June 30th in history:
A large explosion occurred a few miles over Siberia on June 30th, 1908, flattening trees and causing other extensive damage. The object that exploded is thought to have been a comet or meteorite, and the blast might have been one thousand times as powerful as the atomic bomb blast at Hiroshima.
On this date in 1956, two passenger planes collided over the Grand Canyon, killing all 128 people aboard the TWA and United flights. The planes were flying around clouds, and the pilots apparently didn’t see each other until it was too late. Wreckage from the planes still remains in the canyon. (Ironic note for fans of “Airplane!”: the pilot of the United flight was named Capt. Shirley.)
And on June 30th, 1859, French acrobat Charles Blondin made the first of his famous tightrope walks across Niagara Falls.