November 6, 2003
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
How does HVO watch the eruption?
Kilauea's eruption is 24/7; it needs no sleep, takes no days off, and cares not if rain is falling in buckets. HVO's staff is not 24/7; it needs sleep, takes days off, and can't do much observing in heavy rain. How, then, does HVO watch the eruption?
The information comes from three general sources: continuously operating instruments, aerial and ground observations by staff members, and reports from national park rangers and the general public. This information is cross-checked for consistency and then reported to the public on a daily or more frequent schedule.
Several instruments provide real-time information that proves crucial for evaluating activity near Pu`u `O`o. Probably the most important is a network of three tiltmeters, two on the cone itself and another a short distance up the rift zone. The tilt information is radioed to HVO, where it is immediately displayed on a computer screen.
The two tiltmeters on the cone respond to changes of magma pressure beneath Pu`u `O`o. They tell us when the changes occur, how long they last, and how large the tilting was in response to the pressure changes. The tiltmeter up the rift zone shows much smaller changes but can tell us if the pressurization is large enough to affect the area between Pu`u `O`o and Napau Crater.
Increased pressure under Pu`u `O`o is often a time of moderate to low eruptive rate; the conduit is not open enough for magma to flow freely to the surface, so a back pressure results. When the pressure is released, the cone deflates and eruption output increases.
A seismometer 1.8 km (1.1 miles) uprift of Pu`u `O`o provides information about the strength of the volcanic tremor, the occurrence of earthquakes, and the frequencies at which seismic energy is being released. Often, for example, the strength of tremor or the frequency of energy release changes during the slow rise and rapid drainback of magma accompanying gas-piston events in the crater of Pu`u `O`o. Without visual observations, the seismicity can tell us that gas pistoning is taking place.
An in-house, radio-linked video camera on the rim of the crater reports back visible activity. Unfortunately, the crater is often obscured in fume or clouds, and the camera has a relatively narrow field of view that doesn't include important areas. We are currently upgrading to a tilt-pan-zoom camera but will never be able to cut through clouds and fume. The camera is especially useful at night to check on incandescence and glow.
Thermal sensors operated by the University of Hawai`i perch on the crater rim next to the camera and report temperatures at several locations in the crater. They are especially useful to determine the timing of extrusive events. For example, the temperature at the far west end of Pu`u `O`o crater rose at about 0430 on October 31, just the time that tiltmeters on the cone started to deflate. That time was when extrusion and spattering started in West Gap Pit and the adjacent crater floor.
Field observations of the entire flow field are made at least weekly by HVO scientists in helicopter and on foot. Flows are mapped, samples of lava are collected at favorable localities, the flux of lava through tubes is estimated, and the sulfur dioxide output (a prime constituent of vog) is measured by observing the gas plume from the Chain of Craters Road.
Each morning, predawn observations are made from Highway 11 and from along the Chain of Craters Road, triangulating the sources of glow and incandescence using a sighting digital compass. Lava is often visited if it is within easy walking distance of the road.
Reports of national park interpreters and rangers help fill gaps in our observations, particularly in the afternoon and evening by workers at the end of Chain of Craters Road. Hikers to Napau, whether park employees or the public, provide important documentation of events near Pu`u `O`o. Overflights by visitors and tour pilots alert us to important events taking place.
All of this information is assembled each morning and used to prepare the morning update on our web site, generally available by 0700 at http://hvo.wr.usgs.gov.
Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued 24/7 during the past week. Surface flows, issued from vents in the southwestern sector of Pu`u `O`o crater, covered the entire western floor of the crater. Vents immediately outside of the crater on the uprift (western) side fed short flows that filled collapsed areas and repaved earlier flows. A large breakout near the top of the Mother's Day tube system supplied a flow heading to the southwest. Breakouts from the Kohola arm of the Mother's Day flow only occur on the higher reaches of Pulama pali. The east side of the Mother's Day flow, and the coastal flat below Paliuli, continue to be dark. No lava is entering the ocean.
Two earthquakes were reported felt in the week ending on November 6. A resident of Leilani Estates felt an earthquake at 11:11 p.m. on Saturday, November 1. The earthquake responsible was a magnitude-2.3 event located 3 km (1.8 mi) east of Pu`ulena Crater at a depth of 1 km (0.6 mi). A magnitude-2.4 earthquake at 4:01 a.m. on November 5 was felt in Kealakekua. The temblor was located 2 km (1.2 mi) east of Honaunau at a depth of 45 km (27 mi).
Mauna Loa is not erupting. The summit region continues to inflate. Seismic activity remains very low, with no earthquakes located in the summit area during the last seven days. Visit our website (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time earthquake information.
Updated: December 21, 2003 (srb)