Rocks crumble, dissolve away, collapse, or flake off over time in a process called weathering. Whether in cold climates or hot, wet climates or dry, all rocks and minerals deteriorate over time. Most ancient and classical architecture is built from rock, including some of the world's most famous buildings (for example, Rome's Coliseum, China's Great Wall, or Egypt's Pyramids). As these ancient structures collapse over time, it becomes more important that we understand how rocks break down. Popular sites such as Venice (in Italy), Macchu Picchu (in Peru), Beijing (in China), and Petra (in Jordan, photo at right)) all attract millions of visitors each year who touch, walk, and climb these spectacular buildings and structures. To ensure their longevity as cultural attractions, scientists are investigating rock weathering influences, rates of decay, and conservation techniques in an attempt to save them for generations to come.
Do rocks rot in the desert? Yes, even in arid regions weathering processes are at work, although structures in dry climates tend to decay more slowly than in other regions, making them more difficult to study. In the summer of 1989, Professor Tom Paradise with the University of Arkansas Geosciences Program and the Fahd Center for Middle East & Islamic Studies began one of the largest sandstone weathering research projects in the world in Petra, Jordan (see map). Dr. Paradise's investigation focused on the various causes of deterioration of Petra's Nabataean and Roman architecture in order to better understand the rates at which these buildings were responding to natural decay processes and human misuse. Petra is a useful site for this study because many of the more than five hundred buildings, tombs, and temples were carved from the steep sandstone cliffs about 2,000 years ago and have been fairly unmodified since – a very rare, but ideal circumstance for weathering research. In addition, since it is believed to have been abandoned after a number of devastating earthquakes in the 5th through 8th centuries, the ruined city of Petra was relatively unused by humans until it was "re-discovered" by the Swiss explorer, J. Burkhardt in 1812 and reintroduced to the curious and eager tourists of the 19th century.
In weathering studies, it is essential to consider two categories of variables that affect rock: intrinsic influences, such as hardness, fracturing, and molecular composition, and extrinsic influences such as temperature, moisture, and abrasion (perhaps human-induced). This is why stone weathering studies are often complicated; we need knowledge of mineralogy, climatology, weather, architectural history and construction techniques, and local and regional land use, in addition to an understanding of current stone conservation technology. During the 1990s, Dr. Paradise's research measured mapped, and carefully photographed many of Petra's tomb and temple facades to determine climatic and lithologic variables including yearly moisture and temperature distribution, insolation quantity, rock type, rock density, and clast and matrix composition. However, an important additional variable proved to be the human factor. At Petra, the number of visitors increased from 100,000 in 1990 to 350,000 in 1998. And with this increase in human visitation came people climbing on, touching, and scratching the sandstone, as well as collecting bits and pieces of architecture. In fact, Roman and Nabataean buildings at Petra that have remained relatively unaffected over the past 2,000 years now show signs of deterioration. The names of visitors carved into Petra's facades and inner chambers, newly worn footpaths in hewn Roman sandstone staircases, and human urine-accelerated decay are only a few of the human influences observed at Petra.
One of the outcomes of Dr. Paradise's research has been an increased awareness of this accelerated deterioration, and the importance of conservation and management practices at cultural heritage sites. Many American universities, like their partners in Europe, Asia, Africa, and Australia, now have multidisciplinary programs in rock deterioration and conservation studies. Furthermore, national organizations such as the National Science Foundation, U.S. Agency for International Development (USAID), and the Fulbright Programs all support stone architecture weathering studies, in addition to international entities such as the United Nations Educational, Scientific, and Cultural Organization (UNESCO). A new emphasis is now placed on the continuation of interdisciplinary weathering research at local, regional and global levels, and the use of scientific findings in stone conservation technologies and sound visitor management policies. Thus, a primary component of rock weathering studies emphasizes the role of weathering science in conservation and management practices aimed at preservation of the world's great architectural wonders.
This project was undertaken under the approval of the Petra National Trust, a Jordanian N.G.O. supervised by Aysar Akrawi, and H.R.H. Queen Noor of Jordan.
Using information from the chapter on weathering in your text (Chapter 13 in Geosystems and Chapter 10 in Elemental Geosystems), discuss several physical and chemical weathering processes that occur in arid regions.
To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
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