Bench collapse, temporary draining of lava tube are prominent events of the past three weeks
[Previous eruption updates may be accessed through our archive index.]
In the three weeks since February 4th,
Aerial oblique view of Pu`u `O`o cinder-and-spatter cone, looking west-southwest. Visible in foreground are crater overflows that occurred chiefly in 1997. Main crater floor lies 30-40 m below the east rim. The feature known as "crater vent" is the heavily fuming area in upper left of crater floor; it forms a shallow depression about 100 m long within the crater floor. Only scant fresh lava was visible in the crater vent when this photo (p0910) was taken February 12, 1988. Distance across crater is about 200 m (left to right).
The Pu`u `O`o vent area has remained relatively unchanged in February. Fumes issue from cracks in the cone and surrounding area. In the past month, fuming from new cracks near the north rim (right side of previous photo) has masked the view of our remote surveillance cameras. Even helicopter overflights are commonly greeted with such profuse fuming that little of the crater vent may be visible at any one time.
Low aerial oblique view looking south across the upper flow field toward coast. Yellow-orange spot is a skylight or opening into a lava tube at the 1860-ft elevation; opening is about 4 m wide, and the stream of lava is 6.5 m beneath the ground surface. About 50 m beyond skylight is shiny flow that issued from a skylight on January 15, 1998; the site of blue-gray smoke marks the old skylight now crusted over by the recent flow. Photo p0926, taken February 12, 1998.
Lava travels in tubes from the Pu`u `O`o vent area to the ocean. Surface lava flows have been sparse in the past three weeks. A small flow has issued every 4-5 days from the lava tubes across the coastal plain. These flows escape from weak points in the tube roof. Most breakouts have been near the Waha`ula ocean entry. The photo above shows a skylight and five-week-old lava flow on the upper flow field.
Lava from the ongoing eruption enters the ocean at two sites. New land is built in these areas as the lava progrades seaward. Waha`ula, the easterly site, is named for a heiau (ancient Hawaiian temple) that was overrun by lava in August 1998.
Aerial oblique view southwest along south shore of Island of Hawai`i. Foreground steam plume marks lava entry at Waha`ula; behind it is the entry at Kamokuna. Distance between the two plumes is about 900 m. Coastal plain has been covered by lava flows emplaced in the past 15 years as far west as the pale yellowish-brown ground 6 km distance. Entire scene is within Hawai`i Volcanoes National Park. Photo p0919, taken February 12, 1998.
The westerly site at Kamokuna shows many features characteristic of the lava-ocean interface. A 10- to 15-m-high cliff borders the ocean, and the new land forms a low shelf or bench at the foot of the cliff. The bench grows seaward, but the steep submarine slope favors periodic failure when the bench becomes too massive. At these times, the bench and its substrate collapse abruptly into the ocean. Such a collapse occurred most recently sometime between February 16 and 19, destroying 4 hectares (10 acres) of land that had been built since the previous collapse five weeks earlier on January 15.
Aerial oblique view west at Kamokuna lava entry. Outline shows extent of bench that was extant prior to mid-February collapse. Large collapses are commonly accompanied by explosions as hot rock and lava are abruptly mixed with sea water. Debris from the explosion is thrown inland of the cliff for tens of meters.
Eruption-viewing opportunities change constantly, so those readers planning a visit to the volcano should contact Hawai`i Volcanoes National Park for the most current eruption information (ph. 808-985-6000). Additional photographs and descriptions of east rift eruptive activity may be found on the University of Hawai`i's web site.