My Thesis Area is Misbehaving: 6.0 Earthquake Near Walker, California

 

That was exciting. I live in the Central Valley of California. The valley is famously boring for a number of reasons, and one of the good ones is because we rarely feel earthquakes here. But that wasn't the case today. I was at my computer station and the desk started vibrating and I had to look and see if my wife was shaking it. She wasn't and she was not looking happy. 

It took a while for the USGS to untangle the many wave signatures in the seismic network (there was a brief report of a 4.8 quake just 20 miles from us), but as things have settled out, it looks like the quake took place smack dab in the middle of my masters thesis area in the eastern Sierra Nevada at the small town of Walker, California. The most recent estimate of the magnitude is 5.9 (upgraded to 6.0). The quake has the signature of a normal fault, the kind of faulting to be expected in a crustal region that is being stretched apart. 

Walker is the village in the picture above at the south end of the Antelope Valley, which exists because of faulting. The valley has sunk as the mountains on the right side of the photograph rose along the fault indicated by the solid black line. The epicenter of the quake would be just out of the picture on the lower right side (the picture is looking south).

Antelope Valley sits astride the boundary of the Sierra Nevada and Basin and Range provinces, where the solid block of the Sierra is being sliced up into a series of fault-bounded grabens. The picture below shows the upper (southern) end of the valley from Monitor Pass, with the Sweetwater Mountains in the distance. 

The next picture is from the hill behind Walker looking north. The break in slope on the left is where one would look for evidence of recent earthquakes, but slopewash has covered the fault terraces (scarps) in most places except for the streams and alluvial fans that cross the fault trace. That was what I was searching for when I was doing my masters thesis many years ago in this valley. I was very pleased when I found some.

The person who did the original mapping in the 1950's was working primarily on the rock exposures, and wasn't really looking for recently active faults. By the 1980's a number of people were looking a lot harder, trying to determine the seismic hazard for the region. Fresh alluvial fans provide a possibility of dating the occurrence and size of the last earthquake to cause ground rupture in an area.

The picture below is the Mill Creek fan, at the extreme south end of Antelope Valley. Under normal circumstances, an alluvial fan should be a smooth, gently sloping surface. Here at Mill Creek, the surface steps down to the left, forming a terrace. Immediately after the earthquake this terrace may have been essentially vertical (examples of scarps are shown on this post - Slinkard Valley lies immediately west of Antelope, and the post has a nice cut-away showing the arrangement of the fault blocks).

Scarps like these show that the last major earthquake took place in the recent geologic past, very likely less than 10,000 years ago, and maybe as recently as 3,000 years ago . The length of the fault and the size of the scarps are characteristic of quakes in the range of magnitude 6.5-7.0. A magnitude 5.8 event, the Double Springs Flat earthquake, shook the extreme north end of the Antelope Valley fault system in 1994. Today's quake one-upped that event, but do not be surprised if the magnitude is revised upward or downward (NOTE: the quake was revised upward to 6.0). It takes awhile to fully analyze the seismometer records. It is not inconceivable that some small cracks may appear along some of these older scarps.

I'm listening to reports of a rockfall off the cliffs above Meadowcliff Lodge. That would be very close to the epicenter.

I will revise this post as more information comes in. 

Postscript: I finally got to my office at Modesto Junior College to download the seismogram of the quake, and here it is. The shaking was off-scale for nearly two minutes.

The second shows a compressed version of the quake, along with some of the larger aftershocks.

All My Faults are Normal, But Not Really: Travels in Death Valley

Death Valley is the ultimate expression of the extensional forces that have ripped apart the crust of the western United States. The affected area reaches from northern Nevada and Oregon, east to central Utah, and south into Arizona. The broken up crust has resulted in the formation of countless fault basins and high mountain ranges (the entire region is called the Basin and Range Province). But few of those basins (really just one, the Owens Valley) approach the grandeur of Death Valley.




The valley (which is just part of the larger national park) is more than a hundred miles long, and it's deep. The vertical distance from the summit of Telescope Peak to the valley floor at Badwater is more than two miles (11,331 feet). Few places in America display greater relief. And the valley was not carved by water or any other erosional force: it is the result of faulting, the movement of the crust of the earth.

Most students of geology are taught early on that fault valleys are called grabens, and that they are formed by normal faulting. That begs the question of "what is normal?" (a concept I'm sure we all struggle with). Faults displaying vertical motion often have a sloping fault plane, and the fault block that "hangs" over the other is called the headwall (which therefore covers the footwall). When the crust is stretched, or extended, the headwall drops relative to the footwall, and that is what defines a "normal fault". If the crust is compressed, the headwall will move up relative to the footwall, forming an "abnormal fault"...no wait, that's my bad joke from the classroom. It's called a "reverse fault".

Death Valley is in an isolated lonely region, except for the main tourist area, which lies mostly along Highway 190 and Badwater Road which leads to...Badwater. But Badwater Road doesn't end there. It continues on to the south end of Death Valley and eventually over Jubilee Pass to the village of Shoshone. Few tourists ever venture this way. But there are things to see out there in the deep desert.

There is an odd little hill on the floor of Death Valley at the south end near the Ashford Mill (the remains of an old mine). It's a cinder cone, a small eroded pile of volcanic cinders and bombs that erupted tens of thousands of years ago. It's out on the valley floor in the midst of the alluvial fans, made up of the gravel and sands eroded from the surrounding mountains. The short climb from West Side Road provides a fine view of the graben of Death Valley. It's odd because it may be the only mountain you will ever climb whose summit is below sea level (-73 feet to be exact).
There are other reasons it is odd. Being in the middle of the valley, there seems no obvious way for lava to reach the surface of the valley. For another, it's in pieces. One half can be seen in the photo mosaic below.

From the main highway (below) it becomes apparent that the two pieces are offset from each other. It's been torn apart by faulting, but not by the kinds of faults we looked at above. The side are moving laterally. This kind with the lateral motion is caused by shearing and is called a strike-slip fault. The presence of the fault provides an explanation for the presence of the cinder cone (the magma was able to follow the fault fracture to the surface). But what are strike-slip faults doing in the Death Valley graben?

There are two kinds of strike-slip faults, right and left lateral. The type can be determined by looking at what the opposite block has done from the observers position: notice below that Pokey moved to Gumby's right. But from Pokey's point of view, Gumby has moved to Pokey's right. That's a right lateral fault.

One can therefore see that Cinder Hill in the Google Earth image below is offset in a right lateral manner, with the southwest portion moving northwest. That's a coincidence (not really) because the San Andreas fault, many miles away to the west, is also a strike-slip fault, and it is moving in the same direction. The two faults are roughly parallel. And that provides a clue about the nature of the faults in the Death Valley region.

There are other strike-slip faults in Death Valley, and they "step over" in such a way that a gap opens between the ends of the fault. In that area the crust is being stretched apart, forming a "pull-apart basin" (below). Death Valley National Park is being stretched apart to form grabens, but the overall motion is towards the northwest as the Sierra Nevada pulls away from the rest of the Basin and Range Province.

The clues to the broad forces affecting the crust of the planet show up in the way that they deform and fracture the rocks at the surface. Observations of an obscure little cinder cone at the south end of Death Valley reveals that the park is part of a much bigger process of continental motions that divide the North American plate from the Pacific plate. The faults might seem normal, but not all of them actually are.

Faulting, Volcanism, and Life in Northernmost California: the Tulelake Graben

Gillem's Bluff at Lava Beds National Monument

Lava Beds National Monument at the extreme north end of California is a fascinating place. It preserves hundreds of lava tubes and lava flows only a few thousand years old. It also preserves the memory of a people, the Modoc tribe, who were destroyed so settlers could raise alfalfa and potatoes. And there are lakes that formerly gave life to millions upon millions of birds. The smaller lake that persists (with human help) provides shelter for the migratory birds who remain. The lake basin below Lava Beds is protected as the Tulelake National Wildlife Refuge.

Multiple fault scarps (the shadowed terraces) cross the region north of Lava Beds National Monument

It began with faulting. The crust in this region has been stretched beyond the breaking point, and some of the fault blocks have sunk against the others, forming a series of horsts (the uplifted blocks), and one deep graben (the sunken block). The main fault scarp in the top picture is called Gillem's Bluff. One can just make out the waters of Tulelake at its base.

The faults provided an avenue for basaltic magma to reach the surface. The rough blocky a'a lava in these photographs is the Devil's Homestead flow, which emerged just over 10,000 years ago from fissures at the Fleener Chimneys in Lava Beds National Monument.

The graben became a collecting sump for waters in the Klamath River drainage. The present incarnation of Tulelake covers only about 15 square miles (five miles long and three miles wide), but the lake once extended across one hundred square miles. Diversions of the rivers that fed the lake caused vast portions of the lake to dry up and the new land was converted to agricultural fields. Not that the original European settlers particularly cared, but the lake was a critical stop where migratory birds rested and fed during their long journey between the Arctic regions and their winter homes in central and southern California. The topography literally funneled the birds through to Tulelake and  the Klamath Lakes a bit farther north. The lands here are mostly arid, and the water was a sanctuary.

The birds still come, Sandhill Cranes, Ross's and Snow Geese, Greater White-fronted Geese and many others, more than a million each year, but they face challenging conditions of overcrowding and disease, especially in dry years when there is less water and food (the lake is at the end of the receiving line in terms of water allotments). Avian cholera sometimes kills thousands of them. But they've survived, and I hope they will continue to do so.

Earthly violence in the form of earthquakes and volcanic eruptions created this strange landscape, but water made it productive and full of life. It's a fascinating place to visit, especially in spring and fall when the bird migrations peak.

Like a Gigantic Babushka Doll, One Death Valley inside Another Death Valley

Death Valley is a deep structural trough called a graben, formed by faults that stretched and broke the continental crust, mostly within the last two or three million years. It is just one of dozens that are present across the deserts of eastern California, all of Nevada, and much of western Utah, a region known as the Basin and Range Province.  But as grabens go, Death Valley stands out. It is almost twice as deep as the Grand Canyon, as the Panamint Mountains slope 11,000 feet down to the valley floor that sits below sea level. It's also one of the flattest places you can stand on planet Earth.

But the valley we see is only part of the story. As is always true of any mountain, if it sticks up into the atmosphere, it will be eroded. It doesn't matter how dry the climate is, erosion happens anyway, albeit at a slower pace perhaps. Sediments have been filling in these valleys. As high as the mountains are, another two miles are hidden by the sediments that fill the valley floor.

I imagine some people wonder what's under all that salt. Wouldn't it be cool to see some of the history revealed in those sediments?

All I can say is that Death Valley is one awesome piece of geology. Whatever you might seek about geological processes or history, there is probably a world-class example of it at the park. So you want to see what Death Valley would look like from the inside-out? We've got you covered! There have actually been two Death Valleys, and one of them has been turned on end for us to explore.

About 5 or 6 million years ago, extensional forces were stretching the crust in the Death Valley region, but from a different direction. A major fault graben opened up in a northwest/southeast direction, mountains rose on either side, and erosion began to fill in the trough. Eventually the sediments accumulated to a depth of a mile. Sometimes a permanent lake filled much of the valley, resulting in the deposition of layers of fine silt and clay. At other times, the lake dried up, leaving behind halite (table salt), gypsum, and borate minerals. Alluvial fans, composed of gravel and conglomerate, sometimes spread across the valley floor. There were occasional volcanic eruptions as well.

The sequence of sediments and lava flows is called the Furnace Creek formation. Few fossils are found in the rock, but trackways of horses, camels, mastodons, large cat and wolf ancestors, and birds have been found. These fossils point to a diverse ecosystem that was not quite as dry as that of today's Death Valley, but is certainly analogous to the Death Valley that existed during the ice ages.

Then things changed.

The regional stress pattern shifted and new faults formed, the faults that produced the present-day Death Valley graben. The deeply buried rocks of the Furnace Creek formation were pushed upwards, folded and tilted, and ultimately exposed to erosion. In the harsh desert climate soils do not develop on the fine silts, so the barren slopes give way to deep gullies and furrows called badlands topography.

And so today, we can have a look at Death Valley from the inside out.

Most tourists who visit Death Valley observe the Furnace Creek formation at the spectacular view from Zabriskie Point or from the resort area at Furnace Creek. We usually do a field exercise at Zabriskie, but the entire area was closed this year for renovation. So we headed up Twenty-Mule Team Canyon for a look at the colorful outcrops. The gravel road winds for several beautiful miles through the badlands.

The Furnace Creek formation was the greatest source of riches in the Death Valley region. Forget gold or silver or copper. The borate minerals, formed from geothermal hot springs in the graben of the Furnace Creek formation, were mined for their use as soaps and detergents, a flux in glass-making, in cosmetics, and numerous other applications. For a number of years in the late 1800s the only economic sources of the borate minerals in the world were in Turkey and Death Valley. They were still being mined in Death Valley as recently as 2005.

The Furnace Creek formation is a spectacular part of the scenery of Death Valley National Park, but the colorful exposures provide a window into the geologic history of the western United States as well. Peel away the surface layers and we find pieces of the past when conditions were far different. Peel back that layer, and we find another story.The Furnace Creek formation is but one of dozens of geologic strata exposing more than a billion years of changing environmental conditions. The park is one giant Babushka doll of geologic history.

Out of the Valley of Death: Hitting the Lowest of the Low, the Driest of the Dry, and the Hottest of the Hot

Just how low can one go? Just how far can people descend in life before they hit bottom? In Death Valley National Park, there is a precise answer: -282 feet, or -85.5 meters at a spot called Badwater. That's also the lowest you can go in North America, but if you look at the big picture, there are seven other places around the world where you can sink even lower:

Earth’s Lowest Elevations (Courtesy of the National Park Service)

• Dead Sea (Jordan/Israel) -1360 feet (-414 m)
• Lake Assal (Djibouti, Africa) -509 feet (-155 m)
• Turpan Pendi (China) -505 feet (-154 m)
• Qattara Depression (Egypt) -435 feet (-133 m)
• Vpadina Kaundy (Kazakstan) -433 ft (-132 m)
• Denakil (Ethiopia) -410 ft (-125 m)
• Laguna del Carbón (Argentina) -344 ft (-105 m)
• Death Valley (United States) -282 ft (-86 m)
• Vpadina Akchanaya (Turkmenistan) -266 ft (-81 m)
• Salton Sea (California) -227 ft (-69 m)
• Sebkhet Tah (Morroco) -180 ft (-55 m)
• Sabkhat Ghuzayyil (Libya) -154 ft (-47 m)
• Lago Enriquillo (Dominican Republic) -151 ft (-46 m)
• Salinas Chicas (Argentina) -131 ft (-40 m)
• Caspian Sea (Central Asia) -92 ft (-28 m)
• Lake Eyre (Australia) -49 ft (-15 m)

I had this awesome idea! I bet no one has ever thought to take their picture here before!

As the park service notes, most of these lowest points have a few things in common: they are very dry, and the origin of their low altitude is tectonic. The Basin and Range Province of which Death Valley is part of has been described as "The Broken Land" by Frank DeCourten, and indeed it is: fault after fault breaks up the Earth's crust into high mountain ranges (horsts) and deep fault basins (grabens). Death Valley is the ultimate expression of the process with relief of 11,330 feet between Telescope Peak (11,049 feet) and Badwater (-282 feet). The highest point in the United States outside of Alaska, Mt. Whitney (14,505 feet), is only 76 miles away as the crow flies.

If erosion wasn't a thing that happened, Death Valley would be even deeper. The sand and gravel that fills the Death Valley graben extends to a depth of about 9,000 feet, meaning if the gravel weren't there, the total relief would be 4 miles!

Fault scarps interrupt the smooth surface of this alluvial fan just south of Badwater.

From Badwater, it's not hard to see the evidence of the tectonic activity that formed the vast trough. In the picture above, two fault scarps are visible cutting across the relatively smooth profile of the alluvial fan. The earthquakes that caused these scarps happened in the last few thousand years, but they look fresh because of the lack of erosion in the dry climate.

Did we mention that Death Valley is also the driest place in North America? Average rainfall here is less than two inches a year. The Sierra Nevada and the other mountains of the Basin and Range province are very effective rain shadows (orographic barriers). Badwater lies at the edge of the Death Valley salt pan, a 200 square mile flat surface covered by salt and other evaporite minerals. It is hard to imagine a place more inhospitable to life on the planet. There are a few salt tolerant plants that grow on the edges of the pan, but I've heard of nothing that lives in the interior areas (except maybe some microbes here and there?).

To stand on the salt flat and look off in all directions is a lesson in isolation. Were it not for the vehicles and the ice chests and water bottles parked over against the mountain, this would be a moment of great concern. If it weren't February and summertime instead the concern would be near panic. We can easily forget the harsh nature of this environment when we are largely insulated from it. Furnace Creek, about a dozen miles north of this location, recorded a temperature of 134 °F (57 °C) in 1913. With the dethroning of the improperly recorded temperature in Libya from 1922, this is the hottest officially recorded temperature in world history. The hottest overnight temperature ever recorded, was 107 °F (42 °C) on July 12, 2012. That day, the average temperature was 117.5 °F (47.5 °C), the world's hottest 24-hours on record.

We talked about the geology and got back into the vans and headed north, up the valley towards Furnace Creek.

As we drove towards camp, we had a look at the edge of the vast turtleback fault surface at Badwater that forms the Proterozoic core of the Black Mountains (in the picture above). The long smooth slope in the shadow on the right is just about all fault surface. The sunlit rocks in the center  and on the left have slid off the fault to the north. They are composed of Miocene volcanic rocks of the Artist's Drive Formation.

The sunlight was a pleasant surprise. For much of the day the skies had been overcast, but in the latest part of the afternoon, the clouds parted for a moment and the rocks glowed orange and gold. The sediments and flows of the Artist's Drive formation are colored by oxidation of various metals in the volcanic ash and tuff layers, and are striking in almost any conditions, but they are especially bright at sunset.

The sun disappeared into the clouds again and the harsh edges of the valley blurred as the evening arrived. We headed back to our camp at Stovepipe Wells.

Into the Great Unknown: Vulcan the Fire God says "You Call That Little Piece of Concrete a Dam?"

Dam engineers sure love their dam creations. The Colorado River, being the only river of note draining the Colorado Plateau, was a target of their fevered dreams, and major projects have "tamed" the river, most notably at Hoover Dam/Lake Mead, and Glen Canyon Dam/Lake Powell (above). Those who administer the giant concrete plugs love to cite the statistics: Hoover holds back 28 million acre feet, Powell 24 million, Mead is 112 miles long when full, Powell is 186 miles. It can't be denied that the concrete monsters have had a huge effect on the ecosystems of the river. Glen Canyon is entirely submerged. The river downstream runs cold all year, and surges high and low in response to electrical production needs. Native fish and flora struggle to survive in the new regime.

We were at the end of our thirteenth and starting the fourteenth day of our journey into the Great Unknown, a rafting trip down the Colorado River from Lees Ferry to Diamond Creek. I had taken an involuntary swim through Lava Falls Rapid that afternoon, but with the swim having been a far less terrifying experience than the first flip back at Crystal, I was feeling okay. Passing through Lava Falls represents to many the climax of the trip, and the last two or three days are sort of a winding down of the journey, with few large rapids.

For me though, the last two days were some of the most astounding because we had reached the site of one of the most extraordinary geological stories in the entire history of the Grand Canyon. Visitors to the main tourist areas on the north and south rims of the canyon never see the rocks that lined the canyon walls around us, and are often surprised to find they exist at all: miles and miles of basaltic lava flows!

The edge of the Colorado Plateau is punctuated by a series of north trending extensional ("normal") fault zones. They represent the boundary zone between the thick crust of the Colorado Plateau, and the thin extended crust of the Basin and Range Province that reaches across Arizona, Nevada and eastern California. When the crust stretches and breaks, pressure is released in the Earth's mantle below, allowing partial melting of the hot pliable rock. The resulting magma follows the fault zones to the surface. Between 1.8 million and just 1,300 years ago, at least 150 eruptions took place in the vicinity of the western Grand Canyon, covering 600 square miles, forming the Uinkaret Volcanic Field.

Most importantly, at least 13 of these flows spilled over the edge of the canyon and filled the canyon bottom. Vulcan, the fire god, had built his own version of Bureau of Reclamation dams. They weren't small dams. They were hundreds of feet high, and one topped out at least 2,500 feet (Glen Canyon Dam is 710 feet tall). It was the remnants of these lava flows and lava dams that surrounded us as we floated down the river. It was the first time I had seen these rocks. I was mesmerized (yes, we geologists are a strange lot).

What's even more incredible are the lakes that formed behind the dam. The largest dam formed a lake that backed the river up into Utah. If it happened today, the lava dam lake would inundate Lake Powell. It would make for a long hard rafting journey, but the rapid at the end would have been memorable...

Even more mysterious would be how the lakes met their end. It's still the subject of some research, but evidence suggests that at least five of the lava dams failed catastrophically, collapsing and ending the lake in days rather than years. What kind of evidence? The most compelling would be river deposits containing basalt boulders 115 feet across. How do you move boulders that big?

The amount of water unleashed on the lower canyon by such a failure is almost unimaginable. A modest 'fake' flood produced by releasing water from Glen Canyon Dam up the river might involve flows of 40-45,000 cubic feet per second. The largest historically recorded flood (in 1884) produced flows of about 300,000 cfs. A researcher has found evidence of a flood of 400,000 cfs around 4,000 years ago. Estimates of major floods during the Pleistocene ice ages range in the vicinity of a million cubic feet per second.

The collapse of a 1,500 foot tall lava dam may have produced a flood of 15 million cubic feet per second. That's more than 30 times larger than the biggest flood ever recorded on the Mississippi River. That's how you move 115 foot boulders.

Pictures of gigantic floods filled my imagination as we drifted past lava flow after lava flow. At first, the most vivid outcrops were the flows that had spilled over the rim in the vicinity of Lava Falls and Whitmore Wash. As we floated downstream, the basalt flows tracked along the river, forming low cliffs that went on for miles. The longest flows traveled more than sixty miles down the river bed.

In places the lava flows were thick enough to develop columnar jointing, similar to places like Devils Postpile in California or the Giant's Causeway in Ireland. The columns form when the lava flow pools and then contracts while it cools. The contraction causes the vertical fractures to develop, and they characteristically form hexagonal columns or sometimes rosettes. All in all, the day had been fascinating.

Lava wasn't the only feature of the day. At Whitmore Wash we had a chance to hike up to some interesting pictographs on a sandstone panel a few hundred feet above the river.

 The view up the river was fantastic...

We camped at the very creatively named 202 Mile Camp. While I was cooking, my nephew came up to report that the bank of the river was collapsing. I wandered down to have a look and found that an underwater slide was causing large slabs of sand to be pulled towards the river, forming a large arcuate landslide scarp. After seeing a gigantic normal fault to begin the day, it was interesting to see a small-scale version of the same kind of faulting along the riverbank. The little collapsed block in the center would be called a graben.

The slide ultimately ate up a lot of the shoreline, more than 30 feet, and it was clear that a lot of sand was being lost to the deeper part of the river channel. Ever since the floodgates of Glen Canyon Dam closed in 1963, sand has been disappearing along all the shorelines of the river. There have been a few attempts to produce artificial floods that have temporarily moved sand back onto the beaches, but without the sand that is now trapped in Lake Powell, the beaches are going to continue to disappear.

At the end of the day, the moon made an appearance. It was the first we had seen of it on pretty much the entire trip. I had enjoyed seeing the Milky Way each night, and the moon would have obscured many of the stars, but it was nice to see the beautiful crescent setting over the basalt cliffs.

With the last of the twilight, I hit the sack, realizing we were down to our final two days on the river. Our takeout at Diamond Creek was only 24 miles downstream.