On May 18, 1980, following a period of heavy tremors and small eruptions, the north face of Mount St. Helens slid off in the largest landslide in recorded history before erupting violently, destroying a large part of the top of the volcano. The eruption flattened the forest up to 20 km north of the volcano, killed 57 people, flooded the Columbia River and its tributaries with ash and mud, and blanketed large parts of Washington eastward and other surrounding states in ash, making day look like night.