July 19, 2001
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Facts and Fallacies about Hualalai Volcano
Every so often we receive a number of inquiries from anxious people in Kona about a possible eruption of Hualalai Volcano. The latest spate of questions is apparently being triggered by a personal web site that contains inaccurate information about the volcano. We hope to dispel the rumors by presenting the results of our ongoing observations.
The U.S. Geological Survey's Hawaiian Volcano Observatory constantly monitors Hualalai Volcano. Our seismic network is capable of locating very small earthquakes, and we have not detected any swarm of earthquakes from Hualalai since 1929. If Hualalai were ready to erupt, there would be thousands of earthquakes centered there, but we locate only a handful per year.
We have been periodically measuring distances between points on Hualalai with a laser-ranging instrument since 1971. We also have been measuring the tilt, or change in slope, of the volcano since 1984. With the development of the Global Positioning System (GPS), we have occupied points on the slopes of Hualalai since 1987. Last year, we emplaced a volumetric strainmeter, or dilatometer, in Hokukano Ranch near the saddle of Mauna Loa and Hualalai. All of these geodetic monitors have not detected any change in Hualalai.
If magma is accumulating within the volcano, the edifice must deform to accommodate the added mass. Our measurements indicate that no deformation is occurring. The Hokukano strainmeter is so sensitive that it has detected changes from stresses produced by magma movement in Kilauea Volcano, yet it sees nothing taking place at Hualalai.
This year marks the 200th anniversary of the last eruption of Hualalai, and because the eruption occurred in historical time (when there is a written record), Hualalai is classified as an active volcano. It was never considered extinct. The last two eruptions in 1800 and 1801 were from the northwest rift zone, one of three rift zones of Hualalai.
The 1800 and 1801 eruptions produced the Ka`upulehu and Hu`ehu`e flows, which are noted for their shiny black surface and abundant olivine nodules. The Ka`upulehu flow is located between Kona Village Resort and Kiholo Bay. The Hu`ehu`e flow is beneath Kona International Airport.
The oldest lava deposits on the surface of Hualalai are the Pu`u Wa`awa`a cone and the associated Pu`u Anahulu lava flow. This eruption occurred slightly over 100,000 years ago. When viewed from the Queen Ka`ahumanu highway, the relationship of Pu`u Wa`awa`a and the Pu`u Anahulu flow is apparent. The short length and the 275-m-(900-ft-)thickness of the flow are the result of the trachytic composition of the lava. Trachyte is a very alkalic lava that is exceedingly viscous -- therefore the stubby lava flow. Everywhere else on Hualalai, the flows are composed of fluid alkalic basalt.
We have published a lava flow hazard zone map of the island based upon the likelihood of an area being covered by lava. Areas in zone 1 have the highest likelihood, those in zone 9 the lowest. Most areas of Kilauea and Mauna Loa Volcanoes are in zones 3 or lower. Hilo, Kea`au, Pahala, Na`alehu, Captain Cook, Anaeho`omalu, and Kealakekua are in lava flow hazard zone 3. All of Hualalai Volcano is in lava flow hazard zone 4.
We know that Hualalai Volcano will eventually erupt again some day, but at this time, our seismic and geodetic monitoring efforts give no indication that the volcano is reawakening. So people in Kona can now sleep easier at night and only worry about whether the fish are biting.
Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. Lava moves away from the vent toward the ocean in a network of tubes and descends Pulama pali in two separate areas. Small surface flows, primarily ooze-outs from inflated areas supplied by the tubes, are occasionally observed in the coastal flats. Lava from the eastern tube continued to enter the ocean in the area east of Kupapa`u throughout the week. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the new land. The steam cloud is extremely hot, highly acidic, and laced with glass particles.
One earthquake was reported felt during the week ending on July 19, 2001. A resident of Leilani Estates subdivision felt an earthquake at 6:03 p.m. on the evening of July 17. The magnitude-2.9 earthquake was located 2.5 km (1.5 mi) east of Pu`ulena crater at a depth of 1.83 km (1.1 mi).
Updated: July 23, 2001 (pnf)