The 1912 eruption that formed Novarupta was the largest to occur during the 20th century . It began on June 6 , 1912 , and culminated in a series of violent eruptions . Rated a 6 on the Volcanic Explosivity Index , the 60-hour-long eruption expelled of ash , thirty times as much as the 1980 eruption of Mount St. Helens . The erupted magma of rhyolite , dacite , and andesite resulted in more than of air fall tuff and approximately of pyroclastic ash-flow tuff . During the 20th century , only the 1991 eruption of Mount Pinatubo in the Philippines and the 1902 eruption of Santa María in Guatemala were of comparable magnitude ; Pinatubo ejected of tephra. , and Santa María just slightly less . At least two larger eruptions occurred in the Dutch East Indies ( now Indonesia ) during the 19th century : the 1815 eruption of Tambora ( of tephra ) and the 1883 eruption of Krakatoa ( of tephra )
1883 eruption
1883 eruption of Krakatoa
Novarupta