USGS Preliminary Analysis_LERZ_7-15-18_v1.1

Home

northeast, but chaotically, with activity starting and stopping and shifting back and forth along the rift zone. This behavior was similar to that displayed during the early part of the current activity, but ramped up more quickly, with longer -lived fissures, higher fountains and spattering, and more voluminous lava flows. There was also considerable steam and ash venting, which has only been a very minor part of the current activity. The lava erupted in 1955 was among the most differentiated lavas on Kilauea. The first eruptive period in 1955 ended abruptly on March 7, but seismicity continued southwest of the initial breakout point near the current site of the PGV facility. The second period of the eruption began March 12 in the area where the continued seismicity was occurring. This area is south of Puu Kaliu, which is on the southern edge of Leilani Estates. The second set of 1955 fissures overlap with the western part of the current fissure system, but are south of it. This lava was less evolved (fresher) than the magma erupted during the first eruptive period that had been stored underground for at least decades. Activity associated with the second period of the eruption (34 days) along a 7 km (4.3 mi) long fissure system to the southwest of the first eruption period fissure system, also ramped up quickly, producing fountains within a few days that were higher than any that have occurred during the current activity, and sending lava to the ocean. Outbreaks continued to occur progressively farther southwest, with some exceptions, producing fast-moving flows. Fountaining exceeded 250 m (820 ft) by the end of the first week. Most of the fissures were short-lived (hours to a few days), and a few vents started and stopped repeatedly. The activity stopped on April 7. After a pause of 16 days, during which seismicity continued, the third period of the eruption started unexpectedly on April 24 with a resumption of activity at the western fissures. The eruption was episodic and relatively weak initially, but its vigor gradually increased through mid-May. On May 16, there was a sudden increase in output near the west end of western fissure system, with fountaining and new fast-moving flows. After 32 days of activity, fountaining ended abruptly on May 26, accompanied by a marked decrease in subsequent absence of notable seismicity. About 81 x 106 m3 of lava erupted (dense rock equivalent using 25% void space). The time -averaged dense rock equivalent (DRE) discharge rate of 14 m3/s over the 66 days of actual eruption. Considered separately, the three eruptive periods equate to time -averaged DRE discharge rates of 31 m3/s (period 1),18 m3/s (period 2), and 7 m3/s (period 3). 1960 LERZ eruption: January 13—February 19 (see Richter et al., 1970) The 1960 eruption, which lasted for about 5 weeks, opened along nearly the entire 1.4 km (0.9 mi) length of its fissure system at the onset of the eruption. These fissures behaved erratically for the first few days, often starting and stopping, but coalesced around a few points and began feeding fountains more than 400 m high by the end of the first week of activity. Early activity often included phreatic steam and ash venting. The high fountaining was accompanied by heavy tephra fall, and a large tephra cone was built. 14