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Volcanowatch

June 1, 2000

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


The next eruption of Mauna Kea

Mauna Kea's peaceful appearance is misleading. The volcano is not dead. It erupted many times between 60,000 and 4,000 years ago, and some periods of quiet during that time apparently lasted longer than 4,000 years. Given that record, future eruptions seem almost certain.

Before the next one, we should have ample warning provided by our current seismic and geodetic monitoring systems. A number of earthquakes occur beneath Mauna Kea each year, and you can bet that we pay close attention to them. However, they all appear to be associated with tectonic faulting rather than movement of magma.

The telescopes on top of the volcano may be the first to indicate that something is amiss. The coordinates used for tracking their observations will begin to drift unexpectedly as the volcano is swelling. In a sense, the telescopes will serve as very expensive tiltmeters.

We cannot now say when the next eruption will take place, except that it is unlikely to be in the next several months, given the current lack of any precursory signs. Whether the timing is years, centuries, or millennia is entirely unclear.

But we can say something about the probable nature of the next eruption, because we know what the most recent ones were like, thanks to recently published research by Ed Wolfe, former staff member of HVO, and colleagues.

The next eruption could take place anywhere on the upper flanks of the volcano. As Mauna Kea evolved from its early shield stage (equivalent to Kilauea and Mauna Loa today) to its present postshield stage, the volcano lost its rift zones. Consequently, the postshield eruptions are not concentrated along narrow zones but instead are scattered across the mountain.

For example, the most recent eruptive period, 6,000-4,000 years ago, involved eight vents on the south flank of the volcano between Kala`i`eha cone (near Humu`ula) and Pu`u Kole (east of Hale Pohaku). During this same period, eruptions took place on the northeast flank at Pu`u Lehu and Pu`u Kanakaleonui. Lava from Pu`u Kanakaleonui flowed more than 20 km (12 miles) northeastward, entering the sea to form Laupahoehoe Point.

The next eruption will likely produce a lava flow, because each eruption in the past 60,000 years has done so. The longest flows will reach 15-25 km (9-15 miles) downslope. Most of each flow will be `a`a, but pahoehoe may form near vents.

A prominent cinder cone will probably be constructed at each vent. The cinder cones responsible for the "bumpy" appearance of Mauna Kea's surface formed during the 60,000-4,000-year interval. The cones mentioned by name above, and several others, were built during the latest eruptive period 6,000-4,000 years ago. The next eruption will likely produce a similar cone.

Cinder cones form at vents that are point sources, not elongate fissures. All activity is concentrated at one place, so that fountaining and spattering build a high cone rather than a long rampart. Past eruptions-and hence future ones-probably lasted months to several years, providing enough time to construct a substantial cone. Those eruptions spread voluminous ash deposits far beyond the cinder cones themselves, and the next eruption will probably do so, too.

Possibly, however, there will not be enough spattering to build a lasting cone. Such an eruption happened about 1 km (0.6 miles) southeast of Hale Pohaku, when a vent put out a moderate volume of lava without building a spatter or cinder cone.

The next eruption of Mauna Kea is unlikely to occur in our lifetimes, but it could. There is no reason to fear such an eruption. It would not threaten human life, provided due care were taken, though it could prove devastating to property and infrastructure, particularly if a lava flow traveled to the Hamakua coast or the Waimea area.

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 near the eastern boundary of Hawai`i Volcanoes National Park. A large skylight of the main tube is intermittently visible on Pulama pali. The tube system is now well-established, and surface flows from breakouts of the tube system are rarely seen in the coastal flats these days. Lava is entering the ocean mainly at Waha`ula and at a site 900 meters (1000 yards) to the west. 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.

Three earthquakes were reported felt during the past week. Residents of Glenwood felt an earthquake at 4:10 p.m. on Monday, May 29. A minute later, residents of Hilo and Glenwood were shaken by another earthquake. The origin of both temblors was 10 km (6 mi) southeast of the summit of Kilauea Volcano. The first earthquake was 6.5 km (3.9 mi) deep with a magnitude of 2.8, and the second earthquake had a magnitude of 3.9 with a depth of 4.5 km (2.7 mi). The third felt earthquake occurred on May 29 at 9:53 p.m. and was reported by a resident of Leilani Estates. The magnitude-1.8 earthquake was located 4 km (2.4 mi) southeast of Pu`ulena Crater at a depth of 2.7 km (1.6 mi).


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Updated: 5 June 2000