Realizing their dangerous situation, the pilot put the plane into a steep dive to gain speed, and thus was able to outrun the rapidly mushrooming eruption cloud that threatened to engulf them. The Stoffels were fortunate to escape, and other scientists were fortunate to have their eyewitness account to help unscramble the sequence and timing of the quick succession of events that initiated the May 18 eruption. The collapse of the north flank produced the largest landslide-debris avalanche recorded in historic time. Detailed analysis of photographs and other data shows that an estimated 7-20 seconds (about 10 seconds seems most reasonable) elapsed between the triggering earthquake and the onset of the flank collapse. During the next 15 seconds, first one large block slid away, then another large block began to move, only to be followed by still another block. The series of slide blocks merged downslope into a gigantic debris avalanche, which moved northward at speeds of 110 to 155 miles an hour. Part of the avalanche surged into and across Spirit Lake, but most of it flowed westward into the upper reaches of the North Fork of the Toutle River. At one location, about 4 miles north of the summit, the advancing front of the avalanche still had sufficient momentum to flow over a ridge more than 1,150 feet high. The resulting hummocky avalanche deposit consisted of intermixed volcanic debris, glacial ice, and, possibly, water displaced from Spirit Lake. Covering an area of about 24 square miles, the debris avalanche advanced more than 13 miles down the North Fork of the Toutle River and filled the valley to an average depth of about 150 feet; the total volume of the deposit was about 0.7 cubic mile. The dumping of avalanche debris into Spirit Lake raised its bottom by about 295 feet and its water level by about 200 feet. - NEXT PAGE - - NEXT PAGE - Schematic cross sections of Mount St. Helens showing the cryptodome of magma that produced the bulge and the three major blocks that collapsed to form the debris avalanche (After USGS Professional Paper 1250). Compare with photographs in "The Catastrophic First Minute."
May 18, 1980 activity 1300 ft of the summit vanished Debris avalanche was more than half a cubic mile 235 square miles were devastated by blast cloud and volcanic debris 57 people dead or missing Miles of road and bridges destroyed Crater left was 1.2 miles wide, 2.4 miles long, 2000 ft deep
Current eruption over The nearly three and a half years of eruption at Mount St. Helens is over for now and on July 10, 2008, scientists lowered the volcano alert level from Advisory to Normal and the aviation color code from Yellow to Green. Mount St. Helens reawakened in October 2004 when four explosions blasted steam and ash up to 10,000 feet above the crater. Growth of this lava dome continued until late January 2008. Five months have passed with no signs of renewed eruptive activity. Earthquakes, volcanic gas emissions, and ground deformation are all at levels seen before the eruption began.