<P> At 7: 05 p.m. on June 12, a plume of ash billowed 2.5 miles (4.0 km) above the volcano . At 9: 09 p.m. a much stronger explosion sent an ash column about 10 miles (16 km) skyward . This event caused the Portland area, previously spared by wind direction, to be thinly coated with ash in the middle of the annual Rose Festival . A dacite dome then oozed into existence on the crater floor, growing to a height of 200 feet (61 m) and a width of 1,200 feet (370 m) within a week . </P> <P> A series of large explosions on July 22 broke more than a month of relative quiet . The July eruptive episode was preceded by several days of measurable expansion of the summit area, heightened earthquake activity, and changed emission rates of sulfur dioxide and carbon dioxide . The first hit at 5: 14 p.m. as an ash column shot 10 miles (16 km) and was followed by a faster blast at 6: 25 p.m. that pushed the ash column above its previous maximum height in just 7.5 minutes . The final explosion started at 7: 01 p.m. and continued for over two hours . When the relatively small amount of ash settled over eastern Washington, the dome built in June was gone . </P> <P> Seismic activity and gas emission steadily increased in early August, and on August 7 at 4: 26 p.m., an ash cloud slowly expanded 8 miles (13 km) into the sky . Small pyroclastic flows came through the northern breach and a weaker outpouring of ash rose from the crater . This continued until 10: 32 p.m. when a second large blast sent ash high into the air, proceeding due north . A second dacite dome filled this vent a few days later . </P> <P> Two months of repose were ended by an eruption lasting from October 16 to 18 . This event obliterated the second dome, sent ash 10 miles (16 km) in the air and created small, red - hot pyroclastic flows . A third dome began to form within 30 minutes after the final explosion on October 18, and within a few days, it was about 900 feet (270 m) wide and 130 feet (40 m) high . In spite of the dome growth next to it, a new glacier formed rapidly inside the crater . </P>

What events lead to the eruption of mt. st. helens