Crystals tell a lot about Kilauea’s eruption


Petrology, the study of the origin, or genesis, of rocks, is an important aspect of a multifaceted approach to monitoring the current eruptions of Kilauea Volcano. As part of Hawaiian Volcano Observatory’s routine petrologic monitoring, scientists have collected Pele’s hair and tears on the rim of the active lava lake at Halemaumau since 2008 and also hair, tears and other fresh samples of lava in or near Puu Oo since 1983.

At first glance, all lava samples appear to be a black mass of solid glass. With as little as five-times magnification, however, it’s possible to see mineral crystals that have formed within the magma during its storage and transport under the volcano. Scientists visually identify and characterize the shapes and sizes of these minerals. In addition, they chemically analyze individual crystals, their surrounding glass and any microscopic bits of glass they may include in aptly termed melt inclusions. All of this information is used to infer the temperature and pressure under which magma has been transported and stored within the volcano.

Eruption petrology tells us that more than 99 percent of the nearly 0.5 cubic mile of lava that poured out of east-rift vents during the first 18 years of eruption, from 1983 to 2001, was transported very efficiently through the summit and directly out of the upper-middle east rift zone.

Throughout the 1980s and 1990s, lava was erupted at temperatures of up to 2,138 degrees F and contained a healthy sprinkling of well-formed olivine (peridote) crystals. Most of these tiny green gems formed within two days in magma tapped from a subsurface summit reservoir circulating at up to 2,192 degrees as it cooled another 86 degrees while flowing through the east-rift conduit.

Most of the 0.3 cubic mile of 21st century lava issued from vents at or near Puu Oo has erupted at temperatures as low as 2,084 degrees and contains distinct clusters of crystals. These clusters are not just olivine, but also pyroxene and plagioclase — minerals that crystallize from Kilauea magma, along with olivine, at temperatures below 2,012 degrees.

Laws of thermodynamics tell us that the eruption cannot sustain itself at temperatures much lower than this, and yet the eruption goes on with renewed vigor and no signs of stopping any time soon. Ironically, this persistent low-temperature, crystal-rich pre-eruptive condition is hardly an indication of eruption stagnation. In fact, quite the opposite is apparent.

A significant surge in the supply of magma beneath Kilauea’s summit began in 2003 and culminated on Father’s Day, 2007, when a very small eruption of 2,129-degree lava breached the rift conduit four miles uprift of Puu Oo at Kane Nui o Hamo. The vents at, and near, Puu Oo were reactivated soon thereafter but continued to erupt the same low-temperature, crystal-bearing lava.

By March 2008, magma that had forged its way into the summit during “the surge” finally made its spectacular debut in Halemaumau Crater, beginning an era of tandem Kilauea eruptions.

After an explosive beginning, the summit eruption has settled into a mode of perpetual churning of a consistently hot, olivine-bearing magma. Eruption temperatures of 2,129 degrees in 2008 steadily declined to 2,111 degrees by fall 2011. Since then, Pele’s tears shed from the lava lake surface indicate gradual heating to the current temperature of 2,120 degrees.

Lava petrology studies have exposed the hot truth behind lower-temperature rift lava. Chemistry and textures of crystals that are both dissolving and growing, along with their melt inclusions, tell a story of mixing between hot, gas-rich and cooler, gas-poor magma, prior to eruption on the rift.

This evidence suggests that, during the surge in magma supply, a new shallow magma chamber developed within the magma plumbing along the east rift, like an aneurysm in the well-worn artery to Puu Oo, and in which stagnating magma is perpetually recirculated and flushed by pulses of fresh, hot magma from the summit.

The petrologic details of simultaneously erupted summit and rift zone lava provide opposing perspectives on magma complexities prior to rift eruption. Combined with geophysical and behavioral observations, petrologic monitoring at both ends of this eruption has led to better understanding of how and where magma is transported, stored, erupted and recharged within the edifice of Kilauea Volcano.

Kilauea activity update

A lava lake within the Halemaumau Overlook vent produced nighttime glow visible from the Jaggar Museum overlook and via HVO’s webcam during the past week. The lake level was relatively steady over the past week because of a lack of deflation-inflation cycles, and was roughly 160 feet below the floor of Halemaumau.

On Kilauea’s east rift zone, breakouts from the Peace Day tube remain active above the pali and on the coastal plain. Small ocean entries are active on both sides of the Hawaii Volcanoes National Park boundary. In addition, the Kahaualea flow, fed directly from a spatter cone on the northeastern edge of Puu Oo’s crater floor, continues to advance very slowly toward the northeast across a plain of 1980s-era aa flows. The flow had traveled about 2.8 miles when last measured on March 22.

There were no felt earthquakes in the past week.

Visit the HVO website at hvo.wr.usgs.gov) for Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.

Volcano Watch is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.