People praying at Western Wall on Tisha Be'av.
(photo credit: MARC ISRAEL SELLEM/THE JERUSALEM POST)
While the crevices in Jerusalem’s Western Wall provide ample space for visitors to tuck in their thoughts and prayers, geologists have found that these very cracks may be indicative of erosion and structural instability.
Researchers from Hebrew University of Jerusalem recently published their findings on the subject in a Geology journal article, called “Limestone weathering rates accelerated by micron-scale grain detachment.”
The article takes a look at how weathering of carbonate plays a significant role in the change of landscapes – focusing on the limestone degradation of the Western Wall.
To calculate the amount of erosion that has occurred throughout the Western Wall, the researchers – led by senior lecturer Dr. Simon Emmanuel and Phd student Yael Levenson, of the Earth Sciences Institute – generated 3D models by using lidar remote sensing laser technology.
In their research, the scientists reported that various types of limestone found in the wall eroded at vastly different rates.
For example, stones made up of relatively large crystals were resistant to wear, making them almost unchanged in 2000 years, whereas stones with very small crystals eroded much faster.
The researchers discovered that tine-grained micritic limestone portions of the wall were “as much as two orders of magnitude higher than average rates estimated for coarse-grained limestone blocks at the same site,” according to their article.
In areas of the wall with this type of fine-grained stone, some portions had receded by up to tens of centimeters and consequently weakened the entire site’s structure, the researchers argued.
“Understanding such weathering processes could help guide the development of effective preservation techniques,” Emmanuel said.
In order to come to such an understanding, Emmanuel and Levenson collected samples of the different types of rocks from ancient quarries thought to have supplied the stones for the Second Temple.
Looking at samples of the stones under an atomic force microscope, they saw that the fine-grained micritic limestone dissolved particularly quickly in water.
These elevated reaction rates were likely the result of “rapid dissolution along micron-scale grain boundaries, followed by mechanical detachment of tiny particles from the surface,” the authors wrote.
Such experiments simulated the way in which rain interacts with limestone in nature, and might explain why some rocks experience more weathering than others, the researchers found.
Through continued research efforts in labs like theirs, the scientists expressed hope that not only could methods be developed to help protect the structural stability of the Western Wall, but also of ancient landmarks across the globe.
“For example, it may be possible to develop materials that slow the rate of erosion by binding the tiny crystals in the rock together,” Emmanuel said. “Advanced engineering techniques like this should assist efforts to protect not only the Western Wall, but other cultural heritage sites in Israel and around the world.”
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