From years of monitoring and research at HVO, Kilauea's volcanic "plumbing system" is now relatively well understood. This system links the processes involved in the formation, transport, storage, and, ultimately, eruption of magma to build and feed Hawaii's active volcanoes.

Kilauea's plumbing system is believed to extend deep beneath the Earth's surface, where basaltic magma is generated by partial melting of material beneath the Pacific Plate as it passes over the Hawaiian hot spot. This belief is based on the persistent recurrence of earthquakes 30 or more miles beneath Hawaii. Earthquakes occurring in the depth interval 20-30 miles are probably related to the accumulation and upward movement of magma. Seismic data for levels shallower than 20 miles can be interpreted to define diffuse zones of continuous magma rise, one leading to Kilauea and another to Mauna Loa.

Before Kilauea eruptions, most of the magma entering the volcano is stored temporarily within a shallow reservoir. Earthquake data and ground-deformation patterns suggest that this reservoir is located 1 to 4 miles beneath the summit and consists of pockets of magma concentrated within a crudely spherical volume about 3 miles across. Earthquakes do not occur within the reservoir, because liquid magma does not rupture to generate and transmit certain seismic waves.

Kilauea eruptions occur either at its summit or within two well-defined swaths (called rift zones) that radiate from the summit. During summit eruptions, the magma reservoir deflates only slightly, if at all. This relation implies that the rate at which magma is erupted nearly equals that at which the reservoir is refilled by new magma from depth. During an eruption in a rift zone, called a rift or flank eruption, however, the summit region undergoes a significant and abrupt deflation as magma moves quickly from the summit reservoir into the rift zone. Similar summit deflation occurs during a rift intrusion, during which magma injected into the rift zone remains stored there rather than breaking the ground surface in an eruption. When the rift eruption or intrusion ends, the summit region reinflates as the shallow reservoir is refilled by magma from depth. Small pockets of summit-fed magma may be stored for a while within a rift zone and form transient secondary reservoirs.

The volcanic plumbing system for Mauna Loa is less well known. Analysis of data from the well monitored 1975 and 1984 eruptions, however, suggests that the essential features of Kilauea's plumbing system are shared by Mauna Loa, despite the difference in size between the two volcanoes. Mauna Loa's magma reservoir also may be larger than Kilauea's, which would be consistent with the observations that Mauna Loa eruptions tend to be characterized by higher lava-output rates, longer eruptive fissures, and larger lava flows.

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Maintained by John Watson
Updated 05.01.97