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Volcanowatch

May 19, 2005

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


25 years later, what have we learned from Mount St. Helens?

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The plume from Mount St. Helens rose nearly 3,000 feet (1,000 meters) above the volcano's rim. May 19, 1982. USGS Photograph by Lyn Topinka.

This week marks the 25th anniversary of the May 18, 1980, eruption of Mount St. Helens. At 8:32 a.m. that Sunday morning, a magnitude-5.1 earthquake occurred, and the north flank of the volcano collapsed in the largest landslide ever witnessed.

As the mountainside slid away, magma that had been accumulating within the volcano for the previous 2 months exploded outward in a lateral blast unlike anything observed before. The landslide and blast destroyed 230 square miles of forest and killed 57 people, including USGS geologist David Johnston, who was observing the volcano from a ridge 5 miles away.

Mount St. Helens erupted for the rest of that day, blasting hot ash and gas 15 miles into the atmosphere and sending numerous pyroclastic flows down the flanks of the mountain. The landslide also generated a destructive mudflow that traveled all the way to the Columbia River. This slurry reduced the depth of the shipping channel in the river from 40 feet to 14 feet overnight and stranded numerous ocean-going vessels in upstream ports.

In the 25 years since that fateful Sunday morning, the science of volcanology has dramatically changed, thanks, in part, to lessons learned from that eruption. Prior to 1980, the landslide and lateral blast had never previously been witnessed and were completely unknown to volcanologists.

A similar landslide and blast occurred at Bezymianny volcano in Kamchatka, Russia, in 1956, but no people or cameras were there to document the activity. Only after the 1980 eruption of Mount St. Helens was the style of the Bezymianny eruption fully recognized.

In fact, similar volcano landslides, called sector collapses, have now been identified at over 200 volcanoes around the world. Detailed studies of the sector collapse, lateral blast, and large mudflow at Mount St. Helens led to a reassessment of volcano hazards at other sites in the United States and around the world, better preparing communities situated near such volcanoes for possible future eruptions.

In addition, studies of eruptions at Mount St. Helens following the May 18, 1980, explosion demonstrated that volcanic eruptions could indeed be accurately predicted. The growth of a lava dome in the newly formed crater between 1980 and 1986 provided an ideal natural laboratory with a series of repetitive "experiments" (eruptions) for scientists to observe.

Through continuous monitoring and bold research by a team of interdisciplinary earth scientists using gas emissions, earthquake activity, surface deformation, and other techniques (many of which had been developed at HVO before their application at Mount St. Helens), 14 eruptions of lava between 1980 and 1986 were successfully predicted within days to weeks of their occurrence.

This well-organized effort was made possible by the creation of the Cascades Volcano Observatory (CVO), based on the model of the Hawaiian Volcano Observatory, in existence since 1912.

The experience gained from Mount St. Helens by CVO, along with the years of pioneering research at HVO, demonstrated the value of the observatory concept, where a group of scientists with different backgrounds could focus their efforts on understanding volcanic processes.

Within a few years of the Mount St. Helens blast, a mobile volcano observatory, the Volcano Disaster Assistance Program, had been established by the U.S. Geological Survey to respond to volcanic crises around the world. In addition, new volcano observatories were established to study Alaskan volcanoes, Long Valley caldera in California, and Yellowstone caldera in Wyoming.

Still, there is much progress to be made in understanding how volcanoes work, and why and when they will erupt. As the sudden, unanticipated reawakening of Mount St. Helens in September 2004 demonstrated, constant vigilance is essential for identifying and heeding signs of impending volcanic activity.

Although we have learned much from the May 18, 1980, blast at Mount St. Helens and other eruptions, including the now 22-year-long eruption of Kilauea, volcanoes continue to challenge us, teaching new lessons with every eruption.

Activity update

Eruptive activity at Pu`u `O`o continues. On clear nights, glow is visible from several vents within the crater and on the southwest side of the cone.

The PKK lava tube continues to produce intermittent surface flows from above the top of Pulama pali to the ocean. Three ocean entries were active as of May 19. The two largest are at East Lae`apuki and East Kamoamoa, with a much smaller entry halfway in between. The East Lae`apuki and East Kamoamoa entries both have benches about 350 m (385 yards) long and up to 75 m (80 yards) wide. Surface flows are active intermittently inland of the entries. The East Lae`apuki entry is the closest activity to the end of Chain of Craters Road, in Hawai`i Volcanoes National Park, and is located about 4.5 km (3 miles) from the ranger shed. Expect a 2-hour walk each way and bring lots of water.

Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Remember-the beaches that sometimes form next to an active bench are just as dangerous as the bench itself. Stay off both, and heed the National Park warning signs.

During the week ending May 18, 3 earthquakes were reported felt on Hawai`i Island. A magnitude 5.1 earthquake on May 13 at 0:06 a.m. was felt widely across the island. The event was located 5 km (3 miles) east-southeast of submarine Lo`ihi Volcano at a depth of 40 km (25 miles). A magnitude-3.2 quake occurred 14 km (9 miles) northwest of Na`alehu at a depth of 16 km (10 miles) at 5:14 a.m. on May 16; this earthquake was felt at Na`alehu. Another magnitude-3.2 quake occurred 1 km (0.6 miles) east-northeast of Pahala with a depth of 11 km (7 miles) at 6:28 a.m. on May 17; the quake was felt in the Volcano Golf Course area.

Mauna Loa is not erupting. During the week ending May 18, 7 earthquakes were recorded beneath the summit area. Inflation has slowed beneath the summit and flanks over the last few weeks.

Visit our web site (hvo.wr.usgs.gov) for daily volcano updates and nearly real-time Hawai`i earthquake information. skip past bottom navigational bar


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Updated: May 23, 2005 (pnf)