July 5, 2007
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Lava back in the Pu`u `O`o crater as scientists mull over Kilauea's future
The answer to the question asked by Hawai`i's residents and volcano enthusiasts since June 19?where is Kilauea going to erupt next?is clear, now that lava is back in the crater of Pu`u `O`o.
Small flows in the deepened crater were spotted early Monday. As more lava erupted onto the crater floor, a slowly circulating lava pond was formed by July 4th.
Time will tell whether lava will continue erupting in the crater, overflow the rim as it did in 1997, erupt from the side of the cone as it has for many years, withdraw again for a short time, or quit erupting altogether.
The events of the past three weeks are a strong reminder of the ever-present potential for Kilauea to suddenly and unpredictably change its style. The nearly 25-year long eruption is not the volcano's norm, when compared to the past several hundred years of activity.
In fact, it is nearly impossible to define what is normal for Kilauea, except frequent changes in location of eruptions and underground intrusions of magma at the volcano's summit or along its rift zones. Change is what we should expect from Kilauea as time passes?both in the nature and locus of activity?instead of decades of activity at Pu`u `O`o.
For now, it is not possible to anticipate the next intrusion and eruption, based on the pattern of activity scientists have observed and worked hard to characterize.
It is possible, however, to narrow the possibilities when there is a sudden, rapid change in the location of hundreds of small earthquakes and volcanic tremor and deformation of the ground, as detected by continuously recording instruments.
Wherever such activity begins, we know that it can migrate sometimes uprift toward the summit, but almost always downrift, away from the summit. The earthquakes and changing ground movements indicate the direction magma is moving toward or away from the summit, and upwards, toward the surface. Being ready for such sudden change requires constant vigilance.
Scientists must have extensive and well-maintained networks of monitoring instruments around the summits and the very long rift zones of Kilauea and Mauna Loa volcanoes. A robust alarm system is also required to notify scientists around the clock of important changes that may signify eruption in a new location or significant change in an ongoing eruption.
For example, on June 17 within 5 minutes of the volcano-monitoring system?s recording and detection of a sudden change in tilt at the summit of Kilauea at 2:14 a.m., several scientists were automatically notified of a "tilt alarm." A scientist was at the observatory within 15 minutes, and 5 more arrived within the hour to assess the activity.
Scientists quickly determined that magma was moving from the summit reservoir into the upper east rift zone beneath the Mauna Ulu area. The magma continued moving episodically downrift a few kilometers (miles) and erupted by early morning on June 19. The monitoring and alarm system worked very well, indeed.
Is it back to business as usual at Pu`u `O`o or has something changed that may affect Kilauea?s near-term future?
Between 1983 and 2002, the summit area was continuously subsiding. A simple interpretation is that less magma was entering the summit reservoir from the deep, hot-spot source than was moving into the east rift zone to erupt at Pu`u `O`o.
Beginning in early 2003, the summit area began inflating for the first time during the long-lived eruption. If the same reasoning is applied, more magma was moving into the summit reservoir than was leaving the reservoir and erupting at Pu`u `O`o. This would mean that the summit reservoir was becoming increasingly pressurized with new magma.
With this simple explanation, it was not surprising, then, that the Father?s Day intrusion and eruption occurred. When the pressurized magma reservoir system sprang a leak, magma rushed into the upper east rift zone in an area where many intrusions have occurred in the past 50 years.
Kilauea is slowly inflating again. Perhaps, if the trend continues as it has since 2003, one or more additional intrusions or eruptions will occur?not at Pu`u `O`o?but elsewhere at Kilauea in the coming months.
This past week, activity levels at the summit of Kilauea Volcano remained low. Seismic tremor levels remain low; earthquakes continue to be concentrated in the upper east rift zone. The summit caldera is again inflating.
Lava has returned to Pu`u `O`o after a two week vacation. Early in the morning on July 2, Pu`u `O`o reawakened and began to intermittently erupt lava from a vent in the center of the crater floor. The vent is almost directly below the site of the former Beehive vent. This part of the crater floor dropped about 100 meters during the first few days of the recent Father's Day intrusion.
As of this writing (July 5), lava continues to erupt from the new vent, and the crater is filling relatively rapidly. Nearly the entire crater floor has been resurface by a ponded lava flow. This has provided spectacular viewing, especially at night, via the Pu`u `O`o webcam (http://hvo.wr.usgs.gov/cam/index.htm). Lava has not yet appeared outside of Pu`u `O`o cone, though, with the rapid rate of refilling, this may not be the case for long.
One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.8 earthquake occurred at 12:28 p.m. on Tuesday, July 3, and was located 1 km (1 mile) northeast of Hakalau at a depth of 40 km (25 miles).
Mauna Loa is not erupting. One earthquake was located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates which have slowed further since May 2007.
Updated: July 9, 2007 (pnf)