Volcano Watch — Pele's Cooking More Than Vog -- "Precious" Jewels Also Stewing in Her Cauldron

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After the series of explosions at Halema`uma`u Crater, the overlook area appeared to be a stark, boulder-strewn field completely devoid of life.

Pele's Cooking More Than Vog -- "Precious" Jewels Also Stewing in H...

Both opague and glassy crystals are native, or pure, sulfur. The glassy crystal is about 2 mm (0.08 inches) long. Photo by M. Sako

(Public domain.)

To the casual observer, little beauty could be seen in this otherworldly landscape. But on closer inspection, the field of rocks that covers Halema`uma`u reveals an array of colors - rocks blood-red and ochre, canary yellow, pinks of every hue, and a broad range of whites. These colors can appear as non-glossy lacquer, or as a brilliant glass, reflecting light. Photos don't do justice to the astonishing beauty of these rocks. But under the microscope their radiance is clearly revealed.
Some of the minerals have familiar names, like sulfur and gypsum. Others are, perhaps, more foreign, like alunite and jarosite. Individual colors usually cannot be assigned to specific minerals, because many mineral share the same, or similar, colors. Because of this, a geologist in the field uses a combination of color, shape (also known as crystal habit), and other physical characteristics to identify a mineral.

At Halema`uma`u, however, the number of minerals present is relatively small, and some generalizations based on color can be made. For example, the canary-yellow rocks are almost always composed of native sulfur. Perhaps you've seen the conspicuous yellow patches of ground in Halema`uma`u or at Sulfur Banks. Native sulfur is a very common mineral at volcanic fumaroles around the world.

The ochre, blood-red, or yellowish-red rocks are usually iron-oxide minerals, like hematite or goethite. These minerals are also very common in volcanic terrains.

The white minerals at Halema`uma`u are among the most difficult to identify, because so many different minerals may take on this color. However, most of the white-colored rocks you see there are actually the white crusts formed by a family of related minerals known as sulfate salts. Gypsum is one of these salts.

As beautiful as these Halema`uma`u minerals can be, they are of little economic value. But as the saying goes, one person's lead is another's gold. Indeed, for a geologist seeking to understand how the volcano works, these minerals are priceless jewels.

By studying volcanic systems like Kīlauea, geologists have come to understand that each mineral is formed from a recipe that specifies temperature, pressure, and chemical elements as ingredients. Changes in the recipe usually form specific minerals or families of minerals in a predictable fashion.

The rocks that were ejected from Halema`uma`u during the first explosion of March 19 contained a collection of minerals that resulted from a high-temperature recipe with relatively low amounts of sulfur and water. These observations suggest that the explosion was not caused by volcanic vapor interacting with lower-temperature ground water. Thus, we believe that the mechanism which caused the March 19th explosion differed from the ground-water-driven explosions at Halema`uma`u in 1924.

More recent rocks ejected from Halema`uma`u contain minerals that suggest a similar recipe to that of the March 19th explosion, but with an interesting twist; the family of sulfate salts (of which gypsum is a member) had subtlety changed. New members have shown up; sulfate-salt minerals, such as alunite and jarosite, have been seen in the mix. Although in the same family, these minerals differ from gypsum because they require a highly acidic broth of sulfur and water. Thus, their presence indicates that, deep within the cauldron of Halema`uma`u, the stew is becoming more acidic and sulfur-rich through time.

In the history of observations at Kīlauea Volcano, this eruption marks the first time that these sorts of relationships have been recorded, along with other detailed observations, such as gas chemistry and temperature measurements. As such, our understanding of these processes is rapidly evolving. So as Halema`uma`u continues to brew, we walk out on that ostensibly stark landscape in search of more of these "jewels."

We encourage readers to explore and learn more about minerals discussed in this article on line at Wikipedia and WebMineral.


Volcano Activity Update

Kīlauea Volcano continued to be active at two locations: a vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. The resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala, during trade wind cycles and communities adjacent to Hawai`i Volcanoes National Park during kona wind periods. Pu`u `O`o continued to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast. Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava from the 2007 Thanksgiving Eve Breakout (TEB) flow, erupting from fissure D of the July 21 eruption, continues to flow through what remains of the Royal Gardens subdivision and across the coastal plain to the ocean within well-established lava tubes. Over the past week, the Waikupanaha ocean entry has produced vigorous small explosions, with ejecta fallout limited to the new delta.

The public should be aware that lava deltas could collapse at any time, potentially generating large explosions in the process. This may be especially true during times of rapidly changing lava supply conditions, as have been seen lately. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves that are suddenly generated during delta collapse; these beaches should be avoided. In addition, the steam plumes rising from the ocean entries are highly acidic and laced with glass particles. Check the County of Hawai`i Civil Defense website or call 961-8903 for information on public access to the coastal plain and ocean entry.

Mauna Loa is not erupting. One earthquake was located beneath the summit. Extension between locations spanning the summit, indicating inflation, has resumed following a period of stagnation.

No earthquakes beneath Hawai`i Island were reported felt within the past week.

Visit our Web site for daily Kīlauea eruption updates and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. skip past bottom navigational bar