Volcano Watch — Quake starts Kīlauea off on a busy two weeks

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The last two weeks have been particularly busy on Kīlauea Volcano. On October 2, starting about 3:30 p.m., the tremor near Pu`u `O`o began to increase, and it appeared as if another phase of the episode 51 eruption would be under way soon.

 

Quake starts Kīlauea off on a busy two weeks...

Quake starts Kīlauea off on a busy two weeks

(Public domain.)

The last two weeks have been particularly busy on Kīlauea Volcano. On October 2, starting about 3:30 p.m., the tremor near Pu`u `O`o began to increase, and it appeared as if another phase of the episode 51 eruption would be under way soon. Sometime before about 8 p.m., the episode 51 vents apparently began to erupt before a magnitude 4.3 earthquake rattled the south flank of Kīlauea at 7:51 p.m. and disrupted the south flank of the Pu`u `O`o cone. The earthquake was followed by reports of a glow from a new location on the south side of the cone, although our monitoring equipment showed nothing different from previous times when episode 51 restarted.

Around 3:00 a.m. Saturday the amplitude of tremor recorded near Pu`u `O`o increased dramatically to levels not seen recently. The flow reported soon after the earthquake and the dramatic increase in tremor at 3:00 a.m. suggest that the new episode 52 eruption began quietly immediately after the earthquake and that, at 3:00 a.m., the new vents began to erupt vigorously.

The following day, we mapped a new fissure, 215 feet long, on the south side of Pu`u `O`o. A series of four spatter cones were scattered along the fissure, with the most active one closest to Pu`u `O`o. By early afternoon, an `a`a flow had advanced about two miles downslope toward the south to the 2,100-foot level. The episode 51 vents were inactive in the morning and early afternoon, but a small, sluggish began issuing from the vents at about 3:30 p.m. The lava pond inside the Pu`u `O`o cone was deep - about 230 feet below the rim - as it usually is during eruptive intervals. The fume from the cone was also very heavy, thereby making visibility poor.

On October 4, activity at the episode 51 vents was greater and at the episode 52 vents was less, compared to the previous day. Only the northernmost of the episode 52 spatter cones was still active. The lava erupted from the episode 52 vent was ponding at the base of the Pu`u `O`o cone at the 2,400-foot level, and the distal end of the `a`a flow as breached and sent a large flow moving toward the east, covering the earlier erupted `a`a flows from the same vent.

By evening, the volume of lava erupting from the episode 51 vents exceeded that erupting from the new episode 52 vent although the flows from the episode 52 vent were advancing into the forest to the southeast of Pu`u `O`o. By October 7, the episode 52 vents were almost inactive. Only a small flow oozed from the last remaining active vent. Farther downslope, the lava flows from the 52 vents were stagnant. At the same time, the episode 51 vents became increasingly active and emitted a strong flow, but no spatter, from the largest spatter cone. The lava flowed downslope to the base of the episode 51 shield and ponded. Pahoehoe flows advanced to the 2,300-foot level. By this time, the pond inside Pu`u `O`o had risen slightly to about 215 feet below the rim.

On October 8, the large lava pond, located at the base of the episode 51 shield, which was filled by lava erupted from the episode 51 vents, drained and extended the active pahoehoe flows to the 2,240-foot level. The episode 52 vents remain barely active, with a small flow near the last active vent. By the following day, the episode 52 vents were inactive, but the flows from the episode 51 vents were burning trees at about the 2,150-foot level. On October 10, the episode 51 flows had advanced to the 2,000-foot level. However, by the following day, these flows had stagnated, and lava was overtopping the channel farther upslope. On October 12, a last, small lava flow issued from the episode 52 vents; this appears to have been the last activity from these vents. On this same day, the pond inside Pu`u `O`o was so deep that we could not see it from our normal vantage point on the rim. Flows continue to issue from the episode 51 vents as of this writing on Friday morning.

As can be gleaned from the above account, the numbering of the eruptive episodes has become somewhat confusing. In this case, the old episode 51 vents have continued to be active, while then new episode 52 vents started and stopped. We have been calling an episode by a new number if lava erupts from a new vent, regardless of whether the previous vent continues to be active. We suspect that activity will not return to the new episode 52 vents, as they appear to have sealed themselves with lava. However, the episode 51 vents continue to be active. This same situation occurred last November when a new fissure broke out between Pu`u `O`o and Kupaianaha. We called the new fissure eruption episode 49, even though the eruption at Kupaianaha (episode 48) continued throughout the episode 49 eruption.

The main purpose of the numbering scheme is to keep track of which eruptive vents are active. All 52 episodes have been part of a single eruption that began in January 1983. The changes we are currently monitoring signify how unstable and episodic the system has become, following the nearly five years of steady-state eruption from the Kupaianaha shield. These changes still appear to be a stage in the process of winding down this longest historic rift eruption on Kīlauea Volcano. We do not know how long this winding-down process will take, but expect the next months - to perhaps a few years - to be characterized by increasing instability and further changes in the vent locations.

In addition to the earthquake that preceded the start of eruptive episode 52, four others with magnitudes greater than 3.0 occurred in the last two weeks. The first two, which occurred on October 1 at 10:58 p.m. and on October 2 at 8:05 p.m., were in the same area as the larger magnitude 4.3 earthquake that triggered episode 52. They had magnitudes of 3.0 and 3.3 and were located 3.7 and 2.6 miles deep, respectively. The magnitude 4.3 earthquake was slightly deeper (4.3 miles deep). The next moderate earthquake was located nearly 30 miles below Leleiwi Point just east of Hilo and was widely felt (even as far as Maui) because of its great depth. The last earthquake in this two-week period occurred on October 14 at 5:55 p.m., was located about 4 miles beneath the Ka`oiki fault zone between the summits of Kīlauea and Mauna Loa Volcanoes, and had a magnitude of 3.0. All of these earthquakes, except the deep one beneath Leleiwi Point, were caused by seaward movement of the southflank of the island. The earthquake beneath Leleiwi Point was caused by weight of the island bending the outer, brittle layer (the lithosphere) of the Earth.

The column was missing last week because I was on an oceanographic ship working on the submarine extension of the East Rift Zone of Kīlauea Volcano. Those of you living in the Kapoho to Pohoiki areas may have seen a large, yellow-beige ship working offshore. The ship, the "Laney Chouset," is the support vessel for the Navy's manned submersible "Seacliff," which is capable of diving to depths of 20,000 feet. Dr. Jim Anderson from the Geology Department of the University of Hawai`i at Hilo and Dr. Ken Hon, former staff geologist from the Hawaiian Volcano Observatory, joined me in this work and dived in the submarine. I will expand on the objectives and results of this program in a future column.