Wikipedia
Elugelab (or Elugelap; Marshallese: , ) was an island, part of the Enewetak atoll in the Marshall Islands. It was increased in size, and then destroyed by the world's first test of a hydrogen bomb on 1 November 1952, by shot " Mike" of Operation Ivy. Prior to being enlarged, and destroyed, the island was described as "just another small naked island of the atoll".
The fireball created by Ivy Mike had a maximum radius of . This maximum is reached a number of seconds after the detonation and during this time the hot fireball invariably rises due to buoyancy. While still relatively close to the ground, the fireball had yet to reach its maximum dimensions and was thus approximately "three and one quarter" miles (5.2 km) wide.
The detonation produced a crater in diameter and deep where Elugelab had once been; the blast and water waves from the explosion (some waves up to twenty feet high) stripped the test islands clean of vegetation, as observed by a helicopter survey within 60 minutes after the test, by which time the mushroom cloud had blown away. The island "became dust and ash, pulled upward to form a mushroom cloud that rose about twenty-seven miles into the sky. According to Eric Schlosser, all that remained of Elugelab was a circular crater filled with seawater, more than a mile in diameter and "fifteen stories deep". The blast yielded 10.4 megatons of explosive energy, 700 times the energy that leveled central Hiroshima.
Aerial footage of Elugelab and adjacent islands well before Mike shot at a time prior to the connecting causeway being created is available, as is footage after the causeway was finished that supported the diagnostic Krause-Ogle box light pipe system, with numerous trees removed in preparation of the shot also plainly evident, along with footage of the aforementioned helicopter survey of the Mike crater soon after the detonation, and finally, high altitude footage of the crater accompanied with details of its depth - "175 feet deep" - equivalent to the height of a "17 storey building" and with an area large enough to accommodate about "14 pentagon buildings".
The detonation also collapsed some natural crevices in the reef, some distance away from the rim of the crater.
Full radioecology recovery surveys were documented before and after each test series. For a brief online introduction into some of these studies - with specific reference to the ecological effects of the 1.69 megatons Operation Castle Nectar shot, detonated in 1954 on a barge just north east of the crater of the 10.4 megatons Ivy Mike thermonuclear test - see 1 a report by the University of Washington's Laboratory of Radiation Biology and 2.