Volcano Watch - Kalapana gets sandy volcanic ash from Kīlauea's summit

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"Curiouser and curiouser," said Alice after falling down the rabbit hole into Wonderland, and that's what some HVO researchers are saying about a late 18th-century explosive deposit from Kīlauea.

Photo of Ed Bonsey, volunteer for HVO and his wife Katie

Farewell Ed Bonsey, volunteer for HVO since 1992. Ed and his wife Katie are moving to Oakland, California

(Public domain.)

Among other things, the deposit is like the Energizer Bunny; it keeps going and going and going.

Field work during the past several weeks documents that the deposit can be found all the way from Kīlauea's summit to Kalapana and Black Sands Subdivision, 30 km (18 miles) away. Near the summit, the average diameter of the ejected rocks is about 3 mm (with many rocks of gravel size mixed with the sand). The grain size becomes finer eastward, and it averages only about 0.3 mm in Kalapana and Black Sands Subdivision.

The fine grain size is probably why the deposit has not previously been recognized in those areas. Even today the careful observer is likely to miss the sand, because it has been mixed thoroughly with still finer ash and organic material by a process called bioturbation. Worms, other organisms that live in soil, and roots have effectively stirred all the fine-grained material together during the more than 200 years that the volcanic deposit has existed. Today, there is no sign of ash layers in the loose soil resting at the surface.

It is easy to recognize the fine-grained sand, however. Scrape 500-1,000 g (a pound or two) of soil from the top of a lava flow in the area. Put it in a shallow pan and run water over it. Stir the goopy mix and pour off the dirty water, which will contain lots of roots and leaves, as well as fine clay-like ash. Do this several times, until the water is relatively clean. Then put the pan in the sun to dry. What's left are tiny sand grains; you can tell that by running the palm of your hand carefully over the residue. You need a magnifying glass-or better, a microscope-to recognize that the sand is dense and looks much different from the porous pieces scraped accidentally from the underlying lava flow.

You'll probably have only a few grams of sand after all that washing. That shows the deposit wasn't very thick before mixing with the other material.

The fallout at such long distances would have been irritating but not dangerous. Fallout from a similar explosion today would be more irritating, because of possible contamination of catchment water.

A once-curious feature of this deposit is that it spreads eastward from the source of the explosion, not in the trade-wind direction. But what's curious today becomes commonplace tomorrow. We now realize that large Kīlauea explosions send ash high enough to be blown eastward by the prevailing strong westerlies at heights above about 9 km (30,000 feet).

What about the north-south width of the fallout from the explosion? Just last week, coarse sand from potentially the same explosion was recognized at several localities in Fern Forest Estates, well north of Kīlauea's east rift zone. Previously found along the Chain of Craters Road near Ka`ena Point, the fallout not only extended at least 30 km (18 miles) east of Kīlauea's summit but may have a remarkable north-south width of more than 20 km (12 miles). Possibly the sand found in Fern Forest is from another explosion, and we are working hard to test this idea. At the moment, though, early Alice's "curiouser and curiouser" comment is apt.

This Volcano Watch is dedicated to Ed Bonsey, volunteer for HVO since 1992. Ed and his wife Katie are moving to Oakland, California. A native of Maui, Ed was attracted to geology while attending Oberlin College, Ohio, in the 1950s but felt the call and entered the ministry instead. As a volunteer for the national park and for HVO, Ed wrote summaries of Kīlauea's geology to aid park interpreters and led field trips discussing geology and other elements of the park's natural history. Ed was constantly seeking answers to geologic questions. The topic of this column is appropriate as a dedication to Reverend Ed Bonsey, for the volcanic ash reached far into the heavens before returning to earth.

Volcano Activity Update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone.

Lava continues to flow through the PKK lava tube from its source near Pu`u `O`o to the ocean, with very few surface flows breaking out of the tube. Small flows are visible intermittently on the steep slope of Pulama pali and on the coastal plain. During the past week, the ocean entry at East Kamoamoa stagnated, and, as of August 18, there is a single ocean entry at East Lae`apuki. Several partial collapses of the East Lae`apuki bench have occurred during the last two weeks. One of these removed as much as 5 acres over a two-hour period. Access to the ocean entry and the surrounding area has been closed due to significant hazards. 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.

Two minor earthquakes were felt on Hawai`i Island during the week ending August 18. At 11:50 a.m. on August 14, a magnitude-3.0 earthquake located 7 km (4 miles) south-southwest of Pu`u `O`o at a depth of 9 km (5 mi) was felt in Volcano. At 3:31 a.m. on August 15, residents of Hilo felt a magnitude-3.1 quake located 43 km (27 mi) north-northeast of LauPāhoehoe at a depth of 5 km (3 mi).

Mauna Loa is not erupting. During the week ending August 18, nine earthquakes were recorded beneath the summit area. Six were deep, long-period quakes, the remainder were shallow and intermediate depth short-period events. Inflation continues.