The February 1969 east rift eruption of Kilauea Volcano, Hawaii

Abstract

Between February 22 and 28, 1969, about20x 10 6 m 3 ofbasaltic lava covered more than 6 km 2 of the upper east rift zone of Kilauea Volcano, probably the largest recorded eruption on the upper rift to that time. The eruption broke out along a discontinuous, 11-km-long fissure zone extending downrift from near Aloi Crater. A 70-m-deep lava lake formed in Alae Crater, near the site of the most prolonged activity. The lava is olivine-poor tholeiite; its hybrid chemistry can be explained by mixing of magma of 1967-68 summit vintage with that erupted during the early part of the 196~ 71 Mauna Ulu eruption and with lesser amounts of differentiated magma like that erupted in October 1968. The eruption followed a 4-month-long period of summit and east rift tumescence and was accompanied by moderate summit deflation and severe uplift and dilation near the eruption site. The centers of horizontal and vertical deformation in the summit area migrated laterally before and during the eruption in response to the filling and emptying of a complex reservoir system. Comparison of depths to the summit reservoir derived from five theoretical models and a graphic approach shows poor agreement, although all agree on depths ofless than 5 km. The pattern of seismicity, timing of deformation and eruptive events, and chemistry of the lava imply the presence of a shallow magma reservoir on the east rift near Makaopuhi Crater. Seismic data suggest the existence of a nearly unobstructed magma conduit within the rift zone long before the eruption. Dikes that fed magma to the surface issued from this conduit, not directly from the summit reservoir.