The eruption of August 1963 and the formation of Alae lava lake, Hawaii

After the seismic episodes and summit collapses of May, July, and early August 1963, Kilauea Volcano, Hawaii, erupted along the east rift zone in and near Alae Crater from August 21 to 23, only 8lh months after the December 1962 eruption in nearby Aloi Crater. The eruption started at 18hlom, August 21, after nearly 4lh hours of summit deflation, low-amplitude tremor, and many small earthquakes. Fountains on the floor and north wall of Alae Crater fed lava, at rates as high as 2.3 X 10m per hour and at maximum temperatures of about 1,160°C, into a growing lava lake in the southeast pit of the crater. During the last 12 hours of the eruption, a decrease in the rate of extrusion to near zero, accompanied by a decrease in temperature to 1,140°C, led to stagnation of the lava lake at its maximum volume of 8.4X10~• Near the end of the eruption at 08h10m, August 23, 1.8X10m of lava drained back into the vents leaving a stagnant lake 305 m long, 245 m wide, and as much as 15 m deep, composed of homogeneous tholeiitic basalt containing 3.5 percent olivine. A low spatter ridge partially covered and bordered the northwest side of the lake and continued as coalescing spatter cones on the north wall of the crarter. The flat central floor of the lake was 14.0 m deep, but the northern part thinned to 11.3 m over a buried spatter ridge. The surfac'e of the lake was complex in detail and showed a variety of flow features, which are a record of the many events that took place during and after the eruption. A 30 . m wide levee of discontinuous slabs and pressure ridges bordered all but the northwest margin of the lake and was in turn bounded for most of its length by a moat as deep as 5 m. The main part of the lake was crossed by pressure ridges and linear oozeups, which marked the position of glowing cracks during the eruption. Shear zones marked the boundaries between crust formed on relatively static lava and crust formed on lava flowing out from the vent area. Observation during the eruption and later mapping of the surface feature's indicated that during the later part of the eruption, the lava lake consisted of an outer stagnant part and an inner part marked by active lava circulation; lava flowing outward from the vent rafted crust against the stagnant margin, shoving up piles of broken slabs and buckling the crust along lines of weakness. The surface of the lake was broken by cracks formed largely as the result of stresses induced by thermal contraction of the cooling lava. Cracks that developed near the end of the eruption formed a random, orthogonal network outlining 0.3to 0.7-m-high hummocks, which were divided by orthogonal cracks into 3to 6-sided polygons averaging 1% m in diameter. Many new cracks, mostly short ones near the crests of hummocks, opened during a period of heavy rainfall 5 to 9 months after the eruption. Most of these cracks were sites of deposition of sublimates of sulfur and calcium · sulfate. Between 1 and 2 years! after the eruption, when the lake had completely solidified, the surface was broken by long swarms of short cracks that originated in the zone of maximum cooling at depths of 5 to 10 m in the lake and propagated upward to the surface. Field stud,ies of the August 1963 lake ended in February 1969, when the lake was covered by 72 m of new lava.