August 8, 1997

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

Eruption Update--August 8

Pele continued her march to the sea in the two months since our last eruption update through Volcano Watch. Lava reached the ocean on July 12 and occasionally since then. Also, lava flows were emplaced north and west of Royal Gardens but are not presently threatening any residential areas.

Eruptive activity has been focused at three main vents. The first, crater cone, is a large spatter cone inside Pu`u `O`o Crater. It intermittently produces large flows that enter the pond occupying the eastern crater floor. Subterranean cracks drain the pond as fast as it fills. Periodically the cracks became blocked, causing the pond to fill and overtop the crater rim. On several occasions, lava in the crater has risen until it overflows through the gap in the west wall of the cone and also through the old southeast spillway. On August 6, the pond overflowed eastward to form a lobate sheet that reached for nearly a mile. None of these flows was active for more than three hours because the pond resumes its draining, which interrupts the overflow process.

The second vent, the mini-shield, hugs the south slope of Pu`u `O`o cone. It erupts intermittently to produce short flows that extend no more than 30 m (100 feet) from the vent.

The third vent, south shield, lies about 300 m (1,000 feet) south of Pu`u `O`o. South shield has been the prolific producer of flows that mantle the flow field, including all large flows produced in July and early August. From July 12 to July 29, a tube-fed flow from this vent entered the ocean at East Kamokuna in Hawaii Volcanoes National Park. This flow built a lava bench approximately 350 m (1,150 feet) long (parallel to the shoreline) by 60 m (200 feet) wide. The ocean entry was marked by the usual large billowing steam plume and by mild steam explosions, which hurled spatter a short distance onshore, building two small shoreline, or littoral, cones.

Beginning about July 18, another flow from the south shield followed a more easterly course toward the upper edge of the Royal Gardens subdivision. On July 28 the flow was burning into the edge of the forest 1.6 km (1 mile) above the subdivision. This flow has since ceased.

The south shield vent shut down early on July 29. The lava tubes within the Royal Gardens flow and the ocean entry flow were empty by midday. The ocean entry stopped except for a trickle of lava from the draining tube. This was not an eruptive pause for episode 55, however, because the Pu`u `O`o crater cone remained active.

The south shield resumed erupting that night, July 29. By the morning of the 30th, lava had reoccupied the upper reaches of the tube leading to the ocean, and breakouts from the tube formed channeled 'a'a flows on the upper slopes of Pulama pali, the steep fault scarp that rises above the coastal plain. The new flows followed the course of the earlier July flows, and within two days, the tube was reoccupied down to the coastal plain.

By August 4, lava had again reached the ocean at the East Kamokuna entry. An easterly lobe from this flow branches at the foot of Pulama pali. It advanced to within 800 m (2,500 feet) of Waha`ula Heiau, a 700-year-old, rock-walled structure 450 m (1,500 feet) east of the East Kamokuna ocean entry.

Vigorous eruptive activity within Pu`u `O`o crater lit the skies on the night of August 7 and rewarded viewers with a spectacular display of moderate fountaining.

Recent Big Island Earthquakes

A resident of Mauna Loa Estates subdivision reported feeling an earthquake at 4:42 a.m. on Thursday, August 7. The temblor was located 6 km (3.6 mi) southeast of the summit of Kilauea Volcano at a depth of 2.7 km (1.6 mi) and had a magnitude of 2.7.