MAGMA SUPPLY TO KīLAUEA VOLCANO, HAWAII: BUILDING ON THE FOUNDATION ESTABLISHED BY DON SWANSON

In 1972, Don Swanson published a manuscript in Science that provided the first-ever estimate of magma supply from the mantle to Kīlauea Volcano. Based on the effusion rate during three eruptions lasting months (in 1952, 1967–68, and 1969) and the lack of coincident summit deformation indicating subvolcanic magma storage, Don calculated a magma supply rate of approximately 0.11 km³/yr. This estimate has held up remarkably well over the ensuing decades; subsequent analyses of geodetic, geologic, and gas emission measurements, and combinations of those datasets, cluster around that value. It would seem that Don’s estimate of magma supply to Kilauea from the volcano’s mantle source was largely accurate for the 50 years between 1952 and 2002.

In 2003, however, the character of volcanic activity at Kīlauea changed. The volcano began a multi-year period of inflation, accompanied by an increase in carbon dioxide and sulfur dioxide emissions (the latter implying a heightened lava effusion rate), that culminated in 2006–08 with the formation of new eruptive vents at the summit and along the East Rift Zone. By the early 2010s, the lava effusion rate had declined. Even though new eruptive vents continued to form on the East Rift Zone, such activity seemed to be controlled by processes local to the eruptive vents themselves (for example, conduit constriction), rather than volcano-wide unrest.

We developed a model that relates magma supply to surface deformation, sulfur dioxide emission rates, lava effusion, and magma composition, and that also accounts for magma compressibility, loss of sulfur to the hydrothermal system, and possible magma storage in the volcano's deep rift zones (processes mostly neglected in previous supply rate estimates). Our estimate of magma supply prior to 2003 is consistent, to a high degree of confidence, with Don’s 1972 calculation. By 2006, however, magma supply had increased as part of a surge from the mantle. Following this surge, the supply appears to have decreased to below the long-term average. This lull, which continued through the 2014–15 Pāhoa lava flow crisis, might have been responsible for the sluggish nature of those flows far from their source vent, possibly preventing lava from traveling far enough to severely impact downslope communities.