Funny! The only way Southern California could
separate from the rest of California in thirty
years is if: (a) they establish themselves as an
independent state, or (b) there was a GIGANTIC
landslide and the entire land area fell into the
ocean. If the latter did happen, Southern
California would indeed separate from the rest of
California, but would no longer be above the
Gigantic landslides have occurred (the
Nu'uanu landslide, in which one-third of O'ahu
fell into the ocean, e.g.) but I don't think this
is a realistic assumption for California. The
bulk of the US (the part that sits on the North
American plate and includes northern and central
California) is moving northwest and the little strip of landmass that is on the Pacific plate (from San Francisco south to the tip of Baja) is also moving northwest but at an even faster rate, so it's separating from the rest of California. (Geologists map faults in such a way as to indicate the relative direction of movement, so it looks like the North American plate is actually moving southeast, but it's not. This is if you look at long-term averages. The reality is that the plate boundary is really a system of faults, some of which are moving horizontally and some of which are moving vertically (as in the case of the North ridge earthquake), and none of which are really moving at the same rates or at the same time.
The most famous fault is the San Andrea's Fault. It is one of the best-studied faults because it's above ground and easy to study and because it generates high-energy earthquakes near
densely-populated cities like LA and San
Francisco, so there is a lot of work to try and
predict the next "big one" so people can evacuate.
There are many other faults that make up this
system, including the Hayward, Calavaras, Concord,
Greenville, Rodgers Creek, San Gregorio, and San
Jacinto faults, to name a few.
Movement along faults isn't really uniform but is sort of "herky-jerky". The idea is that the faults are usually locked shut, causing pressure to build up in the rocks on either side of the fault from motion far away, along other regions of the plate boundary. This pressure causes the rocks to stretch and bend until they give way. At this point, the rocks along the fault rupture and move all at once. Then they lock up again, and the whole process starts over ("elastic rebound theory").
Based on past rates of movement, it took
about 20 million years to move the Pacific Plate
north about 200 miles. A good map/math exercise
would be to have your students look at a map of
plate boundaries, estimate the distance that the
Pacific plate would have to move to separate LA
from the rest of California by a narrow ocean (the
map would have to have a scale on it), have them
calculate the past rate of plate movement (200
miles/20 million years = 10 miles every million
years, or use the more current estimate of 37
miles every million years) and then have them
predict how long it would take, assuming the
plates don't change direction or speed. (Hint:
it's not 30 years.)
Geologists make these sorts of assumptions all the time. In technical terms, these assumptions are called "uniformitarianism" (the idea that "the past is the key to the future").
In the 1970's there were fears that San Francisco would fall into the ocean, and that hasn't happened. I think there was a song about it. When a non-scientist makes a claim about something as unrealistic as Southern California breaking away from the continent in 30 yrs, you can reliably assure them that it isn't true and they don't need to worry. I've heard about the
possibility of Southern California and Northern
California becoming different states, and I suppose that's possible in the next 30 yrs; do you suppose that's what the student was hearing
Here's a website from the US
Geological Survey about earthquakes hazards:
has Frequently Asked Questions and other info.
I'm going to start from the beginning.The
uppermost part of the Earth is composed of rigid
plates called lithospheric plates, which move over time. This process of shifting plates is called plate tectonics. Where plates collide, mountain chains and volcanoes form. This is happening today along the northwestern coast of the U.S. (OR and WA), along the coast of Chile, and in the Himalayas, for example. Where plates separate or rift apart, large basins form. Major rifts occur, for example, at the bottom of the Atlantic Ocean, forming the ocean basin.
A third type of relative plate motion is where plates grind past one another but aren't colliding or separating. This is what is happening now in southern California. The San Andres Fault separates the rest of North
American (which sits on the North American plate)
from southern CA (which sits on the Pacific
plate). Relative to North America, the Pacific
Plate carrying southern CA is moving north at a
rate of somewhere around 20-40 mm/yr. So,
southern CA is not tearing away from the rest of
the country only moving slowly north, a trip that will take millions of years.
The San Andrea's Fault is dragging the western
side of the fault, including Southern California,
northward relative to the rest of North America.
It's not so much separation as it is dragging, so it will never be completely separated. It moves a little bit each year (a few millimeters), or a bit more during a major earthquake (up to a few meters).
At the current rate, it will take western
California about sixty million years to reach
Alaska. >Baja California, on the other
hand, is separating and already has, hence the
Gulf of California's existence. It is now going to
get dragged north with the rest of southwestern
California northward to Alaska.
Click Here to return to the search form.