Geologic Background:
The Yellowstone Plateau volcanic field developed
through three volcanic cycles spanning two million years
that included some of the world's largest known
eruptions. Eruption of the >2,500 km3 Huckleberry
Ridge Tuff about 2 million years ago created the more
than 75-km-long Island Park caldera. The second cycle
concluded with the eruption of the Mesa Falls Tuff around
1.3 million years ago, forming the 25-km-wide Henrys Fork
caldera at the western end of the first caldera. Activity
subsequently shifted to the present Yellowstone Plateau
and culminated 630,000 years ago with the eruption of the
1,000 km3 Lava Creek Tuff and the formation of the
present 45 x 75 km caldera. Resurgent doming then
occurred at both the NE and SW sides of the caldera and
voluminous (1,000 km3) intracaldera rhyolitic lava flows
were erupted between 150,000 and 70,000 years ago.
Phreatic eruptions produced local tephras during the
early Holocene. The caldera presently contains one of the
world's largest hydrothermal systems including the
world's largest concentration of geysers.
Historic Activity:
- Very large geothermal system with thousands of hot
springs and geysers.
Recent Activity:
- On September 5, 1989, Porkchop Geyser in the Norris
Geyser Basin (roughly 44.7 N, 110.7 W) of Yellowstone
National Park was destroyed by a shallow steam
explosion.
- Earthquake swarm along mapped faults in June
1999.
- Large eruption of Steamboat geyser on May 2,
2000.
Data Sources:
- Smithsonian's SEAN Network (V. 14, No. 9).
- Global Volcanism Network (V. 17, No. 3 to V. 25, No.
5)
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