Super-Kamiokande is the world's largest underground neutrino observatory. A joint Japanese-American facility, it is located in the Kamioka Mine, about 200 kilometers north of Tokyo. It consists of a tank of ultra-pure water, 40 meters in diameter by 40 meters tall, that is monitored by thousands of sensitive phototubes. Super-Kamiokande was badly damaged in November 2001 when a large number of the phototubes imploded in a chain reaction. However, repairs were carried out following an inquiry into the accident and the observatory resumed collecting data in January 2003.