May 3 marks the one year anniversary of the start of Kilauea Volcano’s 2018 lower East Rift Zone eruption.
During the past year, USGS Hawaiian Volcano Observatory geologists and collaborators have closely studied the vast amount of data collected during the summer eruption. Now is a good time to explore what’s been learned — and what’s still unfolding.
The lower East Rift Zone eruption, as well as the 2018 summit collapses, are providing many new insights on Kilauea. This week’s Volcano Watch focuses on a few aspects of the lower East Rift Zone eruption that are helping us better understand volcanic hazards in Hawaii.
First, ongoing work is telling us how the changing chemical composition of the magma erupted in 2018 controlled the lava-flow hazard.
The first two weeks of the eruption (May 3-18) produced low eruption rates and relatively small flows. Chemical analyses indicated the lava originated from pockets of older magma stored underground in the lower East Rift Zone. This cooler and less fluid magma was probably residue from earlier eruptions.
This stored magma was presumably forced out by the intruding dike of magma that originated from Pu‘u ‘O‘o. University of Hawaii at Hilo researcher Cheryl Gansecki says chemical analyses indicate the dike might have intersected two, or even three, separate stored magma bodies.
About May 18-19, the eruption vigor changed as hotter and more fluid magma was erupted. This magma was presumably draining from the summit magma reservoir. The eruption rate increased roughly 10-20 times, and the flows became larger, faster-moving and much more hazardous.
A similar — although less dramatic — chemical change occurred during the 1955 lower East Rift Zone eruption, but it was not recognized until long after that eruption ended. Daily tracking of lava composition during the 2018 eruption was important because it allowed us to identify the chemical change in early May, and to correctly anticipate that hotter, more fluid magma — and more hazardous lava flows — might be around the corner.
Taken together, the 2018 and 1955 eruptions point to the possibility that future rift zone eruptions can start deceptively small in the opening days as older, stored magma is erupted. But once the magma “spigot” is opened, and fresher, hotter magma arrives, rift zone eruptions can switch to large, fast-moving, and hazardous lava flows.
Magma composition also helped explain another hazard of the 2018 eruption.
In mid-May, brief explosions occurred frequently from fissure 17, throwing lava bombs several hundred meters (a few hundred yards). An initial explanation was that they were driven by groundwater seeping into the fissures, causing steam blasts.
However, chemical analyses revealed that fissure 17 erupted lava with an unusual composition. Nearly all lava erupted on Kilauea is basalt, but fissure 17 erupted Kilauea’s first documented andesite.
Andesite is higher in silica than basalt, and is, therefore, less fluid. The more viscous consistency of andesitic lava makes it easier for large gas bubbles to coalesce and burst with high pressure, which provides a likely explanation for the explosive activity at fissure 17.
The eruption also highlighted the close connection between Kilauea’s East Rift Zone and the volcano’s summit magma reservoir.
In June and July 2018, there were near-daily summit collapse events, each with the equivalent of a magnitude-5.3 earthquake.
Time-lapse cameras monitoring the fissure 8 lava channel observed that the eruption rate began to increase within minutes after a summit collapse, eventually peaking 2-4 hours later. At least once, the increased eruption rates produced overflows from the lava channel that could have threatened adjacent residential areas.
The short delay before lower East Rift Zone eruption rates increased indicates that the “surge” in eruption vigor was driven by a pressure pulse originating from the summit collapse and transmitted down the 40-km- (25-mi-) long magma conduit to the lower East Rift Zone — akin to a hydraulic press. The 2-4-hour delay in peak eruption rates allowed HVO and emergency managers, in at least one instance, to anticipate and prepare for the overflow hazard.
These are just a few of the new insights gained from Kilauea’s 2018 lower East Rift Zone eruption. They show how unraveling each volcanic process helps us better understand the hazard, and, in turn, to forecast and prepare for hazards in future eruptions.
Volcano activity updates
Kilauea Volcano is not erupting and its USGS Volcano Alert level remains at Normal.
Rates of seismicity, deformation and gas release have not changed significantly during the past week. Deformation signals are consistent with refilling of Kilauea’s deep East Rift Zone magma reservoir. Sulfur dioxide emission rates on the ERZ and at Kilauea’s summit remain low.
Two earthquakes with three or more felt reports occurred in Hawaii this past week: a magnitude-2.9 quake 4 km (2 mi) southwest of Volcano at 0 km (0 mi) depth at 3:58 p.m. April 20 and a magnitude-3.4 quake 19 km (12 mi) southeast of Waikoloa Village at 16 km (10 mi) depth at 2:27 p.m. April 18.
Hazards remain at the lower ERZ and summit of Kilauea. Residents and visitors near the 2018 fissures, lava flows and summit collapse area should heed Hawaii County Civil Defense and Hawaii Volcanoes National Park closures and warnings. HVO continues to closely monitor Kilauea for any sign of increased activity.
The USGS Volcano Alert level for Mauna Loa remains at Normal, which means the volcano is in typical background or noneruptive state.
Visit HVO’s website (https://volcanoes.usgs.gov/hvo) for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Call 808-967-8862 for weekly Kilauea updates. Email questions to askHVO@usgs.gov.
Volcano Watch (https://volcanoes.usgs.gov/hvo/hvo_volcano_watch.html) is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.