What was the last high-yield thermonuclear weapon design test conducted by the US at Bikini Atoll?
Castle Bravo
When Bravo was detonated, within one second it formed a fireball almost 4.5 miles (7.2km) across. This fireball was visible on Kwajalein atoll over 250 miles (400km) away. The explosion left a crater 6,500 feet (2,000m) in diameter and 250 feet (76m) in depth. The mushroom cloud reached a height of 47,000 feet (14,000m) and a diameter of 7 miles (11km) in about a minute, a height of 130,000 feet (40km) and 62mi (100km) in diameter in less than 10 minutes and was expanding at more than 100 meters per second (360km/h; 220mph). As a result of the blast, the cloud contaminated more than 7,000 square miles (18,000km2) of the surrounding Pacific Ocean, including some of the surrounding small islands like Rongerik, Rongelap, and Utirik.[28]