January 3, 1997

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

Kilauea Eruption: 15 Years and Counting

On January 3, 1997, Kilauea's east rift zone began its 15th year of continuous eruption, the longest rift-zone eruption in written history. Throughout this period, scientists at the U.S. Geological Survey's Hawaiian Volcano Observatory have monitored the eruption to forecast changes in the eruptive process, predict the spread of lava into inhabited areas, and provide Civil Defense and the National Park Service with information needed to protect lives.

Since the eruption began in 1983, lava has covered 37 square miles of existing terrane. Some areas have been mantled repeatedly and are now buried beneath 80 ft of lava. The volume of erupted lava is nearly 2 billion cubic yards--enough new rock to pave a two-lane highway 1.2 million miles long, encircling the globe 50 times.

Lava flows destroyed 181 residences, several community centers, and one commercial site, all within the first eight years of the eruption. Eight miles of highway have been covered by flows during the past 14 years. These losses are estimated at $61 million.

Air quality has diminished on the Big Island owing to gases from the eruption. One of the gases, sulfur dioxide, has been released in amounts ranging from 350 to 1,850 tons per day. The effects of volcanic air pollution include damage to natural vegetation, cultivated crops, automobiles, and machinery. The cost of this incremental damage is unknown.

The most prominent vent of the eruption is Pu`u `O`o, a 760-ft-high cinder-and-spatter cone. Other vents include two major lava shields and numerous spatter cones that have grown along the three-miles of east rift zone where eruptive fissures have been focused. The active vent today extends from beneath Pu`u `O`o to a collapse pit just west of it. Small pits have developed on the cone in past years, a result of undermining by subterranean molten rock. Recently, two pits coalesced on the west flank of the cone, forming a pit that extends to within 25 ft of the summit peak. If adjacent large unstable blocks fall eastward into the lava pond of Pu`u `O`o's main crater, they may trigger small ash-producing explosions.

Today, lava flows through a 7-mile-long tube from the Pu`u `O`o vent area to the sea. The tube system has proven so efficient that in recent months lava only rarely escapes to form surface flows, except at the coastline. There the lava and ocean struggle relentlessly. Lava has won the short-term battle, extending the shoreline seaward and adding 540 acres of new land along the steep southern slope of the Big Island since the eruption began. Periodically the new land proves unstable, failing under its own weight and sliding into the ocean. These areas of ground gained and lost are excluded from the reported new acreage.

The eruption continues unabated, with no end in sight. Major eruptions of this type may end abruptly or might wane for many months. No one could have predicted that this eruption would last for 14 years. Its future remains equally uncertain.

There were no felt earthquakes on the Island this past week.