A reminder that the next Pahoa eruption information meeting will be held at 5 p.m. Wednesday, August 29, 2018 at the Pahoa High School cafeteria. There will be no meeting tonight (Aug 21). Also, future eruption meetings will be held bi-weekly.
This animation begins a month earlier on April 1 to start with a more typical earthquake pattern and proceeds forward in time at a rate of one day per second of animation time. Circles indicate the location of earthquakes as they occur, with their size indicating their magnitude and their color representing their depth. Three days before the swarm began the lava within the “Overlook crater” inside of Halema‘uma‘u overflowed. Then on April 30 the 35-year-old Puʻu ʻŌʻō eruption ceased and its cone partially collapsed. This event coincided with the start of a swarm of volcanic earthquakes on Kilauea’s East Rift Zone, a feature extending from the volcano’s summit that carries magma underground through its flanks. Eruptions can take place anywhere along this rift zone as well as at the volcano’s summit. Earthquake occurrence then moved northeast along the East Rift Zone away from the summit, suggesting the movement of magma below ground in this direction. Magma reached the surface and erupted as lava on the afternoon of May 3, eventually building channelized lava flows, destroying about 700 homes, and covering more than 12 square miles including Kapoho Bay. In this animation a growing orange field represents these lava flows.
Lava began to drain from the “Overlook crater” at the same time and by May 15 its lava lake had dropped hundreds of feet before producing steam-driven explosions when it interacted with ground water. Some of these explosions were strong enough to register as magnitude 5.0 earthquakes and sent ash clouds to 30,000 ft. above sea level. By the end of May, however, these explosions changed their character such that they no longer produced large steam-driven ash clouds. The walls of Halema‘uma‘u had begun to collapse, thus widening it and burying its “Overlook crater” as magma continued to drain from the summit to feed the flank eruption. These “collapse explosions” seemed to release trapped volcanic gas rather than groundwater steam and yielded only small ash clouds, though they still released explosive energy greater than magnitude 5.0 earthquakes and occurred about once per day. In this animation black circles represent these volcanic explosions with their size indicating their energy release in equivalent earthquake magnitude. No explosions have occurred since August 2 but it is too early to tell whether similar explosions will happen again.
This animation includes charts showing some statistics about the earthquake activity. The top graph shows the maximum earthquake magnitude per day. The bottom graph shows the total number of earthquakes per day. On April 30 the frequency of earthquakes increased to about 100 per day and their magnitudes exceeded magnitude 4.0. The largest earthquake struck on the afternoon of May 4 with a magnitude of 6.9 that produced numerous aftershocks that continue today. This largest earthquake also moved the flank of Kilauea Volcano as much as 20 inches seaward. With the subsidence of Kilauea Caldera and the collapse of Halema‘uma‘u the number of earthquakes dramatically increased to more than 700 per day by June 15 and continued until August 4 when they suddenly returned to normal background levels, coinciding with the pause of the vigorous eruption of lava.