Observed ground deformation at Hekla, Iceland prior to and during the eruptions of 1970, 1980–1981 and 1991

Abstract

Abstract Ground tilt measurements in the vicinity of Hekla have demonstrated a slow rate of deformation during periods of repose and rapid deformation during eruptions. An eruption started at Hekla on January 17, 1991 after a repose period of almost 11 years. This eruption was preceded by a slow inflation of the volcano, centered 4 to 6 km north or northwest of the summit. An uplift rate of 3 to 4 cm/yr is indicated with a probable depth to the source of deformation of 5 to 6 km. A deflation during the eruption is centered at the same location, and the maximum subsidence was 30–40 cm. The volume of the subsidence bowl is estimated as 0.05–0.1 km 3 . If this subsidence is the result of removal of magma from a shallow reservoir, then the volume of escaped magma is approximately twice the volume of the subsidence bowl. Hekla has erupted four times since the initiation of deformation measurements in 1968, first in May–July 1970, then in August 1980 and again in April 1981, and finally in January–February 1991. If the vertical component of ground deformation is used to estimate the relative magnitude of these eruptive events, then the 1991 event is similar to or smaller than the 1970 event, while the 1980 and 1981 events are significantly smaller.