Map Key: Tbh-historic terrestrial lava; TbQ—prehistoric lava; Stb-submerged terrestrial lava; Fb—fragmental quenched lava (lava that erupted, crossed the shoreline, and was quenched and fragmented in the water); SbQ, SbK—subaqueous lava (lava that erupted and was quenched in water); Ls, La—landslides; As—abyssal sediment-including sediment and volcanic ash. Dashed and dotted line—boundaries between lava of adjacent volcanoes; dotted line—submerged shorelines; line with dot at bottom—fault; thin dashed line—volcanic rift zone, a narrow zone with volcanic cones, vents, and fissures where most eruptions occur; thick dashed line—axis of the Hawaiian deep, a trough or depression in the ocean floor surrounding the Hawaiian islands caused by the pressure of the volcanic islands on the underlying Pacific oceanic plate.
At the center of this figure is Mauna Loa, the largest active volcano on Earth. It covers over half the surface area of the island of Hawaii, and it may also be the world's highest mountain. Although it rises only 4 km above sea level, the submarine flanks descend to the north-central Pacific seafloor an additional 5 km. The seafloor of the Pacific plate, in turn, is depressed by Mauna Loa's great mass a further 8 km. Put these figures together, and the total height of this volcano is 17 km.
Mauna Loa is also among the most active of the world's volcanoes. It has erupted more than 30 times since its first well-documented historical eruption in 1843. The last eruption occurred in 1984, and another is anticipated this century. Mauna Loa was exceptionally active in the middle of the 19th century (1843–1887) at a time when its more diminutive sibling, Kilauea volcano (to the right of Mauna Loa in the figure above), was attracting visitors to Hawaii.
Although Mauna Loa has not erupted with the frequency of Kilauea, it produces about as much lava as Kilauea does. Consequently, Mauna Loa eruptions tend to be much larger, resulting in extensive lava flow fields that cover the volcano's surface at a rate of 40% every 1000 years with flows that travel many kilometers from the vents; five have reached the coast since 1868. These frequent, high-volume, far-traveling flows pose a hazard to the 75,000 people on the lower slopes of the volcano and along the coast.
For these reasons, Mauna Loa was chosen along with 14 other volcanoes for special study as part of the Decade Volcano Project by the International Association of Volcanology and Chemistry of the Earth's Interior. Unlike some of the other volcanoes in the project, Mauna Loa is expected to erupt before the end of the project.
Excerpted from Mauna Loa Revealed: Structure, Composition, History, and Hazards, edited by J. M. Rhodes and John P. Lockwood, American Geophysical Union, Geophysical Monograph 92, Washington, D.C., 1995.
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