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Volcanowatch

November 1, 2007

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


Changes in lava flows intensify questions to scientists


Aerial view looking west at the end of the active flows moving east from the open channel (flows are black in middle foreground). A new lava tube is feeding lava to the flow front, located about 3.5 km (2.2 miles) from the end of the lava channel as of October 31. A tube was also supplying lava to less active pahoehoe flows on the north side of the flow field (out of view, middle right). The breached cone (Pu`u Ki`ai) and channel in lower left were erupted in 1977. This older channel fed lava flows that traveled south to within about 1.6 km (1 mi) of Kalapana. Pu`u `O`o can be seen fuming near top left, and Mauna Loa is the huge hump at top right. Photograph by Tim Orr, U.S. Geological Survey; 31 October 2007.

As soon as lava began flowing on the north side of Kilauea's east rift zone from a new vent on July 21, questions arose among residents of the Puna District.

How long will the new vent remain active? Where is the lava going? Could flows eventually threaten our community? How long will it take flows to travel the 16 km (10 miles) to Highway 11? Will the lava keep moving northeast toward us or will it move south away from us?

Answering these and other questions was the main reason why scientists of the Hawaiian Volcano Observatory (HVO) stepped up its monitoring efforts and prepared a report about lava flow hazard from the new activity. The report was released only five weeks after the new vent erupted (available online, http://pubs.usgs.gov/of/2007/1264/).

Many of the same questions are still being asked, but development of a lava tube within the past two weeks has created a new sense of urgency among Puna residents for an update on the current hazard assessment.

The challenge for scientists is twofold: (1) providing frequent, accurate updates of the activity and location of flows; and (2) modifying the assessment of hazards to lower Puna based on significant changes in the activity.

So far, even with the recent development lava tubes, updating the assessment is not yet warranted. All of the flows since mid-August have only widened the lava flow field. No flow has moved in a consistent direction for more than 1-3 weeks at a time, and none have moved more than the 6.3 km (4 miles) maximum length reached by an `a`a flow in August.

Since late August, lava flows have (1) spilled over the lava channel to build it as high as 30 m (100 ft) above the surrounding ground; (2) poured on top of, or alongside, the earlier flows (thereby widening and thickening the flow field); and (3) leaked from the sides of the perched channel, traveling, at most, a few hundred meters (yards) from the channel.

In the hazard assessment, scientists wrote that the longer the current activity continues, the greater the likelihood of a lava tube developing. Lava tubes insulate lava, keeping it hotter and more fluid than surface flows. The tube-transported lava can travel greater distances from the erupting vent, enabling the formation of fluid pahoehoe flows farther away.

The formation of a tube does not mean that lava is now on a fast track to Highway 11 or to the communities in the Puna District. A tube formed early in an eruption rarely remains intact for weeks to months. Changes in the channel or lava supply may "starve" the tube or form several new ones in different locations.

During the Pu`u `O`o and Kupaianaha activity, it took from weeks to months to form a well-developed lava tube system that fed lava flows farther and farther from the vents. It will take even longer to form a well-developed tube system over the very gradual to nearly flat terrain of the current activity.

How long will it take? For flows moving northeast from the channel, it will likely take at least a few months to build a robust tube system within several km (miles) of the vent, especially if there are multiple flows going in different directions at the same time. It will take even longer for the flows to spread far enough to begin threatening communities and infrastructure.

In the past week, scientists observed at least two lava tubes fed directly from the lava channel, possibly three. Lava from these tubes are forming pahoehoe flows on the north and south sides of the flow field, and `a`a and pahoehoe flows on top of the flow field. All the flows are less than 5 km (3 miles) from the vent-no farther than the mid-August flows.

The lava channel and flow field near the vent continue to change, sometimes rapidly and in spectacular fashion. Though frustrating to many, it is not possible for scientists to predict lava flow behavior-speed, direction, and extent-and final outcomes of the current activity. Lava flows are continually building new features and changing their course by the week, both of which affect the channel geometry and paths of future flows.

But HVO can, and will, keep the public apprised of the current activity via the media, Web site (http://hvo.wr.usgs.gov), and community presentations, and continue to focus efforts to assess the implications for communities of the Puna District that may be affected by the new activity.

Activity Update

The July 21 eruption continues to supply lava into a perched channel from eruptive fissure D, 2.3 km (1.4 mi) northeast of Pu`u `O`o. The lava forms a discontinuous, north-northeast-trending molten stream about 1.4 km (0.9 mi) long. The stream is discontinuous because, when the lava level in the channel is high-as it has been since mid-October-the narrow sections of the channel roof over to form bridges over the lava stream. Frequent, brief overflows from both sides of the channel continue to build up the channel walls. Lava backing up behind the bridges has elevated each upstream section of the channel above its downstream neighbor, giving the channel a stair-stepped appearance dropping downstream to the northeast.

Near the end of the channel, lava drains into two lava tubes-one carrying lava to the north, and the other carrying lava to the east. As of Wednesday, October 31, the southeastern tube was the more dominant and was supplying lava to a slowly advancing pahoehoe flow that had reached about 3.5 km (2.2 miles) from the channel. This flow was moving east along the crest of Kilauea's east rift zone over lava erupted in 1977. Besides these flows, small `a`a flows continue to be fed from seeps low on the northern flank of the channel and from the end of the channel.

At Pu`u `O`o, no incandescence has been seen on the Webcam at night for the last several weeks. The heavy fume coming from Pu`u `O`o completely obscures any view into the crater. As in years past, Pu`u `O`o likely is serving as a large chimney, beneath which lava is stored briefly and degassed substantially enroute to the erupting fissure. Sloughing of Pu`u `O`o into its own crater since late August has left numerous fresh cracks on the north rim and south flank of the cone.

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, which have slowed further since May 2007.

Three earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.2 earthquake occurred at 11:42 a.m., H.s.t., on Thursday, October 25, 8 km (5 miles) west of Laupahoehoe at a depth of 13 km (8 miles). A magnitude-4.0 earthquake occurred at 6:57 p.m. on the same day, and was located 6 km (4 miles) north-northeast of Keana Point at a depth of 9.9 km (6.2 miles). A magnitude-2.1 earthquake occurred at 3:54 a.m., H.s.t., on Saturday, October 27, 1 km (0.6 mi) east of Pu`ulena Crater at a depth of 2 km (1.2 mi).

Visit our Web site (hvo.wr.usgs.gov) for daily Kilauea eruption updates and nearly real-time Hawai`i earthquake information.

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Updated: November 4, 2007 (pnf)