Yellowstone National Park is a thermally active area with an extensive system of hot springs,
fumaroles,
geysers, and
mudpots. There are also several hydrothermal explosion craters, which are not to be confused with
calderas, which are collapse features. Eight of these hydrothermal explosion craters are in hydrothermally cemented glacial deposits, and two are in
Pleistocene ash-flow
tuff. Pocket Basin was originally an ice-dammed lake over a hydrothermal system. Melting ice during the
last glacial period caused the lake to rapidly drain, causing a sudden change in pressure triggering a massive hydrothermal explosion.
Geysers A hydrothermal explosion is similar to a geyser's eruption except that it includes surrounding rock and mud and does not occur periodically. One well-known hydrothermal geyser is
Old Faithful which throws up plumes of steam and water approximately every hour and a half on average. Rarely has any steam explosion violently hurled water and rock thousands of feet above the ground; however in
Yellowstone's geological history these colossal events have been recorded numerous times and have been found to have created new hills and shaped parts of the landscape. The largest hydrothermal explosion ever documented was located near the northern edge of
Yellowstone Lake, on an embankment commonly known as "Mary Bay". Now consisting of a 1.5 mile crater, it was formed relatively recently, approximately 13,800 years ago. It is believed this crater was formed by a sequence of several hydrothermal explosions in a short time. What triggered this series of events has not yet been clearly established, but
volcanologists believe a large earthquake could have played a role by accelerating the melting of nearby glaciers and thus depressurizing the hydrothermal system. Alternatively, rapid changes in the level of Yellowstone Lake may have been responsible.
Recent explosions Most of Yellowstone's recent large hydrothermal explosions have been the consequence of sudden changes of pressure deep within the hydrothermal system. Generally, these larger explosions have created craters in a north–south pattern (between
Norris and
Mammoth Hot Springs). It is estimated that all of the known hydrothermal craters were created between 14,000 and 3,000 years ago. Volcanologists believe no magma has ever broken through the fragile crust of Yellowstone Park or stirred the movement of magma in the reservoir beneath Yellowstone. Several small hydrothermal explosions have been recorded since the opening of Yellowstone National Park. During the 1880s,
Excelsior Geyser in
Midway Geyser Basin was known for significant hydrothermal explosions. while others are linked to changes in plumbing below geysers or hot springs, such as the 1989 explosion at Porkchop Geyser in the
Norris Geyser Basin. Small hydrothermal eruptions occur nearly yearly, although many occur in Yellowstone's backcountry. On 23 July 2024, a small hydrothermal explosion was witnessed by several tourists coming from the Black Diamond Pool hot spring in
Biscuit Basin. The explosion, probably caused by a change in the plumbing under the hot spring, launched a plume of water and rock fragments into the air. Although there were no injuries, the explosion forced the closure of Biscuit Basin for the rest of the 2024 season. == See also ==