!

Meander bends on Mississippi River, Louisiana

Meander bends on the Mississippi River floodplain, Louisiana

 

Salt Evaporators, San Francisco Bay. Flying into San Francisco is always great because you get to see the incredible evaporation ponds near the south end of the bay. I always love the colors, caused by differing concentrations of algae –which respond to differences in salinity. And for some reason, salt deposits always spark my imagination. Salt covers the floor of Death Valley, a place where I do most of my research, and Permian salt deposits play a big role in the geology of much of southeastern Utah, another place I know and love.

Salt evaporators, San Francisco Bay, California

Salt evaporators, San Francisco Bay, California

 

Bonneville Salt Flats and Newfoundland Mountains, Utah. And then there are the Bonneville Salt Flats! They’re so vast –how I’d love the time to explore them. They formed by evaporation of Pleistocene Lake Bonneville, the ancestor of today’s Great Salt Lake. When the climate was wetter during the Ice Age, Lake Bonneville was practically an inland sea –and this photo shows just a small part of it.

Bonneville Salt Flats and Newfoundland Mtns, Utah

Aerial view of Bonneville Salt Flats and Newfoundland Mountains

 

Stranded meander loop on the Colorado River. I like this photo because it speaks to the evolution of this stretch of the Colorado River. Just left of center, you can see an old meander loop –and it’s at a much higher elevation than today’s channel. At one time, the Colorado River flowed around that loop, but after breaching the divide and stranding it as an oxbow, it proceeded to cut its channel deeper and left the oxbow at a higher elevation.

Stranded meander loop, Colorado River, Colorado

Stranded meander loop (oxbow) on the Colorado River, eastern Utah

 

San Andreas fault zone and San Francisco. See those skinny lakes running diagonally through the center of the photo? They’re the Upper and Lower Crystal Springs Reservoirs –and they’re right on the San Andreas Fault. And you can see just how close San Francisco is to the fault.  As the boundary between the Pacific and North American Plates, its total displacement is about 200 miles. See this previous post for more photos of the San Andreas fault.

San Andreas fault zone and San Francisco

San Andreas fault zone and San Francisco

 

And my favorite: Aerial view of the Green River flowing through the Split Mountain Anticline –at Dinosaur National Monument, Utah-Colorado. Another photo I’ve so longed to shoot –but didn’t have the opportunity until last year.

The Green River cuts right across the anticline rather than flowing around it. It’s either an antecedent river, which cut down across the fold as it grew –or a superposed one, having established its channel in younger, more homogeneous rock before cutting down into the harder, folded rock. You can also see how the anticline plunges westward (left) because that’s the direction of its “nose” –or the direction the fold limbs come together. The quarry, for Dinosaur National Monument, which you can visit and see dinosaur bones in the original Jurassic bedrock, is in the hills at the far lower left corner of the photo.

Split Mountain Anticline, Utah-Colo

Split Mountain anticline and Green River, Utah-Colorado

 

So these are my ten favorites from 2019. Thanks for looking! There are 88 more on my website, at slightly higher resolutions and for free download. They include aerials of the Sierra Nevada and Owens Valley, the Colorado Rockies, including the San Juan Volcanic Field, incised rivers on the Colorado Plateau, and even the Book Cliffs in eastern Colorado. Just go to my geology photo website, and in the search function type “aerial, 2019” –and 98 photos will pop up. Boom!

 

 

 

 

 

 

 

Posted in aerial geology, aerial photography, Geology, geophotography, Uncategorized, volcanoes and tagged , , , , , , , , , , , , , , , , , , ,
23 Jul 2018
4 Comments

Devil’s Punchbowl –Awesome geology on a beautiful Oregon beach

You could teach a geology course at Devil’s Punchbowl, a state park just north of Newport, Oregon. Along this half-mile stretch of beach and rocky tidepools, you see tilted sedimentary rocks, normal faults, an angular unconformity beneath an uplifted marine terrace, invasive lava flows, and of course amazing erosional features typical of Oregon’s spectacular coastline. And every one of these features tells a story. You can click on any of the images below to see them at a larger size.

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View southward from Cape Foulweather to the Devil’s Punchbowl.

 

180629-58ceThe rocks. They’re mostly shallow marine sandstones of the Astoria Formation, deposited in the early part of the Miocene, between about 16.5 to 22 million years ago. The rocks are tilted so you can walk horizontally into younger ones, which tend to be finer grained and more thinly bedded than the rocks below. This change in grain size suggests a gradual deepening of the water level through time. In many places, you can find small deposits of broken clam shells, likely stirred up and scattered during storms –and on the southern edge of the first headland north of the Punchbowl, you can find some spectacular soft-sediment deformation, probably brought on by submarine slumping. Later rock alteration from circulating hot groundwater caused iron sulfide minerals to crystallize within some of the sandstone. Read more…

Posted in Geology, geophotography, Oregon Coast, photography, science, Unconformities and tagged , , , , , , , ,
24 Dec 2015
3 Comments

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Posted in aerial geology, aerial photography, Geologic Time, Geology, Geology, Geologic Time, geophotography, mountains, national parks, photography, Uncategorized and tagged , , , , , , , , , , , , ,
19 Feb 2015
17 Comments

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.

 

 

 

Posted in Geologic Time, Geology, Geology, Geologic Time, geophotography, Uncategorized, young earth creationism and tagged , , , , , , , , , , , , , , , , , , , , , , , ,
07 Oct 2014
4 Comments

Geologic history of the western United States in a cliff face in Death Valley National Park

Of the many geologic events that shaped the western United States since the beginning of the Paleozoic Era, five really stand out.  In approximate chronological order, these events include the accumulation of tens of thousands of feet of sedimentary rock on a passive margin, periods of compressional mountain building that folded and faulted those rocks during much of the Mesozoic–likely driven by the accretion of terranes, intrusion of subduction-related granitic rock (such as the Sierra Nevada) during the Jurassic and Cretaceous, volcanic activity during the late Cenozoic, and mountain-building by crustal extension during the late Cenozoic and continuing today.  This photo on the western edge of Panamint Valley in Death Valley National Park of California, captures all five.

View of canyon wall on west side of Panamint Valley in SE California --part of Death Valley National Park. See photo below for interpretation.

View of canyon wall on west side of Panamint Valley in SE California –part of Death Valley National Park. See photo below for interpretation.

The photograph below shows an interpretation.  Paleozoic rock is folded because of the Late Paleozoic-early Mesozoic compressional mountain-building; it’s intruded by Jurassic age granitic rock, an early phase of Sierran magmatism that took place just to the west; the granitic rock is overlain by Late Cenozoic basalt flows, and everything is cut by a normal (extensional) fault.  And there is also a dike that cuts the Paleozoic rock –probably a feeder for the basalt flows.

Interpretation of top photo.

Interpretation of top photo.

So this is all nerdy geology cross-cutting relations talk –but here’s the point: in this one place, you can see evidence for 100s of millions of years of Earth History.  Earth is old old old!  THAT’S why I love geology!

And for those of you who crave geologic contacts?  This photo has all three: depositional, between the basalt and underlying rock; intrusive, between the Mesozoic granite and the folded Paleozoic rock; fault, the steeply dipping black line between the basalt and the Paleozoic rock.  Another reason why I love geology!

click here to see photos and explanations of geologic contacts.
or click here for a slideshow of Death Valley geology.

Posted in Geologic Time, Geology, photography and tagged , , , , , , , , , , , , , , , , , ,
04 Oct 2014
1 Comment

Geologic Time in a mountainside –the Wallowa Mountains from Joseph, Oregon

Joseph, Oregon is a wonderful place for geology.  The town sits right at the foot of the Wallowa Mountains in the northeastern corner of Oregon.  The mountains rise some 4-5000′ abruptly from the valley floor along a recently active normal fault.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

The Wallowa Mountains rise along a fault zone just south of the town of Joseph.

In the mountains, you can see some bedrock relations that speak to great lengths of geologic time.  An erosional remnant of the Columbia River Basalt Group caps Sawtooth Peak in the photos below; it sits directly on granite of the Wallowa Batholith –and just a little bit south, on the next peak, the granite intrudes Martin Bridge Limestone!  So, from oldest to youngest, the rock units are the Martin Bridge Limestone, the Wallowa granite, the Columbia River Basalt.

Sawtooth Peak (right) capped by Columbia River Basalt. Beneath it is granite of the Wallow Batholith --and off to the left, are the bedded rocks of the Martin Bridge Limestone.

Sawtooth Peak (right) capped by Columbia River Basalt. Beneath it is granite of the Wallowa Batholith –and off to the left, are the bedded rocks of the Martin Bridge Limestone.  See below for labels.

Rock units and contacts described in the text

Rock units and contacts described in the text

Never mind that we know the Martin Bridge Limestone is Triassic –so more than 200 million years old –and that the Wallowa Batholith formed at different times between 140 to about 120 million years ago –and that the basalt is about 16 million years old.  You can throw out radiometric dating, but even so, you’re looking at a great span of geologic time.  The limestone first had to be deposited, layer after layer –and then buried –and then intruded at a depth of 5-8 km by the granite –which THEN had to get uplifted to Earth’s surface so the basalt could flow over it.  After THAT, it all had to get uplifted to its present elevation along the normal fault just south of town and much of the basalt had to erode away.

Honestly, we have influential people in this country who spout off things like the Earth is only 6000 years old.  They also deny the overwhelming evidence for climate change.  I guess I should stop writing now before I get too worked up!

More photos of the Wallowas at Geologic Photography.

Posted in Geologic Time, Geology, mountains, photography and tagged , , , , , , , , , , , , , , , , ,
01 Oct 2014

Glacier National Park –Proterozoic rock and fossil algae

Glacier National Park’s one of my favorite places.  It’s soaring cliffs, waterfalls, and colors are positively amazing –especially the colors.  Green green vegetation, and red, white, green, and tan rocks.

To think that these mountains were carved from sedimentary rock that was deposited at sea level and now host glacial cirques and valleys, and even a few remaining glaciers… The rocks are part of the so-called “Belt Supergroup”, which was deposited probably in a large inland sea over what is now much of western Montana, northern Idaho, eastern Washington, and southern BC and Alberta.

Peaks of Glacier National Park and St. Marys River.

Peaks of Glacier National Park and St. Marys River.

And the rocks are really old–radiometric dating has them as between about 1.4 and 1.5 BILLION years old.  Even without that knowledge though, you can guess they’re pretty old because, just about everywhere, they host fabulous sedimentary features like cross-beds, ripple marks, and mudcracks.  The sediments were deposited before critters were around to stir up the sediment.

Belt sedsrs pic

There are some fossils though: stromatalites, which are basically fossilized algae.  The algae grew as mats on the ocean floor, and because they were kind of sticky, trapped carbonate sediment.  Then they grew over the sediment –and then trapped more.  And more –until they created a mound, which in cross section looked like the photo just below –and in plan view, looked like the bottom photo.

cross-sectional view of a stromatalite in the Proterozoic Helena Formation, Glacier NP.

cross-sectional view of a stromatalite in the Proterozoic Helena Formation, Glacier NP.

Stromatalites of the Helena Formation as seen in plan view.

Stromatalites of the Helena Formation as seen in plan view.

for more photos of Glacier National Park, type “Glacier National Park, Montana” into the  geology photo search.
Or click here for a freely downloadable geologic map of Glacier National Park.

Posted in Geologic Time, Geology, mountains, photography and tagged , , , , , , , , , , , , , , , , | Leave a comment
27 Sep 2014

Glacially carved granite in Rocky Mountain National Park, Colorado

This landscape is so smooth and rounded that you can easily imagine the ice that must have covered it some 20,000 years ago.  And the ice must have been deep!  Look halfway up the mountain in the foreground on the left; it shows a distinct change of rock weathering akin to a bathtub ring–and the ring persists around much of the photo.  It likely marks the upper surface of the ice at maximum glaciation.

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Upper Glacier Gorge, a glacial cirque in Rocky Mountain National Park, Colorado.  View of the Spearhead (left) and McHenry’s Peak (just behind)

Like most landscapes, this one’s pretty young–and those glacial effects are even younger.  When compared to the age of the rock, it seems almost insignificant.  The granite bedrock, which is granite, is 1.4 billion years old!  Elsewhere in Rocky Mountain National Park, the granite intrudes even older metamorphic rock –1.7 billion years old.  Just .3 billion years older.  I think we forget that “just .3 billion years” is 300 million years –about the same length of time as the entire Paleozoic!  And the Pleistocene Epoch, during which the glaciers grew?  It started some 2 million and ended about 10,000 years ago

Granite sill intruding gneiss, Colorado.
1.4 billion year old granite intruding 1.7 billion year old gneiss in Rocky Mtn National Park.

images can be downloaded for free at marlimillerphoto.com

Posted in Geologic Time, Geology, mountains, photography and tagged , , , , , , , , , , , , , , , , , , , | Leave a comment
06 Apr 2012
1 Comment

San Andreas Fault

Here’s a view of the San Andreas fault and Pt. Reyes in northern California, looking northward.  The fault runs right up the narrow Tomales Bay–and in just a few miles, runs along the edge of San Francisco.

The San Andreas fault is amazingly well-studied –it’s probably the most-studied fault zone in the world.  After all, it is capable of generating huge earthquakes in heavily populated areas, so the more we know about it the better.

San Andreas fault and Tomales Bay

Aerial view of San Andreas fault and Pt. Reyes --just north of San Francisco. View is to the north. The fault runs down Tomales Bay, the narrow arm of the ocean that runs diagonally across the photo.

One thing we know about the San Andreas is that it generally moves in a side-by-side way (strike-slip) so that rock on the east side moves south relative to that on the west side.  And over time, the fault has moved the eastern rock more than 300km relative to the western rock.

Now, 300 km –that speaks to millions of years of geologic time.  We can measure the rate at which the Pacific Plate moves relative to the North American Plate –about 4.5 cm/year.  The San Andreas takes up most of that –but not all.  But if we assume it takes it all, we’re looking at a total of 300km at 4.5cm/year –so at least 6.6 million years.

Of course… if you think planet Earth is only 10,000 years old, that means the fault’s moved some 300 meters (3 football fields) every 10 years.  And considering that the displacement was about 6 meters during the M 8.3 1906 San Francisco Earthquake…that’s a lot of earthquakes in just a short period of time!

Or another way of putting it, if planet Earth were 10,000 years old AND the San Andreas fault formed at the very beginning, 10,000 years ago… then there must have been 50 of those San-Francisco-sized Earthquakes every ten years –or… 5 of those every year.  Yikes!

But of course… we know that the San Andreas isn’t as old as the planet.  It cuts that granite at Pt. Reyes… which is related to the Sierra Nevada granite –which is really pretty young –but older than 10,000 years by about 100 million.

click here if you want to see more photos of the San Andreas fault –with a map!

Posted in Geologic Time, Geology, photography and tagged , , , , , , , , , , , , , ,
04 Apr 2012
4 Comments

Great Unconformity in Montana –and rising seas during the Cambrian

Here’s yet another picture of the Great Unconformity –this time in southwestern Montana.  Once again, Cambrian sandstone overlies Precambrian gneiss.  You can see a thin intrusive body, called a dike, cutting through the gneiss on the right side.  You can also see that the bottom of the sandstone is actually a conglomerate –made of quartzite cobbles derived from some nearby outcrops during the Cambrian.

Great unconformity in SW Montana.

Photo of Cambrian Flathead Sandstone overlying Proterozoic gneiss in SW Montana.

 

And that’s me in the photo.  My left hand is on the sandstone –some 520 million years or so old; my right hand is on the gneiss, some 1.7 BILLION years old.  There’s more than a billion years of missing rock record between my two hands.  Considering that the entire Paleozoic section from the top of the Inner Gorge in the Grand Canyon to the top of the rim represents about 300 million years and is some 3500′ thick… yikes!

And… just like in the Grand Canyon and elsewhere, there is Cambrian age shale and limestone above the sandstone.  This rock sequence reflects rising sea levels during the Cambrian.  It’s called the “Cambrian Transgression”, when the sea moved up onto the continent, eventually inundating almost everywhere.  If you look at the diagram below, you can see how this sequence formed.

Marine transgression

Sequence of rock types expected during a transgression of the sea onto a continent.

If you look at time 1, you can see a coastline in cross-section, with sand being deposited closest to shore, mud a little farther out, and eventually carbonate material even farther out.  As sea levels rise (time 2), the sites of deposition for these materials migrates landward, putting mud deposition on top the earlier sand deposition and so on.  At time 3, the sequence moves even farther landward, resulting in carbonate over mud over sand.  If these materials become preserved and turned into rock, they form the sequence sandstone overlain by shale overlain by limestone –just what we see on top the Great Unconformity.

 

 

 

Posted in Geologic Time, Geology, Geology, Geologic Time, photography and tagged , , , , , , , , , , , , , , ,

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