Mount Pinatubo in the Philippines is getting ready to explode, dumping tonsof water on villages below. The latest eruption of Mt. Etna in Sicilyproduced dramatic nighttime images of hot rolling lava and explosivefireworks. But these volcanoes are small compared to what scientists sayAmerica will experience one day. Sooner or later, they warn, a “supervolcano” will strike right here in the U.S.A.

The eruption of pent-up energy will cover half the United States in ash, insome places up to 3 feet deep. Earth will be plunged into a perpetual winterthat lasts years. Some plant and animal species will disappear forever. Evenhumans could be pushed to the edge of extinction – it’s happened before.

Geologists have long known that the 10,000 hot springs and geysers inYellowstone National Park are evidence of magma, hot molten rock below thesurface. And they know that long ago the region experienced colossaleruptions on a scale never seen in recorded history. Is Yellowstone dying orjust hibernating? Geologists think it has at least one last gasp in store.New geologic evidence shows that Yellowstone National Park will eventuallyobliterate its own beauty, and may take parts of surrounding states with it.

In the July 2001 issue of the journal Earth and Planetary Science Letters,University of Wisconsin geologists Ilya Bindeman and John Valley reportednew evidence indicating “a high probability of a future catastrophiceruption sometime within the next million years, and possibly within thenext hundred thousand years.”

Crystals of zircon and quartz serve as veritable time capsules of geologicevents. Analyzing these minerals, Bindeman and Valley have found evidencesuggesting Yellowstone goes nuts every few hundred thousand years. Hot magmawelling up from below melts surface rock, forming giant chambers of lavathat build up over long periods. Eventually, the chambers burst and releasetheir fury.

Today’s Yellowstone landscape represents the last in a sequence ofcalderas – the broad crater-like basins created when volcanoes explode andtheir characteristic cones collapse – that formed in regular progressionover the past 2 million years. The near-clockwork timing of eruptionsthere – 2 million years ago, 1.3 million years ago and 600,000 years ago -suggests a pattern that may foreshadow an eruption of catastrophicproportions.

A hot spot deep beneath Yellowstone acts like a burner. “It’s a constantsource of heat that acts on the upper crust and forms magma chambers thatcontain tens of thousands of cubic kilometers” of molten rock, saysBindeman. And one of the massive plates that helps make up the crust of theEarth, the North American plate, is slowly moving over the hot spot. “Theplate has been moving across the heat source which makes it seem like thevolcanoes are moving across the continent. Moreover, we have a progressionof explosive eruptions which seem to have some periodicity.”

But well before such a calamity, warning flags will show up on the computersof geologists around the world who monitor an increasingly useful stream ofsatellite data.U.S. and European satellites have been trained to see “hot spots,” whereunderground molten rock is pushing its way to the surface. This is givingresearchers an unprecedented peek into how volcanoes work. Sometimes whatthey see is frightening.

Chuck Wicks of the U.S. Geological Survey uses the relatively new satellitetechnique called satellite radar interferometry (InSAR) to watch the groundrise, fall and morph around volcanoes and other volcanically active areas.While the Global Positioning System can also show ground movement, it doesso only for locations where a monitor is in place on the ground. But withradar interferometry, geologists can map the topography of an entire region,then watch it change over time.

n one early application of InSAR, large-scale ground movements caused bythe 1995 earthquake in Kobe, Japan, were studied by comparing an image mademore than a year before the earthquake with another produced just after.

In 1997, Wicks and his colleagues used the technique to document uplifts atYellowstone, meaning that the lava below was pushing its way to the surface.”Yellowstone is alive and very active,” Wicks says. But no one can say if orwhen it might become dangerous.According to Wicks, “Super explosions, about 1,000 times more materialerupted than Mt. St. Helens in 1980, happen about every 600,000 years atYellowstone. And it’s been about 620,000 years since the last superexplosive eruption there.”

More recently, in May, Wicks saw an alarming batch of data while studying aregion of Oregon called Three Sisters, where a trio of ancient volcanicpeaks dominates the landscape. He spotted a bulls-eye pattern in histopography data that showed the ground had risen as much as 4 inches over anarea more than 9 miles in diameter sometime between August 1996 and October2000.

The uplift, forced from below by rising magma, surprised him because thelast eruption in the area was 1,500 years ago and there has been noearthquake activity that might hint at moving magma. He believes there aretwo possible outcomes for the Three Sisters uplift: It will die out as otheruplift phenomena have been known to do or it will continue, eventuallygenerate earthquakes, and then lava well erupt through to the surface.

The InSAR system cannot monitor all volcanic regions around the world allthe time. But because of the early warning it provided, a seismometer hasbeen set up on the Three Sisters uplift to sense any possible earthquakes,and a GPS receiver now provides continuous monitoring of ground movement.”InSAR tells people living around a dormant volcano that they need to keep awary eye,” Wicks says.

To spot ground deformation over time, a radar interferometer measures thesame location of the Earth’s surface on subsequent satellite orbits. Butsometimes the radar is bounced off trees, instead of the ground. Andresearchers realized they sometimes accidentally measured the slightmovement of a leaf on a tree, blowing in the wind. “If the leaf is in adifferent position by a few centimeters, that’s enough to mess it up,” saysTom Farr, a geologist at NASA’s Jet Propulsion Laboratory. Researchers atJPL are now working to create animations of lava flows by imaging a volcanowith each satellite pass (every 24 hours with some systems).

Volcano forecasting has proved notoriously difficult. And people die, evenin modern times. Mt. St. Helens killed 57 people in 1980. In 1991, after 600years of dormancy, Mount Pinatubo in the Philippines rumbled for days beforeerupting and killing about 750 people, including journalists who had beenstationed at a supposedly safe distance, and it’s threatening to eruptagain.

Mount Etna, Europe’s highest and most active volcano, has been pouring outrivers of lava for two weeks. Active since at least the beginning of the16th century, Mount Etna was responsible for one of the world’s worstvolcanic eruptions in 1969. It lasted 4 months and killed 20,000 people.

The recent eruption has already swallowed up several farmhouses, arestaurant, stretches of road, and a ski-lift station. It also has beenthreatening the village of Nicolosi, a community of about 5,000 people.Although the two main fronts oozing down the slopes have shown signs ofabating in the last 48 hours, officials said that the state of emergency isnot over. “It is a situation of relative calm, it is too early to crow overvictory,” says Franco Barberi, of Italy’s Department of Civil Protection anda professor of volcanology at the University of Pisa.

Despite the new satellite technology, sensors stuck on the mountainside arestill the best way to predict an imminent eruption. Gene Ulmer, a geologyprofessor at Temple University, was in the village of Nicolosi, on theflanks of Mt. Etna, on June 18. He and 20 other geologists had just visitedthe mountain and were eating dinner at a restaurant.

In came a team of researchers, Italians and other Europeans. They announcedthat Etna, which had been relatively quiet for months, would erupt thefollowing afternoon at 1:30. More than a half-dozen ground observationdevices fed a computer model that gave them this information.

The next day, Ulmer and the other visiting geologists waited at a spot threemiles from the volcano, recommended as safe but with a clear view. “At 1:33p.m., the mountaintop blew out,” Ulmer says. “Within 10 minutes the summitwas completely obscured in a cloud of dust and black plumes rising as muchas 10,000 feet into the air. There was a tremendous noise.”

Heavy ash fell to the ground. Within a couple of hours, finer ash began tosettle back to the surface. The air, choked with the tiny particles, lookedlike milk, Ulmer recalls. “As it came down, it was like someone was paintingevery ravine with white paint.” What he witnessed was the start of what hasdeveloped into a major set of eruptions that are still continuing.

But what Ulmer marveled at most was the accuracy of the prediction. “All ofus in volcanology are excited that maybe we have finally found out the rightmonitoring instruments to put into the mountain so we can make somelife-saving predictions about possible eruptions,” he says.

One of those instruments comes from the Apollo mission. Reflecting devicessimilar to those left on the Moon are stationed at various points on themountain. From miles away, researchers bounce lasers off the mirrors. Ifthey have moved, the laser beam shifts.Other devices on the mountain sense changes in temperature and the output oftelltale gases.

Ulmer was forced to leave Italy earlier than he had planned. He is now homein Philadelphia, where he is recovering from a volcano-induced staphinfection. No matter how good a volcanologist’s boots are, they fill withvolcanic ash that he describes as having the consistency of flour. But theash is made up of small glass shards that, once inside his boots, groundinto his skin. His feet blistered and then became infected. He had a firstaid kit with antibacterial ointment and pills, but the kit had not beenupdated in three years, and the medicines were not effective.

It turns out that Mount Etna contains a rare type of lava that is settingoff alarm bells among scientists monitoring the eruption of Sicily’sinfamous volcano. “The lavas flowing at the heights of 6,890 and 8,360 feetcontain amphiboles, crystals which incorporate water and had not beenpresent in the lava for 15,000 years,” says Sonia Calvari of Catania’sInstitute of Volcanology. “This magma is ascending from great depths.Instead, the lava river flowing at the height of 8,860 feet isamphibole-free, thus more superficial.”

“If it is true that these new lavas contain amphibole, it would be verydisturbing. It would show that the lavas have been derived from a muchdifferent type of magma supply area than previously and thus have muchgreater potential for explosive activity – because of the increased watercontent,” says American volcanologist John Lockwood.

While it is encouraging that only gas and ash are coming out of Etna at themoment, experts worry that the amphibole lava flowing at 6,890 feet mightform underground tunnels filled with magma. “Amphibole is a more explosivelava type,” says Steve Anderson of Black Hills State University, SouthDakota, who has been working on the lava flows at Etna for the past 3 years.”The intense fountaining at Etna suggests that this magma is arriving at thesurface with a lot of water still present. This indicates that the magma iseither rising very quickly from the magma chamber through the conduit, orthat the conduit is not very permeable to gas flow, or a combination ofboth.”

74,000 years ago, in what is now Sumatra, a volcano called Toba erupted witha force estimated to have been 10,000 times that of Mt. St. Helens. The skydarkened around the globe as ash blocked out the Sun. Temperatures plummetedby as much as 21 degrees at higher latitudes around the planet, says MichaelRampino, a biologist and geologist at New York University. He estimates thatthree-quarters of the plants in the Northern Hemisphere may have died.

Stanley Ambrose, an anthropologist at the University of Illinois, suggestedin 1998 that Rampino’s work might explain a curious bottleneck in humanevolution, a phenomenon observed by other researchers who study DNA – Theblueprints of life for all humans are remarkably similar given anevolutionary timeline known to stretch back more than 2 million years.

Ambrose thinks that early humans, struggling as always against the elements,were pushed to the edge of extinction after the Toba eruption. Perhaps onlya few thousand survived. Humans today would all be descended from these few,and in terms of the genetic code, not a whole lot of evolution occurs in74,000 years.

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