September 13, 2007

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

Kilauea抯 eruption building perched lava channel and feeding many short flows

Aerial view of the current eruption of Kilauea Volcano, looking toward the southwest. The shiny, gray lava surfaces are recent pahoehoe flows resulting from overflows of the open lava channel. The channel is about 1 km long (0.6 miles) and as wide as 60 m (200 feet). Lava can be seen spreading from the lower end of the lava channel and feeding a flow that is moving east (left) at the base of Kupaianaha (left middle; note crater atop the shield). Active `a`a flows can also be seen in lower left. Whitish fume rises from Pu`u `O`o, at top right. The distance from Pu`u `O`o to Kupaianaha is about 3 km (2 miles). USGS photograph, Tim Orr.

Lava flows from the ongoing eruption of Kilauea Volcano have traveled only short distances during the past week from the impressive open lava channel that developed in late July.

The locations of these flows change by the day, if not by the hour, as lava intermittently fills the channel, then overflows somewhere along the edges or leaks from the base at the channel抯 lower end. The lava flows include `a`a and, recently, an increasing number of pahoehoe overflows from both sides of the channel.

The open lava channel developed shortly after a new fissure erupted east of Pu`u `O`o on July 21. Of the four original fissure segments, only the easternmost segment erupted lava after early August. Lava from this vent spread to form an irregular channel as wide as 60 m (200 feet) across and about 1 km long (0.6 miles). The top of the channel now reaches 10-20 m (35-65 feet) above the surrounding ground.

Close view of the perched lava channel that is being built higher and higher above the surrounding ground as lava overflows the sides of the channel to form relatively short flows. The short pahoehoe flows are covering the early lava that was erupted from the developing channel (dark flows, middle right) and older flows erupted from Pu`u `O`o during 1983-1986 (brown, lower right). Kupaianaha shield, erupted between 1986 and 1992, is visible at top left; the shield is 56 m (185 feet) high. USGS photograph, Tim Orr.

During the first few weeks of the current activity, lava streams from the lower end of the open channel fed a series of `a`a flows that traveled northeast as far as 5�km (3�miles) from the vent. Poorly developed lava tubes beneath the `a`a also fed budding flows from along its margins.

These earlier flows have obstructed the emplacement of more recent flows. As a result, no single flow has moved more than about 3 km (2 miles) from the lower end or sides of the channel in the past two weeks. This is well short of the distance traveled by the longest flows梩hose emplaced in August梐nd none of the flows pose a direct, immediate threat to communities.

Instead, repeated overflows and leaks have built the walls of the channel higher and higher so that the entire channel system has become perched prominently above the surrounding ground. Most of the overflows have spread only a few hundred meters (yards) from the channel before stagnating.

When viewed on September 11, one of the larger overflows from the south side of the channel was feeding a pahoehoe flow moving along the south side of earlier flows and heading east around Kupaianaha. A small `a`a flow was also active a few hundred meters (yards) away.

The lava flows are changing the topography alongside the channel day by day, which likely will affect the paths of future flows. The Hawaiian Volcano Observatory regularly posts photographs and maps of the current activity and flows (2-3 times weekly) on the Web site http://hvo.wr.usgs.gov. Significant changes in the activity, especially in the development of new flows, will be reported immediately.

Activity Update

The July 21 eruption remains active. The lava flows through an open lava channel and into a pond about 0.6 miles from the vent. In the past week, a slow-moving `a`a flow, fed by lava seeping from a rupture at the base of the pond wall, moved eastward along the south side of flows emplaced in early August.

For the last several days, most of the lava has been accumulating in the area just north of the Kupaianaha shield. Frequent, small pahoehoe overflows from the channel and pond have caused them to become perched up to 50� feet above the surrounding lava surface. Upward growth of the channel and pond walls has decreased the slope of the lava channel to nearly horizontal. This has led to even more overflows, including small overflows right at the vent itself.

As of Thursday, September 13, in addition to the numerous small overflows, there were two larger pahoehoe flows being fed by the eruption. One, from the north side of the perched pond, was moving slowly across early Pu`u `O`o flows along the north side of the current flow field. The other pahoehoe flow was being fed by an overflow from the southeast side of the channel and was wrapping east and south around the north side of Kupaianaha. The slow-moving `a`a flow mentioned above also turned toward the southeast and continues to advance.

At Pu`u `O`o, no incandescence has been seen on the Webcam at night for the last few weeks. The heavy fume coming from Pu`u `O`o completely obscures any view into the crater. As has been seen in years past, Pu`u `O`o could be acting as temporary storage for lava that passes beneath the cone on its way to the erupting fissure. There have also been a number of collapses in Pu`u `O`o crater since late August, and cracks on the north rim and south flank of the cone seem to be widening.

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.

Four earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-3.1 earthquake occurred at 9:22 p.m. H.s.t. on Saturday, September 8, and was located 46 km (29 miles) southwest of Kailua at a depth of 34 km (21 miles). The largest earthquake of the past week, a magnitude-3.5 event, occurred at 11:22 a.m. H.s.t. on Sunday, September 9, 6 km (4 miles) north of Ka`ena Point at a depth of 10 km (6 miles). A magnitude-3.4 earthquake occurred at 5:10 a.m. on Monday, September 10, and was located 11 km (7 miles) west of Pahala at a depth of 7 km (4 miles). A second earthquake on September 10 was a magnitude-2.5 event that occurred at 2:58 p.m. H.s.t.; the earthquake was located 4 km (3 miles) north of Holualoa at a depth of 15 km (10 miles).

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