April 27, 2000

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

Strainmeters to be installed on Mauna Loa this summer

Mauna Loa Volcano last erupted 1984. Lava flows from vents in its northeast rift zone reached within seven kilometers (four miles) of Hilo. When and from where will it erupt next?

Eruptions in 1975 and 1984 were preceded by a sharp increase in the number of earthquakes and the rate of ground deformation starting about a year before the eruption. No such increase in the rate of earthquakes or ground deformation has been detected.

Mauna Loa is a dangerous volcano. It erupts frequently and produces profuse lava flows that can move quickly down its steep slopes. Although we currently detect no signs of unrest, we are watchful and continue to improve our monitoring data and its analysis in preparation for the next eruption.

This summer, HVO scientists are installing a new type of monitoring instrument, a strainmeter, that allows unprecedented detection and tracking of events occurring deep within Mauna Loa.

The type of strainmeter we are installing is called a dilatometer. It is basically a stainless steel balloon cemented deep in the ground. Dilatometers are used to monitor volcanoes and earthquakes in Japan, Iceland, and the mainland U.S.A. These will be the first dilatometers installed in Hawai`i.

A network of three dilatometers will allow detection and tracking of strain changes that signal a developing eruption. Along with ongoing seismic-monitoring upgrades, the new strainmeters will greatly enhance our ability to forecast when and where Mauna Loa will next erupt.

How does a dilatometer work? Magma movements, earthquakes, and other natural phenomena deform the volcanic edifice. This distortion squeezes the dilatometer, which is filled with oil. The amount of strain is precisely measured by metering the flow of oil into or out of the dilatometer. Dilatometers are so sensitive that they can easily detect the small deformations of the Earth's crust caused by gravitational attractions of the sun and moon and by the loads applied to the Earth's surface by passing weather fronts.

Hawaiian volcanoes erupt frequently and provide a natural laboratory to test and develop volcano monitoring techniques. Analysis of strain changes recorded by dilatometers and data from other monitoring instruments allow us to track the movement of magma to the surface in real-time.

These efforts will result in improved risk mitigation for those living near active volcanoes.

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. A large skylight of the main tube is visible on Pulama pali. Many surface flows are active in the coastal flats from the base of Pulama pali, to the Royal Gardens subdivision private access road, and beyond to the coast. Lava is also intermittently entering the ocean at various locations along a 1.4 km (0.8 mile) stretch of coastline east of Kamokuna 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.

There were no earthquakes reported felt during the week ending on April 27.