Sources of crustal deformation associated with the Krafla, Iceland, eruption of September 1984

A decade-long plate-boundary rifting episode in northern Iceland ended with the September 1984 fissure eruption of Krafla volcano. We apply a nonlinear inversion method to geodetic data collected before and after the eruption to infer the location, geometry, and strengths of deformation sources associated with the eruption. The net outflow of magma from a 3-km-deep magma chamber beneath the Krafla caldera was 30 - 120 x 10(6) m(3). A similar volume of magma. 50 - 70 x 10(6) m(3), was emplaced in a 1-meter-wide, similar to 9-km-long dike extending from the surface to similar to 7 km depth. Furthermore, at least 110 x 10(6) m(3) of magma erupted. Accordingly, a surplus of magma must have been expelled from a second reservoir, the location of which, although uncertain, is likely to lie at depths greater than similar to 5 km beneath Krafla volcano. It would be difficult to detect this deeper source because of the narrow aperture of the geodetic networks.