What Is the Floating Log Raft Still Drifting Across Spirit Lake?

When Mount St. Helens erupted on May 18, 1980, the blast sent a wall of water surging up Spirit Lake’s slopes, and when it crashed back down, it dragged thousands of uprooted trees with it — creating a floating log raft that has drifted across the lake for more than 40 years.

What Happened to Spirit Lake During the Eruption

The May 18, 1980 eruption of Mount St. Helens triggered the largest landslide in recorded history. The debris avalanche dumped so much rock and sediment into Spirit Lake that the lake bottom rose nearly 300 feet. The surface rose about 200 feet — roughly the height of a 20-story building — buried under rubble in a matter of minutes.

The eruption also decapitated the mountain itself. Mount St. Helens lost approximately 1,300 feet of its summit, dropping from 9,677 feet to 8,365 feet in elevation. Fifty-seven people lost their lives that day.

How Did a Million Trees End Up in the Lake

The lateral blast from the eruption flattened entire forests across a wide swath of the surrounding landscape. When the lake’s water was violently displaced up the hillsides by the landslide, it stripped and carried thousands of trees back into the lake as it slid back down. Estimates suggest roughly one million trees were sent into or toward the lake, forming a dense, tangled raft of logs that at its peak covered most of Spirit Lake’s surface.

Why the Log Raft Is Still There Decades Later

The sheer volume of timber deposited in the lake explains the raft’s longevity, but its slow disappearance is equally remarkable. Wave action continuously strips bark and branches from the floating trunks. That bark and woody debris sinks to the lake bottom, accumulating in thick organic layers. Over time, logs become waterlogged and slip beneath the surface entirely. The raft is shrinking — it once blanketed most of the lake, and today it covers roughly a fifth of the surface — but the process is gradual, playing out across decades rather than years.

The Drain Tunnel That Saved Downstream Communities

Spirit Lake posed a serious secondary hazard after the eruption. The debris dam holding the lake back threatened to overflow or collapse, which could have unleashed a catastrophic flood on downstream communities. To prevent this, the U.S. Army Corps of Engineers drilled a 1.6-mile tunnel through solid bedrock to permanently drain the lake to a safe level. The tunnel was completed in 1985 and continues to regulate Spirit Lake’s water level today.

What Is Happening at the Bottom of Spirit Lake

The sunken bark and wood accumulating on the lake floor is far from inert. It feeds insects and microbes that form the base of Spirit Lake’s food web — an ecosystem that had to rebuild itself almost entirely from nothing after the eruption sterilized the lake. Today, rainbow trout thrive in Spirit Lake and grow to unusually large sizes, sustained by the rich biological community that the log raft’s slow decay has helped support. The disaster that nearly destroyed the lake is, in a quiet way, still feeding it.