Volcano Watch — Cooking rocks—Hawaiian-style and continental cuisine, with special recipes for volcanic disaster

The branch of geology that embraces the culinary art of lava-making is called “experimental petrology.” Petrology laboratories are like “Xtreme kitchens” where oven temperatures exceed 3,000°F., “pressure cookers” operate at hundreds of thousands of PSI (pounds per square inch), and “dish washing” entails soaking platinum crucibles and wires in concentrated hydrofluoric acid!

Experimental petrologists are the “lava chefs” who provide recipes for the glass and minerals that make up lava. Sophisticated furnaces and vessels are used for melting, crystallizing, and cooling a wide range of lava “ingredients.” A veritable buffet of lava-types can be reproduced in experiments conducted under carefully controlled conditions of temperature, pressure, and gas saturation.

Various mixtures, cooked and cooled at various temperatures and pressures, create man-made lava that varies in the amounts and types of melt, crystals, and gas-bubbles. Each of these lava components varies with the recipe. By comparing our lab-generated lava with naturally-formed lava, we can deduce the pressures and temperatures of natural lava before it was erupted (when it was magma). This kind of analysis is crucial to understanding magma processes that drive volcanic activity.

Experimental studies of Hawaiian basalt show that the primordial magma, which often bears green-colored nodules of mantle material, ascended quickly (within hours) from the Earth’s upper mantle, where it was formed at 20 to 100-km depth (12-60 miles). These so-called “mantle diapirs” underlie active Hawaiian volcanoes, like Lo`ihi, Kīlauea, and Mauna Loa.

Another finding is that lava typically erupted by Kīlauea (including the 1983-to-present eruption) and Mauna Loa is stored at shallower depths. Prior to eruption, it is usually mixed with reservoirs of older, colder magma trapped in the shallow volcano plumbing system. This Hawaiian-style lava recipe for reconstituted “leftover magmas” accounts for most of the summit and rift-zone lava-flow eruptions that build shield volcanoes.

In contrast to Hawai`i’s islands of basalt, the lava erupted by subduction-zone volcanoes is a distinctly “continental cuisine” conveyed in cookbooks full of complex recipes (a.k.a. papers in scientific journals) endorsed by world-class lava chefs. Stratovolcanoes are the local eruptive centers famous for an ethnic blend of “juicy” crust- and “spicy” mantle-derived magma served over melting slabs of water-bearing subducted oceanic crust.

The recipe for the nearly solid dacite lava erupting since October 2004 at Mount St. Helens, for example, starts with a gas-poor, crystal-laden magma that is continuously stirred while simmering for decades at depths of 4-15 km (2.5-9 miles). Like thick, lumpy gravy, dacite magma ascends to within 1 km (1/2 mile) of the surface in 3-4 days. At this shallow depth, its final, pre-eruptive state is “frozen-in” as this well-mixed stew quenches to a nearly solid lava plug forced out of the ground as lava spines that crumble to form the huge, dumpling-shaped lava dome.

For both Hawaiian and continental lava chefs, magmatic concoctions for potential volcanic disaster are far less palatable. Decompression of gas-rich magmas can cause volcanoes to pressurize and explode, ejecting ash and tephra high into the atmosphere as manifested during the catastrophic eruption of Mount St. Helens on May 18, 1980.

Similar fare from Hawaiian cauldrons is, in fact, a product of caldera-forming eruptions. Possible potions for ash explosions in Hawai`i include injecting a summit magma chamber with gas-charged, “carbonated” magma or basting hot, rising magma with cold ground water, as in the 1924 eruption of Halemaumau Crater at Kīlauea’s summit.

Stay tuned for future Volcano Watch articles about the wondrous petrology of “hot stuff.”

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Volcano Activity Update

This past week, activity levels at the summit of Kīlauea Volcano have remained at background levels. The summit caldera has been expanding, indicating inflation, since the beginning of 2007. The number of earthquakes located in the summit area is at low levels (usually fewer than 10 per day are large enough to locate). There have been local concentrations of earthquakes beneath the southeast edge of the summit caldera, near Makaopuhi Crater in the upper east rift zone, and near `Apua Point on the south flank.

Eruptive activity at Pu`u `O`o continues, though the level of activity seems somewhat subdued compared to the last few years. On clear nights, glow is visible from three vents within the eastern half of the crater. Occasional glow from outside the crater suggests that sporadic, small breakouts continue from vents on the southwest flank of Pu`u `O`o. Lava is still flowing through the PKK lava tube, at least to where the Campout tube branches about 1 km south of Pu`u `O`o. The Campout tube then carries lava to the ocean at Kamokuna located inside Hawai`i Volcanoes National Park.

The flow field has also been very quiet for the past week. Almost no breakouts have been seen on the slope of Pulama pali or on the coastal plain. In addition, the ocean entry at Kamokuna has had only a small, wispy plume, suggesting that little lava is entering the water. Overall, is seems that the volume of lava being erupted has declined.

Access to the sea cliff near the ocean entries is closed, due to significant hazards. The surrounding area, however, is open. If you visit the eruption site, check with the rangers for current updates, and remember to carry lots of water when venturing out onto the flow field.

One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.7 earthquake occurred at 5:16 a.m. H.s.t. this morning and was located 5 km (3 miles) southeast of Pu`u `O`o Crater at a depth of 10 km (6 miles).

Mauna Loa is not erupting. Four earthquakes were located beneath the summit. Extension of distances between locations spanning the summit, indicating inflation, continues at steady slow rates.