GEOLOGY

Detailed explanation-1: -The 1980 eruption of Mount St. Helens in Washington, which ripped apart the volcano’s summit, was a Plinian eruption of Volcanic Explosivity Index (VEI) 5.

Detailed explanation-2: -St. Helens has been studied experimentally and found to have a viscosity that declines from about 1015 at 800°C to 103 poise at 1500°C. Its yield strength declines from about 2 × 106 dynes cm−2 at 800°C to less than the precision of our measurements (104 dynes cm−2) above 1050°C.

Detailed explanation-3: -The basalt magma erupted by Kīlauea contains about 52% silica and about 0.5 % water while the dacite lava erupted by Mount St. Helens in 1980 contained more of both: about 64% silica and about 4% water.

Detailed explanation-4: -On the morning of May 18, 1980, after weeks of small tremors, a magnitude 5.1 earthquake shook beneath Mount St. Helens and triggered an enormous eruption. The eruption involved a complex series of events that unfolded over the next 12 hours, with many events going on simultaneously.