One of the most frequent questions asked of U.S. Geological Survey Hawaiian Volcano Observatory scientists during the past several months has been, “Is the lower East Rift eruption over?”
But the same question could — and should — be asked of the Pu‘u ‘O‘o eruption.
On Jan. 3, 2018, we marked the 35th anniversary of Pu‘u ‘O‘o. For the past three and a half decades, lava erupted almost continuously from the middle East Rift Zone. Minor pauses in surface activity mostly occurred between the fountaining episodes from 1983-86, and subsequently during a few episodes marked by subsidiary fissures, intrusions or partial crater floor collapses.
Given the longevity of the Pu‘u ‘O‘o eruption, we’d grown accustom to the luxury of having nearly uninterrupted access to lava. The lure of reliable lava viewing beckoned to millions of tourists around the globe.
We say “nearly uninterrupted” because there have been more than 100 brief pauses in surface activity throughout the 35-year event, most lasting hours to a couple of days. The six longest pauses during the Pu‘u ‘O‘o activity were each 1-2 months long and all occurred between fountaining episodes in the first two years.
Specifically, long pauses between fountains occurred spanning episodes 3 and 4 (65 days), episodes 32 and 33 (52 days), episodes 12 and 13 (50 days), episodes 39 and 40 (49 days), episodes 25 and 26 (43 days) and episodes 31 and 32 (38 days).
After the fountaining episodes, there were several Pu‘u ‘O‘o eruption pauses lasting between one week and one month.
Specifically, there was a 10-day pause in February 1992 after the Kupaianaha vent shut down, ending episode 48. A year later there was an eight-day pause in February 1993 after an uprift intrusion caused Pu‘u ‘O‘o’s crater floor to collapse. A nine-day pause in February 1996 occurred after an observed surge in effusion rate.
The longest eruption hiatus after the fountaining phase lasted 24 days following the episode 54 fissure in Napau Crater in February 1997. In September 1999, there was an 11-day pause during episode 55 after a partial collapse of the Pu‘u ‘O‘o crater floor.
Most recently, there were two pauses in 2011: an 18-day pause after the March Kamoamoa fissure and a six-day pause after the episode 60 west flank breakout in August.
However, on April 30, 2018, everything changed.
The catastrophic collapse of Pu‘u ‘O‘o left the iconic eruption site and surrounding lava flow fields devoid of lava through the rest of 2018. Dec. 30 marked seven months of no surface activity at Pu‘u ‘O‘o, an anniversary that is effectively a concluding milestone for this long-lived event.
As a refresher from a previous article, the Smithsonian Institution’s Global Volcanism Program (https://volcano.si.edu/) classifies the end of continuous volcanic activity based on an absence of eruptive activity throughout a 90 day period (three months).
Statistically, after a 210-day gap in activity, it is extremely unlikely lava will resume activity within Pu‘u ‘O‘o. Based on historical knowledge of rift zone eruptions, pauses lasting more than 3 1/2 months ended their respective eruptions.
Given the GVP criterion, no signs of imminent unrest and that Dec. 30 marked seven months of no lava, the Pu‘u ‘O‘o eruption could be considered done.
This does not mean Kilauea Volcano is dead.
New eruptions previously began elsewhere on Kilauea after months to decades of quiet. Magma is being supplied to the volcano, and deformation data shows evidence for movement of molten rock through the magmatic system, refilling 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 increase rapidly.
The USGS Hawaiian Volcano Observatory continues to closely monitor Kilauea Volcano through ground-based observations, helicopter overflights and geophysical instrument networks. Significant changes will be noted in HVO’s weekly updates.
Volcano activity updates
Kilauea is not erupting. Rates of seismicity, deformation and gas release have not changed significantly during the past week.
Deformation signals are consistent with refilling of the middle ERZ. Sulfur dioxide emission rates have been below detection limits in the lower ERZ since early September, though minor amounts of volcanic gas are still present.
Hazardous conditions still exist at the lower ERZ and summit. Residents in the lower Puna District and Kilauea summit areas should stay informed and heed Hawaii County Civil Defense closures, warnings and messages (http://www.hawaiicounty.gov/active-alerts).
The USGS Volcano Alert level for Mauna Loa remains at Normal.
There was one seismic event with three or more “felt reports” in the Hawaiian Islands during the past week. At 8:24 a.m. Jan. 27, a magnitude-3.5 earthquake occurred in the upper Southwest Rift Zone of Mauna Loa at a depth of -0.5 km (0.3 mi above sea level).
Volcano Watch (https://volcanoes.usgs.gov/hvo/hvo_volcano_watch.html) is a weekly article and activity update written by USGS Hawaiian Volcano Observatory scientists and affiliates.