Nearly 3 months into one of its most voluminous and destructive eruptions in recent history, Hawaii’s Kīlauea volcano abruptly went quiet over the weekend, with new lava from the volcano’s flank slowing to a trickle and seismic activity at its summit going quiet.
Although Tina Neal, scientist in charge at the Hawaiian Volcano Observatory (HVO), called it a “dramatic shift in activity,” she said it was too soon to say whether the changes were a pause in activity or a sign that the eruption was truly coming to an end.
“Volcanoes worldwide can go through pauses or lulls or periods of diminished activity during the course of an eruption,” she said. “A pause of days or weeks is not completely out of the question.”
A U.S. Geological Survey (USGS) overflight crew on Monday morning observed a weakly to moderately bubbling lava pond within the cone at fissure 8, the opening that has been the primary source of lava flows since May. They also saw a weak gas plume and a completely crusted lava channel.
Later in the morning, crews on the ground confirmed that the upper section of the lava channel was empty of new lava, although small amounts of molten material continued to ooze out of the ground nearer to the coast. Those observations “are all consistent with something turning off the spigot to the surface,” Neal said.
At the same time, the pattern of seismic activity and subsidence at Kīlauea’s summit that has continued since May and has caused the summit crater to grow dramatically wider and deeper abruptly came to a standstill, she said.
Caught by Surprise
The sudden slowdown appeared to have caught scientists by surprise. Less than 3 weeks earlier, HVO had issued a report to Hawaii County Civil Defense officials warning that the eruption could take months or even years to wind down.
The current eruption began on 3 May, when lava began gushing out of fissures on Kīlauea’s lower east flank. At the same time, volcanic activity ceased at Pu‘u ‘Ō‘ō, a vent around 20 kilometers to the west that had been erupting continuously since 1983. Meanwhile, at the mountain’s summit, Halema‘uma‘u Crater began to subside, eventually sinking more than 450 meters over 2 months.
In total, around 500 million cubic meters of lava are estimated to have erupted to date, according to geologist Janet Babb of HVO. The eruption has wiped three communities off the map, destroying more than 650 homes.
Scientists have several hypotheses as to what might have caused the slowdown, Neal told reporters at a hastily organized telephone briefing on Monday. There might be some kind of blockage in the volcano’s system that is preventing further draining, or there could be a slowdown in magma supply to the volcano from deeper within Earth. “We’re continuing to search for explanations as to what’s going on,” she said.
Kīlauea, however, can be fickle. “Don’t let the volcano fool you,” USGS spokeswoman Leslie Gordon added. “As soon as you think one thing, something else will happen.”
Signs of a Slowdown
Although they were not obvious at the time, Neal says scientists now recognize that the volcano may have been giving signs since mid-July that the eruption was going to change.
At the summit, scientists observed a gradual increase in the periods of rest between collapse events: explosions or rockfalls that were causing the crater to grow wider and deeper. Meanwhile, in the eruption zone on the volcano’s eastern flank, levels within the lava channel would sometimes drop below levy rims, and fountain heights at fissure 8 would decrease.
Scientists also noticed another puzzling change in the volcano’s behavior: an increase in gas emissions at Pu‘u ‘Ō‘ō. Although the old vent had been inactive since early May, a white plume has been rising from it since mid-July. On an overflight last week, they measured an emission rate of more than 1,000 metric tons per day of sulfur dioxide, the highest rate observed at the vent in several years. Emissions were down to 200 metric tons per day as of Tuesday.
Neal called it a “long shot” to think that eruption might resume at Pu‘u ‘Ō‘ō but said it was too soon to say. “We’ll be keeping an eye on that,” she said.