352 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



ceased in the outermost vents and by 4 a.m. on November 15, only two 

 fountains remained. One of these lasted through the early afternoon, 

 when it too died ; the other gi-ew in size, eventually reaching the un- 

 precedented height of 1,900 feet on December 17, during tlie 15th phase 

 of the eruption. 



With the eruption confined to a pit crater, samplmg and observation 

 were greatly facilitated ; there was little danger to human life and only 

 minor damage to the land and forest (pi. 1, fig. 1). Furthermore, 

 rather precise calculations of the volume and rate of lava extrusion 

 could be made, much the same as in a graduated cylinder. The first 

 phase of the summit eruption lasted a half hour less than a week, 

 forming a lava pond in Kilauea Iki 335 feet deep and containing 40 

 million cubic yards of fresh basaltic lava. After a brief 5-day respite 

 activity resumed. Sixteen additional eruptive phases of much shorter 

 duration occurred in the 3-week period that ended December 20, 1959, 

 and contributed an additional 11 million cubic yards of lava to the 

 pond, increasing its depth to a maximum of 414 feet. 



Although the duration of the later phases decreased, the rate of lava 

 output increased. In the first phase a maximum of 500,000 cubic yards 

 per hour was measured ; the 16th phase spewed out its lava at the phe- 

 nomenal rate of 1,600,000 cubic yards per hour. From the end of the 

 second phase when the level of the pond rose above the volcanic vent, 

 liquid lava drained back into the vent each time the fountain stopped. 

 In fact, almost all the lava erupted after the end of the sixth phase 

 poured back down the vent. The rates for this withdrawal were also 

 phenomenally high. Although less accurately determined than the 

 extrusive rates, backflow rates exceeding 3 million cubic yards per 

 hour, or almost four times the average rate of extrusion, were meas- 

 ured. Inasmuch as the lava of these later phases was still heavily 

 charged with gas and had not decreased in temperature significantly, 

 it appears that the lava draining back into the vent was not recycled 

 but merely added to the enormous bulk of magma in the intricate sys- 

 tem underneath the summit which fed the vent. 



The temperature of the lava erupted at Kilauea Iki was consistently 

 measured between 1,120° and 1,190° C. The percentage of silica in 

 the lava varied between 46.3 and 49.5 during the early phases, but more 

 or less stabilized at 46.8 after the fourth phase. Petrographically the 

 lava is a tholeiitic picrite basalt, consisting of olivine phenocrysts set 

 in a fine-grained groundmass of plagioclase feldspar, pyroxene, and 

 glass. The high temperature, mineralogj^ and chemistry correlate 

 with the generally "primitive" nature of the lava, modified only by 

 accumulation of olivine. 



After the cessation of surface activity in Kilauea Iki on December 

 20, 1959, only small harmonic tremor, indicating minor lava movement 



