Gleaning secrets from freshly quenched lava

It’s been a nearly a year since Volcano Watch last focused on chemical studies of Kilauea’s lava.

Well, you can rest assured that our petrologist has been working hard behind the scenes, enthusiastically scrutinizing every lava sample that gets bagged by those intrepid HVO geologists.

As soon as the rocks arrive in his lab, our rock doctor performs “sample triage” and carefully assesses lava fragments for signs of changes related to eruptive conditions. Portions of Pele’s hair, tears and lava are sorted for different types of chemical analyses that will ensure a complete and thorough diagnosis of Kilauea’s internal plumbing.

With surgical precision, small crystals are extricated from every glassy morsel and impeccably polished for electron microscope analysis. The glassy rock matrix provides eruption temperatures, because magma composition changes as it cools and crystals form. The composition of the crystals also varies according to temperature and can be used to track the path that magma takes to the surface.

By analyzing tiny pockets of glass that are occasionally entrapped by crystals as they form (called melt inclusions), our petrologist has been gleaning some of Madame Pele’s best-kept secrets. Sulfur is one of the last gases to emerge from basalt magma as it approaches the surface. Thus, tracking sulfur concentrations in melt inclusions enables the petrologist to evaluate physical changes in the shallow plumbing system that feeds and regulates Kilauea’s eruptive behavior.

A little over a year ago, spectacular fissure fountains broke out near Kamoamoa, just west of Pu‘u ‘O‘o. The chemistry of lava samples from this eruption shows that the fountains ruptured through magma that had been sitting underground in this area since eruptions in the 1960s. About three weeks after the event, as magma steadily fed the volcano from beneath, the shallow plumbing system soon repressurized, and magma began refilling lava lakes at the summit and at Pu‘u ‘O‘o.

The summit quickly resumed its steady-state eruptive condition of perpetual magmatic gargling in the throat of Halema‘um‘au. Beneath the billowing summit plume, hot and corrosive magma is roiling to the surface, disgorging its gases, and swallowing and regurgitating newly formed crust. Lava levels rise and fall like a barometer in response to summit inflation and deflation. Slowly but surely, magma consumes the walls of the vent itself.

Analysis of Pele’s hair and tears collected from the Halema‘uma‘ u overlook indicate that the lava at the surface has steadily cooled from 2,140 degrees Fahrenheit at the onset of the summit eruption in March 2008, down to 2,110 degrees Fahrenheit in recent months. Some of Pele’s tears contain crystals of peridot, some of which have melt inclusions. The range of crystal compositions and of sulfur preserved in melt inclusions tell us that the summit eruption has drawn from a magma reservoir as hot as 2,190 degrees Fahrenheit and as deep as 6/10 of a mile.

At present, the summit vent consistently taps magma at 2,120 to 2,110 degrees Fahrenheit within 330 feet of the surface, where it is rising, degassing, and recirculating.

Meanwhile, out on the rift, one year after reappearing in the bottom of Pu‘u ‘O‘o, lava is now vigorously flowing through a network of lava tubes and surface flows toward the ocean. Throughout the year, and just as it did before the Kamoamoa eruption, Pu‘u ‘O‘o lava has erupted at relatively low temperatures of 2,085 to 2,095 degrees Fahrenheit.

Rift lava continues to bear a complex mixture of higher- and lower-temperature crystals, with textures indicating they are simultaneously dissolving and regrowing in a dynamic environment. High variability of sulfur trapped by crystals in the rift samples points to the continuous mixing of hotter, sulfur-rich magma from the summit with cooler, denser, and degassed magma in a shallow reservoir in the rift zone. Kilauea’s shallow plumbing system continues to mature after almost 30 years of eruption. Frequent petrologic checkups ensure us that there are no signs it will expire any time soon.

Kilauea activity

update

A lava lake present within the Halema‘uma‘u Overlook vent during the past week resulted in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is normally about 300 to 380 feet below the floor of Halema‘uma‘u Crater and visible by HVO’s webcam, rose and fell slightly during the week in response to a series of deflation-inflation cycles.

One earthquake beneath Hawaii Island was reported felt this past week. A magnitude-2.6 earthquake occurred at 10:12 a.m. Friday, March 30, and was located 10 miles northwest of Hawi at a depth of 21 miles.

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