VOLCANOES NATIONAL PARK — One of the most frequently asked questions of USGS Hawaiian Volcano Observatory (HVO) scientists over the last several months has been, “Is the eruption over?”
It’s no surprise that Hawaii Island residents would like to see Kilauea’s activity behind them, given its toll on lower Puna communities this summer. The lower East Rift Zone (LERZ) erupted a volume of 1 cubic kilometer of lava and destroyed over 700 structures. Two-thirds of the erupted lava flowed into the ocean through the vigorous channelized flow from fissure 8.
The question was first asked in early August 2018, when summit collapses stopped and the volume of LERZ fissure 8 lava diminished. But fissure 8 wasn’t quite done. During Sept. 1-4, one more appearance of lava occurred inside the cone before draining away completely.
And now, Wednesday marks the three-month (90-day) anniversary of no surface lava activity at Kilauea. This is a milestone for this summer’s eruption. The Smithsonian Institution’s Global Volcanism Program (GVP) classifies the end of continuous volcanic activity based on an absence of eruptive activity over a three-month period. With this GVP criterion and no signs of imminent unrest on Kilauea, the LERZ eruption could be considered over.
However, magma is still being supplied to Kilauea Volcano and geophysical datasets continue to show evidence for movement of molten rock through the magmatic system, including the refilling of the middle ERZ. It’s important to note that Kilauea is still an active volcano that will erupt in the future and associated hazards have not changed. When a new eruption does occur, ground cracking, gas emissions, seismicity, and deformation can rapidly change.
The GVP three-month period is a global statistical average from all known eruptions. If we look at only Kilauea’s past 200 years of activity, this 90-day period still holds true.
But eruptive pauses have occurred in the past. There is one known example (Mauna Ulu, 1969-74) in which Kilauea’s rift zone activity resumed after a 3½-month pause. And, while Mauna Ulu has had the longest known mid-eruption pause, other examples of long pauses occurred during the first three years of the Puu Oo eruption. Breaks between 44 episodes of high lava fountains in 1983-1986 ranged from hours to 65 days long. Six of those pauses were between one- and two-months long.
All other known pauses during Kilauea eruptions have been one month or less before eruptive activity resumed. All known temporal gaps on the rift zones lasting more than 3½ months have ended their respective eruption. New eruptions would begin elsewhere on Kilauea after months-to-decades of quiet.
Volcano Activity Updates
Kilauea is not erupting. Low rates of seismicity, deformation, and gas release have not changed significantly over the past week.
Earthquakes continue to occur primarily at Kilauea’s summit area and south flank, with continued small aftershocks of the May 4, 2018, magnitude-6.9 quake. Seismicity remains low in the lower East Rift Zone (ERZ).
Deformation signals are consistent with slow refilling the middle ERZ. At the summit, tiltmeters showed minor fluctuations this week, with a small deflation-inflation cycle.
The USGS Volcano Alert level for Mauna Loa remains at normal.
Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.