Volcano Watch — What's cooking at Kīlauea?

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Pele has been restless lately-she has changed her mood twice since late last year.

Through November 2001, as the 19th year of the Pu`u `O`o eruption drew to a close, lava tubes were feeding flows into the ocean at two places: the East Kupapa`u entry on the east-central side of the flow field and the Kamoamoa entry on the west-central side. Behavior of this sort-tube-fed lava flows leading from the vent to the ocean-had prevailed for the previous two years. During that time, the eruption was interrupted by only two brief pauses, both in 2000. Activity within Pu`u `O`o Crater was rare and brief.

This relatively steady behavior then began to change in early December 2001. The first clue was persistent breakouts from the lava tube system above Pulama pali and the concurrent decline in the amount of lava flowing through the tube system below the breakouts.

Then, in mid-December, hornitos began to form over the tubes above Pulama pali. Hornitos are strangely shaped spatter mounds and spires that form when tubes that are completely filled with lava spit out clots of lava through weak points in their roofs. Activity at the two ocean entries began to wane and, by the end of January, had completely stopped.

Some of the tube breakouts quickly died, but others were persistent and began to build low hills of lava-termed rootless shields-over the tube system. By the end of January, three separate shields were under construction. The lava that had been supplying the flows for the past two years was now being used to build a chain of rootless shields over the tube system above Pulama pali. Pu`u `O`o Crater reawakened in late January with new lava flows on the crater floor.

The shield-building continued, at times with as many as four rootless shields active at once. Lava from the underlying tube flowed upward like an artesian well, often feeding a lava pond which, in turn, sent short lava flows outward in all directions. Shields would only build to a height of a few tens of meters (yards) before activity shifted to an adjacent shield-free tube segment. The shield-building was accompanied by activity within the crater.

At the end of April, Pele had another mood swing. A breakout from the central part of the chain of shields sent two lava flows to the southeast: one just outside the boundary of Hawai`i Volcanoes National Park toward the surviving part of the Royal Gardens subdivision (the HALP flow), and one just inside the Park boundary (the Boundary flow). At the same time, activity within Pu`u `O`o Crater abruptly stopped. This marked an activity shift away from shield and hornito construction back to tube-fed lava flows.

This shift was confirmed on Mother's Day, May 12, when a vigorous new lava breakout appeared on the southwest flank of Pu`u `O`o. The resultant lava flow rapidly moved southeastward along the west margin of the Pu`u `O`o flow field, consuming the forest in its path and igniting forest fires. The National Park Service responded with a fire-fighting effort, because the fires threatened endangered Hawaiian plants.

The U.S. Geological Survey's Hawaiian Volcano Observatory has worked closely with the National Park Service in the mitigation effort, tracking the flow's progress and forecasting its path and advance rate. The Mother's Day flow reached the coastal plain on June 10 and is now working its way toward the ocean. The Park has removed its facilities-which were in the probable path of the flow at the end of the Chain of Craters Road-and moved them about 0.8 km (0.5 mi) to the west.

On May 26, the HALP flow overwhelmed a house in Royal Gardens--the 189th structure destroyed since the Pu`u `O`o eruption began. This flow is still active, though rather subdued. The terminus is narrow and is now below Pikake Street, between Prince and Royal Streets. The terminus of the sluggish Boundary is now on the coastal plain, about 1.75 km (1.1 mi) from the ocean.

Volcano Activity Update

Eruptive activity of Kīlauea Volcano continued unabated at the Pu`u `O`o vent during the past week. The "Mother's Day" lava flow is spreading and inflating at the base of Paliuli with the terminus of the flow located 0.6 km (0.4 mi) from the end of the Chain of Craters road. With the Kupukupu fire contained, the National Park Service has lifted their restrictions, and visitors can now hike out to the active flow area all day.

The two flows emanating from the "rootless" shields are still active. The actions of the lower Boundary flow and the mauka HALP flow are described in the article above. At least four houses are in the probable path of the HALP flow.

There were no earthquakes felt during the week ending on June 20, but one earthquake was reported felt in Hilo at 8:13 a.m. on June 2. The magnitude-2.9 earthquake was located 7 km (4.2 mi) northeast of Ka`ena Point at a depth of 5 km (3 mi).