Largest  crater from an underground nuclear explosion
Semipalatinsk Test Site
Kazakhstan (Semipalatinsk Test Site)
A 104 kiloton nuclear device was detonated at the Semipalatinsk Test Site, Kazakhstan 178 m. (583 ft.) beneath the dry bed of the Chagan river on January 15, 1965, leaving a crater 408 m. (1338 ft.) wide with a maximum depth of 100 m (328 ft.). A major lake later formed behind the 20-35 m. (65-114 ft.) upraised lip of the crater, which was then cut through with earthmoving equipment to allow it to be used as a reservoir. The Soviet test was a near-copy of the US Sedan test explosion of 1962 at the Nevada Test Site, which resulted in a crater 390 m. (1,280 ft.) wide with a maximum depth of 97.5 m. (320 ft.). The Kazakh crater is known locally as Lake Chagan. Its crater slopes later subsided, reducing its storage capacity by a quarter. A water control structure was later built on the left bank of the river to control water levels. Water from the reservoir is drunk by local cattle. The head of the Medium Machine Building Ministry, responsible for the Soviet nuclear effort, is supposed to have taken a swim in the lake to prove the water's safety.