Mount Spurr as seen during an AVO flyby on March 11. The summit crater is located at lower center, and the peak of the crater is at center left. (Image credit: USGS AVO)
A massive volcano in Alaska appears to be “heading toward an eruption,” say scientists monitoring it.
Spurr Volcano, 81 miles (130 kilometers) west of Anchorage, is currently emitting abnormally large amounts of volcanic gases both near its summit and from a side vent that last erupted in 1992.
The 11,000-foot (3,370-meter) volcano experienced a surge in earthquakes and melting snow and ice on its slopes last year, indicating magma was moving beneath the surface. Now, scientists at the Alaska Volcano Observatory (AVO) say the seismic activity is likely to lead to an eruption.
That's an increase in risk from the observatory's last assessment in February, which showed Spurr was equally likely to “brew” or “erupt.” Now, observations of rising emissions of carbon dioxide and sulfur dioxide from the volcano have tipped the scales toward an eruption, said Matt Haney, the scientist in charge of AVO at the U.S. Geological Survey.
“This period of turmoil will likely eventually culminate in an explosive eruption similar to those that occurred in 1953 and 1992,” Haney told Live Science.
Both of those eruptions took place at Crater Peak, a side vent about 2 miles (3.2 kilometers) from the stratovolcano’s summit. The mountain’s summit likely last erupted more than 5,000 years ago, Haney says, so scientists don’t expect an eruption there — the rock between the erupting magma and the summit crater is likely well-hardened, making it difficult for magma to push through.
The eruption is most likely to occur at Crater Peak, which has been active recently and likely has easier pathways for magma to move to the surface.
Crater Peak erupted three times over several months in 1992 and once in 1953, sending ash at least 50,000 feet (15,240 meters) into the atmosphere in both cases, Haney said. One of the explosions in 1992 sent an ash cloud drifting over Anchorage, blanketing the city in an eighth of an inch (3.1 millimeters) of dust. In 1953, Anchorage received a quarter of an inch (6.4 millimeters) of ash.
If the movement of magma beneath the volcano continues, the next sign of an eruption will likely be volcanic tremors, Haney said.
Unlike the short, small earthquakes that have rocked the volcano over the past year, volcanic tremors are long, continuous shaking that can last minutes, hours, or even days. They indicate that magma is rising and that an eruption is likely imminent.
In 1992, volcanic tremors began about three weeks before Mount Spurr erupted. Another nearby volcano, Mount Ridout, erupted in 2009 and showed volcanic tremors for two months before its explosion.
“If we see [tremors],” Haney said, “that would be the next sign that Spurr is continuing to move toward an eruption.”
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