February 28, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Pele revisits Royal Gardens
After a few brief forays into the upper reaches of the Royal Gardens subdivision over the last several weeks, the Thanksgiving Eve Breakout (TEB) flow has mounted a new attack on this beleaguered development. Earlier flows were caused by the sudden release of stored lava following the collapse of rootless shields. But the current activity is being fed by a continuous supply of lava through a juvenile lava tube system.
The TEB flow originates from a vent on Kilauea's east rift zone between the Pu`u `O'o cone and the Kupaianaha shield. The vent supplying the TEB flow began erupting on July 21, 2007, and initially sent flows to the northeast through an open lava channel. Frequent overflows from the channel built up the channel's banks and caused the lava stream to become elevated above the surrounding area. This "perched" lava channel and the flows it fed were the dominant eruptive activity until they were superseded by the TEB flow this past November.
The character of the TEB flow is quite different than that of the perched lava channel. Rather than flowing as an open stream, the TEB flow quickly began to build what are called "rootless shields." The term "shield" refers to the low, broad hill created by accumulating lava, while "rootless" means that the shield is not situated over a volcanic vent erupting lava from deep within the earth. Instead, the shields are built over a lava tube carrying lava that has already erupted from the TEB vent and, thus, do not have a deep magma source root.
More than a dozen new rootless shields adorn the landscape to the southeast of the TEB vent. These shields are several hundred meters (yards) across but rarely more than 30 meters (yards) high. The rootless shields act as a secondary source of storage, and each is cored by a body of molten lava. Not surprisingly, the flanks of these shields sometimes fail, and the stored lava gushes out. This is exactly what happened on January 8, January 26, and February 13 of this year, when `a`a flows came very close to, and even crept into, the upper reaches of the Royal Gardens subdivision before stalling.
Over the last few weeks, however, the building of rootless shields has largely given way to an advancing pahoehoe front. Rather than rushing out as an `a`a flow and quickly stagnating, the current flow has moved slowly, but steadily, downslope and again entered Royal Gardens last Sunday, February 24th. Though active lava spread over a broad area above Royal Gardens, the flow branched into two main lobes once in the subdivision-one following Royal Avenue and the other following the adjacent Prince Avenue.
The flow picked up speed along the steep slope of the subdivision. By Tuesday it had advanced two-thirds of the way through the subdivision, destroying two abandoned houses in its path. By Thursday (the time of this writing), one of the flows had reached the coastal plain, and at least one more abandoned house had been destroyed.
Unless conditions change upslope, the flow will advance across the coastal plain. If this flow continues and is not cut off from above by changes in supply rate or a rupture of the tube, lava may again be heading toward the ocean. With all this dry weather we've been having, Pele may need to quench her thirst and satisfy her legendary hunger for fish.
Kilauea summit and Pu`u `O`o continued to slowly deflate. Seismic tremor levels and sulfur dioxide emission rates at the summit are elevated to several times background levels since late 2007. Earthquakes were located primarily beneath the general summit area, the southwest rift zone, and the south flank faults.
Lava from the 2007 Thanksgiving Eve Breakout (TEB) flow, erupting from fissure D of the July 21st eruption, advanced through what remains of the Royal Gardens subdivision and, as of this writing, has reached the coastal plain. This multi-fingered pahoehoe flow is being fed from the end of the rootless shield complex constructed southeast of the TEB vent since November.
An area of persistent breakouts on the northeast side of the shield complex also continues to produce small flows. These northeast-directed flows are not advancing and are restricted to a broad, flat area on the south side of Kupaianaha.
Weak incandescence has been intermittently observed in Pu`u `O`o in the past week. As in years past, Pu`u `O`o likely is serving as a large chimney, beneath which lava is briefly stored and substantially degassed on its way to the eruption site.
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 20 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. 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. To minimize these potentially harmful effects, the Hawai`i Volcanoes National Park has closed all access to the southern half of Kilauea caldera.
One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-2.9 earthquake occurred at 00:30 a.m., H.s.t., on Saturday, February 23, 2008, and was located 3 km (2 miles) southeast of Captain Cook at a depth of 14 km (9 miles).
Mauna Loa is not erupting. Two earthquakes were located beneath the summit. Extension between locations spanning the summit, indicating inflation, continues at steady, slow rates.
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: March 3, 2008 (pnf)