Mount St. Helens National Volcanic Monument – South Side
Washington State Road 503
From I-5 take exit 21 (Woodland) and follow Road 503 East. After the town of Cougar, turn into Road 83 and follow the signs to Lahar and Lava Canyon.
When the volcano erupted in May 18, 1980, large portions of the glaciers on the east side of the volcano melted and created a large lahar (volcanic mudflow). The debris went into Pine Creek and Muddy River. Lava Canyon was flooded with raging water, boulders, and trees. The mudflow permanently altered the landscape, revealing numerous ancient lava flows.