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Volcanowatch

June 3, 2010

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.


Should Maui residents be concerned about lava flows?

Lava flow hazard zones on East Maui

Molten lava flows downhill. This simple fact has spurred many residents on the Island of Hawai`i, where Kīlauea Volcano has been erupting for more than 27 years, to think about the likelihood of an eruption occurring upslope of their homes. But what about residents on the other Hawaiian islands? Should they worry about lava flows, too?

For the most part, probably not. The exception is Maui, the only other island with a volcano classified as "active."

Haleakala, the volcano that forms East Maui, erupts every 200 to 500 years. This estimate is reached by averaging the number of eruptions over the past 10,000 years. Because little has changed about the volcano during this time, future eruptions should be expected. In fact, the probability of renewed eruptive activity is sufficiently large that the need for lava flow hazard zones on East Maui cannot be ignored.

Volcano hazard assessment always fails to answer the one question raised most frequently by island residents and visitors, namely, when and where the volcano will erupt next. In the absence of volcanic or seismic unrest, scientists can offer only statistical information-probabilities-about future volcanism.

On East Maui, the most likely site of the next eruption will be along a line of vents that ascends the southwest rift zone from La P?rouse Bay and crosses the length of Haleakala Crater. The volcano's east rift zone is generally less active, but an area of vents upslope of Wai`anapanapa and the Hana airport has matched the extent of eruptive activity in the Crater area and southwest rift zone.

Each of these areas has seen at least five eruptions in the past 1,500 years and, on this basis, are assigned to Maui lava flow Hazard Zone 1. No eruptions have occurred in the last 450 years ago, however.

Lava invades the other three hazard zones even less frequently. Zone 2, which encompasses the north and south flanks of Haleakala's southwest and east rift zones, includes land that was covered by lava at least once in the past 13,000 years. Ke`anae Valley and the Kaupo area are also in Zone 2, because they are downslope of lava flows that might erupt within Haleakala Crater.

Maui zones 3 and 4—most of East Maui—encompass areas with essentially no hazard under most lava-inundation scenarios. In large part, Haleakala Crater gets the credit for sheltering so much of East Maui because it blocks rift-zone lava flows from any but a few paths downslope. Also, new vents pop up infrequently within zone 4.

The numbers assigned to lava flow hazard zones are unique to each island. East Maui's eruptive potential pales in comparison to that of many places on the Big Island. In terms of eruptive frequency, Maui's Zone 1 is most like Hawai`i Island's Zone 4, a zone that corresponds to Hualalai volcano.

But even this correlation is imperfect because, when Hualalai erupts, lava flows tend to coat substantially larger areas. In the past 1,500 years, Hualalai eruptions (on Hawai`i) have paved twice the area covered by Haleakala lava flows (on Maui) in the same interval of time-174 versus 89 square km; or 67 versus 34 square miles. All parts of Hualalai's rift zones seem capable of eruptive activity, whereas some parts of Haleakala's rift zones have been inactive for more than 50,000 years, a fact that further diminishes the likelihood of future lava inundation on East Maui.

None of this discussion is intended to raise or lower concern for Maui residents. Haleakala is currently inactive and shows no sign of disturbing the peace in the near future. However, Maui residents should know that Haleakala has experienced lava-producing eruptions in the past and will do so in the future. Our safety is always heightened by knowledge of the environment in which we live.

Kīlauea Activity Update

Over the past week, most of the activity on the east rift zone flow field has been focused on the construction of low shields, topped by lava ponds. This activity was located high above the Pulama pali over the breakout point of the Quarry flow, which is still weakly active on the pali and coastal plain. As of Thursday, June 3, small breakouts had reached to within a few hundred meters (yards) of the ocean just west of the Ki ocean entry, which is now inactive. In addition to that lava erupting and flowing through the TEB tube system, lava is also erupting from two vents within Pu`u `Ō `ō. These vents are supplying lava to a growing lava pond that is slowly filling Pu`u `Ō `ō's crater.

At Kīlauea's summit, a circulating lava pond deep in the collapse pit within the floor of Halema`uma`u Crater was visible via Webcam throughout the past week. The baseline lava level has been slowly rising, and was also punctuated a few times by short-lived lava-level increases that brought the lava surface to its highest level yet recorded. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.

Four earthquakes beneath Hawai`i Island were reported felt during the past week. Three of them—a magnitude-3.2 earthquake at 3:05 a.m., a magnitude-3.1 at 1:24 p.m., and a magnitude-2.9 at 6:54 p.m. on Friday, May 28, 2010, H.s.t.—were located in the same area 10-19 km (6-12 miles) northwest of Na`alehu at a depth between 7-10 km (4-6 miles). A magnitude-2.6 earthquake occurred at 10:52 a.m. on Tuesday, June 1, and was located 7 km (4 miles) east of Captain Cook, at a depth of 8 km (5 miles).

Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.

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Updated: June 8, 2010 (pnf)