On this day in 1984, Japan Airlines cargo flight 36, en route to Anchorage from Tokyo, encountered a mysterious mushroom cloud approximately 200 miles in diameter that rapidly rose to a height of 60,000 feet. Lack of residual radiation ruled out a nuclear weapons test, nor was there any volcanic activity in the region. The event has been likened to the 1908 Tunguska explosion; in that it has never been explained.