BILLINGS, Mont. (AP) – An unexpected eruption of steam in a Yellowstone National Park geyser basin that sent people scrambling for safety and basketball-sized rocks flying overhead highlighted a little-known hazard that scientists hope could to predict someday.
Tuesday’s hydrothermal explosion in Biscuit Basin did not cause injuries as dozens of people fled down the boardwalk before the boardwalk was destroyed. The explosion sent rocks, steam, water and dirt high into the air, according to a witness and a scientist who reviewed video footage of the event.
It came in a park full of geysers, hot springs and other hydrothermal features that attract millions of tourists every year. Some of them, like the famous Old Faithful, are pushing like clockwork and are well understood by the scientists who monitor the seismic activity of the park.
But the kind of explosion that happened this week is as common as it sounds, and could be more dangerous since they happen without warning.
“This drives home that even small events — and this one in the scheme of things was relatively small, if dramatic — can be really dangerous,” said Michael Poland, chief scientist at the Yellowstone Volcano Observatory. “We are very good at being able to understand the signs that a volcano is waking up and could explode. We don’t have that knowledge base for hydrothermal systems like the one in Yellowstone.”
Poland and other scientists are trying to change that with a new monitoring system recently installed in Yellowstone’s other geyser basin. It measures seismic activity, deformations in the Earth’s surface and low-frequency acoustic energy that could indicate an eruption.
The hydrothermal explosions are believed to be the result of clogged passages in the extensive natural plumbing network under Yellowstone, Poland said. A bell could cause the heated, pressurized water to immediately turn to steam and explode.
Tuesday’s explosion came without much warning.
Witness Vlada March, who captured a widely circulated video of the explosion, said steam began to rise in the Biscuit Basin “and within seconds, it became this huge thing. … It exploded and became like with a black cloud that covered the sun.”
March tour guide Isaac Fisher told The Associated Press he heard a hiss coming from Cliff Pool and told his group it was unusual. It looked like a geyser was erupting 60 to 70 feet (18 to 21 meters) in the air for a few seconds and then, “Ba-boom!” he said.
“You felt the shock wave hit your chest and vibrate the bones in your chest,” he said. “The explosion was so significant you felt your legs shake. You felt the boardwalk shake and you felt everything shake.”
He estimated that the entire event lasted about 25 seconds with the debris rising to about 100 meters (328 feet) in the air.
“I can’t believe anyone got hurt,” Fisher said. “There were rocks whizzing over our heads the size of basketballs.”
Marta’s mother, who was closest to the eruption, pulled her hood over her head and face and was not injured, Fisher said.
Some of the rocks soared into the air about a meter (3.3 feet) across, Poland said.
Yellowstone caldera contains a huge, slumbering volcano that shows no sign of erupting anytime soon but provides the heat for the national park’s famous geysers, hot springs, mud pots and various other hydrothermal features. Although much less common than geyser eruptions, hydrothermal eruptions occur often enough in Yellowstone to be studied—and to be a safety concern.
Scientists don’t know if they will be able to devise a way to predict the explosions, Poland said.
For a geologist, seeing one in person is a payday. That’s what happened in 2009, when Montana Tech Geology Professor Mike Stickney and several other geologists were nearby when one happened near the site of Tuesday’s explosion in the Biscuit Basin.
“It was very sudden and with no discernible warning, just standing there on the boardwalk. It was just one ‘whoosh’ and it was done. Nobody saw it coming,” Stickney said.
Although it did not register on a sensitive seismometer at Old Faithful a few miles (3.2 kilometers) away, he estimated the recent explosion to have been 10 times larger.
In May, after scientists discovered a crater several feet (1-2 meters) wide in Norris Geyser Basin 18 miles (29 kilometers) north of Biscuits Basin, they consulted acoustic and seismic data from a system new monitoring of the basin and determined hydrothermal. an explosion that occurred on April 15, just a few days before roads were opened for the spring tourist season.
However, there were no clear antecedents in the data that could be used to develop a warning system.
University of Wyoming geology professor Ken Sims, who has used ground-penetrating radar and other techniques to identify problems, focuses on a long-term study of where hydrothermal eruptions and other ground disturbances can occur in Yellowstone.
The information is critical to building roads and bridges in Yellowstone, he said.
“Whenever you put in a super active system like that, you have to pay attention to what’s going on,” Sims said.
Developing a detection system takes time and money, with monitoring stations costing about $30,000 each.
But even if explosions like the recent one in Yellowstone could be predicted, there is no feasible way to prevent them, Poland said.
“One of the things people ask me from time to time is, ‘How do you stop a volcano from erupting?’ You don’t get out of the way,” said Poland. “For any part of this activity, you don’t want to be there when it happens.”
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Hanson reported from Helena, Montana, and Gruver from Cheyenne, Wyoming.