Photo and Video Chronology - Kīlauea - December 31, 1997

[Eruption updates are posted approximately every two weeks. More frequent updates will accompany drastic changes in activity or increased threat to residential areas.]

For readers familiar with events of the past few months, recent changes include these:

• If you were born after January 3, 1983, you are younger than Pu`u `O`o and have lived during nearly continuous eruption at Kilauea volcano.
• The vent inside Pu`u `O`o has spilled lava across the crater floor on a more frequent basis recently. This once-common occurrence had become a rarity during November and early December.
• A new pit developed abruptly on Sunday, December 7. Located midway between the south base and rim of Pu`u `O`o, this pit is similar in form and origin to a long-destroyed feature called "the Great Pit."
• Lava from the south shield travels in tubes to the coast, an in-tube distance of about 10 km. Travel time for a particle of melt is probably about 3 hours from vent to ocean. Eruption rate is generally 500,000-600,000 cubic meters per day. Lava escapes occasionally from the tube to form small new surface flows, doing so as recently as December 30.
• Ocean entries remain situated at East Kamokuna and Waha`ula, which are the distal ends of the tube system. At East Kamokuna, a collapse in late December destroyed about 4.4 hectares (11 acres) of land. New lava flows immediately begin rebuilding new land at the ocean's edge. Steam plumes rise as a nearly continuous curtain from the 500-m-long edge of the slowly prograding lava flows of the bench.
• Sulfur dioxide gas emissions from vents in the Pu`u `O`o area remain high, with a rate as high as 7,000 tons per day in the past two weeks.

The 55th episode of Kilauea's15-year-long east rift zone eruption continues. This episode, which began February 24, 1997, was characterized in its early months by shifting vent locations on the west and southwest flanks of Pu`u `O`o cone and by rapid enlargement of the episode 50-55 lava shield. The flow field expanded slowly until, in July, lava reached the sea. The supply of lava to the coast became restricted to tubes, and surface flow activity diminished greatly.

During the last 19 weeks, eruptive activity has been concentrated at two main vents: the crater vent on the Pu`u `O`o crater floor and the south shield, a lava shield about 300 m south of the Pu`u `O`o cone. The most conspicuous of these has been the crater vent, which originated as a spatter cone. In September, however, the spatter cone subsided into its own throat, leaving a pit. The pit is slowly enlarging and now is about 60 m in diameter. Lava froths and sloshes within this cauldron. All of these changes occurred within the already existing crater of Pu`u `O`o.

In the two weeks prior to November 3, magma issued nearly continuously from the throat of the crater vent, spilling eastward across the main crater floor. This activity diminished greatly in the five weeks from November 3 to December 8, with lava remaining instead within the rampart that bounds the vent. Numerous spills began occurring on December 29, perhaps in celebration of the coming new year. None of this lava escapes from the crater of Pu`u `O`o, however.

Perhaps the most remarkable event during the past four weeks was the formation of a new pit on the south side of Pu`u `O`o. The pit results from subterranean undermining of the cone by magma. The resulting crater steepens abruptly with depth--truly funnel-shaped. The pit, 50 m in diameter, formed within a few hours on December 7, according to helicopter-pilot reports.

This is the second such pit in the history of Pu`u `O`o. An earlier pit formed on the southwest flank, roughly along the trace of the east rift zone. After that pit appeared, it enlarged slowly over a period of nearly four years until it encroached into the rim of Pu`u `O`o. The older pit finally was engulfed during a collapse of the cone on January 29, 1997, an event that left a large notch in the southwest flank of the cone.

The other main vent, the south shield, is the source of the flows entering the ocean at the Waha`ula and east Kamokuna sites near the east boundary of Hawai`i Volcanoes National Park. The flows are encased within lava tubes for most of their length and are visible only through skylights in the roof of the tube.

Lava rarely escapes from the tube along its path from vent to ocean. On occasion, however, breakouts occur from weak points in the tube roof. A breakout is initiated by a surge of lava from the vent or by a blockage downtube from the breakout. In either case, the weak section of roof is rafted away by the outward flow of lava. Typically the tube once again becomes the more efficient path for lava transport, and supply of lava to the surface flow diminishes. 

The tubes discharge their lava at the shoreline. The hot lava, about 1,150 degrees Celsius when it reaches the ocean, generates dense plumes of steam upon contact with seawater. The new lava builds benches beyond the low seacliffs that bound the south coast of the Big Island.

Small explosions periodically disrupt the rapidly chilling lava and throw it onto the bench, constructing low nearshore (littoral) cones. These small explosions pose a minor threat for visitors. A far greater threat exists, however; these benches may collapse into the sea without warning, triggering large steam explosions that hurl dense rock and molten spatter tens of meters inland.

Such a collapse occurred in early November (six weeks ago), lopping 1.9 hectares (4.8 acres) of existing episode-55 bench into the ocean at East Kamokuna. A new lava flow from the beheaded tube built a shelf at the foot of the new cliffs created by the collapse. These features may be discernible in the previous photo. The silvery gray lava in the upper right stretch of the bench marks the area where collapse and infilling have occurred most frequently. Thus, the November-December lava flow was filling an embayment created during the abrupt destruction of unstable land.

Sometime between December 23 and 26, another collapse destroyed the newly built bench and additional land behind the cliff, a total of 4.4 ha (11 acres). No one should venture onto the benches, no matter how stable the new land may appear.

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 (808-985-6000). Additional photographs and descriptions of east rift eruptive activity may be found on the University of Hawai`i's web site.