Hydrothermal explosions (also known as phreatic eruptions) are dramatic, natural events that occur when superheated water and steam are suddenly released from beneath the Earth’s surface. A geologic hazard, these explosions can result in the ejection of boiling water, steam, and rock fragments, causing significant changes to the landscape. Hydrothermal explosions are not volcanic eruptions.
Hydrothermal explosions are often associated with geothermal areas, such as Yellowstone National Park, where underground water is heated by volcanic activity.
What causes hydrothermal explosions?
Hydrothermal explosions occur when water trapped in underground reservoirs is heated by magma or hot rock to temperatures well above the boiling point. Under high pressure, this water remains in a liquid state. If the pressure is suddenly released, the water rapidly turns into steam, expanding explosively. This expansion can break through the surface, causing an eruption.
Yellowstone National Park and hydrothermal explosions
Yellowstone National Park is one of the most well-known sites for hydrothermal activity. The park sits atop a volcanic hotspot, providing the heat necessary for hydrothermal systems. Small hydrothermal explosions happen each year within the park.
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According to published research, two distinct hydrothermal systems cause explosions in Yellowstone Lake:
- Neutral- or alkaline-chloride fluids: These fluids, similar to those in Upper Geyser Basin near Old Faithful, can flash to steam when pressure drops suddenly. This type of explosion produces the largest craters, with the most energy and volume.
- Vapor-expansion explosions: These occur in vapor-dominated areas, like Mud Volcano on land. They tend to be smaller but possibly more frequent.
World’s largest hydrothermal explosion crater
The largest-known hydrothermal explosion crater on Earth is the Yellowstone Lake hydrothermal explosion crater, located in Yellowstone National Park, Wyoming, USA. This geological feature, also known as the Mary Bay Crater, was formed approximately 13,000 years ago during a massive hydrothermal explosion.
A sudden 14-meter (45-foot) drop in lake level, likely due to an underwater earthquake, triggered this explosion. The rapid lake-level changes caused significant pressure variations in the hydrothermal system, leading to sudden steam generation and the explosion.
April 2024 Yellowstone hydrothermal explosion
A small hydrothermal explosion on April 15, 2024, on Porcelain Terrace, Norris Geyser Basin in Yellowstone National Park resulted in the creation of a small crater.
Scientists doing fieldwork discovered the aftermath of the hydrothermal explosion. A hydrothermal monitoring site at Norris Geyser Basin includes GPS, seismic sensors, and an infrasound array to detect low-frequency acoustic energy. On April 15, the station recorded a strong acoustic signal from the new crater, confirming it was a surface event and not an earthquake, as indicated by the speed of the signal.
July 2024 hydrothermal explosion
On Tuesday, July 23, 2024, at about 10:19 a.m., a localized hydrothermal explosion occurred near Sapphire Pool in Biscuit Basin, just north of Old Faithful in Yellowstone National Park.
References
Morgan, L. A., Shanks, W. C. P., Pierce, K. L., Iverson, N., Schiller, C. M., Brown, S. R., … & Licciardi, J. M. (2023). The dynamic floor of Yellowstone Lake, Wyoming, USA: The last 14 ky of hydrothermal explosions, venting, doming, and faulting. Bulletin, 135(3-4), 547-574. DOI: 10.1130/B36190.1
Polland, M. (2024, July 22). A small hydrothermal explosion at Norris geyser basin. Yellowstone Volcano Observatory – USGS.gov.
Fonte : National Geographic
