The AEC sets off a five-megaton bomb under Amchitka; the ground lifts 20 feet
On November 6, 1971, the Atomic Energy Commission detonated Cannikin, an announced five-megaton warhead test, deep beneath Amchitka Island in the Aleutians. The ground lifted 20 feet, driven by a force almost 400 times that of the Hiroshima bomb. Environmentalists had warned of earthquakes and a tsunami, and a divided Supreme Court had declined to block the test. Cannikin remains the largest underground nuclear explosion in American history.
President Richard Nixon personally authorized the $200 million test over objections from Japan, Peru, and Sweden, to prove a warhead for the Spartan anti-ballistic missile. The fight to stop it sent a chartered ship named Greenpeace toward Amchitka and made a remote Alaskan island a landmark in American environmental politics.
QHow was a five-megaton warhead lowered into the ground at Amchitka, and how big was the hole?
The test site was a shaft 1,870 metres (6,150 ft) deep and only 2.3 metres (90 in) wide, which put the bottom of the hole more than a mile down. Some 400 tons of equipment went into it along with the device. Cannikin was the largest underground shot the United States ever fired, and the hole that held it was narrow enough that its depth was roughly 800 times its width. Preparing the site was a separate job from preparing the warhead, and it ran inside the five years of work the test required.
QWas Cannikin's yield really five megatons, or is the number softer than it sounds?
Five megatons (21 PJ) is the announced figure, not a measured certainty. Published estimates of the precise yield run from 4.4 to 5.2 megatons, or 18 to 22 PJ, a spread of about 0.8 megatons. The announced number sits inside that range rather than at either end. The test point itself was fixed with precision, at 51°28′13.20″N, 179°6′40.75″E, less than a degree of longitude short of the 180th meridian. The location is known to the second, and the yield is known only to within a range.
QWhat did a 1996 Greenpeace study claim was seeping out of the Cannikin site?
A 1996 Greenpeace study found that Cannikin was leaking plutonium and americium into the environment. Later studies found no indications of radioactive leakage. Concern has continued that new fissures may be opening underground and letting radioactive material reach the ocean. The Department of Energy keeps monitoring the site under its remediation program, which is expected to run until 2025. After that, the plan is to turn Amchitka into a restricted-access wildlife preserve. The group that gave its name to a protest ship in 1971 was still testing the island's soil a quarter-century later.
