Geochemistry, Mineralogy, Volcanology Feature

Lava Clues Chronicled Kīlauea’s Unusual 2018 Eruption

Samples from Kīlauea volcano’s extraordinary eruption that began last May could offer important insights into the behavior of volcanoes and the underlying mantle.

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“Imagine the hottest oven you can, sticking your head in—and it’s hotter than that,” volcanologist Cheryl Gansecki said, recounting what it felt like to approach active lava flows at Hawaii’s Kīlauea volcano, where the sheer volume of lava made the radiant heat extremely intense. “I’ve had a couple of times when I’ve tried to sample from a flow and just couldn’t. It just felt like everything was going to catch on fire.”

When explosive blasts and spattering lava made it too dangerous to approach the flow, scientists got as close as they could and then waited, added Gansecki, a volcanologist at the University of Hawai‘i at Hilo. “You’re watching for [a piece of lava spatter] to fall kind of close to you, then running in and grabbing it and running out again.” To lock the sample into the chemical state it was in when it was collected, geologists would cool the searing blob of molten rock quickly by “quenching” it in a bucket of water. The plunge froze it into glass, preventing the chemical alterations and crystallization that would occur if the lava cooled slowly.

Grabbing fresh lava was one of the first things that volcano scientists did when fissures in Leilani Estates, an area on Kīlauea’s eastern flank that is historically less volcanically active than other areas, suddenly and dramatically began spewing lava in what became a long-unseen type of eruption on 3 May.

For the previous 35 years, the volcano had been reliably releasing lava from a vent called Pu‘u O‘o that lies 21 kilometers (13 miles) from those newly opened fissures. In the 46-second video below, a Hawaiian Volcano Observatory (HVO) geologist scoops up and quenches a bucket’s worth of lava last year from that Pu‘u O‘o vent.

 

Building a Rock Record

As dangerous as lava samples are to retrieve, they provide valuable rewards. For one, lab studies of the traits of the fresh, glassy volcanic rock can give clues to what’s coming next in an eruption. Most critically for public safety, from the time the volcano abruptly changed on 3 May, volcanologists watched for chemical clues that younger, hotter lava was arriving on the scene. Such markers mean the eruption is about to become much faster and more voluminous. Such a change requires emergency crews to deploy more quickly and widely and possibly to carry out additional evacuations.

Other markers may take longer to decipher and require painstaking research to interpret. These markers, researchers told Eos, often come with a more enduring reward: a deeper understanding of the volcano itself and perhaps of volcanism in general.

Bagged Kīlauea lava samples await analysis of properties such as composition and chemicals present.
Bags of Kīlauea lava samples await analysis on a lab bench at HVO this past June. Volcanologists collected the samples from the lower East Rift Zone, where many fissures opened unexpectedly in the spring and summer. Sitting in the lab is USGS HVO geologist Lopaka Lee. Credit: Leslie Gordon, U.S. Geological Survey

Now that Kīlauea has settled down, a history of what transpired remains, written in stone. Over the late spring and summer, HVO teams amassed bag after bag of volcanic rubble, some of it drawn hot from fresh flows, some scoured from tree branches spat upon by the eruption, more just picked up from the ground after it had rained down, and some chipped from solidified flows.

In the heat of what many are calling a once-in-a-lifetime event, scientists were driven to build a collection of lava samples whose chemistry could help tell the story of the volcano’s historic transformation. They raced against time to capture samples of new lava before yet another variety of lava came along and obliterated all traces of what had surfaced not long before.

A Surprising Sample

As a batch of magma sits in the ground under a volcano, it begins to cool. As it cools, certain minerals precipitate out as crystals, leaving behind a liquid that is richer in the remaining elements and depleted of the elements in the crystallized minerals. Volcanologists call this aged magma “differentiated” or “evolved.”

Gansecki works mostly as a laboratory researcher analyzing samples, including many of those captured from Kīlauea’s outpourings. She measures the concentrations of trace elements to determine whether a lava sample is fresh or evolved—and if it is evolved, just how evolved it might be.

In the early days of the eruption, HVO scientists noticed that the erupting lava was very evolved, indicating that it had been sitting under the ground for several years. This isn’t so unusual: New eruptions often start by pushing old magma out of the pipes. The scientists watched the lava closely, looking for signs of fresh magma entering the system. Finally, after 10 days, they saw a change. But it wasn’t the change they expected. Instead of being fresher, this material was actually more evolved than what they had previously seen—significantly more.

The sample, which had a sticky, paste-like consistency when it gunked out of the ground, had extremely high levels of zirconium, an element that becomes concentrated in magma as it differentiates.

Gansecki had never seen zirconium at those levels before. “My first thought was that this was an error—there’s something wrong with the machine,” she said. “The next sample came in and was even higher. We were like, ‘Wow. This is real.’”

Scientists also collected samples of Kīlauea lava that had solidified on its own in the field.
Scientists collect different types of lava for analysis, including already solidified material in the field like these pieces chipped from lava that overflowed the fissure 8 channel in Kīlauea’s lower East Rift Zone on 2 August. Credit: U.S. Geological Survey

The zirconium levels were twice as high as samples taken from other fissures in the Leilani Estates eruption and 4 times higher than lava from Pu‘u O‘o. Gansecki’s lab also measured levels of rubidium, strontium, yttrium, and niobium: four trace elements that provide clues to magma’s age and origins. “All five of [these elements] told us the same story: ‘This is something you’ve never seen before.’”

Andesite Sighted

HVO scientists sent the samples to a lab on the U.S. mainland to test the lava’s silica content, a measurement used to classify lava types. Those results showed that what was erupting out of fissure 17 was not basalt, the kind of lava that usually erupts from Kīlauea, but silica-rich andesite. Although there is a record of some lava from the 1800s with silica that approached andesite-like levels, it’s the first time that full andesite has been observed at Kīlauea, U.S. Geological Survey (USGS) officials said.

“This would certainly be rare for Kīlauea,” said Aaron Pietruszka, an isotope geochemist with USGS in Denver. The more interesting question is how the lava that appears to be andesite formed, he added. “That will tell us a lot about how Kīlauea works.”

A more detailed chemical analysis and comparison to other lavas from the eruption and past eruptions could help answer the question.

Fast, hot lava flows from fissure 8 of Kīlauea’s lower East Rift Zone streamed to the sea.
Fast, hot lava flows like these pouring from fissure 8 in the lower East Rift Zone in June streamed along channels 100 to 300 meters wide, destroying homes and vegetation, until reaching the ocean at Kapoho Bay. Credit: U.S. Geological Survey

One reason the eruption has produced such evolved lavas might be because the area where it was located, called the lower East Rift Zone, isn’t very volcanically active, with decades passing between eruptions. Past eruptions in the area occurred in 1955 and 1840. “It’s a poorly studied part of Kīlauea, because there are relatively few eruptions,” Pietruszka said.

(Not long after the suspected andesite spurted out, the fresher, hotter magma that scientists had been predicting did, in fact, arrive, bringing with it the faster, more voluminous and destructive flows many had feared.)

“It would be good to get a better idea of basic questions, like how much magma is actually stored in the lower East Rift Zone underground, how frequently does magma reach the lower East Rift Zone from the summit. We don’t know,” he added.

Chemical Fingerprints

To pin down the time and place a batch of magma comes from, Pietruszka looks at the abundance of trace elements, as well as four different lead isotopes. “Those characteristics are thought to be mainly inherited from changes going on in the mantle,” he said. “They act like compositional tracers. Fingerprints.”

That’s because the mantle itself is heterogeneous, made of different materials swirled together. The composition of mantle melt rising to Earth’s surface reflects those differences on a scale of kilometers, Pietruszka said. “When you look at lava coming out of Mauna Loa [a Hawai‘i Island volcano that last erupted in 1984], Kīlauea, and Loihi (an active volcano on the ocean’s floor about 35 kilometers east of Hawai‘i Island), they are all different from each other,” he said.

Within a single volcano, those differences can show up over a timescale of decades. Looking at the chemistry of different eruptions and comparing their volumes of lava can offer insights into fluctuations in magma supply being delivered to the volcano from the mantle, he said. That could help explain the extent to which eruptions are driven by fluctuations within the mantle versus geological activity closer to the surface.

“Going forward, an important question to decipher is, Was this new activity on the lower East Rift Zone driven partly by the delivery of a new batch of mantle-derived magma to the volcano?” he said. “If it was, we should see the chemical and isotopic fingerprints of the lava change over time (at the new eruption) to be different from what was previously erupting at Puʻu ʻŌʻō.”

Archiving an Eruption

Kīlauea’s latest activity was a remarkable change in the behavior of one of the best-studied volcanoes in the world, scientists say. The transformation included a sudden, violent shift in the location and volume of eruption from the volcano’s flank and a dramatic subsidence at Kīlauea’s summit as the magma reservoir beneath the mountain drained.

Satellites, seismometers, and other instruments monitored these changes. Ultimately, lava chemistry is expected to provide vital clues into how the events played out beneath the ground.

Fast, hot lava flows from the extraordinary 2018 Kīlauea eruption destroyed more than 700 homes.
Satellite photos taken before (left) and after (right) the destruction wrought by the recent Kīlauea eruption in the Leilani Estates residential neighborhood. Fissuring and high-volume flows originated in this area, particularly from fissure 8, whose cone appears at center right. Lava also buried and incinerated other neighborhoods on its way to the sea. Credit: U.S. Geological Survey

Gansecki said that scientists have built an archive for future study, moving quickly to recover lava samples before they were buried by subsequent flows. “All those early results are buried already, they’re gone,” she said. “So this is the only record we have.”

It’s a record that will be studied by volcanologists for years to come, Pietruszka predicted. The lava’s chemical composition offers clues to what’s going on inside the volcano, he said, including how magma changes chemically over time, what Kīlauea’s internal structure might look like, and maybe even what’s taking place much deeper down, in the mantle of Earth.

“We can look at these chemical fingerprints and trace the different magma batches as they move through the plumbing system of the volcano,” he said.

USGS geophysicist Michael Poland said that lessons learned from the recent eruption could be applied to similar volcanoes around the world. Volcanologists will combine what they learn about the chemistry of Kīlauea’s erupted products with geophysical data and other findings to create new models for how the volcano works. “I think we’re going to learn more about the properties of magma and magma transport from this,” he said.

These studies are much more than an academic exercise: This year’s eruption of Kīlauea destroyed 716 homes. Thus, scientists have a responsibility to make as much headway as they can from the sample archive and other observations, Poland said. “This eruption is giving us an opportunity to learn a lot more about how the volcano works, but it’s coming at a tremendous cost to the people who live in that part of the island,” he said while the eruption was still underway. “So I think we owe it to those people to take every lesson we can from this event.”

—Ilima Loomis ([email protected]), Freelance Journalist

Citation: Loomis, I. (2018), Lava clues chronicled Kīlauea’s unusual 2018 eruption, Eos, 99, https://doi.org/10.1029/2018EO111315. Published on 26 December 2018.
Text © 2018. The authors. CC BY-NC-ND 3.0
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