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Volcanowatch

November 11, 2004

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


Kilauea lava flows pour into sea, Mount St. Helens lava pushes up snow and ice

Lava erupting from the Pu`u `O`o vent is again spilling into the sea and adding new land along Kilauea's shoreline to the delight of red-rock junkies in Hawaii and abroad. In the past week, small streams of lava quietly entering the sea have already built a lava platform jutting 50 m (164 ft) seaward!

As long as lava continues to pour into the sea, the new land is likely to grow then shrink when it collapses beneath the water. This cycle of growth and demolition could be repeated hundreds and thousands of time because the new platform, called a lava bench, builds itself on top of a loose pile of lava and glass fragments on the steep submarine slope immediately offshore.

Depending on how the bench collapses-all at once, just the leading edge, or only subsiding by a few meters (yards) -visitors might be lucky to witness the explosive interaction of lava and water.

Complete collapse of a bench covered with hot flows often triggers a series of strong steam explosions that can hurl lava and solid rocks inland more than 100 m (330 ft). Gradual collapse of the bench, however, typically results in a pulsating plume of tiny lava fragments, glass, and steam shooting into the air above the collapsed area.

When a lava bench subsides, its active lava tubes suddenly are below sea level. Water gaining access to the tubes' lava streams of more than 1,100 degrees C (2,012 degrees F) can trigger explosions that blast lava up through the top of the tube. Such explosions can send giant lava bubbles 10 m (33 ft) onto the bench or create a spectacular lava fountain as high as 100 m (330 ft) up through the tube.

The other U.S. volcano currently erupting lava-Mount St. Helens-is quietly building an impressive mound of lava, called a lava dome, inside the deep horseshoe-shaped crater formed in 1980.

Scientists of the Cascades Volcano Observatory recently estimated the new lava dome and the surrounding uplifted area of the crater floor have been growing in the past month at an average of about 600,000-700,000 cubic meters a day (2.1-2.4 million cubic yards).

By comparison, Kilauea is erupting less than about 300,000 cubic meters (1 million cubic yards) a day. The extremely hot, fluid streams of incandescent basalt lava erupted at Kilauea easily flow across the gentlest ground slopes.

Lava erupting at Mount St. Helens, however, is about a million times more viscous (resistant to flow) than lava erupted at Kilauea. Instead of flowing easily across the ground, the lava tends to pile up around the vent to form circular to elongated-shaped flows in the form of a mound or dome hundreds of meters (yards) in diameter.

Mount St. Helens' lava is also interacting with water, but in a different form. For the last several years, a small glacier was growing on the south crater floor.

At the end of September 2004, cracking in the glacial ice increased dramatically and its surface started to rise. Magma apparently was rising slowly beneath the glacier and pushing it upward instead of melting it away. The glacial ice was effectively insulated by tens of meters of rockfall debris so that little heat was transferred from the slowly moving magma.

New lava was first visible on the crater floor on October 11.

In the past week, the dome has continued to push the glacier and rock debris upward and outward several m (yards) each day as more lava is added to the dome. The visible part of the new dome is about 400 m (1,300 ft) long and 180 m (590 ft) wide. It stands about 250 m (820 ft) higher than the pre-eruption crater floor.

Scientists monitoring both volcanoes are on call 24 hours a day to respond as needed to changes in the eruptions that could lead to more dangerous activity and to learn from activity that has fascinated volcano watchers all over the world-lava flowing across the ground in a myriad of ways with interesting consequences.

Activity update

Eruptive activity at Pu`u `O`o continues. The PKK flow advanced rapidly across the coastal plain last week and entered the ocean on the night of November 5-6. The new ocean entry is at Lae`apuki, 3.6 km (2.2 mi) from the end of the pavement on Chain of Craters Road in Hawai`i Volcanoes National Park. The new bench is about 170 m (490 ft) long (parallel to shore) and 50 m (164 ft )wide. Remember, benches can collapse without warning! Stay well back from the sea cliff, heed the National Park warning signs, and don't even think about descending onto the growing bench. The eruptive activity in the crater of Pu`u `O`o remains weak, with several spatter cones glowing but not doing much else.

No earthquakes were reported felt on the island during the week ending November 10.

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity is elevated over the past several weeks after decreasing in early September. 50 earthquakes were recorded beneath the summit area during the week ending November 10. Nearly all are 40 km (23 miles) or more deep and are the long-period type, most with magnitudes less than 3.

Visit our web site (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time earthquake information. Visit the Cascades Volcano Observatory (CVO) web site (Vulcan.wr.usgs.gov) for Mount St. Helens updates. skip past bottom navigational bar


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Updated: November 18, 2004 (pnf)