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April 20, 2000

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


Atmospheric nuclear explosions and the source of Steaming Flats water

The topics for this article are presented in response to requests from our readers. Many weeks ago, a reader called to express her appreciation for the "Volcano Watch" column and asked if we would write about the Steaming Flats in Hawai`i Volcanoes National Park.

The Steaming Flats, located in a down-dropped section between the Visitor Center and Kilauea Military Camp, is one of the most popular attractions in the Park. The first-time visitor suddenly realizes that this area is not Kansas when clouds of steam suddenly come into view while driving along Crater Rim Drive. The amount of steam visible on any given day is determined by weather conditions, particularly humidity. With more moisture in the air, more molecules of the invisible water vapor are able to condense into the visible steam.

Where does the steam come from? Although water vapor is the most abundant volatile in magma, the steam escaping from the numerous vents is the result of meteoric (rain) water percolating down and being heated by hot rocks of an old magmatic intrusion in the area.

How do we know this? We condense the steam and collect a sample of liquid water to conduct a few tests to determine its origin. One test is for the presence of the radioactive hydrogen isotope, tritium. Since the time when testing of nuclear weapons in the atmosphere began, meteoric water has been contaminated with excess tritium. Primary (magmatic) water does not contain tritium, so the presence or absence of this isotope is a good indicator for the origin of the water.

Another test is for the abundance of silica - the higher the temperature that the water attained, the more silica dissolved in the water. Both tests on the Steaming Flats water conclusively indicate that the water escaping now is meteoric. This was not always the case, because when magma first intruded the area, primary water and other volatiles undoubtedly escaped from the magma bodies.

The Sulphur Banks, on the eastern border of the Steaming Flats, is heated by a young magmatic source. In addition to steam, sulfur gases also escape from these vents. The vents are located along a structure that is part of the caldera complex of ring faults. The ring fractures probably go deep into the volcano and serve as conduits for escaping volatiles, because the presence of volcanic sulfur deposits (solfataras) along this structure.

Steaming vents also are found near the Volcano House hotel, and steam baths in the hotel were naturally supplied by these vents. However, shaking by the magnitude-7.2 earthquake in November 1975 disrupted the steam conduit to the hotel, and the baths were closed.

The large earthquake in 1975 is a segue to the second topic of this article. Shortly after the magnitude-5.0 earthquake earlier this month, we received calls asking whether a tsunami was generated. Calling for information wastes valuable time if you live in a tsunami-inundation zone and must evacuate. Locally generated tsunami can strike within minutes following an earthquake.

If you are in a low-lying area subject to inundation by a tsunami, you should immediately leave the area when you feel an earthquake large enough to make standing up difficult. The yellow-edged pages in the front section of your telephone directory contain tsunami evacuation maps that tell you if you are located in an area at risk. The tsunami generated by the November 1975 earthquake hit Hilo in 20 minutes and Kailua-Kona in 27 minutes. Two campers were killed at Halape, where the waves struck within a few minutes after shaking started.

April is tsunami awareness month in Hawai`i, and all residents should take the time to learn about this hazard and know what to do if one is generated.

Speaking of learning, if you are in Kona on Saturday, April 29, a free seminar on "What's New on Mauna Loa and Hualalai?" will be held from 9:00 a.m. to 12:00 noon in the Kamehameha Ballroom of the Kona Surf Resort hotel. The event is sponsored by the Federal Emergency Management Agency (FEMA), the Center for the Study of Active Volcanism (CSAV) at the University of Hawaii at Hilo (UHH), and the U.S. Geological Survey's Hawaiian Volcano Observatory (HVO). Speakers will be from HVO and from the University.

Eruption Update

Eruptive activity of Kilauea Volcano continued unabated during the past week. Lava is erupting from Pu`u `O`o and flowing through a network of tubes toward the coast. Lava is visible at times on Pulama pali, and surface flows are active in the coastal flats near the Royal Gardens subdivision private access road. For the past few days, the terminal section of the road was being covered by the lava flow. Lava is also intermittently entering the ocean in the vicinity of Waha`ula. The public is reminded that the ocean-entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The active lava flows are hot and have places with very thin crust. The steam clouds are highly acidic and laced with glass particles.

A resident of Pahala reported feeling an earthquake at 9:36 p.m. on April 13. The magnitude-2.7 temblor was located 3 km (1.8 miles) southwest of Pahala at a depth of 2.9 km (1.7 miles).

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Updated: 24 Apr 2000