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October 1, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Dirty research: flushing mud from inside Kilauea

A 1,262-m-deep (4,139-ft-deep) research hole was drilled in the southwest corner of Kilauea's caldera in 1973. At the time, this was the deepest hole in the summit region of any active volcano on earth. Funded by a National Science Foundation grant to the Colorado School of Mines, the hole was drilled to study the hydrothermal system and various geophysical properties above Kilauea's magma reservoir. Standing water was encountered at a depth of about 488 m (1600 ft); below this water table, rocks were saturated all the way to the bottom of the hole, 160 m (525 ft) below sea level. Over the years, much valuable geophysical and geochemical information was acquired that has guided our interpretations of how Kilauea operates.

But the hole is muddy. Drilling mud was not flushed from the hole after drilling. It has settled and gelled into a stiff, pudding-like mass that plugs the hole below a depth of about 473 m (1,554 ft). This causes a problem. Cracks and cavities in the rock surrounding the hole are clogged with mud, so that groundwater can't flow freely in and out of the hole. The hole needs to be cleaned to take advantage of new monitoring methods.

If groundwater can move easily into the hole, its level will rise if the rocks are squeezed and sink if the rocks relax. Think of what happens to a saturated sponge when you squeeze it, and you can get the picture. If we can measure the ups and downs of water in the hole, we have an inexpensive means of measuring earth strain in the caldera. With a clean hole, we can study the changes in rock permeability that control flow of groundwater toward sea level. If there were to be a significant increase in interaction between groundwater and hot rock or magma, we could monitor a possible build-up in steam pressure by a rapid rise in water level. Finally, we can trace changes in the chemical composition of the water before, during, and after eruptions.

A very precise device called a dilatometer may be put in the hole to monitor strain. It is so sensitive that it needs to be at least 200 m (650 ft) underground to take full advantage of its capability. Any shallower, the dilatometer "feels" spurious changes caused by heating and cooling near the earth's surface. If the sides of the hole can be cleaned sufficiently, the instrument can be bonded in place. If this works, a radio will send back to HVO information about the most subtle earth deformation that will help us anticipate the future at Kilauea.

Perhaps it will be possible to have both a reliable water-level gage and a dilatometer in the hole, providing that a bypass can be made through the housing of the dilatometer to allow the water data to be transmitted by cable to the surface. And, we may also put a seismometer in the hole, so that it will be at a level with, or even below, the depth of some of the earthquakes within Kilauea. A tiltmeter will be another instrument in the hole.

The cleaning of the hole is done with a drilling rig. Clean water is poured down the hole, and mud and dirty water are bailed to the surface and dumped into waiting trailers. In principle, it is like the old-fashioned windlass and bucket that were used to bail up water from hand-dug farmyard wells. We hope that enough of the drilling mud can be removed to clean the hole down to at least 300 m (1,000 ft) below the original water table and to establish free-flowing communication between the borehole and the surrounding aquifers. The work began last week and, at the time of writing, was having a big problem penetrating the stiff mud.

Eruption and Earthquake Update

The two sizable earthquakes during the past week did not affect the eruption. Eruptive activity at the Pu`u `O`o vent continued unabated. Lava flows through a network of tubes from the vent to the seacoast where it enters the ocean in two locations near Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

Eight earthquakes were reported felt during the past week. Seven earthquakes originating from a very shallow depth beneath Volcano Village were felt only by residents of the surrounding area. The largest earthquake of the sequence occurred at 9:56 p.m. on Sunday, September 27. It had a magnitude of 4.6 and caused some damage in the neighborhood. Residents and businesses of Volcano reported the falling and breaking of items, the shattering of windows, and the cracking of masonry. The other felt earthquakes from the Volcano Village source occurred on September 26 at 5:27 p.m. (2.9 mag.), on September 27 at 10:10 p.m. (2.1 mag.), on September 28 at 1:59 a.m. (4.1 mag.), 2:17 a.m. (2.0 mag.), 2:23 a.m. (3.1 mag.) and 5:08 a.m. (3.3 mag.).

On Monday, September 28, at 8:39 p.m., a magnitude-4.8 earthquake was felt throughout the island. The earthquake was located 18 km (10.8 mi) southeast of Kilauea summit at a depth of 9.5 km (5.7 mi). Residents of Puna and Hilo reported losses from items falling and breaking.

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Updated: 2 Oct 1998