A mountain takes its own north face off

An earthquake shook loose the bulging north flank of Mount St Helens, and the largest landslide in recorded history uncorked the volcano sideways.

The blast flattened forest across 600 square kilometres in minutes, and the summit came down by nearly 400 metres. Because the mountain failed sideways rather than upwards, it is the standard textbook case for what a lateral blast does, and the reason volcanologists now watch for bulges.