Volcano Watch — Crystals tell us a lot about Kīlauea's ongoing eruption

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Petrology, the study of the origin, or genesis, of rocks, is an important aspect of our multi-faceted approach to monitoring the current eruptions of Kīlauea Volcano.

Crystals tell us a lot about Kīlauea's ongoing eruption...

Pele's hair covers much of the ground in the area immediately downwind of the vent at Halema‘uma‘u Crater. Accumulations about a meter (yard) wide are found on the windward sides of the curbs in the Halema‘uma‘u parking lot, which is closed to the public because of the ongoing volcanic hazard (May 3, 2012).

(Public domain.)

As part of our routine petrologic monitoring, we collect Pele's hair and tears on the rim of the active lava lake at Halema‘uma‘u (since 2008), and also hair, tears, and other fresh samples of lava in or near Pu‘u ‘Ō‘ō (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. We visually identify and characterize the shapes and sizes of these minerals. In addition, we 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 over 99% of the nearly 2 cubic km (0.5 cubic mi) 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 1,150–1,170°C (up to 2,140°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 1,180°C–1,200°C (up to 2,190°F) as it cooled another 30°C (90°F) while flowing through the east-rift conduit.

Most of the 1.3 cubic km (0.3 cubic mi) of 21st Century lava issued from vents at or near Pu‘u ‘Ō‘ō has erupted at relatively low temperatures of 1,140°C–1,145°C (as low as 2,080°F) and contains distinct clusters of crystals. These clusters are not just olivine, but also pyroxene and plagioclase—minerals that crystallize from Kīlauea magma, along with olivine, at temperatures below 1,150°C (2,010°F).

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 Kīlauea's summit began in 2003 and culminated on Father's Day, 2007, when a very small eruption of 1,165°C (2,130°F) lava breached the rift conduit 6.4 km (4 mi) uprift of Pu‘u ‘Ō‘ō (at Kāne Nui o Hamo). The vents at, and near, Pu‘u ‘Ō‘ō 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 Halema‘uma‘u Crater, beginning this era of tandem Kīlauea 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 1,165°C (2,130°F) in 2008 steadily declined to 1,155°C (2,110°F) by fall 2011. Since then, Pele's tears shed from the lava lake surface indicate gradual heating to the current temperature of 1,160°C (2,120°F).

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 Pu‘u ‘Ō‘ō, 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 Kīlauea Volcano.


Volcano Activity Update

A lava lake within the Halema‘uma‘u Overlook vent produced nighttime glow that was 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 due to the lack of deflation-inflation cycles, and was roughly 50 m (160 ft) below the floor of Halema‘uma‘u.

On Kīlauea'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 Hawai‘i Volcanoes National Park boundary. In addition, the Kahauale‘a flow, fed directly from a spatter cone on the northeastern edge of Pu‘u ‘Ō‘ō's crater floor, continues to advance very slowly toward the northeast across a plain of 1980s-era ‘a‘ā flows. The flow had traveled about 4.5 km (2.8 miles) when last measured on March 22.

There were no felt earthquakes in the past week on the Island of Hawai‘i.