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Pause in Eruption Leads to
New Surface Flows

This update is current as of February 10, 1999. Eruption updates are posted every 4 to 6 weeks; more frequent updates will be made when there are drastic changes in activity or when residential areas are threatened by lava flows.

Photograph by H. McGiffert on February 7, 1999
Pahoehoe flow on coastal plain, Kilauea Volcano

Overview

The eruption of Pu`u `O`o continues to deliver lava to the sea through the lava-tube system that developed on the coastal plain in August 1998. Between November and early February 1999, there were very few surface flows on the volcano, except for many small pahoehoe flows on the active lava delta. This changed abruptly on February 7 following a brief pause in the supply of magma to Pu`u `O`o. When lava reoccupied the tube system leading from Pu`u `O`o, lava spilled from several skylights and fed both `a`a and pahoehoe flows above and below the pali. Some flows were still moving slowly on February 8. In mid January, intermittent bubble fountains played from the delta as water temporarily gained access to the tube within the delta. A new littoral cone was built by the bubble fountains.

Summary of pause #22

On Friday evening, February 5, Kilauea's summit region went through an abrupt deflationary event (see tiltmeter plot below). The deflation was followed by a decreased supply of magma from the summit to Pu`u `O`o, the active vent on the volcano's east rift zone. Whether this reduction resulted from constriction along the subterranean path or from changes at the summit magma chamber is uncertain. Regardless, supply of lava to the tube system dwindled, and by early afternoon on Saturday, Feb. 6, the steam plume at the coast ceased. These conditions persisted until after midnight.

Early on Sunday morning, Feb. 7, the summit underwent about 7 microradians of inflationary tilt along an axis N50W-S50E, measured in our borehole tiltmeter near Uwekahuna vault. The inflation lasted little more than one hour and was followed by summit deflation. About two hours later a substantial supply of magma must have reached the vent area, because GOES satellite imagery shows a thermal spike between about 3:15 and 3:30 a.m. By dawn, lava flows were visible from the end of the Chain of Craters road, a popular viewpoint place for park visitors.

Record showing tilt along azimuth N50W from summit borehole tiltmeter at Uwekahuna vault. Tilt is recorded in microradians; one radian equals 57.3 degrees. (For those unfamiliar with tilt units, one microradian is roughly the tilt created by inserting a dime beneath the end of one-kilometer-long beam.) The tilt record shows an episode of deflation on February 5, which led to a cutoff of magma supply from the summit to the east rift zone eruption. Early Sunday morning, an abrupt 7-microradian inflation of Kilauea's summit area was followed by abrupt deflation. This latter event coincided with resupply of magma from the summit to the east rift zone, and about two hours later (3:30 a.m.) new lava flows were spreading across the flow field.

Photograph by C. Seaman on February 8, 1999

When the eruption resumed at Pu`u `O`o early on February 7, lava poured from several skylights to feed surface flows above and below Pulama pali. In the photo above, the white line marks the edge of an `a`a flow that spilled down the pali.

`A`a flow; February 7	Pahoehoe flow; February 7
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Lava delta explosive activity in mid-January

Photograph by C. Seaman on February 8, 1999

Aerial view east toward the active lava delta (light-toned surface), which is about 150 m wide. White fume clouds rise from areas where lava is entering the sea. The littoral cone near the southeast edge of the delta was built by spectacular explosive activity in mid-January, caused when water temporarily gained access to the lava tube within the lava delta. Blue-colored fume in upper left escapes from a lava-tube skylight.

Cone on lava delta; January 28	Lava bubble burst; January 18
[Medium-sized image] [Large-sized image]	[Medium-sized image] [Large-sized image]

Flow-field Map

Map showing area covered by lava flows emplaced during the Pu`u `O`o - Kupaianaha eruption between 1983 and February 8, 1999. Flows emplaced between February 7 and February 8, 1999, are shown in pink. The lava tube delivers lava to the ocean a few hundred meters west of a prominent littoral cone (star) at Kamokuna (click map for a larger view of the map).

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Eruption-viewing opportunities change constantly, refer to the HVO home page for current information. Those readers planning a visit to Kilauea or Mauna Loa volcanoes can get much useful information from Hawai`i Volcanoes National Park.

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