February 7, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Volcanic Hazards Continue, Rain or Shine
The rain did succeed in obstructing views of the eruption through our Webcams and has induced our tiltmeters to record erroneous signals. The rest of our monitoring networks worked just fine throughout this weather event - a great testimony to the HVO staff who install and maintain them. All our data tell us that there are three areas of current concern - Royal Gardens, the vent area (including Pu`u `O`o, the rootless shields, and the July 21 channel), and Kilauea's summit.
The main activity at the eruption site is rootless shield building. The Thanksgiving Eve Breakout (TEB) flow field comprises a series of rootless shields southeast of the TEB shield. The TEB shield itself is "rooted," or fed directly by fissure D.
Media attention has focused on the plight of Royal Gardens subdivision, which is directly downslope of the field of rootless shields. Twice during January, the southeasternmost rootless shield collapsed, releasing a considerable amount of stored lava into a long, narrow flow that has threatened the subdivision. We are nearly certain that it will continue to collapse and produce subdivision-threatening flows.
The collapse of the rootless shields is just one of the many hazards in the area that includes Pu`u `O`o and fissure D vents. Pu`u `O`o cone continues to collapse. Cracks abound at the crater's edge, where large chunks of the rim have fallen into the pit with little warning. The crater is also emitting more than one thousand tonnes of noxious sulfur dioxide (SO2) per day. Changes in wind conditions can cause these emissions to go in any direction, with the worst levels close to the vent. Both the National Park Service (NPS) and the State of Hawai`i Department of Land and Natural Resources have closed public access to their respective portions of the vent area as the best way to minimize these hazards.
One more hazard was posed by Kilauea within the last several weeks. At the summit, HVO gas geochemists recorded eye-popping increases in SO2 emission rates beginning late last year. By end of January, the rates had quadrupled!
To appreciate the implications of this increase in gas emission, it is useful to translate it into what is inhaled. SO2 is a toxic gas that is perpetually emitted from sources within and around Halema`uma`u Crater and is the most noticeable ingredient of vog. At background emission rates, trade (northeasterly) winds blow the SO2 emissions out of the caldera and dilute them before the gas reaches populated areas. Weak or southerly winds cause the gas to accumulate to the point where hazardous concentrations are reached.
The National Park Service (NPS) operates air quality monitors at Kilauea Visitor Center and Jaggar Museum. When those sensors indicate that concentrations have exceeded 1 ppm (parts per million), buildings are closed, and visitors and employees are advised to seek clean air elsewhere.
The currently elevated SO2 emissions have created hazardous conditions downwind of Halema`uma`u Crater despite trade-wind conditions. Visitors to Crater Rim Drive between the southwest rift zone pullout and the Halema`uma`u overlook parking lot are experiencing SO2 concentrations in excess of 1 ppm, the "RED" action level at Jaggar Museum and Kilauea Visitors Center.
Everyone will notice SO2 at these levels. The effects of SO2 are most severe for children, whose lungs are still growing, and people with respiratory conditions, such as asthma or chronic obstructive pulmonary disease. More on the health effects of SO2 can be found at http://www.dur.ac.uk/claire.horwell/ivhhn/guidelines/gas/so2.html.
NPS rangers and emergency responders have handled two respiratory emergencies a week over the past few weeks. Prior to the rapid increase in SO2 emission rates, such emergencies were rare. In 1993, one visitor with known sulfur sensitivity died in the Halema`uma`u overlook parking lot during normal emission levels.
Toxicity increases with exposure time. The NPS is considering placing temporary restrictions within the south caldera areas to protect people from becoming overexposed to these emissions. Heed the warnings and stay safe.
Kilauea summit and Pu`u `O`o continue to contract. Seismic tremor levels at the summit are elevated close to moderate levels. Summit sulfur dioxide emissions have nearly quadrupled since early January 2008. Earthquakes were located primarily beneath the general summit area and the south flank faults.
On July 21, 2007, lava began erupting from a set of fissures on the east flank of Pu`u `O`o. Eruptive activity soon stabilized at fissure D, 2.3 km (1.4 mi) northeast of Pu`u `O`o. For several months, lava was directed entirely into a perched lava channel that generally fed flows to the northeast and east. At dawn on November 21, lava began to erupt directly from fissure D, outside the perched channel, creating the Thanksgiving Eve breakout (TEB) flow. The perched channel continues to sporadically host minor activity, but most of the activity is now focused on the TEB flow.
The TEB flow has built a series of low shields, extending southeast from the vent, over the last several weeks. Three weeks ago, the front of the southeast-most shield collapsed, and a large volume of lava surged out to form a rapidly moving `a`a flow. The flow advanced about 3.4 km (2.1 miles), reaching to within 180 m (~590 ft) of the top of the Royal Gardens subdivision before stagnating. The eruption then resumed its construction of low shields within about 2 km (1.2 miles) of the TEB vent. The same shield collapsed again on January 26, sending an `a`a flow 650 m (0.4 miles) into the Royal Gardens subdivision three days later, before stalling. Shield construction promptly resumed, and slowly advancing pahoehoe flows continue to be shed east and southeast from the shield complex.
No incandescence has been seen from within Pu`u `O`o for the last several weeks. As in years past, Pu`u `O`o likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially on its way to the erupting fissure.
Vent areas are hazardous. Access to the eruption site, in the Pu`u Kahauale`a Natural Area Reserve, is closed (http://www.state.hi.us/dlnr/chair/pio/HtmlNR/07-N076.htm).
Sulfur dioxide (SO2) emission rates from the summit area have been substantially elevated at 2-4 times background values since early January. During these conditions, SO2 concentrations frequently exceed 1 ppm for half or more of Crater Rim Drive between Halema`uma`u parking lot and the southwest rift zone. SO2 concentrations exceed 10 ppm for approximately 200 m (650 ft) of the road between the Halema`uma`u parking lot and the south caldera pullout.
The increase in sulfur dioxide emission rates at the summit means that SO2 concentrations are much more likely to be at hazardous levels for visitor areas downwind of Halema`uma`u, especially during weak wind conditions or when winds blow from the south. Most people are sensitive to sulfur dioxide at these levels, especially children, individuals with asthma, chronic obstructive pulmonary disease (COPD), or other breathing problems. These people should avoid areas in the south caldera: southwest rift zone, south caldera pullout, and the Halema`uma`u overlook parking lot. Stay informed about SO2 concentrations in continuously monitored areas (Jaggar Museum and Kilauea Visitor Center) by visiting the Kilauea Visitor Center and the web at: http://www2.nature.nps.gov/air/webcams/parks/havoso2alert/havoalert.cfm
Mauna Loa is not erupting. No earthquakes were located beneath the summit in the past week. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates, which have slowed further since May 2007.
One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.6 earthquake occurred at 1:13 a.m. H.s.t. on Wednesday, February 6. The earthquake was located 4 km (3 miles) north of the summit of Kilauea Volcano at a depth of 25 km (16 miles).
Visit our Web site (hvo.wr.usgs.gov) for daily Kilauea eruption updates and nearly real-time Hawai`i earthquake information. Kilauea daily update summaries are also available by phone at (808) 967-8862.
Updated: February 19, 2008 (pnf)