Volcano Watch — Earthquakes swarm beneath Kīlauea Volcano

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The most notable event on Kīlauea Volcano this past week was a swarm of small earthquakes, mainly on January 13. This swarm included two earthquakes with magnitudes larger than 3.0 (see figure) and numerous smaller earthquakes. 

The swarm was recorded by the U.S. Geological Survey's permanent seismic network, which located the swarm beneath the Holei Pali on the south flank of Kīlauea downslope from Mauna Ulu, a lava shield that formed in 1969-1974. The earthquakes were located about 6 miles deep and are caused by seaward movement of the south flank of Kīlauea. This seaward movement of the south flank is ultimately caused by injection of magmainto the East Rift Zone. The injected magma pushes the adjacent rocks aside. Because the north flank of the rift is buttressed against Mauna Loa, it cannot move easily. However, the south flank of the rift zone is free to slide seaward. 

Following the November episode 49 eruption, small earthquakes have been abundant along the upper East Rift Zone between the summit and Pauahi Crater; these earthquakes indicate that magma has been injected into, and stored within, the upper East Rift Zone during this time period. At the same time, the summit of Kīlauea reinflated rapidly from late November to the end of December but has shown almost no change since. 

Much of the magma supplied to Kīlauea from beneath the volcano was apparently stored under the summit until the end of December, but since that time, magma has moved into the upper East Rift Zone. This addition of magma into the upper East Rift Zone caused the numerous small earthquakes in this region between November and January and pushed the south flank seaward this past week. Similar sequences of events caused significantly larger earthquakes in 1975 (magnitude 7.2 Kalapana earthquake) and 1989 (magnitude 6.1 Kalapana earthquake). Following the recent swarm of earthquakes beneath the Holei Pali, the summit has once again begun to inflate, thereby suggesting that magma is again being stored beneath the summit. The summit is now slightly more inflated than before episode 49. 

The eruption on the East Rift Zone of Kīlauea Volcano continues with low-volume, steady effusion of lava from the breakout at about the 1,900-foot level of the tube downslope from the Kupaianaha vent. This is the same area that has had active flows for the last several weeks. The volume of lava traveling down the tube to the eruption site continues to decline slowly and is now estimated to be less than 30,000 cubic yards per day. The lava pond within Pu`u `O`o has been quite active, as seen by the bright glow at night and the occurrence of short bursts of more intense tremor recorded on nearby seismograph stations. The pond has also risen to within 130 feet of the spillway - the highest level reached before episode 49 in November. The recent storm knocked out a seismic station near Pu`u `O`o, so we cannot remotely monitor the activity in the crater until the station is repaired.

It is likely that the Kupaianaha vent will stop erupting in the near future and episodic fissure eruptions will commence in the vicinity of the episode 49 vents or, possibly, along the upper East Rift Zone near Pauahi Crater.