Could Masada fall again?

Scientists try to assure geologic stability of historic site.

May 8, 2006 20:29
Could Masada fall again?

massada 88. (photo credit: )

Masada is one of the most renowned symbols of Jewish endurance. Rising 230 meters above the Dead Sea valley, the site of a mass suicide of Jewish Zealots in 73 CE, it is, next to Jerusalem, Israel's most popular tourist site. Elite units of the Israel Defense Forces hold ceremonies atop its heights, pledging, "Masada shall not fall again." But it might. Not today, not tomorrow, but one day. Seismic tremors, climatic change and, inevitably, gravity continue to threaten the stability of the historic remains and the mountain that supports them. Engineering professors from Beersheba's Ben-Gurion University of the Negev and the University of California-Berkeley have teamed up to make sure that doesn't happen. Using state-of-the-art monitoring devices and advanced computer modeling techniques, and armed with a four-year grant from the United States-Israel Binational Science Foundation, Beersheba's Yossi Hatzor and Berkeley's Steven Glaser are breaking new ground in geological engineering. Masada is their test case. "Masada has been degrading for 2,000 years," said Hatzor, head of BGU's Rock Mechanics Laboratory and founder of the geological engineering team working on the problem. "There's no imminent danger," he said. "Nothing is collapsing. We're talking about long-term preservation of a World Heritage site." The imposing, reddish-gold mountain sits directly on the Syrian-African Rift, an active fault line. Since Herod the Great built his luxury palace on the mountain's northern face more than two millennia ago, at least five major earthquakes have hit, causing rock slides and damage to the man-made structures. Harsh desert weather continues to impose its own disintegrative effect. "The terraces of the palace were much larger than what they are today," Hatzor said. "There have been failures and erosions since Herod built it. We can see deterioration of the stones due to rain even in the time period we have been involved in preservation efforts on the mountain." Masada is not one solid rock. It is composed of horizontal layers of sedimentary rock, and is fractured by vertical cracks or "joints" formed by tectonic stresses in the earth's crust. These horizontal and vertical joints give the mountain its particular wall-like appearance of huge irregular bricks piled one on top of the other. They also make it vulnerable to seismic tremors. Work began in 1998, when the Israel Nature and Parks Authority began construction of a cable car to ferry greater numbers of visitors up Masada. They called in Hatzor to evaluate the mountain's stability, something that had never been done. Hatzor and his team studied the Snake Path cliff on the mountain's eastern side, which connects the cable car station to an adjoining bridge, and found several large rocks precariously poised. Using a three-dimensional stability analysis, the team determined that some blocks of rock in the cliff face might dislodge even in a relatively small tremor. Hatzor recommended "cable bolting," an engineering technique he'd studied a decade earlier as a doctoral student at Berkeley. He suggested inserting 18-meter long steel cables through individual blocks and into the solid rock, so the rock's own weight pushing against the cables would act as a stabilizing force. Stepping off the cable car one morning last month, Hatzor pointed to an enormous yellow block of rock that hovered menacingly over the walkway visitors traverse on their way to the ruins. Following his instructions, 30 anchors were inserted into the rock block before the new cable car was built. Though the enormous block still seems to be hanging in mid-air, Hatzor said it was now perfectly safe. Rock-colored covers hide the end of the anchors from view, preserving the aesthetics. Hatzor's monitoring system also showed, for the first time, the effects of climatic change on rock movement. "Why does a block decide to move?" Glaser asked. "Yossi's preliminary monitoring suggested that perhaps it's due to very small changes in temperature, to expansion and contraction of rock over time." The findings caused quite a buzz in international geological circles. After the cable car project, Hatzor's team was asked to study the stability of Herod's palace on the northern side of the mountain. They conducted a computer simulation using dynamic Discontinuous Deformation Analysis, a new numerical method, also developed at UC-Berkeley, for measuring the risk of rock movement. Using data from a 1995 quake in the northern Sinai in 1995 that registered 7.1 on the Richter scale, Hatzor's simulation found that a similar tremor at Masada could cause shards of rock to come crashing down the cliff. "To ensure lasting preservation of this historic gem, the north face should be reinforced," he said, a project he estimated would require several million dollars. Eitan Campbell, director of Masada National Park, wants to make sure that happens, even though there is no budget for it yet. Campbell has worked at Masada for more than 30 years, starting as a teenager hauling bags of cement for archeologist Yigal Yadin, who directed the initial excavation there in the mid-1960s. Two years of heavy winter rains have caused significant damage to the 2,000-year-old structures, Campbell said. "The whole top of the mountain was one big pool of water, I've never seen anything like it. A couple of the walls collapsed," he said. In mid-August, Glaser expects to arrive from Berkeley with his new monitoring system. He and Hatzor will set up seismic monitoring stations at the visitors center at the base of the mountain and at the watchtower on top. Gauges will be installed to measure the effects of temperature, humidity, barometric pressure and tidal pull on the mouths of cracks, "to measure how the crack opens and closes and whether there's any horizontal movement," Glaser said. In addition, the scientists will compare movement at the mountain's base to movement at its top, examining, for example, how the rock responds to tidal changes at different times of the day. The system has not been tried anywhere else. "This will be its field test," Glaser said. Masada was chosen, he said, because of its historical and archeological importance, and because Israeli interest guaranteed easy and uninterrupted access to the site. "It's more enjoyable to work on something with historic importance instead of a strip mall," he said. Restoration of the palace is already underway, thanks to a government grant of $2.2m. Campbell has had all the Roman frescoes from the lower part of the palace - the part most susceptible to wind and rain - removed. They are being restored, and Campbell plans to mount replicas in their place while displaying the originals in a special museum. Visitor safety, however, is his immediate concern. Tourism slowed down considerably after Palestinian violence increased in late 2000, but it has now picked up. Half a million visitors came in 2005, and even more are expected this year. "Restoration should be a yearly budgeted item," Campbell said. "Masada is subject to the elements. It needs constant attention. "It's our job to pass it on for generations to come," he said.

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