akes, hundreds of small phreatic (steam blasts) , explosions and the north side bulge. A magnitude 5.1 earthquake below the volcano at 8:32 am started the eruption. MSH is still a potentially dangerous and active volcano even though it has been quiet since 1995. In the last 515 years there have been four major eruptions and dozens of lesser eruptions. Two of the eruptions were only two years apart. In 1480, the eruption was about five times larger than the one in May 1980. There have been even larger eruptions during MSH' 50,000 year lifetime. After the May 18, 1980 eruption, there have been five smaller explosive eruptions over a five month period. Since then, there have been 16 dome building eruptions through October 1986 when the new dome in the crater was formed. As the mountain was torn open, the pressure in inside was suddenly relieved. The rock shattered inside the mountain was exploded out the top at speeds over 200 miles per hour. The blast was so strong that it leveled whole forest of fir trees. Geologist call this a "stone wind" since the winds carried the rocks form the blast with them. The rocks gave the winds extra force that let them flatten the trees. 150 square miles of land was leveled. The edges of this area also lost their forested areas from the heat of the blast and the fires it caused. The original blast of the volcano only lasted 10 to 15 minutes. It quickly started up again. A dark cloud of ash and gases went up for miles into the sky and spread for miles in every direction, but mostly eastward. Forest fires broke out everywhere. After abut four hours, the color of the ash became much lighter since the volcano was now throwing out new magma instead of old rock. The temperature of the volcanic flow was approximately 1000 degrees and was traveling extremely fast....about 100 miles per hour. The volcanic flows went on until late in the afternoon. These flows triggered an avalanche. The avalanche poured rocks, tress...
