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Earthquake swarm and ground deformation event at Kilauea Volcano
September 12, 1999
Starting about 1:31 Sunday morning, September 12, a swarm of small earthquakes and associated volcanic tremor began at Kilauea Volcano. The swarm was concentrated along the east rift zone between Devil's Throat and Mauna Ulu, but earthquakes eventually occurred in a broader area involving the summit and south flank areas. The strongest part of the swarm lasted a couple of hours, but earthquakes are continuing at the time of writing (2:00 p.m., September 12), as is tremor from the summit caldera. Many of the earthquakes were felt by residents of Mauna Loa Estates, Volcano, and other nearby areas. Most of the earthquakes were shallow, within 2-3 miles of the ground surface. The largest rift zone earthquake was approximately magnitude 3.0. At 5:59 a.m. the largest earthquake in this episode occurred beneath Kilauea's south flank, near Pu`u `O`o. This earthquake was approximately magnitude 3.7, but final calculations have not yet been made.
Accompanying the earthquake swarm was deflation of the summit area and the east rift zone between the summit and Pu`u `O`o. The deflation, detected by five electronic tiltmeters newly installed in this area, began at about the same time as the earthquakes and tremor. We anticipate that GPS data, currently being processed, will show substantial widening of the rift zone.
The floor of crater in Pu`u `O`o collapsed and is now mostly covered with rubble. Aerial views at about 11 a.m. showed only a tiny pad of weakly spattering lava remaining in the crater.
The flow of lava through the tube to the coast was weak and sluggish when observed between 11 a.m. and noon. One small trickle was entering the ocean at the bench, most of which had collapsed into the sea since about 8 a.m. this morning. By 1:30 p.m., the steam plume had died, and the eruption had entered into another pause, which likely will last from a few days to several weeks.
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Updated : 12 Sep 1999