Eruptions in Grimsvotn, Vatnajokull, Iceland, 1934-1991

During the period 1934 to 1991 evidence has only been found for three or four volcanic eruptions within the Grimsvotn volcanic centre, i.e. the directly observed eruptions in 1934, 1938, 1983, and probably a small eruption in 1984, deduced from seismic tremors. Reported openings in the ice shelf (1945, 1954, 1960) are considered not to be signs of eruptions but could be explained by either steam explosions of hydrothermal reservoirs sealed by impermeable caprock or by increased upwelling of hydrothermal fluid in reservoirs of high permeability. The eruptions of 1934 and 1983 produced hyalo-clastites of volume 30-40 × 10⁶ m³ and 10 × 10⁶ m³, respectively. The eruption of 1938, on the other hand, produced volcanic material of the order of 400 × 10⁶ m³ and may have been the third largest eruption in Iceland this century, after Hekla in 1947 and Surtsey in 1963-1967. -from Authors