geologictimepics

Geology and Geologic Time through Photographs

Archive for the tag “San Andreas fault”

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!

 

 

 

 

 

 

 

California’s largest lake formed by its largest fault zone: the Salton Sea and San Andreas Fault

With a surface area of nearly 1000 square kilometers (381 square miles), the Salton Sea is California’s largest lake.  But it’s relatively shallow –and because it has no outlet, it’s saltier than ocean water.  It formed in 1905 when the nearby Colorado River overwhelmed irrigation canals and flooded the region.  Now it’s an incredibly important migratory bird refuge, fishery, and dumping ground for agricultural waste.  Seems like those things shouldn’t really go together!

Aerial view of the Salton Sea, looking northward.

Aerial view of the Salton Sea, looking northward.

But it just seems young.  The Salton Sea actually occupies part of the Colorado River Delta –and as a result, has been filled with freshwater multiple times since the delta was first constructed, probably near the beginning of the Pleistocene.  It’s also at the remarkably low elevation of 234 feet (71m) below sea level; the deepest part of the lake is 44 feet (13 m) below that.

And the low spot is there because of extension caused by the San Andreas fault system!  The San Andreas fault terminates along the eastern margin of the lake basin, but steps across the lake to the Imperial fault, which forms its western margin.  Both faults are right-lateral –and because they step to the right, they pull the area apart in-between them.  Kind of like central Death Valley –which is even lower in elevation than the Salton Sea!  But more on Death Valley later.

Aerial view of Salton Sea, with the approximate locations of the southern San Andreas and Imperial faults.  Note how right-lateral slip on the two en-echelon faults drive extension between them.

Aerial view of Salton Sea, with the approximate locations of the southern San Andreas and Imperial faults. Note how right-lateral slip on the two en-echelon faults drive extension between them.


click here to see more photos of the San Andreas fault system, or click here to see a photo geology tour of Death Valley, California.

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!

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