Hawaiian volcano named 'Kilauea' erupts in May 2018

The famously active Hawaiian volcano typically erupts at existing fissures and triggers minor earthquakes. This latest event has no such limitations.

In March and April, geologists at the US Geological Survey Hawaiian Volcano Observatory took notice of ground inflation at both the summit and the main vent of Kilauea. Inflation is a sign of pressure building beneath the surface, often because of an intrusion of magma that culminates in an eruption. Such readings are not a surprise: Kilauea, which towers 1.2 kilometers above sea level on the southeastern side of the Big Island, has been erupting nearly continuously since 1983, with most lava flows originating from the summit caldera, Halemaʻumaʻu, and Puʻu ʻŌʻō, a vent in the volcano’s East Rift Zone.

But this time, the magma took a far more destructive path. On 3 May it broke the surface through multiple fissures that opened along the volcano’s eastern flank, toward the tip of the Big Island. New vents opened 40 kilometers away from the crater, in the middle of a residential area. Lava fountains spewed 70 meters into the air and destroyed more than 30 homes over several days. Sulfur dioxide gas plumes billowed to dangerous concentrations. Nearly 2000 residents were impacted.

So far almost everything about the eruption has caught geophysicists by surprise. They don’t yet understand how and why Kilauea started to erupt in a new place, and they are struggling to predict just how the eruption will evolve. In the long term, they’d like to know whether the current event will fundamentally change where magma is stored and how future eruptions proceed. “We need to learn as much as possible about the nuances of what happened and why,” says geophysicist Michael Poland of the US Geological Survey. “This is a terrible tragedy that is impacting people’s lives.”

The first major sign that this was not going to be a typical Kilauea eruption occurred on 30 April, when the crater floor of Puʻu ʻŌʻō began to collapse. The change indicated to scientists that lava was draining away from Puʻu ʻŌʻō and moving elsewhere. In the past few decades, new outlets for eruption always opened within a few kilometers of the main vent, and in each instance the magma eventually returned to Puʻu ʻŌʻō. This time, magma moved down the East Rift Zone, with fissures opening much farther afield than before.

Recent seismic activity supports the hypothesis that magma is traveling tens of kilometers underground and breaking rock in the process. Magma intrusions tend to push on the mountain’s heavily faulted south flank, often causing earthquakes of magnitude 4 or 5 during or just after the intrusion. On 4 May, the day after the eruption began, the Big Island experienced a magnitude 6.9 earthquake.

Ground and lava monitoring at the volcano’s summit indicates that magma is migrating from there to the new eruption site, a radical rerouting that may prove long-lived. On 2 May the summit deflated as pressure in the subsurface dropped. By 6 May the surface of the lava lake at the summit eruptive vent, which has been active since 2008, had dropped 220 meters below the crater rim, a nearly unprecedented plunge. “What’s remarkable is how fast the established eruptive plumbing system was reorganized to direct magma away from the sites of semi-steady eruption,” says geologist George Bergantz of the University of Washington. US Geological Survey officials warned on 10 May that if the lava lake continues to drain, the evacuated but still hot conduit at the summit could mix with cool groundwater and generate high-pressure steam. The result could be a violently explosive eruption capable of launching massive boulders hundreds of meters from the vent.

To find out whether a new lava field is likely to form and permanently displace people from their homes, geologists are monitoring seismicity, steam and gas plumes, and ground deformation. They want to find out how signals like rising magma levels correspond to earthquake activity and how fast those levels could change. Poland says that analyzing and modeling the geophysical data currently being collected will “keep people busy for years.”