ERUPTIONS OF KILAUEA VOLCANO — RICHTER AND EATON 353 



at depth, was recorded on the Survey's seismographs. Tilt measure- 

 ments, however, showed extremely rapid tumescence of the summit 

 area, strongly suggesting that magma was still welling up from the 

 depths and that the eruption was not over. Supplementing the seismo- 

 graph network with a sensitive portable seismograph late in December, 

 Survey scientists followed the development of a swarm of small earth- 

 quakes along Kilauea's east rift zone, 24 miles from Kilauea Iki and 

 not far from the site of the first outbreak of the 1955 flank eruption. 

 It appeared that magma inflating the summit region was also exerting 

 pressure on the plastic cores of the rift zones. As the rift zones 

 yielded, earthquakes revealed where dikes began to open toward the 

 surface. In early January the frequency and size of the earthquakes 

 in the east rift zone increased, and the area from which they emanated 

 moved on toward the sea. On January 13 strong earthquakes centered 

 near the village of Kapoho 28 miles east of Kilauea's summit, and an 

 old graben ^ 2 miles long and half a mile wide, which contained part 

 of the village and most of the farmland that sustained it, began to 

 subside. By nightfall displacements along the faults bounding the 

 graben had grown to several feet (pi. 1, fig. 2), and Kapoho was 

 evacuated. 



At 7:30 that evening the flank eruption began along a line of en 

 echelon fissures 0.7 mile long, a few hundred yards north of the village. 

 Once more the eruption started as a dazzling incandescent curtain of 

 fire that within 2 days shrank to a main eruptive zone, which continued 

 fountaining throughout the flank eruption stage (pi. 2, fig. 1) . Three 

 hours after the initial outbreak, sea water gained access to the main 

 vent area producing dense voluminous steam, salt, and fine ash clouds 

 that roared 2,000 feet into the air. Within a few hours, however, fluid 

 lava efl'ectively sealed the conduits and only occasionally during the 

 following 3 weeks was there appreciable steam emission. 



The main fountain area, 2 miles from the seacoast at an elevation of 

 approximately 90 feet, soon produced a steady stream of lava that 

 slowly flowed down through the graben, reaching the sea on the night 

 of January 15. At the end of the first week of the eruption the low 

 graben area was essentially filled ; and although lava continued to push 

 slowly into the sea, the reduced gradient forced material to spread 

 laterally over the adjacent old land surface (pi. 2, fig. 2). Slowly the 

 lava flows inundated the village of Kapoho, the smaller community 

 of Koae to the north, a U.S. Coast Guard station, and a number of 

 beach residences along the coast. On February 6, w^lien lava extrusion 

 had essentially ceased, approximately 156 million cubic yards of lava 

 had formed a pad of about 2,500 acres, including about 500 acres of 



* An elongated block which has subsided between a pair of normal faults. 



