If Mother Nature had made this summer’s volcano movies instead of Hollywood, they would not have been action-adventure epics. They would have been tense mysteries.
The recent releases “Volcano” and “Dante’s Peak” are filled with pyrotechnics and rushing lava, but the volcanoes in Mexico and the Caribbean that erupted in recent weeks demonstrate a more complex reality. The truly nerve-wracking part of humanity’s uneasy relationship with these towering reminders of nature’s power is not knowing what they are going to do next.
They rumble and belch smoke. They sit quietly. They spew clouds of hot ash and molten rock. They settle down again. They may blow up. They may not.
Given science’s inability so far to predict volcanic eruptions, the potential for catastrophe is always present. And it affects more people than ever. Scientists estimate that 500 million people–nearly 10 percent of the world’s population–live dangerously close to the world’s 1,500 active volcanoes, of which about 500 are on land and the remainder are under sea.
The number of people who have a volcano as a neighbor has been increasing as urban development pushes ever closer to such peaks as Popocatepetl, the Mexican volcano that belched clouds of sulfur dioxide gas and ash two weeks ago. That explosion resulted in the brief closing of the Mexico City airport, some 40 miles away. Up to 100,000 people live in the most vulnerable zone around El Popo, as that mountain is known, but no one has died as a result of the recent eruptions.
On the tiny Caribbean island of Montserrat, however, nine people were killed in late June when the Soufriere Hills volcano unleashed a fiery combination of red-hot rocks and gas that blasted through neighboring villages at speeds of up to 125 miles per hour.
Although these two sites have received the most attention recently, some 50 volcanoes on average are active every month. Volcanologists, the specialists who study volcanoes, say the eruptions are unrelated except for one thing: They are terrifying to behold.
In 1993, Arizona State University geology professor Stanley Williams had just climbed out of the crater of a Colombian volcano when it erupted.
“It threw rocks at very high temperatures in every direction, rocks as big as microwave ovens and basketballs,” recalled Williams. “I just had a fluke of luck and survived.”
Nine people died–six scientists and three tourists who had hiked to the top to see what an active volcano looked like. Williams suffered a skull fracture, and both of his legs were broken. He put out his burning clothes by rolling on the ground. Four years and 16 operations later, he is climbing volcanoes again.
Since the 15th Century, volcanic eruptions have killed an estimated 200,000 people. Down the millennia of human history, these fire-breathing mountains have inspired fear and been endowed with religious significance; the Romans named them after Vulcan, the god of fire.
More recently, volcanoes have drawn intense scientific scrutiny as humankind tries to make sense of the violent and deadly force that lies locked within the peaks.
Volcanoes are one of the signs that the surface of Earth is in motion. The upper layer of Earth is divided into about 15 slabs, called tectonic plates, which butt up against each other as they slowly shift position. Earthquakes are one result of the collisions between plates.
In many places around the world, one plate is riding over its neighbor. As that plate sinks, heat and friction melt it at depths of up to 100 miles beneath the surface. This molten rock, called magma, gradually rises through fissures and cracks or melts the surrounding rock.
When magma reaches the surface, it bursts forth in a volcano, which builds up over eons as layer upon layer of lava, rock and ash accumulate. With enough time, volcanic islands such as Montserrat rise out of the seas or, on land, reach thousands of feet above the surrounding country. Popocatepetl, for instance, is almost 18,000 feet tall.
Lava, a flowing river of magma, is the most dramatic substance that comes out of a volcano, but the force that drives an eruption is the pent-up pressure of water vapor, carbon dioxide and sulfur dioxide trapped in the magma. The way that force plays itself out varies so much that predicting eruptions, especially in enough time to evacuate nearby populations, has proven frustratingly elusive.
A volcano may sputter off and on for years and never do any serious damage. Or it may explode with such violence that it blows apart its mountain, as Mt. St. Helens–the most recent spectacular American volcano–did in 1980, when its north face disintegrated in the eruption.
To volcanologists, that was nothing compared with Mt. Pinatubo, the Philippines volcano that erupted in 1991. Three days after scientists warned that the immediate area should be evacuated, it produced one of the top two or three volcanic outbursts of the century.
Tens of thousands of lives probably were spared, but Pinatubo illustrates another effect of volcanoes. It blasted such a large amount of sulfur dioxide gas high into the stratosphere that it lowered average surface temperatures worldwide.
Even so, most residents near the mountain didn’t realize it was a volcano. It hadn’t erupted in 600 years. Despite the catastrophic destructive power of a volcano, many who live near them grow complacent about the potential danger, researchers say.
“Unfortunately, many people say if the volcano has not been active in their lifetime, they think it’s a dead volcano,” said professor Attila Kilinc, a volcanologist at the University of Cincinnati. “That’s not the case. Look at Vesuvius. It buried Pompeii and Herculaneum in 79 A.D. and it’s active today.”
Once a volcano shows signs of life, residents who live nearby may spend years on alert before the danger passes.
The people of Montserrat have been living with the Soufriere Hills volcano since 1995, when it shook itself out of a 400-year sleep. The southern half of the tiny island has since been evacuated, including the capital city of Plymouth and the island’s airport.
More than a third of Montserrat’s 12,000 residents have departed. The remainder will lead makeshift lives for the foreseeable future, living in churches, schools or old factories if they have no friends, or relatives with whom they can bunk in the still-inhabited north.
Most of the Montserrat eruptions deposit ash on the evacuated areas, where a layer 20 inches thick has accumulated on the abandoned buildings. But when the winds shift, the air in the north fills with blowing particles of rock and fine, soot-like dust.
“We advise people to carry dust masks at all times,” said British Geological Survey volcanologist Gill Norton, citing the health hazard from the fine dust, which can aggravate heart and lung ailments. “If you happen to catch a day when it is very ashy, it becomes rather unpleasant.”
As happens with increasing frequency when a volcano comes to life, an observatory was set up in a rented house in Old Towne, about five miles from Soufriere Hills. Monitoring equipment included 16 seismometers until several were destroyed in the recent eruption.
The observatory, staffed by a rotating crew of seven scientists from the Caribbean, Britain, America and other countries, also uses laser measuring devices to detect changes of only a few millimeters in the shape of the volcano, which can be a crucial indicator that an eruption is brewing.
There is still no substitute for direct observation. Occasionally, geologists fly over the volcano’s crater in a helicopter.
“There’s no perfect technique that’s going to tell us when a volcano is going to erupt,” said Robert Tilling, chief scientist of the U.S. Geological Survey’s Volcano Hazards Program. “And so we use a combination of techniques, and if they all show changes in the same direction, you can have more confidence that it’s going to erupt.”
With increased monitoring and better equipment, researchers have made great progress in reading the signs of an awakened volcano. But in many respects it is still an infant science.
Adding to challenge of predicting eruptions is the fact that data from one volcano can’t simply be applied to another volcano. The best that researchers can hope for is that the information will give them some rough clues as to how other volcanoes of a similar type will behave.
“Volcanoes aren’t unique, but they are individual,” said volcanologist Williams. “I don’t even like to use the word `predicting.’ I talk about probability models. Our forecasting skill is not at all like meteorologists.”
In other words, there is no substitute for setting up a volcano observatory and monitoring the mountain over long periods of time. But only a handful of volcanoes get that kind of attention.
The best known volcano–Mt. Vesuvius–is also the best documented. The world’s oldest volcano observatory is located there.
In the United States, the Cascades Range in Washington is under close monitoring because of the proximity of Seattle. Mt. Rainier is a particular concern because its top is covered with glaciers. An eruption would produce a lahar, an Indonesian word for a heavy mudslide caused by snow and ice that are melted in a volcanic eruption.
There are deposits of previous lahars around Mt. Rainier–deposits that can be found beneath the suburban developments that have sprung up in recent years. So far, according to Tilling, Rainier has stayed quiet.
Although no scientist can say with certainty how the Montserrat and El Popo eruptions will develop, the outlook for Montserrat is for more of the same–periodic eruptions that are more nuisances than threats to life. But while they last, normal life on the island and, more important, the tourist trade–an economic pillar–have come to a standstill.
The outlook for El Popo is less certain: There have been big eruptions in the past, and the area is much more populated than Montserrat. As many as 700,000 people could be affected by a major eruption.
“There was a particularly big eruption 14,000 years ago,” said Tilling. “It left a large deposit of ash on what is now downtown Mexico City. So far, the activity (of El Popo) is nothing on the scale of that, but it is the possibility of that kind of eruption that is causing worry.”
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