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New deep dimple: funnel-shaped crater grows on Pu`u `O`o south flank
This update current as of December 17, 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:
- 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."
- The vent inside Pu`u `O`o has spilled lava across the crater floor for the first time in four weeks. Much of the time, however, the magma column remains 10-20 m below its bounding rampart--out of sight except from the air.
- 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. Although lava will escape occasionally from the tube to form new surface flows, no such breakouts have occurred in the past six weeks.
- Ocean entries remain situated at East Kamokuna and Waha`ula, which are the distal ends of the tube system. At East Kamokuna, small collapses periodically destroy short segments of the bench. Each new embayment is slowly reoccupied by new lava as the bench resumes its seaward growth. 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, about 4,300 tons per day measured along Chain of Craters Road on December 7.
The 55th episode of Kilauea's almost 15-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.
Oblique aerial photo looking southwest across Pu`u `O`o. Lava flows in foreground are east-directed overflows from August and October; photo p0496 taken Dec. 4, 1997. Distance is 200 m between north and south summits. Crater vent lies at base of dense fume cloud in Pu`u `O`o crater.
During the last 17 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 has diminished greatly in the past six weeks, with lava remaining instead within the rampart that bounds the vent. On December 8 and 9, lava escaped from the throat and recoated the crater floor. The limited extent of incandescent lava has reduced the magnificent nighttime glow once so prominent from many vantage points on the east slope of Kilauea Volcano.
Near-vertical aerial photo looking west at Pu`u `O`o; photo p0503 taken Dec. 4, 1997. Incandescent glow is top of magma column in the crater vent within Pu`u `O`o cinder-and-spatter cone. Periodic spills from the vent coat the main crater floor. The newly formed pit on the south flank of Pu`u `O`o hadn't formed by Dec. 4, but its location will be midway on the cone's sloping south (lefthand) flank, just beneath the fume cloud.
Perhaps the most remarkable event during the past two 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. That 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.
Near-vertical aerial view north-northwest into newly formed pit on south flank of Pu`u `O`o. Pit is 50 m in diameter at the surface and about 50 m deep tapering to a shaft of uncertain depth. Visible behind the summit of the cone is incandescent lava within the crater vent pit (in Pu`u `O`o crater). The hieroglyphic texture in upper right is reflection from fresh lava that coats the crater floor. Photo p0526, Dec. 9, 1997.
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.
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.
Oblique aerial view northeast across the East Kamokuna bench. Land newly formed since July 1997 is indicated by the lighter-colored lava. Much of this lava is dull gray owing to salts and solfataric alteration on its surface. Newest flows are the silvery-gray lava in the upper-right reach of the bench. A curtain of steam rises from the zone where hot lava and sea interact. Distance along entire bench is 930 m; breadth is 130 m at widest point. Photo p0487, Dec. 9, 1997.
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. No one should venture onto the benches, no matter how stable the new land may appear.
Such a collapse occurred in early November (six weeks ago), lopping 4.75 acres (1.92 hectares) of existing episode-55 bench into the ocean at East Kamokuna. (No one was on the bench, so only land, not life, was lost.) Since then, a new lava flow from the beheaded tube is building 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 new lava flow is filling an embayment created during the abrupt destruction of unstable land.
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.
This map current as of December 16, 1997
Eruption-viewing opportunities change constantly, refer to the HVO home page for current information. Those readers planning a visit to Kilauea or Mauna Loa volcanoes can get much useful information from Hawai`i Volcanoes National Park.
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