The 1961 eruption of Kilauea Volcano, Hawaii

Abstract

The 1961 eruption or Kilauea Volcano, through the period February 24 to September 25, 1961, consisted of three summit eruptive phases followed by a flank eruptive phase.Tumescence of the Kilauea summit area, which began in the summer of 1960, continued virtually unchanged throughout and after the three periods of summit eruption.Rapid detumescence accompanied the flank eruption.Seismic activity during tumescence was moderate and persistent, but it gave no particular forewarning of imminent eruption.However, a swarm of relatively large earthquakes and strong harmonic tremor preceded the flank eruptive phase by about 16 hours.The three summit eruptive phases were confined to Halemaunrau, the deep crater within Knauea caldera.During the first summit phase, which lasted only 8 hours, on February 24, a small collapse pit on the floor of Halemaumau was filled with 320,000 cubic yards of lava.Within a few hours after fountaining ceased, most of the new lava had drained back through the eruptive vents.During the second summit phase, which lasted from March 3 to 25, the same collapse pit was refilled.The third and most voluminous of the summit phases began on July 10 when lava fountains burst from the crater floor along a zone more than 1,500 feet long.The eruption continued until July 17, forming a new lake of lava 210 feet deep and 17.3 million cubic yards in volume.Backfiow after fountaining resulted in a loss of approximately 1.3 million cubic yards.The 1961 eruptive cycle ended with a flank eruption along a 14-mile segment of Kilauea's east rift zon.e from September 22 to 25. Thirteen small, discontinuous lava flows, whose total volume was about 1.9 :million cubic yards, were produced; and a large number of new cracks emitted volcanic fume and steam.Drainback of large volumes of lava into cracks apparently occurred at all the outbreaks, and no large flows were formed.The futal volume of new lava added to the surface by all the 1961 eruptive phases is • approximately 18.2 million cubic yards.Measured rates of extrusion ranged from 660 cubic yards per hour during the second summit phase to 114,000 cubic yards per hour during the third summit phase.Temperatures of the erupting lava ranged from 1,085° to 1,127° C in the three summit eruptive phases.The lavas range from tholeiite basalt in the summit and upper rift zone areas to tholeiite olivine basalt lower on the rift zone.Variation diagrams based on eight new chemical analyses indi• ca:te that the composition of the 1961lavas was affected by three types of differentiation: {1) removal of magnesian olivine, (2) removal of augite and minor plagioclase, and {3) addition of magnesian olivine.The first type affected the composition of both the summit and flank lavas; the second type produced the characteristic differences between the summit and fi'ank lavas; and the third type was responsible for the range in composition of the flank lavas.Extensive faulting and cracking along the east rift zone preceded, accompanied, and followed the flank eruptive phase.New faults having as much as 20 feet of vertical displacement were formed, and many old faults were reactivated.The 1961 flank activity occurred a:long the north side of the rift zone, which is noticeably bipartite; the north side is characterized by gra• benhorst topography and the south side, by cinder cones.

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