Friday, October 26, 2012

Salton Sea Volcano Mystery Solved

Moonset at Rock Hill, one of five volcanoes that comprise the Salton Buttes. The buttes last erupted between 940 and 0 B.C., not 30,000 years ago, as previously thought, a new study finds.
CREDIT: U.S. Fish and Wildlife Service
Earthquake swarms and a region-wide rotten egg smell recently reminded Southern California residents they live next to an active volcano field, tiny though it may be.
At the time, scientists said the phenomena did not reflect changes in the magma chamber below the Salton Sea. But now, researchers may need to revise estimates of the potential hazard posed by the Salton Buttes — five volcanoes at the lake's southern tip.

The buttes last erupted between 940 and 0 B.C., not 30,000 years ago, as previously thought, a new study detailed online Oct. 15 in the journal Geology reports. The new age — which makes these some of California's youngest volcanoes — pushes the volcanic quintuplets into active status. The California Volcano Observatory, launched in February by the U.S. Geological Survey (USGS), already lists the area as a high threat for future blasts.

"The USGS is starting to monitor all potentially active volcanoes in California, which includes the Salton Buttes," said study author Axel Schmitt, a geochronologist at the University of California, Los Angeles. "With our results, I think this will further enhance the need to look into the system," Schmitt told OurAmazingPlanet.

Schmitt and his colleagues dated zircon crystals in the hardened lava of the buttes with a relatively new technique, a "helium clock" that starts ticking once the minerals begin cooling at the surface.

Resolving the Obsidian Butte riddle

The revised age solves a long-standing archeological conundrum, said Steve Shackley, emeritus professor of anthropology at the University of California, Berkeley. Artifacts created from one of the five buttes, Obsidian Butte, first appear in Native American villages around 510 B.C. to 640 B.C. The Kumeyaay people, whose territory ranged from the coast to the Coso Mountains, crafted projectiles from Obsidian Butte glass, he said. "The men produced some of the best in the world," Shackley told OurAmazingPlanet.

Projectile point made from Obsidian Butte obsidian, collected west of Palomar Mountain in northern San Diego County, and attributed to the Luiseño cultural territory.
CREDIT: Janet C. Harvey/Axel Schmitt

 However, for decades, researchers thought Obsidian Butte erupted thousands of years earlier. To explain why no one collected the valuable obsidian, archeologists hypothesized that Obsidian Butte was submerged under ancient Lake Cahuilla, the precursor to today's Salton Sea. But geologists had long proved that Lake Cahuilla was ephemeral, flooding and emptying over and over again, so the explanation was always problematic.

"If this dating method is correct, then the Obsidian Butte material wasn't even available, and that makes more sense archaeologically," Shackley said.

Rifting brings rising magma

In fact, that Obsidian Butte rises above the Salton Sea is what first attracted Schmitt's attention. A 30,000-year-old butte should have been buried by a combination of sediment and subsidence by now, he said. "It had to be very young," Schmitt said.

The buttes exist because California is tearing apart, forming new oceanic crust as magma wells up from below. The sinking Salton Trough is the landward extension of the Gulf of California, and marks the boundary between the Pacific and North America tectonic plates.

The lava source for the volcanoes is a magma chamber beneath the Salton Sea, which also heats water for a nearby geothermal plant. Decay of uranium isotopes in zircon crystals show magma built up underneath the volcanoes for thousands of years before the latest eruption, the study shows.

If another eruption occurs at the Salton Buttes, it will likely mimic past breakouts, Schmitt said. The volcanoes are made of sticky, slow-moving rhyolite lava. At Obsidian Butte, the lava cooled so quickly it turned into glass. However, pumice and ash found nearby means past breakouts started with a bang.

Schmitt said he hopes to study the area in more detail to better understand the most recent eruption. "The amounts of magma involved are relatively small and the impacts of an explosive eruption, meaning an ash cloud, would most likely be very local," he said. "We don't know very well how far any ash would have been dispersed, and that's something I would like to follow up on in the research."

Researching future hazards

The National Science Foundation's EarthScope project funds an extensive seismic imaging project in the Salton Sea that may soon reveal more information about what's happening deep underground.
"We'll be looking with great interest to see what we can tell from the Salton Seismic Imaging Project," said Joann Stock, a Caltech professor and an expert on the region's volcanic hazards who was not involved in the new study.

"I think [Schmitt's study] is a great contribution," she said. "It's an area where we should be concerned. We know that there's a lot of hot stuff down there," she told OurAmazingPlanet.
In August, an earthquake swarm shook the nearby town of Brawley. The USGS attributed the temblors to faults in the Brawley Seismic Zone. In September, a sulfurous stench emanated from the Salton Sea and wafted across the Inland Empire. The odor was tentatively linked to a fish die-off, but could also have been caused by volcanic gases, Stock said.

source

Wednesday, October 17, 2012

The Salton Sea Volcanics Part I




Recently, a small taped interview appeared on a San Diego news program that sparked some major interest in many. A geologist shot some footage from a chopper that hovered above the southern rim of the Salton Sea that clearly shows a pit of muddy water roiling like a witch's cauldron. The newscaster spoke of volcanic gases escaping to the surface (probably CO2 and/or H2SO4). This geologist stated that this area could be the setting for volcanic activity and that the USGS is keen on that fact. 

Since the time I bought my first real computer in 1998, and the following year as a geology major at Cal State Fullerton, I have known of the Salton Sea volcanoes. Every map of active US volcanoes that the USGS posts online displays the Salton Sea area as an active volcanic threat. And yet, how many people know or care about anything less than the size of Yellowstone or Rainier or Long Valley? Granted a number of factors would have to play into an eruptive episode for such a thing to be disastrous to the beach side meccas of Southern California; chances are that the Coachella and Imperial Valleys would be more imperiled than anywhere.

Inland Southern California is seductive-so much more than its beach front counterparts. As a recent grad in biology, with each trip past the southern mountain ranges I felt my grip lessen on the herpetological aspects of the desert and grasp more firmly on the stories within the strata of rocks. Never mind the close encounters with killer bees, sidewinders, and heat strokes; I had to be there every day off from work and school. But one area became an obsession: the Salton Sea and its inherent volcanoes. I would like to share that obsession with you of this primordial arena that holds so much mystery, more beauty than any work of art, and geological wonders beyond the imagination. 

But first, let's take a little earth history lesson on how this region was formed. Between 150-90 million years ago, the Peninsular Ranges, west of the Salton Sea, were formed from the same areal process that created the South American Andes, the Central American Cordillera, and the Sierra Nevadas: subduction. The Farallon Plate subducted beneath California and hot magma rose from that juncture to cool slowly into large plutons that became the Peninsular Ranges. Then about 30 million years ago, the North American plate overrode the Farallon Plate (aka the East Pacific Rise) and stopped the subduction of the Farallon. There are a few places where the remnants of that enormous plate still subduct, but for our purposes, we will focus only on what affects Southern California. The energy between the East Pacific Rise and the Pacific Plate was transformed (yes, I know, but it's a good pun) along a lateral fracture of the now buried East Pacific Rise and thus created the San Andreas Fault. 



However, do not discount the affect the still, very active East Pacific Rise has on Southern California. The EPR runs between Baja California and Mexico, separating the two and thereby causing a drop in the land where the Salton Sea lies. Molten lava rises along the break of the rise, causing older lava to be replaced by newer and spreading the older farther and farther from the rise itself. As stated, this spreading, conveyor belt of newly formed oceanic crust widens and thins the crust of the Imperial and Coachella Valleys. 
If you travel from Riverside, east on the 10, you'll soon come to the city of Banning in the San Gorgonio Pass. Banning is a small town that sits on the point of the "V" shaped gräben that comprises the previously mentioned counties. Traveling further east through Cabazon and into the heart of Imperial Valley, the elevation drops from 7oo' to below sea level in the city of Indio. This is the obvious change the East Pacific Rise has had on the suroundings, but there is an even more exciting transformation on the landscape: volcanoes.

Thanks to all that widening and thinning of the crust, magma can more easily find an avenue to the surface. There are five volcanoes or more precisely, five rhyolite domes at the south end of the Salton Sea: Rock Hill, Mullet Island, obsidian Butte, Red Island (Red Island has two domes). For the technical information, I turn to C. Dan Miller's thorough report (1989, Potential Hazards from Future Volcanic Eruptions in California: USGS Bulletin 1847) on the area; here are the specs: 

The Salton Buttes rhyolite center:
  • Most recent eruption: Silicic pyroclastic and extrusive eruptions at four vents approximately 16,000 years ago (Potassium-Argon dating);
  • Five silicic domes erupted;
  • At least one silicic lava flow associated with rhyolite dome;
  • Probable small-volume pyroclastic eruptions with tephra associated with dome emplacement at several vents;
  • No recognized debris avalanches or debris flows;
  • Most probably future potential hazard: Explosive and extrusive rhyolitic eruptions; phreatic and phreato-magmatic eruptions.
Although the youngest eruptions in this area are not known to have produced pyroclastic flows and surges, the compositions of lavas of past eruptions and the association of vents with ground water and the Salton Sea suggest that pyroclastic flows and surges and explosive eruptions could occur in the future. Such events commonly are destructive out to distances of at least 10 kilometers (6 miles) from an active vent.
 ... and from:  Robinson, Elders, and Muffler, 1976, Quaternary volcanism in the Salton Sea geothermal field, Imperial Valley, California: GSA Bulletin 87, p.347-360, March 1976 
 
The Salton Sea geothermal field lies in the Salton Trough, the landward extension of the Gulf of California, an area of active crustal spreading. The Salton Buttes volcanoes lie within the Salton Sea geothermal field where temperatures measured in wells drilled for geothermal brines range up to 360 degrees C at depths of 1,500 to 2,500 meters (Helgeson, 1968). The wells produce a hot brine containing up to 160,000 ppm of dissolved solids, chiefly Cl, Na, K, Ca, and Fe (White, 1968). Under the influence of this hot saline brine, the sediments of the Salton Trough are being transformed into metamorphic rocks of the greenschist facies (Muffler and White, 1969). 
 
From this information alone, one can see that even a phreato-magmatic eruption, an eruption that occurs when hot magma encounters saltwater, shouldn't be devastating to areas such as San Diego or Los Angeles. In short, lots of drama without a major impact other than on those living within the Brawley seismic zone, a large agricultural area south of the Salton Sea. The wind generally blows from the NW due to constriction via canyon walls; the ventifacts (rocks shaped by the wind) tell us that the wind has been blowing from this direction for many, many years. Also, west of the Salton, there is a field of Barchan Sand Dunes that attest to the strength of a wind blowing from one general direction.

South and East of the Salton Sea, one can find along dirt back roads, mudpots--some as large as 8' tall. Most are smaller and look much like crawfish holes dug out of Missouri gumbo (gumbo is a thick, gooey type of soil that contains rich sediments that enable the Boot Heel farmers to grow anything from rice to cotton to soybeans).  Near Frink and around Calipatria, there are many such mudpots bubbling and passing the pungent gases that are released from far below the soil.Even around Rock Hill, near the shoreline, the water bubbles as the Salton's water level has increased and has submerged the mudpots and hot springs.

Back to  Miller's report on volcanic hazards in the US, here is a graph from the same that outlines the potential area that would be affected by a future eruption and below this figure, there is an explanation for the type of hazard for this particular color coded zone.




Let's take a quick glance at the geothermal plants in the area:

From the Land Use Database, comes the following:

This cluster of seven geothermal plants is the largest of three major geothermal energy production sites in the Imperial Valley. A network of deep wells drilled in the geothermal field allow water, heated by the earth's mantle, to come to the surface and to power electrical generators. Owned by the CalEnergy Company, the electricity is sold to the local power utility and put on the grid. The seven plants in this field produce enough electricity to power over 100,000 homes.

In the next post, I'll go into more detail about the volcanoes, as well as to provide personal pictures taken on some of my adventures there. Stay tuned...

Lin aka Roxxfoxx

Friday, October 12, 2012

Lassen Peak Eruption Video - I'm not joking!

Last night I had one of the greatest of pleasures I can experience and that is to learn something that would be categorized as "the rest of the story. “Craig Martin relayed to me the tale of his grandfather, Justin Hammer, who lived near Lassen Peak in California in 1914. Hammer made his own camera and shot the following film at Catfish Lake, now Reflection Lake in Lassen National Park, in 1917, very near the north park entrance. 
 
Lassen's eruptions occurred from 1914 to 1917, but the USGS initially did not believe the eruption occurred on the earliest date. However, Hammer who lived so close to the volcano, witnessed the first eruption  in 1914.  Hammer would stay at his cabin unless heat, lava, and ash from the eruption forced him briefly away. Quite the adventurer, Hammer was the oldest man ever to scale the mountain's North Slope at age 70. 

Craig Martin comments, "National Geographic was sold the rights to the film in exchange for saving as much of the film as they could in the 60s. They found the film so brittle that when it was handled, it splintered into pieces. The film you see is all they could save of all the eruptions. The rest was explosive, so it was destroyed." The film was, at one time, over 20 minutes long. Prior to the eruption of Mt. St. Helens in 1980 this was the only film of a volcanic eruption within the continental United States. 
 
Craig has also promised me exclusive rights to his family archive of Lassen photographs; I simply cannot wait to see them. I am elated that Craig's and my paths have crossed and that along with making a new friend, we both can share a story that might otherwise not obtain the attention it so rightly deserves.
 
Lin
 
PS Audio was supplied by Craig, as the film was originally silent.

video 
http://www.youtube.com/watch?v=Q7z6q71uryI&feature=share
 

Remember the 2010 Baja CA Quake? Let's take a trip down Memory Lane...

EARTHQUAKE MOUNTAIN DUST



Oct 11, 2012

The 2010 Baja California earthquake (also known as 2010 Easter earthquake, 2010 Sierra El Mayor earthquake, or 2010 El Mayor – Cucapah earthquake) was an earthquake of 7.2 magnitude on the moment magnitude scale. It started 26 kilometers (16 mi) south of Guadalupe Victoria, Baja California, Mexico, at a depth of 10 km (6.2 mi).

It occurred at 3:40:41 pm Pacific Daylight Time (PDT) on Easter Sunday, April 4, 2010, and it is said to have lasted about a minute and a half.

Brothers Roberto and Adrian Marquez were traveling in Mexico during that fateful Sunday and captured a surreal sight: The power of the quake lifting a layer of dust off a mountain range. The pictures show the area around La Rumorosa, the highest point in Tecate.

For more pictures of the quake’s damage by NBC San Diego, click here. You can also check out some incredible footage of the ‘earthquake mountain dust’ phenomenon in the video embedded below. You can also find the complete report by NBC San Diego here.

source
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