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TSUNAMI WARNING

An earthquake of 8.1 magnitude off the southern coast of Peru generated a tsunami warning clear up here at my house on the southern Oregon coast. What's up with that? Why does Peru have so many earthquakes? What's going on down there anyway?

The reason for the earthquakes is also the reason for the Andes, and the reason for the rich coastal fishing off of Chile and Peru. It's a huge trench in the floor of the ocean, 1100 miles long and over 5 miles deep. The Peru-Chile Trench, as it's called is a subduction trench. It's formed because a hunk of the earth's crust under the Pacific Ocean, called the Nazca Plate is sliding underneath the hunk of earth called the South American Plate that (duh!) the South American continent is riding on. As the Nazca Plate is forced underneath, it bends down, forming this huge, deep ocean trench. The heat generated by the plates rubbing against each other makes magma or melted rock. This magma pool building up underneath Chile and Peru, and the crumbling effect on the South American Plate has formed the Andes Mountains. In a span of just 50 miles, the earth's crust here rises from 23000 feet below the oceans surface to 19000 feet above it. It's one of the most dramatic changes in elevation in the world today.

So anyway, all this rock grinding against other rock doesn't always go smoothly. Sometimes there's a hangup, and the pressure builds as these plates keep pushing. When the force from these two massive chunks of land becomes greater than the obstacle keeping them from moving, there's a huge sudden slip of the plates. And that's what causes the earthquake. And the tsunamis. Pretty cool stuff. It's called plate tectonics, and I learned about it in school, but like a lot of things, I wasn't too impressed by it then.

The Peru-Chile trench also affects the sea life off the western coast of South America. Cold water from the depths of the trench is sucked to the surface by the prevailing trade winds and ocean currents. This water is rich, very rich in nutrients and food, and causes the pelagic fishing off the coasts of Peru and Chile to be among the finest in the world. Under normal circumstances, that is. Recently, El Nino has disrupted that pattern, and the rich waters haven't been surfacing. Accordingly, the fish have moved elsewhere or died off, and the fisheries industries of Peru and Chile have been devastated.

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