Tag Archive: earthquake

Today is the 50th anniversary of the 1964 Alaska Earthquake.

I still remember it, though I was over 300 miles from the epicenter, on the campus of the University of Alaska Fairbanks where I was a graduate student. I had a basement apartment that year, and shortly before dinner the hangers started rattling in the closet. I’d never been in an earthquake before, but when the shaking continued it occurred to me that a basement might not be the safest place. It took me a while to grab a coat and climb the stairs, but when I got outdoors, the flagpole and trees were still swaying and the ground was still shaking.

Were earthquakes supposed to last that long? I wondered as I headed for the university dining commons. The sidewalks were icy, and I slipped and fell, dislocating my knee (a common occurrence at that time) and doing something to my elbow. As usual, I asked a passing student to help me straighten the leg while I put pressure to get the kneecap back in place. (At this time the joint was so used to dislocating I was able to get up and walk as soon as the dislocation was reduced, though I trouble getting everything in place without help.)

In the cafeteria all of the discussion was about the earthquake, and some pretty wild rumors were circulating. (Anchorage had fallen into the ocean; other cities in south central Alaska were wiped out.) As I recall, the phone lines were out and it took a while to find out what had really happened—which was bad enough, even if not as bad as the worst rumors.

Television would have been no help even if I had owned a set. This was before satellite communications, and television news was flown to Alaska (and within Alaska) on tapes to be shown the next day if we were lucky. Even the radio news was pretty confused at first, as most of the news from Anchorage arrived (I think) via shortwave radio hams. (That was definitely true a few years later during the Fairbanks flood.)

As it turned out, Anchorage suffered most from the direct effects of the shaking, but the greatest losses of life were in coastal communities – Valdez, Seward, Kodiak – which were struck by tidal waves triggered by the earthquake.

I’ll be taking an adult learning class next month about the earthquake, and while I understand the basic geophysics of what happened, I hope to learn more. Maybe I’ll do a blog on it. But for now, I wanted to remember the 50th anniversary of the Good Friday Earthquake.

I’m sure you’ve heard, ad nauseum, about the plate tectonics underlying the earthquake and tsunami in Japan. Indeed, it seems that plate tectonics, which produces earthquakes, volcanoes and tsunamis with devastating consequences is a force of destruction, pure and simple. But does it have a positive side as well?

The theory of plate tectonics, which at this point does the best job of explaining the earth’s geology, is based on the idea that the earth’s surface is made up of a number of semi-rigid plates which slide around over the earth’s surface. They interact primarily at their edges, where they may be pulling apart (as in the mid-Atlantic and the African rift valleys) sliding past each other (as in the San Andreas fault of California) or colliding.

Plates are made up of ocean crust, sometimes with relatively light continental crust on top. Ocean crust is dense enough to slide under other plates; the lighter continental rock above it resists being pulled under, and buckles or folds if it is on top of two colliding plates. Thus collisions of two plates with continents on top generally leads to mountain ranges such as the Himalayas.

Collisions between ocean plates and plates with light continental rock atop generally lead to subduction zones, such as the one off the west coast of South America, where the oceanic crust is pulled under the lighter continental crust. The sediments pulled down with the ocean crust are gradually heated and melted, reappearing as volcanic magma. Thus the volcanic spine of the Andes.

If two oceanic plates collide one is normally pulled under the other, but it is less obvious which will be subducted, and in fact this may change over time. The same melting of sediments occurs, and a line of volcanoes, such as the Aleutian Islands, normally develops next to the subduction zone.

Plates don’t slide past each other smoothly. They stick and then break loose, producing earthquakes. If they are just sliding past each other they may produce earthquakes but there is generally not much vertical movement. If one plate is being pulled under another, however, the sticking normally results in a bowing up of one plate, and when that sticking is released, there may be considerable vertical movement. If that movement is under water, a tsunami is created. This is what happened with the great Alaska earthquake, and has now happened off the coast of Japan.

But what would happen if the plates all just stopped? If there were no more plate tectonics? More, if there had never been any plate tectonics?

First, the earth would be flat and completely covered with water, if there were any water on the face of the earth. Mountains are constantly being eroded by the forces of weather. Given far less geologic time than has actually passed, any initial irregularities in the surface of the earth would have been smoothed out. Plate tectonics is and has been the main mountain builder on our planet.

Second, there is some question as to whether we would have an atmosphere. Certainly we’d have a hard time breathing the mixture of carbon dioxide, water vapor and other compounds put out by volcanoes, but then we’d have a hard time breathing the atmosphere prevailing when life evolved. Plants convert the gasses produced by volcanoes into an atmosphere we can breathe.

Third, plate tectonics is part of the way radioactive heating in the earth’s core is transferred to the surface. It’s one of the reasons we don’t have the radical resurfacing we think we see on Venus.

Plate tectonics can certainly produce devastation, but like weather, it’s something we have to live with. Japan has actually done a superb job of preparation, but there are prices we must pay for living on a dynamic planet, one which can support life. One of those prices has just come due.