Represents the frequency of hazardous events that occur at Yellowstone (http://volcanoes.usgs.gov/volcanoes/yellowstone/yellowstone_hazard_42.html)

Yellowstone’s past history of volcanism is likely to lead to more volcanic activity in the future, most likely in the form of hydrothermal eruptions. These small eruptions occur from shallow reservoirs of steam, which are the sources for the plentiful amount of geysers in Yellowstone today. Also known as hot springs, these geysers cause explosions that blast out small chunks craters above them.

Recently, a hydrothermal explosion occurred at Porkchop Geyser in the Norris Geyser Basin in 1989 and the remains from the eruption can still be seen today in the form of rock debris around the surrounding central spring. A little farther back in time in the late 1880s, a series of hydrothermal explosions occurred at the Excelsior Geyser in the Midway Geyser Basin. Since the last large eruption that formed the final caldera, around 30 more eruptions have proceeded to fill the caldera, as well as outside the caldera area.

Today, visitors to Yellowstone National Park walk and drive over these lava flows that have filled the calderas over previous years. The rhyolite lavas are large and thick and cover huge areas of land. If these rhyolite explosions occur today, they would also be followed by volcanic ash and

Map containing post-caldera lava flows from the Yellowstone volcano

pumice in various sizes. Fires would occur and the loss of roads and facilities would be likely, causing problems all across the park. The explosion would not be so large though that it would reach outside of the park’s boundaries.

If by some chance there was another caldera-forming eruption, ash would be produced that would cover a lot of the United States with ash. If these ash particles entered the stratosphere, they would circle the globe causing global temperatures to drop, as well as affect agriculture for up to one to two decades.

An example of earthquake damage in Yellowstone National Park (http://volcanoes.usgs.gov/volcanoes/yellowstone/yellowstone_hazard_46.html)

Yellowstone National Park is one of the most seismically active areas in the United States (USGS). Over the past 3,000 years, earthquakes with 3.0 or 4.0 magnitude have occurred yearly in the Yellowstone Park area and some surrounding areas. The most likely reason for these earthquake occurrences are from tectonic movements involving the Basin and Range extension in the western United States. Earthquakes that have formed from rising magma in the caldera can have a magnitude as large as 6.5. In 1975 near the Norris Geyser Basin, an earthquake around the magnitude of 6.5 was able to be felt throughout the entire region. Another large earthquake with a magnitude of 7.5 occurred in 1959, this time with 28 fatalities and a huge amount of damage.