April 11, 1997

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

Lava Is On The Move Again

The 55th episode of Kilauea's east rift zone eruption has resumed with the vigor that characterized the eruption prior to January 30. We mark the episode's onset as 0700 hrs on February 24, the time when lava first reappeared in the crater of Pu`u `O`o following a 23-day pause. But only in the past two weeks has lava flowed from vents outside the crater's walls. The new flows are all within Hawai`i Volcanoes National Park, along its remote eastern boundary.

The flows are originating at the episode 51 vent on the west flank of Pu`u `O`o, where lava has filled several collapse pits and has intermittently fountained to heights of 15 m (50 ft). Some of these pits have overflowed to the west and southwest to mantle the flank of the episode 51 shield, but most of the lava is entering an old tube system that drained when episode 53 ended on January 30. This tube, which once carried a stream of lava for 10 km (6 mi) to the coast, is now blocked within 2.4 km (1.5 mi) of the vent. As a consequence, the lava breaks out upslope from the blockage and advances downslope as new surface flows.

Currently two major flows are active, each competing for lava from the tube. The largest and most vigorous issues from a breakout at the 2,310-ft elevation and is expanding southeastward as a narrow flow of pahoehoe about 2.5 km (1.6 mi) long. Currently, its front is at the 2,040-ft elevation. So far this flow's path has been along the flow field built in the past five years, although it may soon reach some long strips of forest that were preserved as kipuka during previous episodes.

The more sluggish flow is fed from the 2,250-ft elevation and flows southwestward. This flow is paving new ground along the west side of the flow field and is burning the `ohi`a-and-fern forest. The flow advances, stagnates, then inflates slowly and resumes advancing. Its front had progressed to about the 2,000-ft elevation across gently sloping terrain by April 11. The flow is about 1.8 km (1.1 mi) long, and if it continues on its present course, it will ooze over the pali and down to the coast within the National Park. Its progress has been slowed, however, by the larger flow's success in capturing the supply of lava from the tube.

The idea of competing flows implies winning and losing. In fact, the winner may dictate the pattern of future flow field growth by controlling the location of any new lava tubes that develop beyond the end of the existing tube. If a flow can capture most of the supply from the vent, then the new tube will develop along the path of that lava flow. For volcano watchers, that means more waiting to see where the lava flows will finally come down the pali to the coastal plain.