OK, so I’m watching quakes and things, and this tiny little issue comes up. There are a bunch of them down in Baja. The energy from them tends to wander up my way after a while, so I like to keep tabs on them. Then we got a couple of small ones up by Mammoth “Lakes” a bit north of Death Valley… that’s actually a volcanic Caldera and can get really nasty if it blows it’s top. Think “small super volcano” (if there can be such a thing as a ‘small one’ of them…)
The geology of Southern California can be a bit, er, complex… There is a subducted spreading zone (that starts as a Pacific floor spreading area) and then some of it gets sucked under the North American plate. This “has issues” like spreading out the Basin and Range area a bit and making Utah and Nevada larger… as they sink a little. But a lot of it goes into “other places”. For example, Death Valley. It is below sea level as it is being slowly pulled open into a rift in the continent.
How much of a rift?
The passive margin switched to active margin in the early-to-mid Mesozoic when the Farallon Plate under the Pacific Ocean started to dive below the North American Plate, creating a subduction zone; volcanoes and uplifting mountains were created as a result. Erosion over many millions of years created a relatively featureless plain. Stretching of the crust under western North America started around 16 Ma and is thought to be caused by upwelling from the subducted spreading-zone of the Farallon Plate. This process continues into the present and is thought to be responsible for creating the Basin and Range province. By 2 to 3 million years ago this province had spread to the Death Valley area, ripping it apart and creating Death Valley, Panamint Valley and surrounding ranges. These valleys partially filled with sediment and, during colder periods during the current ice age, with lakes. Lake Manly was the largest of these lakes; it filled Death Valley during each glacial period from 240,000 years ago to 10,000 years ago. By 10,500 years ago these lakes were increasingly cut off from glacial melt from the Sierra Nevada, starving them of water and concentrating salts and minerals. The desert environment seen today developed after these lakes dried up.
So, during the Ice Age Glacials, it’s a lake. Now, not so much… but one can reasonably expect that if we start seeing it fill with water, we’ve got a problem on the way…
And that stretching?
Starting around 16 Ma in Miocene time and continuing into the present, a large part of the North American Plate in the region has been under extension by literally being pulled apart. Debate still surrounds the cause of this crustal stretching, but an increasingly popular idea among geologists called the slab gap hypothesis states that the spreading zone of the subducted Farallon Plate is pushing the continent apart. Whatever the cause, the result has been the creation of a large and still-growing region of relatively thin crust; the region grew an average of 1 inch (2.5 cm) per year initially and then slowed to 0.3 inches (0.76 cm) per year in the last 5 million years. Geologists call this region the Basin and Range Province.
Extensional forces causes rock at depth to stretch like silly putty and rock closer to the surface to break along normal faults into downfallen basins called grabens; small mountain ranges known as horsts run parallel to each other on either side of the graben. Normally the number of horsts and grabens is limited, but in the Basin and Range region there are dozens of horst/graben structures, each roughly north-south trending. A succession of these extend from immediately east of the Sierra Nevada, through almost all of Nevada, and into western Utah and southern Idaho. The crust in the Death Valley region between Lake Mead and the southern Sierra Nevada has been extended by as much as 150 miles (240 km).
Hmmmm…. 150 miles. That’s kind of, er, a lot…
But about those sediments:
These two systems are also offset from each other; the area between the offset is thus put under enormous oblique tension, which intensifies subsidence there; Furnace Creek Basin opened in this area and the rest of Death Valley followed in stages. One of the last stages was the formation of Badwater Basin, which occurred by about 4 Ma. Data from gravimeters show that Death Valley’s bedrock floor tilts down toward the east and is deepest under Badwater Basin; there is 9,000 feet (2,700 m) of fill under Badwater.
Yikes! It’s 9000 feet of “down” from below sea level at the surface. The only reason we don’t have a 9000 foot deep canyon is because the mountains are eroding into it as “fill”… but not quite keeping up as the floor of Death Valley IS below sea level…
So, does this not mean there ought to be some kind of “magma” issue from time to time?
Igneous activity associated with the extension occurred from 12 to 4 Ma. Both intrusive (plutonic/solidified underground) and extrusive (volcanic/solidified above ground) igneous rocks were created. Basaltic magma followed fault lines to the surface and erupted as cinder cones and lava flows. Some volcanic rocks were re-worked by hydrothermal systems to form colorful rocks and concentrated mineral formations, such as boron-rich minerals like borax; a Pliocene-aged example is the 4,000-foot (1,200 m)-thick Artist Drive Formation. Gold and silver ores were also concentrated by mineralizing fluids from igneous intrusions. Other times, heat from magma migrating close to the surface would superheat overlaying groundwater until it exploded, not unlike an exploding pressure-cooker, creating blowout craters and tuff rings. One example of such a feature is the roughly 2000 year old and 800 feet (240 m) deep Ubehebe Crater (photo) in the northern part of the park; nearby smaller craters may be less than 200 to 300 years old.
OK, so we had active volcanic activity 4 Million years ago, and some smaller hydrothermal blowouts as recently as a few hundred years ago.
This is starting to sound a fair amount like Iceland, except the thing is filled with sand and gravel from the mountains eroding into it…
Sediment filled the subsiding Furnace Creek Basin as the area was pulled apart by Basin and Range extension. The resulting 7,000-foot (2,100 m)-thick Furnace Creek Formation is made of lakebed sediments that consist of saline muds, gravels from nearby mountains and ash from the then-active Black Mountain volcanic field.
Additional subsidence of the Furnace Creek Basin was filled by the four-million-year-old Funeral Formation, which consists of 2,000 feet (610 m) of conglomerates, sand, mud and volcanic material. Another smaller basin to the south was filled by the Copper Canyon Formation around the same time.
So we stacked up 7000 feet of “stuff” early on, then up to about 4 My have added 2000 feet more as the place continues to subside. This is starting to sound like an ongoing issue… But during the glacials, it even has a lake on top, for even more “coverage”.
Lake Manly was the lake that filled Death Valley during each glacial period from at least 240,000 years ago to as late as 10,500 years ago; the lake typically dried up during each inter-glacial period, such as the current one. Lake Manly was the last in a chain of lakes that were fed by the Amargosa and Mojave Rivers, and possibly also the Owens River; it was also the lowest point in the Great Basin drainage system. At its height during the Last glacial period some 22,000 years ago, water filled Lake Manly to form a body of water that may have been 585 feet (178 m) deep and 90 miles (140 km) long
So, when the next glacial starts, watch for a new lake and more fishing… Most of Nevada gets lakes, so there will be many from which to choose ;-)
OK, so we’ve got 9000 foot of sediments, 100 of it accumulating during the Holocene, the valley floor is still below sea level, and it used to have an additional 585 feet of water on top. That’s a big, deep area that is spreading and opening in the continent. At the bottom, Badwater Basin is 282 feet below sea level.
Is It A Sign?
This tid bit from the Wiki was intriguing:
In 2005, Death Valley received four times its average annual rainfall of 1.5 inches (38 mm). As it has done before for hundreds of years, the lowest spot in the valley filled with a wide, shallow lake, but the extreme heat and aridity immediately began sucking the ephemeral lake dry.
This pair of images from NASA’s Landsat 5 satellite documents the short history of Death Valley’s Lake Badwater: formed in February 2005 (top) and long gone by February 2007 (bottom). In 2005, a big pool of greenish water stretched most of the way across the valley floor. By May 2005 the valley floor had resumed its more familiar role as Badwater Basin, a salt-coated salt flats. In time, this freshly dissolved and recrystallized salt will darken.
So keep an eye on that lake. If it starts being around more than once every few dozen years, well, we’ve got a problem… and the problem isn’t “warming”…
I’d also suggest that since the lake formed in 2005, we were not all that warm then, either…
But back at what this means for The Grand Canyon.
We know that the Grand Canyon formed when that plateau was uplifted.
The Grand Canyon is a steep-sided canyon carved by the Colorado River in the United States in the state of Arizona.
The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (1.83 km) (6000 feet). Nearly two billion years of the Earth’s geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted. While the specific geologic processes and timing that formed the Grand Canyon are the subject of debate by geologists, recent evidence suggests the Colorado River established its course through the canyon at least 17 million years ago. Since that time, the Colorado River continued to erode and form the canyon to the point we see it at today.
So we’ve got this giant hole in the ground that is hundreds of miles long and over a mile deep.
Where did it go?
Yes, the Colorado River washed it all away, but that’s a lot of washing. And while 17 million years is a very long time for a person, it’s not nearly so long for a geologic process. (And some earlier dating put it at more like 6 to 8 million years). But it all went down the river. So we’d expect to see a giant mountain of sand somewhere. Hundreds of cubic miles of the stuff.
Down The Colorado
Where the Colorado River meets the sea is in the Gulf of California in Mexico. Now, by the time it gets there, it is essentially all used up. We have diverted substantially all of it to agriculture and domestic uses in all the various states along the path and even a little in Mexico. In prior times, great floods would wash sediments down the Colorado. Now they get dumped in Lake Mead behind Hoover Dam. But that lake did not exist in prior times. So where did the sand go?
Looking at the end point of the Colorado, we find a broad alluvial deposit. But it is only about 10 meters high for many many miles. 30 feet is just not enough! but a look from overhead gives a better idea what happened:
I picked up this image here:
that credits these folks:
that says: “Credit for these images should be attributed to:
Liam Gumley, Space Science and Engineering Center, University of Wisconsin-Madison.” So, credit given.
Now run your eye from the Gulf of California in the lower right up toward the upper left, notice all that greenish fan area? (Not the one in the water, the one on land…) That’s the farm land being watered where the Colorado River runs into Baja. Off to the upper right is where the Colorado runs back into the rest of the country. If you continue up toward the middle of the picture, above the fan, you find a lake. That is the Salton Sea. It, too, is below sea level. 69 meters or 226 feet below sea level.
The Salton Sea is a saline, endorheic rift lake located directly on the San Andreas Fault predominantly in California’s Imperial Valley. The lake occupies the lowest elevations of the Salton Sink in the Colorado Desert of Imperial and Riverside Counties in Southern California. Like Death Valley, it is below sea level; currently, its surface is 226 ft (69 m) below sea level. The deepest area of the sea is 5 ft (1.5 m) higher than the lowest point of Death Valley. The sea is fed by the New, Whitewater, and Alamo rivers, as well as agricultural runoff drainage systems and creeks.
It was formed by accident in 1905 when some folk trying to divert some of the Colorado River to agricultural use were a bit too cheap on the safety measures and discovered that rivers can erode new channels (or re-open old ones…)
The creation of the Salton Sea of today started in 1905, when heavy rainfall and snowmelt caused the Colorado River to swell, overrunning a set of headgates for the Alamo Canal. The resulting flood poured down the canal and breached an Imperial Valley dike, eroding two watercourses, the New River in the west, and the Alamo River in the east, each about 60 miles (97 km) long. Over a period of approximately two years these two newly created rivers sporadically carried the entire volume of the Colorado River into the Salton Sink.
One hopes that we don’t have too much more “heavy rainfall” again…
The Southern Pacific Railroad attempted to stop the flooding by dumping earth into the canal’s headgates area, but the effort was not fast enough, and as the river eroded deeper and deeper into the dry desert sand of the Imperial Valley, a massive waterfall was created that started to cut rapidly upstream along the path of the Alamo Canal that now was occupied by the Colorado. This waterfall was initially 15 feet (4.6 m) high but grew to a height of 80 feet (24 m) before the flow through the breach was finally stopped. It was originally feared that the waterfall would recede upstream to the true main path of the Colorado, attaining a height of up to 100 to 300 feet (30 to 91 m), from where it would be practically impossible to fix the problem. As the basin filled, the town of Salton, a Southern Pacific Railroad siding and Torres-Martinez Indian land were submerged. The sudden influx of water and the lack of any drainage from the basin resulted in the formation of the Salton Sea.
Now, can you imagine being the guy who has to call up the boss and tell him you have managed to make a little break in a river bank and, well, you are now flooding Southern California and that the Colorado River no longer flows to Mexico? Oh, and you’ve made this tiny little waterfall of 80 feet high that might grow to 300 feet is something isn’t done; but don’t worry, over 226 feet of it is due to being below sea level… Oh, and you’ve submerged a town and an Indian tribal homeland… Other than that, no problem… 8-0 !!
The continuing intermittent flooding of the Imperial Valley from the Colorado River led to the idea of the need for a dam on the Colorado River for flood control. Eventually, the federal government sponsored survey parties in 1922 that explored the Colorado River for a dam site, ultimately leading to the construction of Hoover Dam in Black Canyon, which was constructed beginning in 1929 and completed in 1935. The dam effectively put an end to the flooding episodes in the Imperial Valley.
So now you know why Hoover Dam was built… To save Southern California from becoming an inland sea any larger than it already was…
OK, look at the photo, we’ve got a nice batch of sand on each side of the green triangle. Nice, but not Grand Canyon Gigantic… Where did the Grand Canyon Go?
Back at that http://www.semp.us/publications/biot_reader.php?BiotID=505 page from the Suburban Emergency Management Project (which has a great write up on the actual “oopsy” that made the Salton Sea. Or, rather, re-made it, as it has sometimes existed on its own… something for So.Cal. residents to look forward to ;-)
A similar interpretation of the formation of the Gulf of California by Elders, et al., is:
“The northeast Pacific plate appears to be a flank of the East Pacific Rise modified by the westward boundary of the North American plate. Marine geophysical studies both in the Gulf of California and in the adjacent ocean strongly support the interpretation that the gulf originated in the spreading apart of the continental crust. It appears that the Gulf of California is part of the active boundary between the North American and Pacific plates”.
Hydrothermal vents jetting water at 380 degrees plus or minus 30 degrees Celsius exist on the axis of the East Pacific rise. Indeed, “the axis of the East Pacific Rise is marked by a zone of recent volcanism approximately 1000 meters wide. Near the center of the volcanic zone, there is a very narrow band of active hydrothermal vents at least 25 vents along a strip 7 km long and only 200 to 300 meters wide”, according to one group of researchers.
OK, so the East Pacific Rise where it runs up the Gulf of Mexico is your typical spreading zone with hot water jets and spreading and volcanism. But that’s not enough to hold The Grand Canyon.
III. Salton Trough
The Mexicali-Imperial Valley is the northern extension of the Gulf of California. “It is a broad structural trough partly filled with lacustrine [lake] and deltaic [Colorado River delta] silts, sands, and gravels of late Tertiary age, and by great thicknesses of Quaternary alluvium and lake sediments”, notes Elders, et al. They continue:
“The trough has “steep, step-faulted margins and a broad, relatively flat basement floor This trough is comparable in shape and size with the deeper submarine basins of the southern part of the Gulf of California, but it is partly filled [in the Imperial Valley] by the vast accumulation of sediments of the Colorado River Delta”.
Elders, et al., believe that “the Salton trough formed by a combination of tensional and right-lateral strike-slip movements associated with the opening of the gulf as Baja California was transferred from the North American to the Pacific lithospheric plates The details of how Baja California was transformed from the American to the Pacific plate remain enigmatic”, they opined.
Scientists mapping San Andreas Fault
Seismic detonations echo through the rifts to chart possible peril
by Thomas Curwen – Mar. 27, 2011 12:00 AM
Los Angeles Times
SALTON SEA, Calif. – Three days after the earthquake and tsunami devastated northeastern Japan, Gary Fuis walked across the San Andreas Fault under a moonlit sky. The desert was quiet. A breeze fanned through the creosote. To the west, he could see the Salton Sea, and to the east, the headlamps of the night crew taking up positions.
In a little more than an hour, they would start detonating their explosives, generating seismic waves that would be recorded by seismometers buried throughout these sandy hills and positioned on the floor of the Salton Sea.
Fuis, 67, a geophysicist with the U.S. Geological Survey, is overseeing an ambitious project to create an underground image of one of the most seismically active and geologically complex regions of the country, a triangle of land extending from Palm Springs to the Mexican border.
Penetrated by volcanoes and cut by the San Andreas and Imperial faults, the region is part of the Salton Trough, one of the few rift valleys in the world not covered by an ocean, a place where geologists can see the continent coming apart and a new crust of the Earth being formed.
“The San Andreas Fault actually appears to be propeller shaped,” he said, drawing a pirouette in the air and describing how the fault tilts to the northeast in this basin, then tilts in the opposite direction father north, past the Mojave Desert.
Many seismologists, he said, assume the fault in this region is largely vertical, a configuration that places the Pacific plate squarely up against the North American plate.
Fuis and a few colleagues, however, believe that the Pacific plate here is wedged beneath the North American plate.
But a greater threat, according to Fuis, is the sedimentary structure of the Salton Trough itself. Excavate this basin of rocks and soil swept down over the millennia from the Rocky Mountains and you’d have a canyon larger than the Grand Canyon.
This formation, sediment nearly 9 miles deep, can trap earthquake energy and amplify seismic waves, resulting in longer, more intense shaking. No one has measured wave speeds in the basin until now.
And there is your answer. The Grand Canyon is in another spreading zone trench. The one splitting off Baja California from Mexico. The one that would have the Gulf of California extending up past the Salton Sea. Were it not for a “Grand Canyon Sized” load of sediments over 9 miles deep.
Now I wonder where that could have come from ;-)
Is there evidence for volcanism near the Salton Sea?
“. The evidence of geothermal activity is also visible. There are mud pots and mud volcanoes on the eastern side of the Salton Sea.”
And is there any natural risk that the Imperial Valley might become a full fledged lake again, all on its own?
There is evidence that the basin was occupied periodically by multiple lakes. Wave-cut shorelines at various elevations are still preserved on the hillsides of the east and west margins of the present lake, the Salton Sea, showing that the basin was occupied intermittently as recently as a few hundred years ago. The last of the Pleistocene lakes to occupy the basin was Lake Cahuilla, also periodically identified on older maps as Lake LeConte, and the Blake Sea, after American professor and geologist William Phipps Blake.
Welcome to life in California. Where it’s normal to not worry that you live a couple of hundred feet below sea level with a 30 foot high pile of sand between you and the ocean, and where it periodically is a lake, on top of one of the world’s most famous earthquake faults, where the continent is being torn apart by one of the few on land spreading zones. But don’t worry, there haven’t been any volcanoes in, oh, years ;-)
The Tres Virgenes, a line of three connected volcanoes, collectively known by that name, are west of La Reforma Caldera. La Vírgen, in the southwest, El Azufre in the center, and El Viejo in the northeast. The volcanoes get larger and younger from northeast to southwest. As recently as 6,500 years ago, La Vírgen experienced a Plinian eruption — a huge, explosive event that produces an enormous column of volcanic rock fragments and gas that reaches into the stratosphere. The eruption produced a column that reached at least 18 kilometers into the air and deposited ash and rock fragments over 500 square kilometers. In later stages of the eruption, pyroclastic flows (pinkish rocks) and lahars (mudflows, grayish rocks) from El Azufre Volcano paved the plain to the north all the way to the Gulf of California.
Cerro Prieto Volcano – John Seach
Baja California, Mexico
32.418 N, 115.305 W
summit elevation 223 m
Cerro Prieto volcano is located at the northern end of the gulf of California, 177 km SE of San Diego, and 30 km from the US border. The volcano consists of a low lava dome.
It’s 30 km away. That’s like, almost a long ways…
The volcano is located in a transition between the East Pacific Rise and the strike-slip San Andreas fault system. It is one of the few areas where on-land spreading is observed.
The heat source for the volcano is thought to be a magma body at a depth of 5–6 km. There is a significant correlation between increases of sustained fluid extraction at the field and earthquakes, with delays of about 1 yr.
An earthquake swarm occurred under Cerro Prieto volcano in Mexico between 8-11 February 2008. The seismic swarm began on 8 February 2008 at 11:12 pm (Pacific Time) with a magnitude 5.1 earthquake. A second magnitude 5.1 earthquake occurred on 11 February 2008 at 10:29 am (Pacific Time) about 4 miles further south. Both events, were shallow, at a depth of less than 3 miles. Sixteen earthquakes greater than magnitude 3 were recorded over 2.5 days. The two magnitude 5 earthquakes were tectonic, consistent with activity on the Cerro Prieto fault.
Cerro Prieto Volcano Eruptions
The last eruption at the volcano is unknown, but may be within the past 10,000 years.
And that’s like, ya’know, almost for-ev-er…
and it’s not like you get really Great Quake sized events in the area:
Well, ok, we get them, but not that often…
So welcome to the world of Sunny Southern California. Palm Springs. Golf Courses. 9 mile deep rift zones with volcanic features, great quakes, imminent inundation, and even the Grand Canyon, in an odd sort of way …
UPDATE: 2 Apr 2011
There was an interesting “chain of pearls” set of tiny quakes just this hour in The Salton Sea, so I though I’d add this image of the moment. I think they pretty much mark the point where the “seas are parting”…