August 28, 2014
Researchers Model Yellowstone Super-Eruption Ash Cloud
April Flowers for redOrbit.com - Your Universe Online
In 1883, a volcanic eruption in a small archipelago of the Dutch East Indies (now Indonesia) changed the world. The eruption and subsequent tsunamis caused by the Krakatau eruption resulted in over 36,000 deaths, including all 3,000 souls on the island. The ocean floor was altered, and temperature and weather patterns didn't return to normal for 5 years. And although the ash in the atmosphere produced spectacular sunsets, the lowered temperatures and acid rains devastated crops around the world.
Neither of these volcanoes are comparable in size to the volcano at Yellowstone. A new study from the United States Geological Survey (USGS) suggests that the ash cloud from a Yellowstone supereruption would blanket the Rocky Mountains several meters deep, and it would deposit at least millimeters of ash at least as far away as New York, Los Angeles and Miami. The results have been published in a recent issue of Geochemistry, Geophysics, Geosystems.
The research team used an improved computer model to develop their predictions. They believe that the large hypothetical eruption would create an umbrella ash cloud — one that expands in all directions evenly — sending ash across North America.
During a supereruption (the largest kind of eruption known), more than 240 cubic miles of material can be ejected from a volcano. This sort of eruption is highly unlikely, but if it should occur, electronic communications and air travel throughout the continent would be shut down, and the climate would be altered.
The underground reservoir of hot and partly molten rock beneath Yellowstone National Park is enormous. We know of three eruptions in the past, at approximately 2.1 million, 1.3 million and 640,000 years ago. According to the University of New Mexico, one of those eruptions formed the 24 by 40 mile caldera which is now Yellowstone Lake. Current geological activity at the park shows no sign that any volcanic eruptions will occur in the near, or even far, future. A relatively non-explosive lava flow near the Pitchstone Plateau was the most recent volcanic activity at 70,000 years ago.
The model, called Ash3D, projects that cities near the supereruption would be covered by a few feet of ash, a few inches would cover the Midwest region of the country, and cities on both coasts would see a fraction of an inch at least.
Scientists can use the findings from this study to understand past eruptions at Yellowstone and the widespread ash deposits left behind. Ash3D is also being used by other USGS researchers to forecast possible ash deposit hazards from restless volcanoes in Alaska.
Typical smaller eruptions deposit ash in a fan formation. A supereruption, however, resembles a bull's-eye; dense in the center and lessening in all directions fairly uniformly. The researchers say that this type of formation is less affected by the prevailing winds than the fan formation.
“In essence, the eruption makes its own winds that can overcome the prevailing westerlies, which normally dominate weather patterns in the United States,” said Larry Mastin, a geologist at the USGS Cascades Volcano Observatory in Vancouver, Washington. “This helps explain the distribution from large Yellowstone eruptions of the past, where considerable amounts of ash reached the west coast,” he added.
The three large past eruptions deposited ash over many tens of thousands of square miles. The deposits have been found across central and western Canada and the US.
Accurately estimating the ash deposits from these past eruptions was made challenging by erosion, as well as the limitations of previous computer models which lacked the ability to accurately determine the mechanism of transportation for the ash.
Depending on the length of the eruption, Ash3D revealed that the leading edge of the ash cloud from a supereruption could expand at a rate that exceeds the ambient wind speed for hours or days. Such an expansion could drive ash both upwind (westward) and crosswind (north to south) more than 932 miles. This would produce the distinctive bull's-eye pattern.
The simulation showed that modern cities near the park - like Billings, Montana and Casper, Wyoming - would be covered by a few inches to more than three feet of ash. Cities in the upper Midwest — like Minneapolis, Minnesota, and Des Moines, Iowa - would receive inches, at least. The East Coast and Gulf Coast would only receive fractions of an inch, while California cities would be between one and two inches. Pacific Northwest cities might receive just over an inch.
Although this might not sound bad because some of these cities receive more than this in snow each year, the effect on the climate of only an inch or less of volcanic ash could be severe. Previous research shows that such a blanketing could reduce traction on roadways, short out electrical transformers, and cause respiratory problems. Other studies also demonstrated that multiple inches of such ash could damage infrastructure, block sewer and water lines, disrupt livestock and damage crops.
The research team discovered that other eruptions that are smaller than the Yellowstone supereruption, yet still powerful, could cause an umbrella ash cloud as well.
"These model developments have greatly enhanced our ability to anticipate possible effects from both large and small eruptions, wherever they occur,” said Jacob Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory.
Image 2 (below): An example of the possible distribution of ash from a month-long Yellowstone supereruption. The distribution map was generated by a new model developed by the U.S. Geological Survey using wind information from January 2001. The improved computer model finds that the hypothetical, large eruption would create a distinctive kind of ash cloud known as an umbrella, which expands evenly in all directions, sending ash across North America. Credit: USGS
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