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 a•ccompanied 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.

Chronological narrative of the 1969-71 Mauna Ulu eruption of Kilauea Volcano, Hawaii

“…1). Thereafter, activity shifted to the upper and middle parts of the east rift zone, with eruptions in August and October 1968 (Jackson and others, 1975) and February 1969(Swanson, Jackson, Koyanagi, and Wright, 1976. Each rift eruption was larger than its predecessor; the February 1969 eruption, with a volume of lava of 20 X 106 m3, was probably the largest historic rift eruption at Kilauea prior to the 1969-71 Mauna Ulu eruption.…”

“…Six episodes of the first stage produced lava fountains 300 m or more in height, and one fountain was 540 m high. Fountain height correlated roughly with the rate of (Swanson, Jackson, Koyanagi, and Wright, 1976) and in mid-August and late September 1971 (Peterson andothers, 1976); all three of these brief eruptions were accompanied by marked changes in ground tilt(A) and horizontal strain (B). 'From Swanson, Jackson, Koyanagi, and Wright (1976).…”

“…The photographs also show that Aloi Crater, earlier filled to a depth of 25 m with a pool of new lava, was now largely empty owing to drainback into a gaping fissure in the floor. Lava was pouring into Alae Crater and had already covered the floor, burying drilling equipment being used in a study of the February 1969 lava lake (Swanson, Jackson, Koyanagi, and Wright, 1976).…”

“…Other eruptions occurred within 1 km of the Mauna Ulu area in August 1963 (Peck and others, 1966) and February 1969 (Swanson, Jackson, Koyanagi, and Wright, 1976), only three months before the 1969-71 Mauna Ulu eruption began. Throughout the 1960's, the area centered around Aloi and Alae Craters was the western limit of volcanic activity on the rift zone, except for a small eruption in and near Hiiaka Crater (pi.…”

“…Such structural complexity may facilitate temporary blockages in magma conduits connecting with the summit reservoir, leading to temporary storage, increased magmatic pressure, and eruption uprift from the blockage. In their discussion, Swanson, Jackson, Koyanagi, and Wright (1976) relate this theme to the origin of magma reservoirs and pit craters along the upper east rift zone. ACKNOWLEDGMENTS Scores of individuals, from long-time personnel of the Hawaiian Volcano Observatory to mainland tourists on their Hawaiian holiday, contributed the observations that make this narrative rather complete despite the long duration and complicated nature of the eruption.…”