On May 18, 1980, a violent eruption blew the top off Mount St. Helens. A landslide covered 24 square miles around, clouds of ash blew up fifteen miles in the air, hot pumice poured down the volcano, heat from the volcano melted snow, causing huge mud flows that roared down the valley. Instead of a snow-covered peak, it was now a crater two miles long and 2,000 ft deep, and the mountain was a much shorter.
Tip: For the west side of Mount St. Helens, follow Route 504 to the end of the road at the Johnston Ridge Observatory, which has the best view of the volcano. The road ends at the Johnston Ridge Observatory, you'll have to return the way you came.
To get to the south side, from Interstate 5, take Route 503 east through Cougar, and follow signs to Ape Cave.