Construction and Collapse
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View toward N; November 24 |
View toward W; December 11 |
When lava began pouring into the ocean 300-400 m west of the prominent littoral cone (left photo) in late August, the former shoreline and sea cliff were quickly covered with many thin flows. The old cliff became nearly impossible to identify landward of the new lava-entry area, which made it difficult for visitors to determine relatively safe areas from which to view the lava-entry area. Sometimes visitors ventured out onto the new land not realizing they had crossed the old cliffline and were walking on unstable and dangerous ground.
In the images above, the approximate location of the old sea cliff is marked with a yellow line. Note that on December 11, the shoreline actually was inland from the old cliff--the collapse event of December 10-11 removed the new land that had been built since August and a part of the older shoreline. This slightly older shoreline was built by lava between 1992 and 1997. Clearly, even the older shoreline is susceptible to collapse when an active lava delta and bench collapse into the sea.
Judging from earlier bench collapses, the missing area most likely slid into the sea in several segments over a period of at least several tens of minutes to several hours. If you happen to be viewing the area when parts of an active lava bench begin to collapse into the sea, make sure that you are already, or retreat to, at least 400 m inland from the former shoreline (as recommended by Hawaii Volcanoes National Park).
The new pit that developed high on the south flank of Pu`u `O`o vent about one year ago enlarged significantly in early 1998, and recent measurements of cracks around the edge of the pit show that its walls are slumping slowly into the pit.
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December 9, 1997 Near-vertical view 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. |
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November 11, 1998 The pit is 150-180 m in diameter and has consumed part of the shield at the base of Pu`u `O`o. In the past few weeks, the pit enlarged so that its upper edge nearly reaches the crater rim of Pu`u `O`o. The pit is becoming shallower as more debris slumps in from its walls. |
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Map showing area covered by lava flows emplaced during the Pu`u `O`o - Kupaianaha eruption between 1983 and August 30, 1998. Flows emplaced between August 14 and August 30 are shown in purple. A new lava tube has developed within this flow field and is delivering lava to the sea 300-400 m west of the east Kamokuna lava tube (black line). On October 19, a surface flow moving from the base of Pulama Pali reached the sea about 400 m west of the the area shown in purple.
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).