What Happened When the US Set Off Nuclear Weapons in One of the Most Geologically Active Places on Earth?

One of the most common questions I get is whether a nuclear bomb could set off a volcano or trigger an earthquake. You might think that all that energy being released in the explosion would be perfect for getting faults or magma to move. So, would you believe that the United States set three nuclear bombs off in one of the most geologically active parts of the world … and nothing happened?

These days it is hard to imagine a world with nuclear testing. However, in the 1940s to 1990s, the US and USSR (amongst others) were setting off bombs like they were going out of style. In the air, on land, under the sea and eventually underground, these “experiments” were both means to develop even bigger weapons and displays of force. The consequences of many of these tests are still being felt thanks to the copious radioactive fallout produced.

One set of the over 1,000 nuclear explosions run by the US was conducted on Amchitka in the Aleutian Islands. Long Shot, Milrow and Cannikin were the code names given to three blasts performed from 1965 to 1971. This included the largest underground nuclear bomb ever detonated, the 5 megaton weapon as part of Operation Grommet.

The most astonishing thing about these tests is that Amchitka Island is in the middle of the Aleutian subduction zone, where the Pacific Plate is diving underneath the North American Plate. There are six potentially active volcanoes within 100 miles of the island. On top of that, the Rat Islands region has produced numerous and gigantic earthquakes across the 20th and 21st centuries. This area is highly volatile, geologically speaking.

So, why run nuclear tests there? For one, it is remote. Very few people live anywhere near these islands. It’s remoteness also allowed Amchitka to be a proxy for the USSR so that the US could work on methods to detect underground nuclear blasts from afar. The island previously hosted a US Air Force base during World War II that had over 15,000 soldiers stationed in this desolate island. This meant that the infrastructure for tests was there after the armed forces moved out.

The first nuclear test on Amchitka was 1965’s Long Shot. It was an 80-kiloton warhead that was used to test early methods of seismic detection of distant nuclear blasts. After that, nothing happened on the island again until 1969. It was realized that the Cannikin test was way too big to do in Nevada, so off to Alaska it went.

Let’s set out stage: the US planned to test a massive nuclear weapon in a shaft last 1 mile (2 kilometers) deep in a location that was volcanically and seismically active. Remember those six volcanoes with 100 miles? They include Semisopochnoi (currently erupting, and prior to test, 1873), Little Sitkin (last erupted 1830), Gareloi (last erupted 1989, and prior to the test, 1952), Davidof (Holocene), Segula (1600s?) and Kiska (last erupted 1990, erupting in 1969!)

On top of that, the M8.7 Rat Islands earthquake that generated a tsunami that swept across the Alaskan coast occurred ~30 miles from Amchitka on February 4, 1965. That was less than 9 months before the Long Shot test! It is hard to imagine how a massive earthquake could happen that close to the test site … and they still went ahead and did it! Combine that with the vivid memories of the 1964 M9.2 earthquake and tsunami in Alaska, and no wonder people were edgy about bomb tests.

Just to show how strange the pre-test ban treaty world was, the US Atomic Energy Commission set off a smaller (1-1.2 megaton, or 12-15 times larger than Long Shot) earlier to calibrate their sensors for the larger blast to come. Later, it was admitted that the Pentagon had run the Milrow explosion to also test if a big blast could, just maybe, cause an earthquake or eruption.

Although the tests were performed under the auspices of the US Atomic Energy Commission, they were really being done for the Pentagon. The Cannikin test was meant to investigate the feasibility of using a 5-megaton warhead as part of an anti-ballistic missile program (the Spartan Missile). Although there was a lot of resistance to the test (see below), President Nixon still went ahead and ordered the test to proceed (with support from the Supreme Court).

Cannikin went off on November 6, 1971. It produced a M7 earthquake from the blast. You can see in this video how the land surface jumped as much as 20 feet during the explosion as the shockwave moved across the island. Thousands of birds and otters died in the shockwave. A crater over a mile wide was produced but even with the same energy released as the 2010 earthquake in Haiti, no tsunami was generated. Supposedly, very little radiation was detected either. In the eyes of the US Atomic Energy Commission and the Pentagon, it was a great success.

Here we have a real-world example of setting of nuclear bombs, some of which buried deep underground, in a place where such an event could conceivably trigger eruptions or earthquakes (or so we’re led to believe in science fiction). Three explosions, all between 1969 and 1971. All right in the middle of an active subduction zone. So, what happened afterwards?

The answer is “not much.” At least in the half a century since the Cannikin explosion, nothing out of the ordinary has occurred in the region about Amchitka. No volcano erupted in the 100 mile zone from the blast until Semisopochnoi in 1987. Since then, there have been documented eruptions at that volcano and Kiska, but that’s about it. The Rat Islands experienced multiple large earthquakes, most recently a M7.9 in 2014, but that is normal for this stretch of the Aleutians. For all intents and purpose, the planet shrugged off the blasts.

The one long-term impact of the tests is the groundwater of Amchitka. Although little radiation was detected directly after the blast, water percolating through the underground remains of the Cannikin blast becomes radioactive. The US Department of Energy doesn’t agree with findings that show elements like plutonium in groundwater at Amchitka, but it does seem that the island still feels the effects of those blasts even today.

The other impact is a human impact. By the late 1960s, environmentalists became increasingly enflamed by the frequency of nuclear weapon tests … and rightly so. The amount of fallout produced by these tests is clearly seen in the deep-sea sediment and ice core records. When word got out about the immense Cannikin test, a group headed out in a rented boat they dubbed “Greenpeace” to try to stop the test, both in fear of fallout and the potential for triggering another earthquake and tsunami like the M8.7 event in 1965. Stormy weather with winds over 120 miles per hour prevented the ship from reaching Amchitka for the test, but the name “Greenpeace” remained as the environmental organization we know today.

Maybe the myth that we can set off eruptions and earthquakes using nuclear weapons can be (partially) put to bed. The only earthquake caused by these explosions were, well, caused by the explosion. Little evidence exists to suggest that the blasts had any trigger effect on faults and volcanoes near Amchitka. However, the enduring impact on the island remains as the copious radioactive elements made when we try to come up with ways to destroy us all keep seeping from their tomb underground.