March 6, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Kilauea following one of several eruption scenarios
Now that lava flows have reached the ocean below Royal Gardens subdivision, the concern 7 months ago of lava pouring northeast from a new vent toward Pahoa and Hawaiian Beaches is, for now, abated.
The flows causing the concern last August were `a`a and were moving northeastward from the east rift zone for the first time since the early years of the Pu`u `O`o eruption which began in 1983. The flows of concern essentially shut down soon after November, when lava was redirected to a new vent west of the open lava channel system. The new downhill direction was to the south, where pahoehoe flows have moved slowly, but steadily, ever since.
A collective sigh of relief was heard across the Puna District when the lava was directed on the eve of Thanksgiving Day 2007, and many who work and live in Puna continue to be thankful for the change in lava flow direction. As long as the active vent remains stable, with a continuous supply of lava, flows will continue moving southward from the east rift zone.
But as Kilauea has shown many times since 1983, the vent location or orientation could change again, thereby altering the direction of lava flows once more and challenging scientists to assess possible future scenarios for island residents.
The current lava flows are following one of the scenarios scientists described in a report as a possible outcome of the new fissure vent that became active on July 21, 2007. The report, Lava Flow Hazard Assessment, as of August 2007, for Kilauea East Rift Zone Eruptions, Hawai`i Island, is available online at http://pubs.usgs.gov/of/2007/1264/.
Three general scenarios were considered possible from the vent.
First, the new fissure could stop erupting. In this case, eruptive activity might revert back to Pu`u `O`o or activity could stop altogether-that is, until Kilauea erupted again somewhere else entirely.
Second, the fissure could continue to feed `a`a flows a short distance to the northeast; an increase in the supply of lava could allow them to move significantly farther than the 6 km (4 miles) they had traveled by the end of August. Also, a change in the vent might allow `a`a flows to move southeastward.
Third, pahoehoe flows could develop and travel all the way to the ocean toward the northeast, but "substantial changes in the configuration of the vent could allow flows to advance southeastward" (quote from the report).
Both the second and third have scenarios occurred. The vent has changed location and configuration, sending lava predominantly southward. A few `a`a flows initially traveled a short distance from the "Thanksgiving Eve Breakout", or TEB, vent, but most recently pahoehoe flows have poured from a series of low "rootless" shields. The new ocean entry is the product of a still-developing tube system that is delivering lava 11.5 km (7.5 miles) to the new ocean entry.
For the third scenario (long pahoehoe flows), scientists identified the likely flow paths pahoehoe lava would take from the vent to the ocean, based on the underlying topography. The flow paths were shown as lines on a map of the Puna District to indicate how lava would drain from its point of origin across the area.
When the vent changed location on Thanksgiving eve, lava eventually followed the forecasted flow paths indicated on the map.
This method of identifying lava flow paths is likely to be used much more in the future as new and more detailed digital elevation models (DEMS) of Kilauea and Mauna Loa volcanoes become available. Of course, lava flows change the topography, so subsequent flows may not follow the initial forecasts. In such cases new DEMS would need to be generated.
Scientists continue to work on improved methods of forecasting the direction and path ways of lava flows when a new vent becomes active.
Kilauea summit is neither inflating nor deflating. Seismic tremor levels at the summit are elevated to nearly moderate levels. Summit sulfur dioxide emission rates have remained elevated at more than four times background levels since early January 2008. Pu`u `O`o continued to deflate. 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 21 eruption, continues to flow through what remains of the Royal Gardens subdivision. From the base of Royal Gardens, a narrow (100-200 yard wide) pahoehoe flow has traveled across the coastal plain over the past week on its march to the sea. On Tuesday evening, March 4, the flow crossed the gravel access road, and on Wednesday night, lava entered the ocean in the vicinity of Kapa`ahu.
The public should be aware that the ocean entry areas could collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. Do not venture onto the lava deltas and benches. Even the intervening beaches are susceptible to large waves suddenly generated during delta collapse; these beaches should be avoided. Check the County of Hawai`i Civil Defense website (http://www.lavainfo.us) for information on public access to the coastal plain and ocean entry.
This 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 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 Pu`u `O`o, TEB vent and rootless shields, 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:
No earthquakes beneath Hawai`i Island were reported felt within the past week.
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 (http://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 10, 2008 (pnf)