Analysis: Lava from the depths

  • The eruption begins May 3, 2018, in Leilani Estates. (Courtesy photos/USGS Hawaiian Volcano Observatory)

HILO — A chemical analysis of lava samples taken during the 2018 Kilauea eruption confirmed theories that the eruption drew from magma deeper than previous eruptions.

At a Thursday presentation at the University of Hawaii at Hilo, geologists Cheryl Gansecki and Lopaka Lee explained what their analyses of Kilauea eruption samples told them about how the volcano operates under the surface.

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Over the course of 113 samples taken throughout the months-long eruption, the component elements of the lava gradually changed, Gansecki said.

Early samples taken during “early phase 1” of the eruption — from May 3 through May 9 — had high levels of zirconium and low amounts of magnesium, and generally indicated an average temperature of 1,110 degrees Celsius (about 2,030 degrees Fahrenheit).

By comparison, the average sample taken from Pu‘u ‘O‘o during that eruption had low zirconium, high magnesium, and an average temperature of 1,150 degrees Celsius.

“Magma’s like a bag of trail mix,” Gansecki said, launching into an extended metaphor that compared some elements to M&Ms and others to broccoli chips.

Much like trail mix, Gansecki explained, you can determine the age of lava by what is not in it. Magnesium, for instance, is common in newer lava, but quickly crystallizes into minerals such as olivine — like a bowl of trail mix left out at a party where the M&Ms are taken more quickly than the rest, elements like magnesium disappear from samples quickly over time.

Because the lava from the early fissures had the composition of older lava, Gansecki and other geologists theorized that it had lingered in the lower East Rift Zone for some time, and would be replaced by fresher lava from deeper within the volcano’s magma chamber.

This was proven right as the eruption went on. Later phases of the eruption saw the chemical composition of the lava approach that of the Pu‘u ‘O‘o samples, with temperatures to match, Gansecki said.

Unfortunately, hotter lava is also less viscous, which allowed the lava to flow more quickly, leading to the devastation of surrounding communities.

One exception to the trend was fissure 17, which opened on May 12 in Lanipuna Gardens.

The northeastern-most fissure to form, fissure 17 released very viscous lava with an exceptionally high amount of zirconium and extremely cool average temperatures of about 1,060 degrees Celsius. The fissure 17 samples indicated a new source of even older lava had been released from within the rift zone, perhaps from a recently unblocked lava tube or dike, Gansecki said.

The latest samples from the eruption revealed average temperatures slightly lower than the Pu‘u ‘O‘o lava — understandable, Gansecki said, as the lava had to travel further — but with higher amounts of magnesium than those samples.

Gansecki theorized that the eruption was disruptive enough to Kilauea’s system that later lava originated from deeper sources of lava than previous eruptions.

Gansecki and Lee said they would hope to improve their data transmission speed during a future eruption — some samples took more than a day to return to the lab for analysis — but their work in the field allowed them to correctly predict the increase in lava volume during the later phases of the eruption.

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“We don’t usually get to see an eruption reflect our data in real time,” Gansecki said. “That was very exciting to see.”

Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.