Volcano Watch — The current state of activity in Kīlauea Volcano's lower East Rift Zone

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In web forums and at recent public meetings, USGS Hawaiian Volcano Observatory (HVO) scientists have been asked about conditions in Kīlauea Volcano's East Rift Zone downrift of Pu‘u ‘Ō‘ō, especially near Leilani Estates and Kapoho.

Many of these inquiries follow anecdotal reports of rising temperatures in spring-fed ponds and increased steaming in some areas of Puna. HVO has not confirmed these reports, but based on our seismic, geodetic and gas monitoring networks, there has been no change in magma supply to the lower part of the rift zone (downrift of Pu‘u ‘Ō‘ō).

Kīlauea's East Rift Zone is over 125 km (78 mi) long, and stretches from the volcano's summit caldera through Cape Kumukahi to the offshore sea floor. The area designated as the "lower East Rift Zone" lies between the Heiheiahulu shield and Cape Kumukahi. Notable recent eruptions along this part of the rift zone include the 1960 Kapoho eruption, as well as eruptions in 1955, 1961, 1840, and 1790. The Pu‘u ‘Ō‘ō vent is located in the middle part of the rift zone.

In terms of seismicity, deformation, and gas emissions, the rift zone between Pu‘u ‘Ō‘ō and Cape Kumukahi is currently at background levels. The number of earthquakes with magnitudes over 1.7 is the lowest in 15 years, and subsidence has dominated the deformation recorded by the permanent GPS network over that same time period. Gas measurements also have not shown appreciable changes in the lower East Rift Zone.

Since the installation of Kīlauea's modern seismic network in the 1950s, lots of seismic activity has been detected in the lower East Rift Zone, including before and during the eruption at Kapoho in 1960, and during earthquake swarms in 1962, 1964, 1966, 1970, 1973, 1975-76, 1980 and 1982. The 1960 Kapoho eruption consisted of many thousands of precursory earthquakes and harmonic tremor (an increase in the background levels of seismic "noise"). Swarms of earthquakes recorded since 1960 have typically lasted days to weeks and consisted of at least 100 events per day, possibly due to magma or hot fluids moving through the lower East Rift Zone.

Interestingly, strong earthquake swarms in the lower East Rift Zone have been absent since the start of the ongoing Pu‘u ‘Ō‘ō eruption, suggesting that little, if any, new magma has been transported downrift of Pu‘u ‘Ō‘ō and associated eruptive vents. In the mid-2000s, minor surface uplift and a slight increase in earthquakes suggested a small increase in magma being transported to the area, but that activity was associated with a surge in magma supply to the entire volcano that has since diminished.

If any magma in the lower East Rift Zone were to begin rising to shallow levels, we would expect to see much stronger deformation and energetic earthquake activity. Based on the absence of these signals, HVO is confident that anecdotal reports of rising pond temperatures and increased steaming are not the result of an increase in magma being transported to the lower East Rift Zone.

However, this is not to say that magma is not present beneath that part of Kīlauea. Drilling operations in the lower East Rift Zone in 2005 actually intersected a small body of magma at a depth of about 2.5 km (1.6 mi). This magma was stagnant and probably just one of many small magma bodies trapped within the rift zone—relicts of past intrusions and eruptions.

Nevertheless, HVO is keeping a watchful eye on all parts of Kīlauea Volcano's East Rift Zone. Lower East Rift Zone eruptions have occurred in the past and can be expected in the future, but any new activity will be preceded by warning signs that will be detected by HVO's monitoring networks.

As with all natural hazards, it's a good idea to have a personal plan in place for responding to future volcanic activity, especially if you live or work in areas located within or near rift zones on Kīlauea or Mauna Loa. Being prepared is always the best defense.

We continue to encourage Puna residents to stay informed about Kīlauea Volcano's active lava flow. Daily updates and recent maps and photos are posted on HVO's website and the Hawai‘i County Civil Defense website. HVO's daily update is also recorded as a phone message at 808-967-8862.


Volcano Activity Update

The June 27th lava flow from Pu‘u ‘Ō‘ō remained active on Kīlauea Volcano's East Rift Zone, and continued to slowly advance in a northeast direction. As of October 8, the flow front was 1.4 km (0.9 mi) upslope from Apa‘a Street/Cemetery Road, as measured along a straight line. Within the Pu‘u ‘Ō‘ō crater, glow was visible above several small outgassing openings and a small lava pond on the crater floor.

The summit lava lake within Halema‘uma‘u Crater produced nighttime glow that was visible via HVO's webcam over the past week. The lava level dropped slowly over the past week, and was roughly 55 m (180 ft) below the rim of the Overlook crater as of this writing (Thurs., Oct. 9).

There were no earthquakes reported felt on the Island of Hawai‘i during the past week.