May 3, 1996

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

Scientists Measuring Mauna Loa

Last week scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory (HVO) began their annual ground deformation surveys at the summit of Mauna Loa Volcano. Comprehensive monitoring of ground deformation and earthquake activity (seismicity) provides the most reliable criteria for forecasting volcanic eruptions.

Changing seismicity and deformation patterns occur when molten rock (magma) rises from deep within the earth to the shallow holding reservoir beneath the summit of the volcano. Magma accumulating at shallow depths causes the ground surface to bulge outward (inflation) and eventually crack the reservoir. Inflation and the earthquakes associated with reservoir cracking are the most reliable precursors to eruption.

In the last 150 years, Mauna Loa has erupted 33 times, with less than one year to as long as 25 years of quiet between eruptions. Only the 1975 and the 1984 eruptions occurred during the "modern" era of earthquake and deformation monitoring at the Hawaiian Volcano Observatory. Both eruptions were preceded by one to two years of increased earthquake activity. Ground deformation measurements indicated elevated rates of summit inflation a few months prior to each of the two eruptions.

Since the eruption in 1984, HVO's yearly surveys have shown that Mauna Loa's summit is steadily inflating. The numbers of earthquakes, however, remain low. Given the precursory patterns prior to 1975 and 1984, HVO scientists believe that the next eruption is not imminent. They surmise that one to two years of heightened seismicity will herald its coming.

Eruptions are an inevitable part of Mauna Loa's future. The hazards associated with this majestic volcano can be anticipated, however, and the risks substantially diminished. Vigilant monitoring of the volcano's current behavior, carefully documenting its past behavior, and educating citizens and political and business leaders can go a long way to reduce loss and disruption.

Volcano Update

The current eruption of Kilauea volcano continued unabated last week, with flows entering the ocean at Kamokuna, Kamoamoa, and Lae`apuki. Sometime between the evening of the 28th and the morning of the 29th, a 900- by 300-foot section of the new lava delta at Kamokuna broke off and slid into the ocean. A magnitude-3.6 earthquake, which occurred on April 28th at 9:22 p.m., located 0.6 miles beneath the Hawaiian Ocean View Estates area, was the only felt earthquake last week.