The eruption of Mount St. Helens on May 18, 1980 was one of the most destructive events in the history of the United States. Within hours, the north side of the volcano collapsed, creating a huge landslide — the largest debris avalanche in recorded history. The avalanche quickly moved to the surrounding lakes and valleys, leaving a trail of destruction 27 km long. Located just 5 miles north-northeast of the volcanic crater, Spirit Lake experienced the full impact of a side blast.
Approximately 1 million trees were blown off the surrounding slope by a superheated wall of volcanic gas, searing ash and rock, eventually crashing into the lake. A debris avalanche temporarily moved much of the lake out of its bed, causing waves 180 meters high to crash into the mountain range north of the lake. As the water rushed back into its pool, it pulled thousands of tree trunks with it. These tree remains formed a floating raft on the surface of the lake, still standing today, more than three decades after the eruption.
Before the eruption, Spirit Lake was a popular and very beautiful place to relax. Six beach campsites and many summer cottages were built. All this was destroyed, and today Spirit Lake is a wasteland with thousands of tons of tree debris and volcanic rock.
When scientists saw the massive destruction, they realized that nature provided them with a rare opportunity to study the bacteriological and chemical transformations, as well as the biological restoration of the lake. To ensure the protection of Spirit Lake and other regenerating ecosystems in the 220 square mile affected area, the St. Helens Volcanic National Monument was created in 1982. Fishing and other recreational activities are prohibited here, potentially interfering with the restoration of Spirit Lake. This is one of the main reasons why no attempt has been made to restore anything in the affected area.
This photo clearly shows the exploded crater of Mount St. Helen with Spirit Lake at the foot: