Volcanics in southern California

[TC]

Volcanoes in southern California is not something people can get a mental image of, ( outside of Hollywood anyway) at least when viewing pictures of the irrigated golf courses around Palm Springs and the agricultural fields of the Imperial Valley. Probably the only clue to any source magma would be the myriad of hot springs that parallel the San Bernardino mountains all the way towards the saltine sea and the Mexican border.

But what resent studies have shown, is that the gulf of California is in the process of un zipping itself further inland. If one looks at a map of the area, the Saltine sea is an extension of this rift of the earths crust and late Plasticine ( roughly 20,000 years) volcanics are clearly visible at the south end of the Salton Sea with five small volcanic domes, they follow alongside of the San Andreas fault system, and known as Obsidian Butte with an estimated activity of less than 15,000 years !

All of this is a consequence of the East Pacific rise, both the earthquakes and the resent volcanics, as well as the widening of the gulf of California. But the root cause of this rift is the passage of the two plates in their north/west collision point, the probable place of the next large quake for the southern California region. As there is no subduction of these two land masses at the southern end of the San Andreas fault, the consequence is that one plate is being forced to literally pivot outwards, splitting open the gulf of California. A geological map shows that surface volcanism runs from the southern end of the San Andreas in a north east direction all the way to the Long Valley calderas, which in magnitude would rival the Yellowstone system in eruptive violence.

Similar hot springs exist north of San Francisco in the Clear lake volcanic district, where magma intrusion is close to the surface as a result of the beginnings of the Cascadia subduction zone, but not relative to rift effect.

It would present an interesting scenario if a major shift with the existing fault line caused a greater crust thinning with the Saltine sea region and allowed the magma source below to reach the surface in a large eruption sequence. It has been speculated that this area could be a future active system, which would more or less reduce southern California to a wasteland. The geologic keys are in place, its just a matter of turning the locks.

[Bob]

RE:It would present an interesting scenario if a major shift with the existing fault line caused a greater crust thinning with the Saltine sea region and allowed the magma source below to reach the surface in a large eruption sequence. It has been speculated that this area could be a future active system, which would more or less reduce southern California to a wasteland. The geologic keys are in place, its just a matter of turning the locks.

And how would this "change" SoCal again?

[TC]

Water.

Southern California has no local water sources... and one the major aqueducts is the Colorado diversion which parallels for miles in this area, as well as the Owens system that crosses the fault at Tehachapi, not to mention ash fall and prevailing winds. If you know the geography, the Imperial Valley is the second largest producer of vegetables next to the Sacramento. Any major eruption would effect an area from everything south of Palm Springs to the Mexican border, and eastwards. And if a west wind prevailed at the time, then the damage would be even worse, involving both Riverside and San Bernardino counties.

[TC]

Where the San Andreas gets a bit fuzzy is north of the Saltine sea around Brawley, it splits into two parallel faults and literally goes around the west side of San Jacinto mountains, and the east side. They meet again north around San Bernardino at El Cajon pass, where the fault becomes a single thrust fault. Both the San Bernardino mountains and the San jacinto are a result of this multiple fracture, and quite dramatic in hight from the desert floor.

I did some searches as to the amount of hot springs on the west side of the fault around Hemit Calif. northwards towards Cajon, a total of 21 geothermal springs! Its almost like looking at a sheet of shattered glass with this region, with hundreds of smaller local faults, and to compound the effects, you have a major diagonal fault crossing this area in an east/west direction ( the turlock fault) which literally cuts through the San Bernardino range.

I'm seeing a real picture here of the shattering effect of the jammed San Andreas, the Pacific plate is smashing into this region and being crushed, this would suggest a massive and very deep blockage, and I suspect its the southern end of the Sierra Nevada range.