Posted on 05/11/2005 5:21:22 PM PDT by Scenic Sounds
In Las Vegas, folks can't wait for the "Big One," the massive earthquake that will some day cause California to fall into the ocean. When it happens, the joke goes, Las Vegas becomes waterfront property.
It's not true, of course. When the "Big One" does strike, today or a thousand years from now, California isn't likely to fall anywhere except down.
Still, don't bet entirely against that notion of new waterfront property. A monster earthquake won't create it, but scientists say the passage of time and giant crustal plates might. Someday, Southern Californians might enjoy ocean views not just to the west, but to the east as well.
"Much of the state is pulling away from the mainland, moving northwest toward Alaska," said Graham Kent, a geophysicist and director of the Visualization Center at Scripps Institute of Oceanography.
"We're in the process of becoming a giant peninsula. In the distant future, people will still be able to drive north, but if they want to go east, they'll need a ferry."
The only geological constant about life in California is that it's constantly changing. The state rests atop the boundary of two chunks of planetary crust: the Pacific plate underlying most of the ocean, and the continental North American plate.
In some places, the Pacific plate subducts or dips below the North American plate, re-dissolving into the Earth's molten mantle.
In other places, like along the 800-mile San Andreas fault, the plates press and grind against one another like two sheets of sandpaper. Occasionally one side slips. The result: an earthquake. When that happens a lot over millions of years, the face of the planet changes.
Crashing plates
The idea of California becoming an ever-bigger peninsula (it's already one if you include Baja California) is about 15 years old and emerged from satellite measurements that indicated most of the state, including the Sierra Nevada mountain range, is in the process of separating from the rest of North America.
Specifically, said Jeff Unruh, a geologist with William Lettis & Associates who has done extensive research on the subject, the Sierran microplate that includes most of California is drifting northwest away from, say, Iowa (which isn't going anywhere, geologically speaking) at a rate of roughly 12 to 14 millimeters a year, or about half-an-inch.
But if the conclusion is easily stated, explaining how and why exactly is not. The forces and factors that dictate our geological future are enormously varied, complex and, in many cases, not well-understood or even known. But any explanation starts with a history lesson, one that begins long, long ago:
It's the late-Cretaceous period, about 85 million years ago. Dinosaurs still roam the Earth, and what's now California is mostly underwater. The North American plate, encompassing both the exposed continent and adjacent sea, is pushing west, driven by tectonics. In its path are several other plates: the huge Farallon, the Aluk, the Kula and a smallish plate in the south called the Pacific.
Where the North American meets these other plates, there is the inevitable bumping and grinding. Great slivers of the North American are ripped away and reattached to the Pacific plate, which carries them north toward what will become Alaska.
Some 50 million years pass. It's now the Tertiary period. Mammals and birds have become the dominant land organisms. The Pacific plate has grown considerably, its girth increased by stolen bits of the North American plate and robust activity along undersea rifts, which add new crust and fuel the plate's movement.
In contrast, the Farallon plate is shrinking. Squeezed by the Pacific Plate, its eastern edge subducts beneath the North American plate. Portions of the North American eventually begin to creep over the Farallon's spreading center – a rift where new crust forms, causing tectonic movement.
In time, the Farallon breaks into smaller plates: the Juan de Fuca platelet in the north, the Magdalena platelet in the south. Other plates disappear entirely, pushed entirely back into the hot mantle.
Eventually, this subduction process slows and begins to peel back. In the mantle below, magma upwells, lifting and expanding the crust above like the surface of an inflating balloon. The result is the "Basin and Range" province of the western United States, which stretches from Oregon through Nevada to Texas.
"The region is characterized by an alternating pattern of north-south-trending mountain ranges and valleys," said Kent. "As the crust extended and thinned, it cracked, uplifting mountains and down-dropping valleys."
Around 6 million years ago, the scene changes dramatically again. For reasons not yet known, the active boundary between the Pacific and North steps eastward, something it had done before. Significant stretches of the southern boundary between the Pacific and North American plates move from offshore to beneath the continent itself. A new spreading center or rift forms beneath the Mexican mainland and, like a zipper opening, it pulls away part of that landmass, creating the Gulf of California.
That process, geologists believe, is ongoing. The Baja California peninsula continues to slide northwest, part of the Pacific plate. The zipper continues to open, causing the gulf to slowly become wider and longer.
"If you want to see our future," says Kent, "look at what's happened in the south."
Moveable east
In simplest terms, what's happening, said Kent, is that the Pacific and North American plates appear to be trying to readjust their partition line so that it runs more north-south.
"In oceans, we see evidence that ridges straighten over time," Kent said. "Large chunks of plate are transferred from one to another so that boundaries move in the easiest manner, with the least amount of work."
But in this case, there's a glitch. It's the San Andreas fault zone, created when part of the boundary moved east. That shift compelled the San Andreas to make a westward turn at the San Bernardino mountains, then curve back northeast along the old boundary through Southern California, up beneath the San Francisco peninsula, along the northern coast before finally veering out to sea near the town of Eureka.
This "big bend" acts like a giant speed bump, slowing plate motion and causing the San Andreas fault to become locked up. As a result, tectonic pressures accumulate until the overlying crust fractures, again and again.
Southern California boasts more than 300 faults, most of them active in varying degrees. When they shift, some pressure is released but more remains.
Researchers estimate about 75 percent of the movement between the Pacific and North American plates occurs in the San Andreas fault zone and adjacent offshore faults. The remaining quarter is accommodated farther east in a region called the Walker Lane belt.
Walker Lane is a north-south corridor of land that runs along the eastern side of the Sierras, from the southern tip of Nevada to south-central Oregon. This is where some geologists believe the Pacific and North American plates are trying to create their new, streamlined boundary.
"A more northward trajectory to the whole system through Walker Lane may ultimately be an easier path for the system to take," said Jim Faulds, a research geologist at the University of Nevada in Reno.
"In 10 million years – it could be more like 15 million – I would envision the San Andreas on the east side of the Sierra Nevada, extending from about the Salton Trough up the east side of the Sierras into western Nevada, through northeast California and finally to the southern or central Oregon coast."
Mobile home
Such a path would spell good news for temblor-terrified Southern Californians of the future. It would mean earthquake country had moved east across the ever-growing Gulf of California.
"It probably means much less seismic activity through most of California, especially in the Los Angeles and San Francisco areas," said Faulds, "but much more activity in places like Landers, Bishop, Reno, Lake Tahoe, Susanville and Klamath Falls."
In other words, Southern California would no longer be a seismic center. It wouldn't even really be southern anymore. Geophysicists project the region will drift more than 300 miles closer to Alaska over the next 10,000 millenniums. By A.D. 10 million, they estimate, San Diego will be where Santa Barbara is now; Los Angeles will have reached the latitude of contemporary San Francisco.
Over the past 5 million years, said Unruh, Walker Lane has gotten wider, the result of the Sierran microplate pulling away with the North American plate. One result has been the creation of huge valleys like the Panamint and Death Valley. Some of this land is below sea level; some will likely drop as a consequence of future plate movement.
In the scenario described by Kent, Unruh, Faulds and others, the Gulf of California in the future will slowly creep northward, its waters tracing the new tectonic boundary, filling low-lying areas along the way. The Salton Sea, for example, would eventually become part of a real sea.
To be sure, this is all well-educated speculation. Like a puzzle, California's geology contains lots of pieces, and geologists can't be sure some aren't missing. Predicting what will happen along a fault is a shaky science indeed.
"There are a lot of factors that come into play," said Tom Rockwell, a professor of geology at San Diego State University. "The San Andreas fault system is evolving, with new faults like the San Jacinto being created. In fact, the San Jacinto seems to be helping the San Andreas to straighten out. If that happens, who knows what comes next?"
There's a joke among geologists that if you get five of them together, you get six different opinions. What happens to California 10 million or 20 million years from now is, at best, an educated guess.
But one thing does seem certain: Unlike those TV ads promoting Las Vegas, nothing around here stays here.
Fascinating!
That reminds me, I need to get my subducts cleaned.
I suppose I could just subduct tape them like last year.
That's one way to keep the illegals out. Or in.
I've got some ocean front property in Arizona... from my front porch you can see the sea...
(Denny Crane: "Sometimes you can only look for answers from God and failing that... and Fox News".)
This would also explain the volcanism around Long Valley. If the ground is literally being pulled apart along the eastern Sierras, it's inevitable that some volcanic activity would make it to the surface.
Ground subsidence into the newly formed crack could also have some very negative implications for most of the Great Basin, and it's possible that much of modern Nevada could become seabed as a result. Even if it didn't sink far enough to drop below sea level, it's position in the Sierra's rain shadow...even if seperated by a narrow sea...would ensure that it remained desert-like. Nevada would likely resemble some of the African or Middle Eastern desert countries, with dry desert running right up to the seashore.
Some parts already are!
Nothing is falling into a pit!
The only question is, will it go down clockwise, or counter-clockwise?
>> There's a joke among geologists that if you get five of them together, you get six different opinions. <<
LOL. I heard a similar joke about economists: if you ask 100 a question you get 125 different answers.
>> What happens to California 10 million or 20 million years from now is, at best, an educated guess. <<
Many years ago Carl Sagan was a guest on a call-in talk show, when a frantic caller - a lady - asked,
"When did you say the earth would be engulfed by the sun?"
"About 10 billion years", Sagan replied.
"Thank God", said the lady. "I thought you said 10 million."
I bet you don't believe in the THEORY of gravity either, huh?
No wonder each auto trip to California takes a few seconds longer every decade or so!
Yeah.. hes correct..
Gravity is not understood to well either..
i.e. string theory.. and quantum mechanics..
It'll look more like the East Coast.
It'll look more like the East Coast.
Mountainous regions are created not only by continental collisions but also by volcanos, and by overthrusts.
BTW, there's a range in the Himalayas comparable to the Wasatch Front. It rose up over a very, very, very short period of time ~
All of the movements are occuring right now and can be measured with extreme accuracy with GPS.
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