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Volcano Watch — The golden pumice of Kīlauea

Hawaiian volcanoes are rich in excitement, beauty, and challenge, but they're not awash in mineral resources. How is it, then, that Kīlauea has a "golden pumice?"

The "golden," of course, refers to the color of the pumice, not to any gold within it. Too bad. Golden Richards, ex-Rainbow wide receiver who starred with the Dallas Cowboys, is another Hawai`i product who could only wish there were gold in golden.

The term "golden pumice" was first used by Professor Bob Sharp of Caltech and two of his ex-students, former HVO staff member Dan Dzurisin and Mike Malin, in a scientific paper published in 1987. The term took off and now is used occasionally by some residents of Volcano to describe the crunchy, porous reticulite pumice at the bottom of the volcanic ash layers in their yards. This use differs from that intended by Sharp and colleagues.

The original golden pumice referred to material erupted in high fountains from Kīlauea's caldera. It is the first recognizable material to have left the caldera after the violent explosions of November 1790 that decimated Keoua's war party. The reticulite pumice in Volcano predates those explosions, forming in about A.D. 1480-1500, so it cannot be the golden pumice that Sharp and colleagues described. In fact, they deliberately used the term to distinguish the younger pumice from the older reticulite pumice.

The golden pumice is readily seen by visitors to Kīlauea's caldera. It forms smooth slopes mantling the caldera rim just south of where Crater Rim Drive reaches the caldera floor. Just beyond the road, the Crater Rim Trail descends a steep, loose slope of golden pumice to the 1974 lava flow. The golden pumice is also well exposed along gullies near the park's Southwest Rift Zone turnout, where it is the youngest deposit except for the 1974 material and a thin cap of 1924 ash.

The layer of golden pumice is as thick as 2.8 m (9 feet), near the topographic rim of the caldera. This exceptional thickness probably reflects both the sustained nature of the lava fountain and the consistent trade winds blowing during the entire eruption. The golden pumice is found only on the southwest side of the caldera and follows the trade-wind direction into the Ka`u Desert. It does not occur at Kīlauea Military Camp or the Visitor Center but can be found near HVO. This distribution suggests that the high, vigorous fountain came from a vent north of where Halemaumau is today.

The pumice is golden because it is made almost entirely of basaltic glass, which has a naturally golden hue like that of Pele's Hair. This color is typical of very frothy pumice and reticulite---the extreme form of pumice with six-sided bubbles resembling a honeycomb. The thin bubble walls quenched from liquid to solid so quickly that no dark minerals could form and color the glass. Any frothy pumice is golden, but there is only one "golden pumice," according to the way that Sharp and colleagues used the term.

The golden pumice is the earliest direct evidence of resumed supply of lava to the caldera following the 1790 explosions. Almost certainly flows and lakes of lava were active during the first two decades of the 1800s, but we have no direct evidence of them, for they would now be buried deeply by younger flows filling the caldera.

The golden pumice rests on a surface eroded into the 1790 and older explosive deposits, so Sharp and colleagues concluded that its eruption was a significant time after the explosions. Rev. William Ellis, walking in the Ka`u Desert near the caldera on August 1, 1823, noted many pieces of "spumous lava [pumice] ... extremely cellular, and light as sponge. They appeared to have been drifted by the wind into the hollows which they occupied." This was probably the golden pumice. Contemporary accounts suggest increased activity in the caldera starting in 1820, and so the golden pumice may have been erupted in the 1820-23 interval.

All that glitters is not gold, but the golden pumice provides valuable evidence for piecing together Kīlauea's eruptive history.

Volcano Activity Update

Eruptive activity of Kīlauea Volcano continued unabated at the Pu`u `O`o vent during the past week. The "Mother's Day" flow is spreading and inflating at the base of Paliuli. The flow's advance to the Chain of Craters road has stagnated, and it remains 430 m (470 yd) away. The National Park Service allows visitors to hike out to a great viewing area near the active flows.

The two flows emanating from the "rootless" shields are still active, but not advancing. The mauka HALP flow is spreading in the upper reaches above the Royal Gardens subdivision. A lobe of the lower Boundary flow is in the channel of an old `a`a on Pulama pali within the subdivision.

One earthquake was felt during the week ending on July 3. Residents of Pahoa and Kea`au felt an earthquake at 9:36 a.m. on June 26. The magnitude-3.5 earthquake was located 6 km (3.6 mi) northeast of Ka`ena Point at a depth of 9.7 km (5.8 mi).


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