Is Halema'uma'u pau? USGS HVO News Release January 7, 2009

Is Kilauea's summit eruption pau? Coming to an end as the New Year begins? This question is currently under discussion at the U.S. Geological Survey Hawaiian Volcano Observatory (HVO). According to Jim Kauahikaua, HVO Scientist-in-Charge, several lines of evidence confirm a decrease in activity at the vent in Halema`uma`u Crater.

"In early December, the gas plume emitted from Halema`uma`u became wispy and translucent, a marked change from the opaque white or brown plumes that billowed from the vent in previous months. The recent rains changed the plume's appearance, so it looks a bit denser now," said Kauahikaua. Using an infrared camera that can "see" through the gas plume, HVO geologists noted on December 31 that a previously open conduit in the Halema`uma`u vent was filled with rubble, or rocky debris from collapse of the conduit walls. The camera also shows that vent temperatures are greatly diminished, perhaps to pre-eruption temperatures.

Sulfur dioxide emission rates have dropped to their lowest values since late 2007. Recent heavy rain converted small amounts of the sulfur dioxide (SO2) to hydrogen sulfide (H2S), so nearby residents may have noticed a slight rotten egg smell in the air last week.

"We've also seen changes in the tephra, or volcanic rock fragments, ejected from the summit vent during the past month," said Kauahikaua. "On December 5, more than half the tephra erupted was derived from molten lava. Two weeks later, the amount of tephra was much smaller and consisted almost entirely of rock dust derived from older, pre-eruption rocks in the vent walls." Kauahikaua added, "If an eruption is defined as a volcanic event that deposits solid material on the ground surface, then the Halema`uma`u eruption stopped in mid-December." He cautions, however, that the summit vent remains in a state of unrest.

Sulfur dioxide emissions, measured at 770 tonnes per day on January 7, are still elevated compared to pre-2008 background levels. Seismic tremor beneath Kilauea's summit also remains elevated. "The eruption may have paused, rather than ended," Kauahikaua concluded. "We can't rule out the possibility that the eruption will resume, so HVO scientists continue to carefully monitor the summit vent in Halema`uma`u Crater."