October 10, 1997

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

Few changes on the flow field

Update: the eruption has settled into a stable vent site, extrusive rate, and route to the sea. This statement would have been unimaginable in the early days of episode 55. Back then, the east rift zone eruption presented a new landscape almost daily, from its inception on February 24, 1997, until as late as August. Why so erratic then and more orderly now?

For starters, let's consider vents. New spatter cones and small lava shields were forming almost weekly as episode 55 became more vigorous. A vent might erupt for a week or two and then become extinct as another vent issued forth.

Each vent brought new lava flows, which blazed paths down the slopes of the flow field. But no single flow was sufficiently sustained to reach the ocean. New flows would stagnate, cool, and then be overrun by successors.

Short eruptive pauses played an important role by causing the flows to sputter and die. Magma extrusion halted completely for as long as 20 hours, each time disrupting the downslope progression of flows by starving them of lava.

In the past three months a landmark was reached when lava finally forged a path to the sea. On the upper flow field, the main lava channel roofed over, creating a lava tube. Fueled by a fairly steady supply from the vent area, the molten cores of the major flows on the coastal plain have slowly constricted to complete the tube system to the coast. The tube provides a thermally efficient conduit, allowing lava to travel 12 km from vent to sea while cooling only a few degrees en route. The extrusion rate remains a steady 500,000 cubic meters per day.

Equally important, the vent locations have remained fixed at two locations. With only sporadic exceptions, lava is erupted from a vent in Pu`u `O`o crater and from an area we call the south shield.

Lava from the Pu`u `O`o vent is usually confined within the crater and drains away through subterranean cracks. Overflows spreading outward from Pu`u `O`o have been observed on about ten occasions, but each is short lived and of minor volume. Lava upwelling at the south shield, 300 m south of Pu`u `O`o, hasn't breached the surface since August. Instead, it passes directly into the tube system that leads to the coast. Thus, new surface flows are sparse, forming chiefly as small-volume breakouts from the tube where it traverses the nearly flat slopes of the coastal plain. On a daily basis, the most obvious changes are now at the shoreline, where lava and ocean meet--always heatedly, sometimes explosively. New lava benches form dangerously unstable new land seaward of the old cliff escarpment.

Each of the past few episodes from Kilauea's east rift zone have progressed to these stabilizing characteristics--long-lived vents, steady supply of melt, and an efficient tube system that carries molten lava to the sea. No day is predictable at a volcano, but for the present, the eruption has settled into a regular pattern.

Kilauea Eruption Status--October 10, 1997

During the past week there was constant effusion of lava from the vent within Pu`u `O`o. Lava continued to flow through a network of tubes to the seacoast where it entered the ocean at two locations -- Waha`ula and Kamokuna. The public is reminded that the ocean areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam cloud is highly acidic and laced with glass particles.

Recent Big Island Earthquakes

There were no reports of felt earthquakes this week on the Big Island.