As good a read as it is throughout, Lawrence Joseph's book, Apocalypse 2012: An Investigation into Civilization's End devotes a spine-tingling chapter to two ticking bombs in our own backyard — Yellowstone National Park and California's Long Valley Caldera. Both locations are home to massive supervolcanoes. And both are overdue for their periodic mega-eruptions, which happen approximately every 640,000 years. An event of this magnitude at either location has the potential to wipe out a huge chunk of the United States.
Yellowstone National Park - rim of the caldera. Photo: Robert B. Smith
A supervolcano is sometimes referred to as a caldera or hotspot. That's because its source of magma differs from the more common types of volcanoes -- shield, strato and cindercone. Neither Yellowstone nor Long Valley lie along the Ring of Fire, where ocean plates dip below continental plates, carrying seawater beneath the surface. That water eventually gets superheated and starts melting underground rock, which generates magma and volatile gases that rise upward and eventually seep (or burst) out of the ground.
In Hawaii, for example, the production of magma is not a violent process. It moves smoothly upward, as if through a stovepipe, resulting in shield volcanoes. In the case of the 1980 Mt. Saint Helens eruption, magma had a much tougher slog breaking through the surface rock. The pressure became so intense, it caused an explosion, and then a huge cloud of scalding hot ash, molten rock and gases burst out in a violent cataclysm. While erosion from the snowcap also contributed to the event, what happened there generally conform to the modus operandi of strato-volcanoes. The Mt. Saint Helens eruption also generated lahars, which are mudflows that travel for 50 miles or more and carry the force of a tsunami.
A supervolcano is a different animal entirely. For one thing, there's no mound, so you may not even be aware that you're standing near one. Hiding beneath a large lake or crater, a caldera is like a witch's caldron, slowly filling up with magma over the course of millenia. The source of that magma, however, is not rock melted by the heat of seawater. Instead, geologists believe it comes directly from the Earth's mantle. Its pathway to the surface is a long chimney-like shaft created by unknown forces. The current best guess is that a meteorite punched a hole in the planet deep enough to breach the crust. To date, more than a dozen calderas (aka hotspots) have been identified around the globe.
Diagram from earthmountainview.com
Interestingly, a hotspot doesn't change its location in lockstep with plate tectonics. As a result, satellite imaging has revealed a series of ancient supervolcanoes extending across the western United States. The data indicates that the Yellowstone Caldera probably started out in Northeastern California (where the alleged asteroid may have struck). Then over time, the crust drifted westward. The Snake River Plateau in Idaho moved over the hotspot, followed by the area that comprises Yellowstone National Park. The geysers and other unique features of the park provide telltale signs that the Earth's mantle is busy seeping its molten contents up towards the surface.
Map of the Yellowstone hotspot, showing the number of years (in millions) it has taken for the North American plate to shift westward over it.
The last caldera to burst its seams was Mount Toba, in Indonesia, about 75,000 years ago. The event is thought to have triggered a mass extinction that included much of the human race. A dust cloud likely covered the Earth after the eruption, kickstarting a thousand-year-long ice age. Climatologists arrived at the date after examining ocean sediments, which revealed a 10-degree drop in sea temperatures at that time. Greenland ice cores from the same period showe a heady spike in atmospheric sulfur, confirming the supervolcano theory. Today, what's left of Toba is a huge lake near the island of Sumatra that's visible from space. For a closer look at the eruption, watchT he History Channel program "Volcanic Winter", part of the Mega-Disasters series.
Incredibly, both the Yellowstone and Long Valley calderas are a lot bigger than Toba. A large-scale eruption could produce a lava field encompassing four hundred miles to the south and east. And not to make you worry, but between January 17 and February 11, 2010, Yellowstone experienced its second largest swarm of earthquakes on record. Some of the over 1,800 tremors included two measuring 3.7 and 3.8 on the Richter Scale, with a total of 14 at 3.0 or more in magnitude. (For comparison, a 5.1 earthquake accompanied the 1980 Mt. St. Helens eruption.)
Lava bed created after the Yellowstone Caldera's last eruption.
Almost a year to the day earlier, at the end of 2009, a similar earthquake swarm rattled Yellowstone. On both occasions, no evacuation orders or volcano warnings were issued. After the second episode, the U.S. Geological Suvey announced that the activity was concentrated along known faultlines, with no direct connection to the caldera. However, they continue to monitor more than two dozen seismograph stations that were set up around the park following a BBC documentary airing in 2005. Geologists also routinely sample sulphur and carbon dioxide levels at geysers around the park. Tilt meters were installed to measure deformity of the land as the magma chamber inches slowly upward, displacing the crust.
Right now, the Yellowstone Caldera covers a surface area that's about three times the size of Manhattan. In the 1990's, satellite imaging revealed that both it and Long Valley were packing far more firepower than previously estimated. (The same can be said of the strato-volcano Vesuvius, in Italy.) Even with all the real-time measurements taking place, some experts question the equipment's ability to forecast an eruption in sufficient time to evacuate everyone within range of it blowing. Suffice to say the scale of such a disaster inspired movie director Roland Emmerich to feature Yellowstone in his blockbuster doomsday film 2012.
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DVDs and TV Programs
History Channel: Mega-Disasters series: Volcanic Winter. How the Earth Was Made Series: Yellowstone, Vesuvius and Mt. Saint Helens.
DVD - NOVA: Mystery of the Mega-Volcano (2006) PBS.
Apocalypse 2012: A Scientific Investigation Into Civilization's End (2007) by Lawrence E. Joseph.
Supervolcano (2007) by John Savino and Marie D. Jones.
Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions by Jelle Zeilinga de Boer, Donald Theodore Sanders and Robert D. Ballard.
Bug Out: The Complete Plan for Escaping a Catastrophic Disaster Before It's Too Late (2010) by Scott B. Williams.
When Technology Fails: A Manual for Self-Reliance, Sustainability, and Surviving the Long Emergency by Matthew Stein .
The Unthinkable - Who Survives When Disaster Strikes (2008) by Amanda Ripley
What Everyone Should Know About the Future of Our Planet: And What We Can Do About It (2008) by Bill McGuire.
"Hundreds of Quakes Are Rattling Yellowstone." New York Times 1/31/10
"Multiple earthquakes rattle Yellowstone." Denver Post 1/3/09
"The Dangerous and Dynamic Thermal Springs in California’s Long Valley Caldera." U.S.G.S. Fact Sheet 2007
"Volcanic Unrest and Seismicity in Long Valley and Mammoth Lakes, California." By Elizabeth Sherrill.
"Yellowstone's Sister Volcanoes." Discovery Channel.
"A supervolcano eruption could put a tsunami in the shade." By Bill McGuire. The Guardian, U.K. 3/10/05
Yellowstone Supervolcano threat
Disaster monitoring site in Budapest.
Respirator Fact Sheet NIOSH