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September 10, 1998

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

Lava flows create new ocean entry as old entry fades away

Rapid landscape changes take place during Kilauea's east rift zone eruption. Visitors to the coastal plain six months ago could have watched lava spilling from tubes at two major ocean entries south of Royal Gardens. By July 11, the eastern entry, at Waha`ula, had ceased. Farther west, however, the east Kamokuna entry remained robust, as a vigorous steam plume marked the interaction between surf and new turf.

And today? New surface flows are spilling over the sea cliff 300 m (1000 ft) west of the east Kamokuna entry. These flows, active since August 14, reached the ocean at 7:30 a.m. on Sunday, August 30. Also, a small flow entered the sea east of the east Kamokuna entry on September 5 but stagnated the next day. Meanwhile, the entry west of the east Kamokuna entry remains active and has added a swatch of land about 500 m (1600 ft) along shore and 80 m (250 ft) wide. Steam billows from the shoreline of these new flows, located about 5 km (3.1 mi) from the end of the Chain of Craters Road.

The flows, almost entirely pahoehoe, have their source in the tube system that originates at Pu`u `O`o. This tube, which fed the east Kamokuna entry from July 11 to August 14, broke open and spawned the new surface flows from a point at the 365-m (1200-ft) elevation of Pulama pali. About half of the tube's discharge was shunted into the surface flows, while the other half continued to move underground down the tube to the east Kamokuna entry. The vigor of the plume at east Kamokuna has declined these past few weeks, reflecting the diminished entry.

While still young, the active lava flows are filled with molten lava. Upon cooling, however, the molten parts of the flows become increasingly smaller and may change into relatively narrow conduits that carry much of the lava still being supplied from upslope. In this manner new tubes are born. The most favorably situated conduits get the lion's share of the magma, feeding new toes and flows down slope. The losers--those tubes within flows that cross extensive flat ground or stub out against uphill slopes with nowhere to go--slowly congeal. Of the new flows active on the coastal plain today, those feeding into the ocean at the western entry seem best positioned to develop major tubes.

The implications? Not much for the eruption overall, because the effects are limited to the last few kilometers of the path to the sea. We are, however, witnessing the growth and evolution of a new tube at the major coastal entry point being built at the west side of the east Kamokuna bench. Geographically, all this action is in the east Kamokuna area, so in the future we'll probably refer to these features as the western and eastern entries at east Kamokuna.

Today, dueling steam plumes from the two active entries will be the spectacle seen by visitors to the Kamokuna site. But the battle is being won by the western plume rising from the new lava flows. The eastern tube has never recovered its full flow of lava since August 14, and the plume there seems to be slowly weakening. In a few months, the landscape will have changed so much that returning visitors will wonder how all this could happen so quickly.

Eruption and Earthquake Update

The public is reminded that the two ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam clouds are highly acidic and laced with glass particles.

There were three earthquakes reported felt during the past week. One was reported at 4:23 p.m. on September 6 below the northwest flank of Mauna Kea. It had a magnitude of 3.4 and a depth of 25.7 km (14 miles). The next day another earthquake was felt in the same area at 9:40 a.m., with a magnitude of 3.0 and a depth of 25.2 km (15 miles). On September 10, an earthquake was felt at 12:28 p.m. while eating lunch at HVO; it had a magnitude of about 3.5 and was centered 31 km (19 miles) south of Apua Point at a depth of 37.4 km (22 miles).

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Updated: 10 Sep 1998