VOLCANOES NATIONAL PARK — The 2018 summit collapse and lower East Rift Zone eruption at Kilauea Volcano were dramatic and, for many Island of Hawaii residents, tragic events. As with all eruptive crises, these events offered exceptional opportunities to learn more about how volcanoes work and to answer some “bigger picture” questions.
What is the significance of the 2018 events when viewed from the historical perspective of similar events at other volcanoes? What impact are they likely to have on volcano science and future generations of volcanologists? What comes next, and how might we find out?
This latest chapter in Kilauea’s remarkable story is still unfolding, but already it’s clear that 2018 marks a watershed for volcano science, not only in Hawaii but also worldwide. Let’s explore some of the reasons why.
First, summit collapses like the one that so profoundly reshaped Kilauea Caldera and Halemaumau earlier this year are relatively rare. At Kilauea, this was the largest summit collapse since at least the year 1800, and it included the strongest summit explosions since 1924. Only three comparable events have occurred at basaltic volcanoes worldwide in the past 50 years. Much larger explosive events have occurred in Kilauea’s past but not since 1790, more than 200 years ago.
Other aspects of the 2018 activity were also unusual. The magnitude-6.9 earthquake that struck Kilauea’s south flank on May 4 was the largest in Hawaii since 1975. The emission rate of sulfur dioxide gas during the main phase of the lower East Rift Zone eruption, at least 50,000 tons per day, was the highest ever measured at Kilauea. The lava production rate from fissure 8 also was unusually high for Kilauea, about three times higher than during the 1955 and 1960 lower East Rift Zone eruptions.
Such extraordinary events give scientists an opportunity to study aspects of Kilauea’s behavior first-hand, to challenge old ideas, and to test new ones. For example, based on visual observations of the 1924 explosive activity at Halemaumau, scientists thought such events were caused by the interaction of groundwater with hot rock or magma. The 2018 collapse was the most thoroughly monitored event of its kind in history, but preliminary analyses of the data haven’t turned up any evidence for groundwater involvement in the explosions.
Scientists love surprises like that, because they challenge conventional wisdom and lead to better understanding. Stay tuned.
Another head-scratcher from Kilauea’s 2018 summit collapse is that it wasn’t chaotic, as you might expect. Instead, the process that left a 1,600 feet deep, rubble-strewn pit where Halemaumau had been was remarkably predictable.
A regular pattern emerged in which seismicity gradually built to a crescendo over one to three days, until the caldera floor suddenly dropped several meters in a matter of seconds. The pattern repeated dozens of times from May to August 2018. A similar pattern was recognized during summit collapse at Miyakejima volcano, Japan, in 2000.
Why would such catastrophic events follow a well-behaved pattern? Scientists love puzzles, too, and they’re already working to solve this one.
What comes next?
Following Kilauea Volcano’s collapse and explosions in May 1924, lava returned to the floor of Halemaumau during seven brief eruptions from July 1924 to September 1934. The same could happen again in the coming months or years.
On the other hand, the longest period of eruptive quiescence in Kilauea’s recorded history followed from 1934 to 1952 — with no active lava on the volcano for 18 years! So, Kilauea could stay quiet for decades.
Regardless, scientists will be probing Kilauea for signs of activity using an array of existing tools and probably some new ones, too. They’re tinkerers on a mission, and new tools are always welcome.
The 2018 summit collapse and lower East Rift Zone eruption at Kilauea were historic events that will continue to advance our understanding of Hawaiian volcanism long into the future.
In the lexicon of Hawaiian volcanology, 2018 now joins 1790 and 1924 as dates of lasting significance.
Volcano Activity Updates
Kilauea is not erupting. Summit and East Rift Zone activity is greatly reduced, with low rates of seismicity, deformation, and gas emissions recorded this past week.
A slight inflationary trend near and east of Puu Oo suggests that magma may be refilling the middle East Rift Zone. Low seismicity and reduced gas emissions do not indicate that the magma is shallow, but HVO continues to closely monitor this area and will report any significant changes.
Sulfur dioxide (SO2) emissions across Kilauea remain drastically reduced, with a combined rate of less than 300 tonnes/day. Small amounts of hydrogen sulfide gas (H2S) are also being released in cooler, wetter volcanic environments, and from decaying vegetation and other organic matter. The human nose is extremely sensitive to the “rotten egg” smell of H2S; some people can detect this gas at less than 0.001 parts per million. Residents have reported smelling H2S downwind of Kilauea, but these concentrations are well below hazardous levels.
Please visit HVO’s website or past Volcano Watch articles, Kilauea and Mauna updates, volcano photos, maps, recent earthquake info, and more. Call 967-8862 for a Kilauea summary update. Email questions to askHVO@usgs.gov.
Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week’s article was written by HVO geophysicist Ingrid Johanson.
