# Volcano Watch — Two eruptions bordering the Pacific plate: one huge, one small but ongoing

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This week is the 91st anniversary of the largest eruption on earth since Krakatau exploded in 1883. We are also ending the 4th week of an ongoing eruption whose final size and violence are not yet known but which so far has been small. Each eruption took place along the margin of the Pacific plate, in the middle of which Hawaii has formed.

Most readers have heard of the Valley of Ten Thousand Smokes on the Alaska Peninsula opposite Kodiak Island. Before June 6, 1912, however, there were no smokes in this valley. On that day, what is now known as Novarupta Volcano erupted with mighty force. A column of ash shot quickly to a height of 33 km (20 miles) and, within 4 hours, showered ash on the village of Kodiak, 150 km (100 miles) away. Eventually more than 30 cm (1 foot) of ash blanketed Kodiak, collapsing some buildings and causing avalanches that destroyed others. By June 9, when the eruption ended, ash stinking of sulfur was falling on Seattle.

But the real changes took place at the site of eruption. Pyroclastic flows-dense clouds of hot ash, pumice, and gas that move at hurricane speeds-filled in the lowland northwest of Novarupta to an average depth of 90 m (300 feet). These deposits took many years to cool; rain and snow falling on the hot deposits created the "smokes" of steam that gave the valley its name.

About 12.5 cubic kilometers (3 cubic miles) of magma were erupted in 3 days. At Kīlauea's current rate of about 0.12 cubic kilometers (0.029 cubic miles) per year, our volcano would take 100 years to produce what Novarupta erupted in 3 days. More than 1.6 billion 10-cubic yard dump trucks would be needed to carry Novarupta's magma. The bumper-to-bumper line of trucks would be 30 times as long as the distance between Earth and Moon.

Nearby Mount Katmai had a magma reservoir that was connected to the one under Novarupta. As the reservoir drained, the top of Katmai collapsed to form a caldera 3 km (2 miles) wide. For many years this caldera was thought to have been the site of eruption. Workers during the 1950s, and later USGS geologists, showed that Novarupta was the actual site of eruption and that the Katmai collapse was secondary to the main event.

USGS volcanologists are currently monitoring another eruption at the edge of the Pacific plate--- Anatahan, in the Commonwealth of the Northern Mariana Islands, which began erupting on May 10. A "Volcano Watch" column two weeks ago described the volcano and its setting 130 km (80 miles) north of Saipan. The following updates the situation.

Typhoon winds on May 23-24 blew ash southward from Anatahan, resulting in a number of flight cancellations involving international airports in Saipan and Guam. A dusting of ash fell on Saipan, and rotten egg smell was reported by residents of the island.

Explosions have continued every few minutes. Puffing eruption clouds that rise thousands of meters (yards) above Anatahan are visible from Saipan and record each explosion. Close-in eyewitnesses report rocks several meters (yards) across flying through the air above the erupting crater. Measurements of atmospheric sulfur dioxide, made by personnel on a research vessel fortuitously nearby, showed high concentrations suggestive of the involvement of magma rather than simply heated groundwater.

A seismometer, installed this week about 1 km (0.6 miles) from the eruption site, is radioing signals back to Saipan. Explosions and volcanic tremor are being recorded. Satellite surveillance is helping to track the eruption. Scientists across the U.S. and in several different agencies are involved in the surveillance effort.

Frank Trusdell, volcanologist from HVO, and Randy White, seismologist from the USGS in Menlo Park, CA, arrived in Saipan on May 30, invited by the Emergency Management Office (EMO) of CNMI. Frank has worked there previously, and Randy is experienced with the seismology of erupting volcanoes similar to Anatahan. They are advising EMO officials and helping to install and interpret monitoring equipment-no small task in a potentially dangerous situation.

Currently there is no way to anticipate how the eruption may play out. This column will keep you posted on important developments.

### Volcano Activity Update

Eruptive activity at the Puu Oo vent of Kīlauea Volcano continued unabated during the past week. Tracks of incandescent lava are seen on Pulama pali along the main Mother's Day flow and the Kohola flow. Glow is also occasionally visible above Pulama pali. Numerous surface breakouts occur in the coastal flats along the eastern margin of the lobe feeding the Highcastle ocean entry where a tiny delta is building seaward from the buried beach.

The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying sudden collapses of the new land. The steam clouds are highly acidic and laced with glass particles. The National Park Service has put warning signs in critical places. Do not venture beyond these signs and onto the lava deltas and benches.

Residents of Pahoa, Pohoiki, and Leilani Estates subdivision felt the earth shake at 1:26 p.m. on May 27. The magnitude-2.9 earthquake was located 1 km (0.6 mi) southeast of Pu`ulena Crater at a depth of 4 km (2.4 mi).

Mauna Loa is not erupting. The summit region continues to inflate slowly. Seismic activity remains low, with only one earthquake located in the summit area during the last seven days.