MEDC
Mount. St. Helens, Washington, U.S.A.
18th May 1980.
Small earthquakes starting on 15th March indicated that magma was moving. A buldge started to grow on the North side of the volcano, as magma couldn't escape from the top. Before the eruption, the buldge measured nearly 150m. An earthquake measuring 5.1 on the richter scale made the buldge collapse, causing a landslide on the north side of the volcano exposing the molten rock to lower pressure, which caused a lateral eruption.
Volcanic Explosivity Index - 5
9,677ft before eruption, 8,363ft after eruption.
Ejected about 0.2 cubic km of ejected material. Ejected about 4 cubic km of unejected material.
57 people were killed.
2,500 people were affected.
$860 million in damages.
LEDC
Mount Ponotubo, Luzon, Phillipines.
7th - 15th June 1991.
Volcanic Explosivity Index - 6
First eruption on 7th June started a formation of a lava dome, which grew to 40m over 5 days. On 12th June, explosions lasting half an hour occured, causing pyrocrastic flows and abundant lightning. A large eruption occured on 13th June after several small earthquakes. The climatic eruption on 15th June coincided with the arrival of Typhoon Yunya causing pyrocrastic flows and lahars.
5,725ft before eruption, 4,875ft after eruption.
Ejected about 10 cubic km of erupted material. Ejected about 4 cubic km of unerupted material.
640 people were killed.
1,036,065 people were affected.
$211 million in damages.