<P> The 57 - year eruptive period that started in 1800 was named after the Goat Rocks dome , and is the first time that both oral and written records exist . Like the Kalama period , the Goat Rocks period started with an explosion of dacite tephra , followed by an andesite lava flow , and culminated with the emplacement of a dacite dome . The 1800 eruption probably rivalled the 1980 eruption in size , although it did not result in massive destruction of the cone . The ash drifted northeast over central and eastern Washington , northern Idaho , and western Montana . There were at least a dozen reported small eruptions of ash from 1831 to 1857 , including a fairly large one in 1842 . The vent was apparently at or near Goat Rocks on the northeast flank . Goat Rocks dome was the site of the bulge in the 1980 eruption , and it was obliterated in the major eruption event on May 18 , 1980 that destroyed the entire north face and top 1,300 feet ( 400 m ) of the mountain . </P>
<P> The 57 - year eruptive period that started in 1800 was named after the Goat Rocks dome , and is the first time that both oral and written records exist . Like the Kalama period , the Goat Rocks period started with an explosion of dacite tephra , followed by an andesite lava flow , and culminated with the emplacement of a dacite dome . The 1800 eruption probably rivalled the 1980 eruption in size , although it did not result in massive destruction of the cone . The ash drifted northeast over central and eastern Washington , northern Idaho , and western Montana . There were at least a dozen reported small eruptions of ash from 1831 to 1857 , including a fairly large one in 1842 . The vent was apparently at or near Goat Rocks on the northeast flank . Goat Rocks dome was the site of the bulge in the 1980 eruption , and it was obliterated in the major eruption event on May 18 , 1980 that destroyed the entire north face and top 1,300 feet ( 400 m ) of the mountain . </P>
when was the last time mount st helens erupted before 1980
when was the last time mount st helens erupted before 1980
1857
1857