Where does the lava come from?

Cross-section of the deep plumbing system of a Hawaiian volcano. Rocks melt in the mantle at a depth of about 40 miles (60 km) to generate magma. The magma rises through conduits to a reservoir beneath the summit of the volcano. From the summit reservoir, the magma can travel directly upward to the summit of the volcano to generate an eruption or move laterally into a rift to generate a flank eruption. Modified from Eaton and Murata (1960, Science, v. 132, p. 925-938).

Simplified diagram of the shallow plumbing system of Kilauea volcano. Magma from the mantle (1) enters the summit reservoir (2). Magma can migrate into the rift and be stored beneath the surface as an intrusion (3). Later batches of magma may intersect and mix with the stored magma to make a hybrid (4). At the present time magma goes directly from the summit magma reservoir to the vent on the flank (5). Modified from Wright and Fiske (1971, Journal of Petrology, v. 12, p. 1-65).

Answer:

Rocks that are moving upward in the mantle beneath Hawaii begin to melt about 40 to 60 miles (60 to 100 km) depth. The molten rock, called magma , rises because of its relatively low density. The magma "ponds" in a reservoir 1 to 4 miles (2 to 6 km) beneath the summit. The magma can follow fractures up to the crater and produce a summit eruption. During the current eruption, the magma has followed a zone of weakness, the East Rift Zone. Magma reaches the surface at a vent, an opening at the surface through which volcanic material is extruded. There have been several vents during the last 10 years. The currently active vent is 15 miles (24 km) from the summit and 6 miles (9.6 km) above the coast.


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