Saturday, April 16, 2005
American volcano eruptions
Yellowstone National Park is located in the northwest corner of Wyoming and includes a little of Montana and Idaho for good measure. The U.S. Government set it aside as a national park more than 100 years ago to preserve its wildlife, including bears, moose, and bison, and many thermal features, such as bubbling mud pots, spectacular hot springs, and geysers.
Many years later, scientists realized that Yellowstone was a volcano – a very large volcano. The volcano appears as a series of calderas, the most recent being 55 km wide by 80 km long (35 miles by 50 miles). Yellowstone caldera is huge compared to calderas in Hawai‘i. The entire island of O‘ahu could fit neatly inside Yellowstone caldera, with room left over.
By comparison, Kilauea caldera is about 4 km by 4 km (2.5 miles by 2.5 miles). Yellowstone’s signature thermal features are driven by heat being released from a magma chamber. The top of that chamber is probably 5 km (3 miles) below the ground surface. Magma is at a similar depth beneath Kilauea caldera. A caldera is formed when the ground surface collapses into a magma chamber after it is emptied of magma.
Usually this collapse occurs after an exceedingly large explosive eruption empties the magma chamber. The most recent of these eruptions at Yellowstone happened about 640,000 years ago and sent ash over most of North America. There have been two other caldera-forming eruptions at Yellowstone in the last 2.1 million years. The caldera-forming eruptions are the most severe type of activity that has occurred at Yellowstone, but they’re not the only type of eruption that has happened there.
Since the last big explosive eruption, about 30 eruptions of lava have occurred inside the caldera. The most recent lava flow is about 70,000 years old. These Yellowstone lava flows are extremely thick by Hawai‘i standards – some as thick as 120 m (400 feet). Of course, Hawaiian volcanoes erupt lava much more frequently. Yellowstone has erupted lava approximately 30 times in the last 640,000 years. Mauna Loa has erupted over 30 times in the last 160 years!
The most frequent type of explosion at Yellowstone is a hydrothermal explosion. Rain and snowmelt percolate into the ground and are heated to near boiling by heat rising from the magma chamber. Deeper water that is under pressure can be heated to even higher temperatures. If the pressure that confines this deep water is reduced quickly, pockets of water may flash into steam, causing an explosion. Several hydrothermal explosions are expected each century at Yellowstone. Like Hawai‘i, the Yellowstone area experiences thousands of small earthquakes every year. Most have magnitudes less than 3, but there have been larger ones.
A magnitude-7.5 earthquake started a landslide that killed 28 people in 1959. Yellowstone caldera is still active and may erupt again. The next geologic event will most likely be a hydrothermal explosion or a strong earthquake. An eruption of lava is at least 100 times less likely than a hydrothermal explosion. A catastrophic, or caldera-forming, eruption is at least 10,000 times less likely than a hydrothermal explosion; the probability is similar to that of a 1-km diameter asteroid striking the earth.
In order to better monitor Yellowstone’s activity, the Yellowstone Volcano Observatory (YVO) was established in 2001. This is the newest of the five volcano observatories set up to monitor volcanic activity in the U.S. YVO is supported jointly by the U.S. Geological Survey, the University of Utah, and Yellowstone National Park. Yogi and Booboo have little to fear. Ranger Smith and the USGS are on watch.
Activity Update Eruptive activity at Pu‘u ‘O‘o continues. Several vents within the crater glow intermittently on clear nights. The Pu‘u ‘O‘o crater web-camera is offline for repair. The PKK lava tube continues to produce intermittent surface flows from above Pulama pali to the coastal plain. Lava is currently entering the ocean at three areas. From west to east, these entries are located at Highcastle, Kamoamoa, and Ka‘ili‘ili.
The closest activity to the end of Chain of Craters Road, in Hawai‘i Volcanoes National Park, is at Highcastle, 3.7 km (2.3 miles) from the ranger shed. Expect a 1.5-to-2-hour walk each way and remember to bring lots of water. Stay well back from the sea cliff, regardless of whether there is an active ocean entry or not. Heed the National Park warning signs.
During the week ending April 6, one earthquake was felt on Hawai‘i Island. A magnitude-2.8 quake occurred 5 km (3 miles) east of Pahoa at a depth of 2.1 km (1.3 miles) at 2:33 p.m. on Saturday, April 2; it was felt at Leilani Estates. Mauna Loa is not erupting. During the week ending April 6, two earthquakes were recorded beneath the summit area. Both were deep and long-period in nature. Inflation also continues beneath the summit.