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December 23, 1999

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


Programs at the USGS

The staff and associates of the U.S. Geological Survey's Hawaiian Volcano Observatory and Kilauea Field Station extend a warm and cheerful holiday greeting to all of the faithful readers of our column. Judging from comments that we receive, this column has proven to be an excellent way to keep you abreast of volcanic and seismic events and to inform you of geologic hazards and features. During the past year, our USGS colleagues from across the caldera at the Kilauea Field Station of the Biological Resources Division also contributed six articles on their biological research. As 1999 draws to a close, we can look back and reflect on HVO's accomplishments in the past 12 months.

Except for brief pauses, the eruptive activity at the Pu`u `O`o vent on the east rift zone of Kilauea Volcano continued nearly unabated during the past year. The HVO geology program steadfastly monitored the eruption and kept the public posted of any changes, most recently on a daily basis via our web site (http://hvo.wr.usgs.gov). A detailed report on the eruption will be the topic of next week's "Volcano Watch" article when the 18th year of the eruption commences.

The earthquake detection program at HVO is the primary method of monitoring the volcanoes of Hawai`i for precursory signs of awakening. The seismic network was expanded in 1999 to include three stations on Haleakala Volcano. The signals from these new stations on Maui are radio-telemetered to HVO via an improved repeater on Hualalai. Now we are immediately able to locate earthquakes on Haleakala.

From January 1, 1999 to December 23, a total of 1,854 earthquakes were located by the seismic program at HVO. Of this total, 87 earthquakes were reported felt, and 11 were larger than magnitude 4. The largest local earthquake in 1999 occurred at 2:56 p.m. on April 16, with a magnitude of 5.6. The origin of this large temblor was 7 km (4.2 miles) north of Pahala at a depth of 9.4 km (5.6 miles). No injuries were reported, but two homes in Pahala collapsed, and many buildings sustained structural damage.

Another major volcano-monitoring program at HVO is geodetic measurement of surface deformation. The surface of the ground around a volcano can be deformed by the change in volume of a magma body or by gravitational loading. HVO operates a network of continuous recording electronic tiltmeters and GPS receivers that can detect changes in the ground surface and transmit that information back to the observatory.

The real-time deformation-monitoring network was increased by four new electronic tilt stations and by 16 new permanent GPS stations on Mauna Loa and Kilauea. Ground deformation caused by the intrusion of magma into the upper east rift zone of Kilauea on September 12, 1999, was measured by the network. The data provided the information that allowed us to model the magma body that was intruded.

The gas geochemistry program at HVO also continuously monitors the volcano. A new automated station measuring sulfur dioxide and carbon dioxide, gases emitted by the volcano, was established near Pu`u `O`o. Data from the station are transmitted to HVO every 10 minutes. Changes in the concentration of these gases indicate a change in the eruption or the magma supply.

The gas geochemistry program is also involved in investigating the chemical composition of volcanic fume coming from Kilauea Volcano. Anecdotal evidence suggests that this fume, known as volcanic smog or "vog," is affecting the health of the residents on Hawai`i island, especially in Kona. We are collaborating with other earth scientists and with health professionals in order to help formulate a better picture of the effects of vog on human health.

The geophysics program at HVO monitors changes in the gravitational, magnetic, and geoelectric fields of the Earth. These geophysical changes are caused by stress or mass changes related to magma bodies. The geophysics group also monitors the volume of lava flowing through the tube from Pu`u `O`o to the coast in a given time period. This is done by measuring the deflection of very low-frequency radio waves as they pass through the heated tube system to obtain the geometry of the tube and by measuring the speed of lava flowing through the tube.

The geophysics program conducted a detailed magnetic survey in Haleakala crater to resolve a long-standing geologic controversy - whether the crater was formed by collapse or by erosion. Results from analysis of the 2,500 individual measurements indicate that the crater was formed by erosion.

The five monitoring programs are supported by the electronics, computer, library, and administrative staff, who keep the programs running.

We appreciate your support and will continue our mission of providing unbiased Earth science information to the public. And if you have ideas for topics you'd like us to discuss in future columns, please let us know.

Eruption Update

The ocean entry at Highcastle stopped last weekend, but a 250-meter-wide (800-feet-wide) lava flow is now entering the ocean near Lae`apuki. This site is 2.3 km (1.4 miles) from the end of the Chain of Craters road in Hawaii Volcanoes National Park. The public is reminded that the ocean-entry area is extremely hazardous, with explosions accompanying unpredictable collapses of the new land. The steam clouds are highly acidic and laced with glass particles.

Another flow is slowly approaching the eastern boundary of the National Park near the Royal Gardens access road.

A resident of Pa`auilo felt an earthquake at 9:56 p.m. on Tuesday, December 21. The magnitude-3.0 earthquake was located 5 km (3 miles) southeast of Honoka`a at a depth of 13.35 km (8 miles).

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Updated: 5 Jan 2000