Geology (cont. 12)

Geology

The rest of the story is in the present. Batiquitos Lagoon exists today because the ice sheets of the last ice age melted 11,000 years ago and sea level rose, flooding the deep stream valley. (This makes our “lagoon” technically an estuary rather than a lagoon, as are the others along the coast of San Diego County. Lagoons are bodies of ocean water, which have been cut off from the sea by sand deposits, and they have no freshwater streams flowing into them, according to geographic definitions. But our estuaries carry the word “Lagoon” in their names, so “Lagoons” they will remain.)

 

Lagoons and estuaries are not permanent features, however. Sediment coming into them is rarely all cleared out by tides. San Marcos and Encinitas creeks, entering Batiquitos at the eastern end, drop their sediment when they reach still water, and muds brought in by tides get dropped into the Lagoon as well. The Lagoon silts up. Our Lagoon would have disappeared with this natural process, had it not been rescued by dredging so that it can once again be a flushing tidal lagoon. New sediments are always being deposited. Human intervention has been necessary often since the Lagoon was restored in the mid-1990s. And, by the way, we are only in a warm interglacial period. If global warming doesn’t stop it, a new ice age could once again lower sea levels around the world, draining the Batiquitos of ocean water. Right now, however, sea level appears to be rising slightly around the world.

 

Because we are on a slice of the Pacific Plate and will continue to move, earthquakes will continue to shake and possibly raise the land again. So this is not the end of the geologic story of Batiquitos Lagoon. Come back and visit in 100,000 years and see if there is still a Lagoon here, and if there are new “mesas” in San Diego County.   

   

Joan K. Lubowe

Revised 12-28-04

SOURCES:

Abbott,Patrick. 1999. The Rise and Fall of San Diego. Sunbelt Publications

 

Bergen, et al.  1997. Geology of San Diego County. Sunbelt Publications.

Educational materials prepared for the San Diego Natural History Museum.

 

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