Question:
What volcanoes in the conterminous United States have erupted since the Nation was founded?
Answer:
Mount St. Helens, Washington
1980-1986: Large explosive eruption on May 18, 1980,
followed by 21 smaller eruptive episodes. The last 17 episodes built a lava dome in the volcano's crater. See USGS fact sheet of activity between 1986 and 2000.
1800-1857: Large explosive eruption in 1800 was followed by extrusions of lava that formed a lava flow on the volcano's northwest flank (Floating Island lava flow) and a lava dome on the north flank (Goat Rocks lava dome).
Late 1700's: Layers of volcanic rocks record a variety of activity related to the growth of a lava dome at the volcano's summit, including pyroclastic flows, lahars, and tephra fall.
Lassen Peak, California
1914-1917: A series of small explosions that began on May 30, 1914, was followed 12 months later by extrusion of lava from the summit and a destructive pyroclastic flow and lahars on May 21, 1915. Minor activity continued through middle of 1917. See USGS fact
sheet about the eruption.
Mount Rainier, Washington
1894 & early 1800's: Several eyewitness accounts describe minor releases of steam and ash-laden steam during November and December 1894. The most recent eruption that formed a thin and discontinuous tephra layer, however, occurred during the first half of the 19th century.
Mount Hood, Oregon
1856-1865 & late 1700's: According to eyewitnesses, small explosive eruptions occurred from the summit area between 1856 and 1865. In the latter half of the 18th century, however, a lava dome was erupted, which was accompanied by pyroclastic flows, lahars, and tephra fall.
Mount Shasta, California
1786: An eruption cloud was observed above the volcano from a ship passing by north coast California, and the activity included pyroclastic flows.
Glacier Peak, Washington
17th - 18th centuries: Between about 200 and 300 years ago, small eruptions deposited pumice and ash east of the volcano, and may have been observed by Native Americans.
Mount Baker, Washington
1840-1870: Historical literature refers to several episodes of small tephra-producing events in the mid 1800's, and increased fumarolic activity began in Sherman Crater near the summit in 1975 and remains elevated today.
