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El Salvador Geology
El Salvador, along with the rest of Middle America (a region
comprising mainly Mexico and Central America), is one of the most
seismologically active regions on earth, situated atop three of
the large tectonic plates that constitute the earth's surface.
The motion of these plates causes the area's earthquake and
volcanic activity.
Most of Central America and the Caribbean Basin rests on the
relatively motionless Caribbean Plate. The Pacific Ocean floor,
however, is being carried northeast by the underlying motion of
the Cocos Plate. Ocean floor material is relatively dense; when
it strikes the lighter granite rocks of Central America, the
ocean floor is forced down under the land mass, creating the deep
Middle America Trench that lies off the coast of El Salvador. The
subduction of the Cocos Plate accounts for the frequency of
earthquakes near the coast. As the rocks constituting the ocean
floor are forced down, they melt, and the molten material pours
up through weaknesses in the surface rock, producing volcanoes
and geysers.
North of El Salvador, Mexico and most of Guatemala are riding
on the westward-moving North American Plate that butts against
the northern edge of the stationary Caribbean Plate in southern
Guatemala. The grinding action of these two plates creates a
fault, similar to the San Andreas in California, that runs the
length of the valley of the Rio Motagua in Guatemala. Motion
along this fault is the source of earthquakes in northernmost El
Salvador.
El Salvador has a long history of destructive earthquakes and
volcanic eruptions. San Salvador was destroyed in 1756 and 1854,
and it suffered heavy damage in the 1919, 1982, and 1986 tremors.
The country has over twenty volcanoes, although only two, San
Miguel and Izalco, have been active in recent years. Violent
eruptions are rare. From the early nineteenth century to the mid1950s , Izalco erupted with a regularity that earned it the name
"Lighthouse of the Pacific." Its brilliant flares were clearly
visible for great distances at sea, and at night its glowing lava
turned it into a brilliant luminous cone.
Data as of November 1988
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