geologictimepics

Geology and Geologic Time through Photographs

Archive for the tag “aerial photo”

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!

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!

 

 

 

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.

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