Hydrothermal explosion in Yellowstone closes area of Sapphire Pool

Tourists usually flock to Yellowstone National Park to see geysers and bubbling pools, but officials closed an area for safety after a hydrothermal explosion Tuesday morning. Sightseers recorded video of the explosion sending debris high in the air.

The explosion occurred just after 10 a.m. near Sapphire Pool in Biscuit Basin, located a couple miles northwest of Old Faithful, according to a news release from the National Park Service. No injuries were reported. Park staff temporarily closed the area, including its parking lot and boardwalks, while keeping open Grand Loop Road.

What caused the explosion? Hydrothermal explosions are caused by water suddenly turning to steam underground. Such blasts occurred in the past at different parts of the park, according to a joint statement by Yellowstone National Park and the U.S. Geological Survey. The park service said that the volcanic system under Yellowstone otherwise showed normal background activity. No other monitoring data showed changes in the region.

When and where were the previous explosions in Yellowstone? A small hydrothermal explosion at Norris Geyser Basin was recorded by monitoring equipment in April, according to the statement. Biscuit Basin had a similar explosion in May 2009. In September 1989, eight tourists saw Porkchop Geyser throw rocks in the air, creating a crater 30 feet wide. Porkchop is also located in the Norris Geyser Basin.