June 29, 2000
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Uncovering more of the Madam's secrets
In recent weeks the U.S. Geological Survey's Hawaiian Volcano Observatory has begun a program to install new instrumentation to help monitor Mauna Loa Volcano. These new instruments, called volumetric strainmeters or dilatometers, will measure rock strain below the ground surface. A secondary benefit of this installation is that we get a rare look at the rocks in the subsurface, because the dilatometers are installed in cored holes 120 to 150 m (400 to 500 ft) deep.
The usual method for deducing the eruptive history of a volcano is to map out the surface flows. So far our work has resulted in approximately 600 mapable eruptive units on Mauna Loa's surface. This thin carapace of flows represents, a 10,000-year period of time. Yet we know that the volcano is made of thousands upon thousands of lava flows stacked one upon another to create the huge mountains rising more than 4000 m (13,000 ft) above sea level. The core from the holes provides geoscientists with a column of rock that represents a portion, admittedly small, of the cumulative eruptive history of the volcano.
In order to effectively monitor the subsurface storage edifice, the holes are spread out on Mauna Loa. One hole is in Hawai`i Volcanoes National Park, along the Mauna Loa Strip Road. The second hole is on Mauna Loa's west flank approximately 6.5 km (4 miles) upslope of Konawaena School. The third is located at the NOAA Weather Observatory on the volcano's north flank. So far two of the dilatometers have been installed. We have crews working long hours to orient, scribe, and catalog the core. The recovered core reflects its eruptive environment.
The first site is downstream from the northeast rift zone. The core here is a mixture of both `a`a and pahoehoe lava flows. In the cored section, none of the flows are particularly thick, because the eruptions from the northeast rift zone are usually short-lived (days to months). Furthermore, fissure systems migrate downrift, spreading the lava out over a large geographic region rather than dumping it in one place. In addition, we found several ash beds, most likely erupted from Kilauea.
The location above Konawaena School, the second hole, is directly downstream from Mauna Loa's summit caldera, Moku`aweoweo. This region was fed from caldera overflows, which last from years to decades. The eruptive style is comparable to the Kupaianaha phase of the current eruption. This type of eruption produces thick pahoehoe flows, exactly as seen in the core.
The second hole produced a few surprises: we recovered several ash layers at different depths. In one of these, we recovered organic material. This is especially exciting, because we can date the material, using the radiocarbon method, and then calculate an accumulation rate for all the units above this horizon. What volcano is the source of the ash? What kind of eruptions produced this material? Further analysis will help us answer these questions.
The third hole is currently being drilled. We expect its core to resemble that of the first hole. The core provides us with unique opportunity to study a portion of the eruptive and geochemical history of Mauna Loa. This is a third dimension normally not available to us. We look forward to discovering more of Pele's secrets as systematic analysis of the core is completed and the new instrumentation comes online.
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. Surface flows from breakouts of the tube system are seen occasionally in the coastal flats and on Pulama pali. Lava is entering the ocean mainly at two locations: Waha`ula and Kamokuna. A third entry, located 500 m (550 yards) to the east of Waha`ula, is erratic and wispy. 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.
No earthquake was reported felt during the week ending on June 29, 2000.
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Updated: 3 July 2000