# Volcano Watch — The Yellowstone Volcano Observatory: Monitoring a restless volcanic giant

May 23, 2002

In 1912, when Thomas Jaggar dug a cellar to house a seismograph on the north rim of Kilauea's caldera, there was only one other volcano observatory on earth, at Vesuvius, in Italy.

Today, there are numerous volcano observatories around the world, including four in the United States besides HVO: the Cascades Volcano Observatory in Washington state, the Alaskan Volcano Observatory, the Long Valley Observatory in California, and our newest sister observatory - the Yellowstone Volcano Observatory (YVO).

YVO was established in May 2001 in order to improve the study and monitoring of active geologic processes and hazards of the Yellowstone Plateau volcanic field. The observatory is a joint effort of the U.S. Geological Survey, Yellowstone National Park, and the University of Utah.

Yellowstone National Park and the surrounding area encompass the largest active magmatic system in North America. Three cataclysmic explosive eruptions over the last two million years ejected huge volumes of lava and ash - up to 2,000 times more material than Mount St. Helens produced in its devastating 1980 eruption. During these catastrophic eruptions, columns of volcanic ash and gas were shot high into the Earth's stratosphere. The volcanic cloud circled the globe, reducing temperatures worldwide. Fine ash falling downwind of the eruptions blanketed much of North America.

Each of these colossal eruptions formed huge calderas. Yellowstone caldera, the most recent of these, formed about 650,000 years ago and is 85 x 45 km (53 x 28 miles) across. These calderas have been buried or mostly obscured by lava flows, the youngest of which is about 70,000 years old.

The spectacular geysers, boiling hot springs, and mud pots that have made Yellowstone famous indicate that there is still a vast amount of excess heat beneath this area. The geothermal features are fueled by heat from a large magma reservoir beneath Yellowstone caldera. The ultimate source of the high heat flow to the region is a hot spot similar to the one currently beneath the Big Island.

Just as the seamounts and volcanic islands northwest of the Big Island indicate the track of the Hawaiian hot spot as the Pacific Plate migrates over it, volcanic centers in the 700-km (400-mile) long Snake River Plain in the western United States indicate the track of the Yellowstone hotspot. The volcanic features become progressively younger toward the northeast, with Yellowstone caldera being the youngest.

The style of volcanism at Yellowstone is very different from Hawaiian and other oceanic island hotspots, because the magma rises through a thick layer of continental crust, melting and incorporating the silica-rich crustal material along the way. It is far more difficult for the viscous magma and associated gas phases to find their way to the surface; pressures can build up and cause huge, explosive eruptions.

As if the geysers and hot springs are not enough evidence of an active geologic system, the region is intermittently rocked by intense swarms of small earthquakes, as well as by occasional larger quakes. For example, a magnitude 7.5 earthquake in 1959 caused 28 fatalities. Earthquakes are not the only symptom of unrest at Yellowstone. Since the first surveys of the area in 1923 to about 1985, Yellowstone caldera rose as much as 1 m (3 ft), then subsided about 30 cm (1 ft). The ground surface appears to be rising again since 1995.

As Paul Doss, the first National Park Coordinating Scientist of YVO said, "While the active geologic processes at Yellowstone do impart some risk to the public, they also make it a unique treasure - it is the volcanic and seismic energy that powers the geysers and hot springs, creates the mountains and canyons, and generates the unique ecosystems that support Yellowstone's diverse wildlife."

### Volcano Activity Update

Eruptive activity of Kilauea Volcano continued unabated at the Puu Oo vent during the past week. The three flows reported last week are still active. The "Mother's Day" flow is igniting fires along the western edge of the Puu Oo flowfield. The distal end of the flow is at the top of Pulama pali, 4 km (2.4 mi) above the end of the Chain of Craters road. The two older flows emanating from the "rootless" shields continue to move forward. The flow along the National Park-Royal Gardens boundary is spreading beyond the base of Pulama pali into the coastal flats and is 2 km (1.2 mi) from the ocean. The higher flow entered the top of Royal Gardens and poses a threat to what remains of the subdivision. There are no ocean entries.

There were no earthquakes reported felt during the week ending on May 23.