March 13, 2008
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Pele gives plenty of heat to Namakaokaha`i
Last week was a family reunion of sorts, as Pele met her sister, Namakaokaha`i, when lava from Kilauea Volcano entered the ocean for the first time since June 2007.
But why was there a gap of 9 months since the last ocean entry at Kilauea, even though the eruption was nearly continuous during this time? Many readers of this column probably know that there was a major change in the activity at Kilauea in mid-2007, with new eruptive vents breaking out along the volcano's east rift zone. These changes appear to have been caused by changes in the most fundamental parameter governing Kilauea's activity.
The Island of Hawai`i lies above a hotspot - a melting anomaly in the Earth's mantle that extends hundreds of miles beneath the surface. The hotspot supplies magma to the volcanoes at the surface, resulting in frequent and, in the case of Kilauea nearly continuous, eruptions.
The extensive deformation monitoring network at Kilauea, coupled with frequent eruptions, allows scientists to calculate how much magma is supplied by the hotspot to Kilauea each year. Estimates of the magma supply rate from the 1970s through the early 2000s are remarkably consistent at about 0.1 cubic kilometers per year (0.02 cubic miles per year). That's enough magma to fill about 15 million dump trucks!
What would happen if the supply rate changed? If less magma came into Kilauea from the hotspot, we might expect eruptions to be less frequent. But what if more magma was being fed to Kilauea from below? Scientists at the Hawaiian Volcano Observatory think that an increase in supply rate is exactly what happened over the past several years, leading to major changes in Kilauea's behavior.
In late 2003, Kilauea's caldera began to inflate like a balloon as more magma began entering the summit magma reservoir than was being erupted at Pu`u `O`o. By 2005, the inflation rate had increased, and soon the amount of lava erupting from Pu`u `O`o increased by about 50 percent. Still the summit inflation continued, with the rate increasing again in 2006.
In addition to the inflation, summit carbon dioxide emissions more than doubled in 2004. Carbon dioxide is contained within magma and is proportional to the amount of magma below ground.
Taken together, the gas and deformation data indicate that the magma supply to Kilauea increased by 2-3 times during 2003-2006. The supply rate exceeded what could be erupted from Pu`u `O`o, so the excess magma was stored beneath Kilauea's summit. As a result, Kilauea caldera inflated and pressure built within the summit magma reservoir. On June 17, 2007, pressure in the reservoir could no longer be contained.
Early that morning, magma from Kilauea's summit moved down the east rift zone to the Mauna Ulu region, approaching the surface and erupting a few days later on the east flank of the Kane Nui o Hamo shield. Pu`u `O`o collapsed as magma supply to the eruptive vent was diverted.
Even when lava returned to Pu`u `O`o in early July, it was clear that things were not quite right. Pu`u `O`o started to inflate rapidly as pressure built beneath that cone. Then, on July 21, 2007, the small magma reservoir beneath Pu`u `O`o ruptured, and a new eruptive fissure formed to the east. Pu`u `O`o collapsed again and, within a few days, the eruption stabilized at a point about 2 km (1 mile) east of Pu`u `O`o. Lava has been erupting there ever since, and only last week did it finally make it over the pali, across the coastal plain, and into the sea.
All of these changes are a result, either directly or indirectly, of the increase in magma supply to Kilauea Volcano - apparently the first sustained magma supply increase at Kilauea in the last several decades.
Although the cause of the increase is as yet unknown, it is clear that changes in magma supply can have a profound effect on the eruptive activity of Kilauea. Only time will tell what will happen next. Some signs indicate that the magma supply to Kilauea has started to decrease. For now, however, Pele apparently has plenty of heat to give to her older sister in the sea.
Kilauea summit is slowly deflating and had two DI tilt events this past week. 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 and across the coastal plain. On Wednesday evening, March 5, the flow entered the ocean in the vicinity of Kapa`ahu. The Waikupanaha delta has grown to be more than 500 m (1640 ft) in width and has several entry points.
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. The rate of extension between locations spanning the summit, indicating inflation, has decreased to values below detection limits.
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 17, 2008 (pnf)