The pipeline shows when the volcano will erupt * In Italy they fear the eruption of Vesuvius

Vesuvius volcano for the last time in 1944 and caused the death of 26 people; In the past, the city of Pompeii was buried under the lava * The magma stops on its way through the earth's crust and accumulates in cracks

Frank Bruni, New York Times

How is the "pipeline" of a volcano connected to the earth? Are there horseshoe-shaped twists in the depths of Mount Pinatubo and how many bends and turns are there in the trenches under Mount Etna? The answer to this is fundamental to understanding how volcanoes work. It can be essential to predict when a particular volcano will erupt.

According to the traditional view, volcanoes are fed by magma chambers located at the base of the Earth's crust. Pipes lead to the surface, each of which ends in a volcanic opening. From time to time, magma - molten rock - erupts from these pipes.

A group of geologists challenges this perception. According to her, the plumbing system that leads the magma to the mouth of the volcanoes is more complex. It is a network of magma-filled fissures through which the molten rock erupts onto the Earth's surface. The team includes Keith Potirka of California State University and Christopher Condit of the University of Massachusetts at Amherst. They believe they have evidence to support their version.

The answer lies in the magma itself. Dr. Potirka and Dr. Condit believe that lava (as magma is called after it erupts) undergoes chemical changes on its journey through the earth's crust. Through the changes you can learn the details of the journey. In an article published this month in the journal "Geology" they apply this method to lava from the Springerville volcanic field in Arizona.

The researchers focused on the composition of a mineral known as clinopyroxene. When magma stops in its journey through the Earth's crust, it begins to cool and crystals form within it, including clinopyroxene. The exact composition of clinopyroxene depends on the pressure exerted on the magma. The degree of pressure depends on the depth at which the crystals form. The greater the pressure, the richer the mineral in sodium. So the percentage of sodium in clinopyroxene makes it possible to learn at what pressure (and hence, at what depth) the magma stopped on its way to the surface.

In Springerville, Potirka and Condit discovered two layers in the Earth's crust where the magma stopped. Magma reservoirs were formed in those layers, which later erupted. The first magma reservoir was in the middle of the crust, at a depth of about 26 km. The second reservoir was much closer to the surface, at a depth of 12 km. Since the researchers found no evidence of magma reservoirs at the base of the Earth's crust (about 40 km deep in Springerville), they concluded that the traditional model was simply wrong.

Additional support for the idea of ​​magma-filled fissures was provided by Bruce Marsh of Johns Hopkins University in Baltimore. Marsh studied an exposed part of the Earth's crust in Antarctica, where pipes and reservoirs intersect in an ancient volcano.

Since it is likely that there is a relationship between the depth of the reservoirs found in the Earth's crust and the type of volcanic eruption on the surface, this information can help predict the behavior of volcanoes. Although the discovery is very new and many details are not known with certainty, it is likely that it will turn out that certain forms of plumbing are prone to creating intense and infrequent eruptions while others yield a steady trickle of lava to the surface.

These hypotheses still need to be tested. Potirka and Condit are working on it now, in other areas where volcanic activity has been discovered. If it turns out that there is a connection between the "plumbing system" of a volcano and the size and timing of the eruption, these discoveries could lead to more accurate long-term predictions about volcanic eruptions.

In Italy they fear the eruption of Vesuvius * residents are offered sums of money to leave

The event took place 59 years ago, but Andrea Boccia still remembers it clearly. The Vesuvius volcano in southern Italy erupted and the earth shook. "There was a rain of rocks and fire," recalled Buche, who was only ten years old at the time. "Whole families walked around with pots on their heads." According to the Vesuvius Historical Society, the 1944 eruption killed 26 people. However, the unusual event did not deter the residents of the area. Despite the danger hovering over their heads, most of them preferred to stay and live in the vicinity of the active volcano.

Many studies have tried to predict when Vesuvius will erupt next, without success. But most of the residents of the area - especially in San Giuseppe and Zobiano - are not worried. This, despite the fact that in AD 79 the eruption of the mountain already destroyed one of the cities in the region - Pompeii, which was buried under a flood of lava. To this day, sooty remains can be seen throughout the city - which has since been rebuilt - that serve as a reminder of the destructive power of Vesuvius.

The local government officials are not as complacent as the residents. In fact, they decided to take the initiative and try to convince the residents to move their place of residence. In September, an operation to relocate residents will begin for the first time: a family that will leave their place of residence near the volcano will receive approximately 30 thousand dollars from the government for a new start in a safer area. The promotion, intended mainly for residents who rent their homes, also offers incentives to homeowners to change the designation of their rented properties to residential.

Marco Di Lello, the director of urban planning in the Campania region that includes Vesuvius, said that the purpose of the operation is to reduce the population of the cities and towns in the danger zone by 20%. active volcano

But the administration's plan may encounter a lack of response from the residents. "Vesov has never let us down," said Francesco Nafi, 26 years old from Somma Vesoviano - a town near the summit of the volcano. "I'm not going anywhere," said Maria Scopa, a 38-year-old resident of Pompeii. "A person may avoid drowning in lava, only to be run over by a bus. Everything is dangerous." According to her, a volcanic eruption also has advantages.

"At least everyone dies together," she said. "It's almost like a party. If one person dies and his family mourns him it is sad. But if the entire city is wiped out at once, that's fine."

Giuseppe Sepa, 50, director of public works of San Giuseppe Vesuviano, is not worried either. According to him, the topography of the area ensures that the lava from Vesuvius will not flow towards San Giuseppe and will not flood the city, so that the only damage caused will be pollution and not fire. "In," 1944 said Sefa, "it was just ashes." But Sefa's 74-year-old father, Mikaela, who remembers the outbreak, described a scene that was a little more frightening. "I remember first the ashes, then the huge burning rocks. One of the rocks hit a two-year-old boy in the head and killed him."

Vesuvius is not the only volcanic threat that the residents of southern Italy have to face. Last October, Mount Etna in Sicily began spewing ash, rocks and lumps of lava. In December, the volcano in Stromboli - a small island near the northern coast of Sicily - also erupted. Both cases did not directly cause any deaths.

* Published in Haaretz, 28/8/03