February 26, 2009
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Size matters when it comes to volcanic islands
The Island of Hawai`i, a composite of five volcanoes, has a surface area almost twice as large as the other main Hawaiian Islands combined. Such a size provides some level of security for the island's residents during volcanic eruptions because, in general, it takes time for lava flows to reach inhabited areas. This is especially true on Kilauea, which has a fairly modest long-term eruption rate of about 3 to 6 cubic yards of lava per second.
When lava from the most recent phase of the eruption began flowing southward in November 2007, it took three months for it to finally reach populated areas along the coast. It took even longer—about four months—for lava flows from the Kupaianaha vent to reach an equivalent distance in 1986. In both examples, there was time for people to move themselves, their belongings, and, in some instances, their homes, before the lava arrived.
Such circumstances, however, are not always the case, and two relatively recent examples are worth mentioning. One took place last summer (2008) on the tiny Aleutian volcanic island of Kasatochi, about 1,100 miles southwest of Anchorage, Alaska. Long considered dormant, Kasatochi Volcano began to stir at the beginning of August. The small earthquakes that started to occur were not detected by seismometers on nearby islands, but were felt by the two U.S. Fish and Wildlife biologists stationed on the island for the summer.
A few days later, on August 6, after the tremors had continued to increase in frequency and magnitude, and finally became detectable by the sparse Aleutian seismic network, an evacuation plan was initiated. To the discomfort of all involved—especially the two biologists—the nearest Coast Guard rescue option was at least 24 hours away. Luckily, a fisherman from nearby Adak Island, about 50 miles away, offered to sail to Kasatochi the following morning.
Anxieties mounted as dawn broke with fog and heavy surf on August 7. Earthquake activity had continued to ramp up overnight, and poor weather raised questions of whether the small fishing vessel would reach the island. Fortunately, the boat arrived, as promised, and the biologists evacuated. Just how dire were the circumstances? As the fishing boat made the difficult return to Adak Island, Kasatochi erupted, sending ash to a height of 35,000 feet and burying the entire island beneath pyroclastic flows.
Though the Kasatochi rescue was a narrow escape, it was still far better than no escape at all-the predicament of Yemeni soldiers on the tiny volcanic island of Jabal al-Tair, off the coast of Yemen in the Red Sea, in September 2007. In that event, the volcano, which is about the size of Kilauea's summit caldera, erupted with little warning, causing a portion of the volcano to collapse into the sea. Much of the rest of the island was quickly buried beneath lava flows.
Most of the soldiers stationed at the small Yemeni naval base on the island were evacuated, but some were forced to flee into the water to escape being overtaken by lava. For them, the struggle then became a fight to avoid drowning or being boiled alive. After hours of treading water, the scattered survivors of this small group—and the bodies of their unlucky comrades—were plucked from the water by search vessels. In total, nine soldiers were killed and dozens of others were injured.
With these two incidents in mind, one might ask if similar close calls or tragedies could occur on Hawai`i Island. After all, the lower portion of Kilauea's east rift zone cuts through the middle of a well-populated part of Puna, and an eruption there could potentially cut off evacuation routes. Likewise, on Mauna Loa's southwest rift zone, the steep slopes and potential for rapidly moving flows could also cut off evacuation routes.
While such scenarios are possible, with dozens of monitoring instruments dotting the volcanoes on Hawai`i, precursory activity to eruptions should be detected at least a few hours in advance, forewarning those in harm's way. If you are aware of volcanic hazards in your area and take heed of warnings, then sleeping with a surf board next to your bed won't be necessary.
Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is emitting elevated amounts of sulfur dioxide gas and producing small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. Using a thermal camera, a small, puffing cone has been visible about 100 yards below the vent rim.
Pu`u `Ō`ō also continues to produce significant amounts of sulfur dioxide. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.
A pair of deflation/inflation (DI) events that began last Sunday (February 22) disrupted the supply of lava erupting from the Thanksgiving Eve Breakout (TEB) vent at the eastern base of Pu`u `O`o. The flow of lava through the lava tube was cut off, and the ocean entries at Waikupanaha and Poupou both died. The east rift zone eruption resumed on the 25th, and lava reached the ocean again late on Wednesday, February 25, at Waikupanaha. The Poupou entry had not restarted as of this writing (Thursday, February 26), but coastal plain breakouts we active nearby.
Be aware that active and recently inactive lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. The Waikupanaha delta has collapsed several times in the past year, with four of the collapses resulting in rock blasts. These blasts have tossed television-sized rocks up onto the sea-cliff and have thrown fist-sized rocks more than 275 yards inland.
Do not approach the ocean entry or venture onto lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Call Hawai`i County Civil Defense at 961-8093 for viewing hours.
Mauna Loa is not erupting. Three earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano, combined with slow eastward slippage of its east flank.
One earthquake beneath Hawai`i Island was reported felt within the past week. A magnitude-3.4 earthquake occurred at 11:25 p.m., H.s.t., on Saturday, February 21, 2009, and was located 9 km (5 miles) west-northwest of Ka`ena Point at a depth of 10.5 km (6.5 miles).
Visit our Web site (http://hvo.wr.usgs.gov) for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov.
Updated: March 13, 2009 (pnf)