# Volcano Watch — Thermal Activity in Yellowstone Sparks Increased Monitoring

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Norris Geyser Basin of Yellowstone National Park has long been recognized as the hottest and most changeable of Yellowstone's famous hydrothermal wonders.

This summer, Norris lived up to its hot, unstable reputation as scientists and visitors alike have seen significant changes in many geysers and increased ground temperatures in the western part of the basin.

Porkchop Geyser, which sprang to life from a small hot spring in 1971, erupted in July for the first time since 1989. Water has drained away from several active geysers, resulting in hissing steam vents and ground temperatures as high as 93 degrees Centigrade (200 degrees Fahrenheit). Still other geysers have erupted more frequently and regularly, while some thermal features that usually release hot water and steam now send steam jetting into the air.

On July 11, the staff of Yellowstone National Park also noted the formation of a new mud pot-a small cauldron filled with boiling acidic water and mud. Within one week, the mudpot turned into a high-pressure steam vent. Also, pine trees are dying in three areas in response to the increased thermal activity.

Norris is one of the more popular geyser basins in Yellowstone, with as many as 4,000 people visiting the nearby museum each week. On July 23, the park superintendent closed access to the western part of Norris Geyser Basin, known as the Back Basin, for public safety (other parts of Norris remain open to the public). About a mile of trail and boardwalk in the Back Basin remain closed because of the hazard to visitors and park staff from the high temperatures. Another potential hazard is from hydrothermal explosions that could send boiling water andd rocks shooting into the air

The concern for public safety is real. Hydrothermal explosions have occurred recently at Norris and other areas of Yellowstone. For example, Porkchop Geyser exploded on September 5, 1989. Rocks surrounding the old geyser were upended by the force of the explosion, and some rocks were thrown more than 66 m (216 feet) from the spouting geyser. Luckily, people in the area were not injured by the flying debris and scalding water.

The cause of the increased thermal activity is not known, but scientists associated with the Yellowstone Volcano Observatory (YVO) launched a temporary monitoring experiment in August in order to learn from the ongoing activity. YVO is a collaborative partnership between the U.S. Geological Survey, the University of Utah, and Yellowstone National Park. The Norris monitoring experiment is also supported by two research organizations-the Integrated Research Institutes in Seismology (IRIS) and University NAVSTAR Consortium (NAVCO).

Scientists installed a network of 7 new seismic stations for recording various types of earthquakes. The instruments, called broadband seismometers, record a wide range of vibrations typical of hydrothermal and volcanic systems. These seismometers are especially sensitive to the long-wavelength ground vibrations that occur as water and gas move through underground cracks.

Five high-precision Global Positioning System receivers also were installed at Norris in order to track movement of the ground in response to underground pulses of groundwater and steam and, in case one occurs, a hydrothermal explosion. Data from the broadband and GPS receivers are being stored on site. The instruments and data will be retrieved in the next few weeks before the onset of winter.

Thermometers were also placed in hot springs and downstream from geysers and other thermal features to continuously measure temperature fluctuations that may occur.

The Norris experiment is intended to document activity within the shallow hydrothermal system that may be causing changes at the surface of the Back Basin. In the coming months, scientists will be pouring over the mounds of data collected by the Norris experiment for possible clues to the renewed heating of Norris. There is no evidence, however, that magma beneath the enormous Yellowstone caldera is directly involved.

Scientists have noted similar changes at Norris in the past, but the current activity is perhaps the best opportunity yet to quantitatively document and better understand hydrothermal disturbances and their possible causes at Yellowstone.

### Volcano Activity Update

Eruptive activity at the Puu Oo vent of Kīlauea Volcano continued unabated during the past week. Surface activity is mainly visible in the westernmost section of the pali flow field. The Kohola arm of the Mother's Day flow has some breakouts on the coastal flat. The breakouts, small and sluggish, are scattered through the flow. The east-side lobe of the Mother's Day flow also remains visible as a series of incandescent patches from the top of Pulama pali out onto the gentle slope below. The August 9 breakout, which starts high up the Mother's Day tube system, has been slowly moving southward and just appeared at the top of Pulama pali on September 10-11. No lava is entering the ocean.

Three earthquakes were felt on the island during the past 7 days. One, of magnitude 3.6, was felt from Captain Cook to Kailua at 12:38 a.m. September 5; it was located west of island, about 45 km (28 miles) west-southwest of South Point at a depth of 54 km (33 miles). Another earthquake, with magnitude 3.4, shook the northern part of the island at 7:14 p.m. September 6. It was felt in the area bounded by Hale Pokaho, Papaaloa, Kohala Estates, and Waikoloa and was located about 5 km (3 miles) west-southwest of Honoka`a at a depth of 12 km (8 miles). Volcano residents awoke to a magnitude 3.4 earthquake at 12:24 a.m. September 10. The earthquake came from the southern part of Kīlauea caldera at a depth of 3.5 km (2 miles).

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