The Mountain Is Rumbling

Each spring, residents of Catania walk the Sicilian's town's narrow streets chanting prayers and touting relics of Saint Agatha, their patron saint and protectress against an eruption of Mount Etna. All the while, the mountain looms overhead, belching smoke, ash and lava. Although villagers have gotten used to these displays of defiance, this year they have reason to pray with more than the usual fervor. In the past few weeks, seismologists have logged hundreds of earthquakes near the mountain's summit. Each quake is far too weak to mean much to the hundreds of villages on Etna's slopes and foothills. But taken together, they suggest that Europe's most active volcano is about to deliver a whopper.

The prospect of Etna's blowing its stack has got scientists in a tizzy. The last big eruption, back in 1669, lasted four months, sent a kilometer-wide river of lava down the mountain and killed 20,000 people. At the very least, an eruption of similar force would cause billions of dollars in damage to the crops, the environment and tourism. Skiers ply the slopes in winter. In summer visitors come to enjoy the unusual scenery: a cable car takes them past hardened lava flows that encase tree trunks, old poles from collapsed funicular lines and even the odd truck chassis. The visitors' center at 7,875 feet stands next to charred skeletons of previous structures--a caution to anybody preparing to make the journey up the summit. Plenty do, and occasionally some get killed by falling lava or hot blasts of volcanic gas. Tourists and scientific research teams make up well over half of the area's income. The rest comes from agriculture. The nutrient-rich soil, fed from minerals in the volcanic acid rains, produces award-winning wines, such as Nerello Mantellato. Curiously large lemons and bumper crops of olives entice farmers to stay in spite of the obvious dangers. About 1 million Sicilians, or 20 percent of the island's population, live in Mount Etna's shadow.

The only insurance against loss of life is scientists' ability to sound the alarm early enough to evacuate residents. Trouble is, when it comes to erupting volcanoes, scientists are a trifle insecure about their predictive powers. At present, a few weeks of warning is about all anybody can hope for. "We're probably OK for the next 15 days," says Danilo Reitano, one of a handful of engineers and geologists who are keeping a 24-hour vigil on the mountain, "but I'm not going to make any guesses beyond that." The imminent eruption has given Reitano and his colleagues at the Uni-fied Center for the Acquisition of Data a bit of performance anxi-ety. "How well we monitor activity on Etna is a valuable source of information for scientists all over the world," he says, "and so are our failures." If scientists knew better the telltale signs of a big eruption, they would feel more confident. Ironically, a big eruption of Mount Etna is their best chance yet of learning what these signs are.

Etna has long been a closely watched volcano, partly because it is one of the world's most complex and interesting. Located on the eastern side of Sicily, it is one in a chain, including Mount Vesuvius and Marsili, a vast underwater mountain, that formed when Africa collided with Europe a couple of hundred million years ago. Active since at least the beginning of the 16th century, Mount Etna has no fewer than four craters and hundreds of smaller--though highly eruptive--cones, or vents, along its flanks. It produces more lava--about 220 gallons per second--than any other volcano except Mount Kilauea in Hawaii. Since it is almost always erupting, it gives scientists ample opportunity to study the mysteries of how lava makes its way from the earth's mantle, through the complex of fissures and channels, to the surface. Etna is unique among volcanoes in that it erupts in four or five different ways, from a constant seeping of lava to the violent, powerful jet eruptions. In the first half of 2000, Etna sent jets of lava one kilometer into the air 66 times, each lasting more than an hour. "These allowed scientists to collect the best available data set on an incredibly rare activity," says Marco Fulle, an astrophysicist and volcanologist at the Italian Astronomic Observatory. "It can teach us things no other volcano of its kind can."

Etna's last significant eruption occurred in 1992. For six months beforehand, the mountain rumbled. Then lava flowed southeast, stopping within a few meters of a farmhouse on the edge of Zafferana Etnea. (Villagers erected a shrine to Saint Agatha on the spot.) Scientists were watching, but unfortunately they lacked today's sophisticated ways of measuring the mountain's antics. (Even so, scientists are certain that Etna's recent rumblings far surpass the 1992 ones, implying a bigger blow to come.) A few years later, thanks to a program funded by scientists across Sicily and several European scientific organizations, they began making up for lost time. They put in place hundreds of devices in the mountain's every nook and cranny to collect data and relay it, via cellular and satellite modems, to scientists. Mostly these devices keep precise tabs on every quiver and shift in the mountain. Lasers beamed at distant reflectors measure the slightest shaking in the ground. Electronic tilt meters, like carpenters' levels, use fluid bubbles to detect minute changes in the ground's orientation. Global Positioning System satellite receivers, in dozens of locations, monitor surface motion of less than a centimeter. Bore-hole strain meters buried 20 miles beneath solid rock measure temperature and other changes in magma. To penetrate the thick clouds of smoke that usually hang over the mountain, satellites take radar images; by combining many of them, scientists can detect ground movement as slight as four tenths of an inch. Scientists are also keeping track of the temperature of the local lakes and the volume and density of the smoke that billows up from the mountain. If and when Etna's next big eruption occurs, Reitano and his cohorts will be the first to know.

One other scenario is still possible: that the mountain stops rumbling as quickly as it started. Scientists doubt it, but they can't rule it out. For Fulle, it would simply show yet another of the mountain's quirks. Not long ago he and a colleague climbing near the summit saw one of Etna's craters belch smoke rings, each 200 meters in diameter. Mount Etna "is like a living entity, a person with character and personality. It is impossible not to remain fascinated with the volcano once you've been up there," he says. "This is much more than science."