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Volcanowatch

March 6, 2003

A weekly feature provided by scientists at the Hawaiian VolcanoObservatory.


Two eruptions at Kilauea's summit in 1982 end an era

The summit of Kilauea has been quiet for more than 20 years. Pu`u `O`o and Kupaianaha have hogged the limelight since January 3, 1983. Two eruptions took place in the caldera in 1982, however, and one was a bit unusual.

The first started at 11:37 a.m. on April 30 and ended 19 hours later. Lava erupted from a fissure about 1 km (0.6 miles) long that cut the caldera floor northeast of Halemaumau, actually extending into the crater. A spatter rampart built along the fissure is prominent today, crossed by the trail from Volcano House to Halemaumau.

Low fountains 5-10 m (15-30 feet) high, with bursts to 50 m (150 feet), played along the entire length of the fissure within about 25 minutes of the start of eruption. Small lava flows spread both north and south, eventually covering 31 hectares (76 acres), including a small puddle on the floor of Halemaumau.

Lava continued to ooze from the interior of the southeast flow for 7 days after the eruption was thought to have ended. Experience with the current eruption suggests that the eruption was actually continuing, feeding a small volume of lava into an inflating flow, pressurizing its interior and forcing lava to break out.

This brief eruption was followed by a larger eruption beginning at 6:45 p.m. on September 25. This eruption was preceded by nearly 2 hours of increased seismicity and abrupt summit inflation. As magma was rising to the ground surface, it reopened old cracks in and near the eastern end of the Halemaumau parking lot, as the first observer discovered at 5:15 p.m. upon arriving near the site of the eventual outbreak. An obvious asphalt patch across Crater Rim Drive hides this crack today.

This eruption was a little unusual because of its southern location. The eruptive fissures were crowded near the south end of the caldera, near the low pali visible from Halemaumau. The eastern and central parts of the fissure system were oriented east-northeastward, the typical direction for fissures on the caldera floor. Fountains 20-40 m (60-120 feet) high, bursting to 70 m (220 feet), played along the entire 350-m (quarter-mile) fissure system within minutes after eruption began.

The western part of the fissure system behaved differently, turning westward as it followed a caldera fault. A tiny pad of lava was actually erupted right at the top of the pali bounding the caldera at about 9:00 p.m. The Crater Rim Trail crosses this dark pad, which stands out in a sea of older explosion debris.

Lava erupted mainly from the eastern and central fissures quickly formed a pond in a broad, shallow basin south of Sand Spit, covering part of the 1921 lava flow in the process. At about 7:30 p.m., lava began to leave the caldera through a narrow gap in the wall, eventually flowing southward about 1.5 km (1 mile).

Lava from the pond spilled across Crater Rim Drive between 9:00 and 10:00 p.m., dropping into the deepest part of the caldera and spreading a short distance northeastward. This created what has become one of the most popular bus stops on the caldera floor, where visitors can touch the youngest lava flow that many of them will ever see.

The eruption had ended by about 8:30 a.m. the next morning, having covered 76 hectares (188 acres). Lava stored in the pond began to drain back into the now-dead fissures. This drainback continued for 34 hours, lowering the level of the pond 2-4 m (6-12 feet), as indicated by an obvious "bathtub ring" on the south side of Sand Spit.

Before drainback, however, the pond underwent at least one episode of crustal overturning, renewing the crust and creating a smooth surface very unlike that of typical pahoehoe lava flows. Visitors can view the overturned surface by walking to the south side of Sand Spit from the Halemaumau parking lot.

These two eruptions, though small, ended a 30-year period of frequent activity at the summit, in 1952, 1954, 1961, 1967-68, 1971, 1974, 1975, and 1982. Whether activity returns to the summit once the current eruption is over is anyone's guess.

Activity Update

Eruptive activity at the Pu`u `O`o vent of Kilauea Volcano continued unabated during the past week. Scattered surface breakouts from the western "Kohola" lobe of the Mother's Day flow are seen throughout the inflating flow. The Kohola ocean entry stopped on March 1, but a new finger along the east margin of the flow is approaching the seacoast just west of Wilipe`a. Lava continues to enter the ocean at the West Highcastle delta.

The public should be aware that the ocean entry areas could collapse at any time, potentially generating large explosions in the process. The steam clouds rising from the entry areas are highly acidic and laced with glass particles. The National Park Service has erected a rope barricade to delineate the edge of the restricted area. Do not venture beyond this rope boundary onto the lava deltas and benches. Even the intervening beaches are susceptible to large waves suddenly generated during delta collapse; these beaches should be avoided.

Four earthquakes were reported felt during the past week. Residents of Hilo, Pepe`ekeo, and Fern Forest subdivision felt an earthquake at 9:15 p.m. on March 1. The magnitude-3.3 temblor was located 6 km (3.6 mi) north of Ka`ena Point at a depth of 9 km (5.4 mi). Two earthquakes were felt in Leilani Estates. The first (magnitude-2.5) was at 2:10 a.m. on March 2, and the second (magnitude-2.4) was at 11:57 a.m. on March 4. Both earthquakes were located 2 km (1.2 mi) east of Pu`ulena Crater at a depth of 4 km (2.4 mi). At 10:36 p.m. on March 3, a resident of Waimea felt the earth move. The magnitude-2.5 event was located 4 km (2.4 mi) southeast of Kukuihaele at a depth of 38 km (22.8 mi).

Mauna Loa is not erupting. The summit region continues to inflate, and the rate of inflation has increased slightly during the past week or two. The earthquake activity is low, with only one earthquake located in the summit area during the last seven days. skip past bottom navigational bar


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Updated: March 10, 2003 (pnf)