Monitoring for Historical Sites

from the Florida Jewish News

Work by CITRIS
researcher Steven Glaser is helping to preserve Masada, a World Heritage
Site in Israel. In mid-August, Glaser will set up seismic monitoring
stations at the visitors center at the base of the mountain and at the
watchtower on top.

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 Glaser are breaking new ground in geological engineering.

Masada is their test case.

“Masada has been degrading for 2,000 years,” says 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 adds. “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 some damage to the man-made
structures. Harsh desert weather continues to impose its own disintegrative

“The terraces of the palace were much larger than what they are today,”
Hatzor says. “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 Israel’s National Parks Service began construction
of a new 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 before.

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
60-foot-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

Stepping off the cable car one morning last month, Hatzor points to an
enormous yellow block of rock that hovers 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 says it is 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 asks. “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 7.1 quake in the northern Sinai in 1995, 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 says, a project he estimates would require several million

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 initially excavated the
site in the mid-1960s.

Two years of heavy winter rains have caused significant damage to the
2,000-year-old structures, Campbell says.

“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 says.

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

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 says.

Masada was chosen, he says, 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 remarks.

Restoration of the palace is already underway, thanks to an Israeli
government grant of $2.2 million. 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 the Palestinian intifada began in
2000, but 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 urges. “Masada is
subject to the elements. It needs constant attention.

“It’s our job to pass it on for generations to come.”