Rat Islands and Atomic Bombs

Amchitka is one of the Rat Islands--35-miles long and only 3-miles wide.  It is located near Kiska and very near the epicenters of those 1957 and 1986 earthquakes of magnitude 8.0 or larger.  The Google Earth image below shows the relative positions of Amchitka and Kiska, the two large islands in center of the image; the Aleutian Trench, part of which is called James Canyon along the bottom of the image; and Buldir Island, where the last remnant of the Aleutian Canada Goose population was found in 1962, in the upper left-hand corner of the image.  Of course, we now know that the very deep Aleutian Trench is actually there because the Pacific Plate is being subducted beneath the North American Plate, on which all these islands are located.  Can you see that when you look at James Canyon in the photo?  And, from the image, you can easily understand why so many of those earthquake epicenters shown along the Aleutians in the last post seem to be located just south of the islands.

Just before the Japanese abandoned Kiska in 1943, Amchitka became a major U.S. military base, but it closed after the war.  In the early 1960's, the U. S. Atomic Energy Commission created a nuclear testing facility on this island.  The WWII-vintage airfield and base camp were reused by crews preparing for underground nuclear tests. 

The first test was an 80-kiloton bomb known as "Long Shot," located 2,400 feet below the surface and detonated on October 29, 1965.  The second, "Milrow," was a one-megaton device located 4,000 feet below the surface and exploded on October 2, 1969.  The third, "Cannikin," was a 5-megaton bomb detonated 6,000 feet below ground level on November 6, 1971.  However, the morning before the Cannikin blast, the test site had hard rain and wind gusts up to 124 miles per hour.  Man may be able to destroy whole cities, but can't control Aleutian weather! 

Cannikin did come as close to being more powerful than nature than anything else man has ever built.  It was the largest underground nuclear explosion in U.S. history.  Some Alaskans, still rebuilding 7 years after the Good Friday Earthquake, were concerned that the explosion could trigger another “Big One.”  In fact, two days after the explosion, a crater more than a mile wide and 40 feet deep did form above the blast site.  But Cannikin generated no 1964-sized earthquakes on the mainland despite producing a shock wave registering magnitude 7.0.  And no Aleutian volcanoes immediately began erupting.

Although I had no role in these tests, I was working in the Denver office of the Engineering Geology Branch of the USGS during the last two tests.  Several other geologists and technicians in my branch were working on all three tests—interpreting post-blast geologic data from the 1965 test and pre-blast data for the second two.  Several of my co-workers also spent months each summer during 1968-1971 performing fieldwork for these tests.  They drilled into the rocks of the test sites to obtain a set of rock “cores” that could be used for geologic interpretation of the blast zone.  These cores and simultaneous geophysical tests were also used to locate faults on which movement might be triggered by the blasts.  But the topics that they most often talked about when they returned to Denver were the poorly-maintained, WWII-vintage “deuce-and-a-half” (2-1/2 ton) trucks they had to use on Amchitka, the difficulty of getting supplies and spare parts for the drill rigs, and—now here’s a surprise—that they had to work outside every day in horrible Aleutian weather!  Of course they couldn’t really talk about the tests themselves because they were classified.

The Amchitka nuclear test facility closed in 1994.  But a government clean-up of the residual radioactive, chemical, and other hazardous waste left on the island continued for years after that.  Today, the buildings, roads, and airfields are gone and Amchitka's World War II role is just a memory, although their sites can still be picked out on Google Earth.  And, apparently, a small plaque commemorating the Cannikin blast is the only reminder of the island’s role in the Cold War.  Well, that and the fact that the island is still off-limits to visitors.  Fortunately, I didn’t have a role in the Amchitka cleanup.

Next time: We are getting anxious to get on the road—only another week to go!  But first, a brief discussion of faults—not the “it’s your fault!” kind, but the geologic “break,” “fracture,” “slip” kind that sometimes generate earthquakes.  The San Andreas Fault in California may be the one we most often hear about because it is responsible for earthquakes in heavily populated Los Angeles and San Francisco.  This post will introduce you to the Fairweather Fault, which is similar to the San Andreas in the way it moves, but much longer and with the potential to generate even larger earthquakes!