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The PETRA PROJECT
ARCHITECTURAL DETERIORATION, CULTURAL HERITAGE MANAGEMENT,
and ENVIRONMENTAL CHANGE
The University of Arkansas
PETRA PROJECT is an ongoing project established in 1990 to assess
and record various aspects of landscape change in the classical period city of Petra, Jordan. Aspects include deterioration influences and rates for limestone and sandstone
architecture and rock, cultural heritage management issues for the UNESCO World Heritage site and region, urban planning and local Bedouin studies (Bdoul) in Wadi Musa and Umm Sayhoun, and prehistoric and historic environmental landscape change and influences. Under the supervision of Professor Tom Paradise, University of Arkansas graduate students in the Department of Geosciences and the Environmental Dynamics Program participate in various components of the research project, completing theses and dissertations while conducting fieldwork in Petra and the region.
Now after more than 100 million voters have chosen Petra, Jordan as one of the NEW SEVEN WONDERS of the WORLD, it is imperative that this ongoing research project continue as tourism will dramatically increase, infrastructure will become increasingly strained, and the environment in and around Petra will be impacted drastically. This magical yet sensitive site needs increased research so that its stewardship may continue now and in the future.
Evidence indicates that Petra
has been occupied since 3000 BCE, and Greek, Roman and Aramaic records mention
Nabataean culture in the region since 500BCE.
However, it was the sacredness of Mount
Hor (or Jebel Haroun) that 
brought
early notoriety to Petra since it
was the reputed burial site of Aaron, the brother of Moses. Many believe that Bedouins have occupied and
roamed the region long before Moses’ arrival about 1250BCE, or later when Rome
annexed the region in 104AD as Felix Arabia Petraea. This hidden Valley passed
into legend with the passage of time and remained unknown until the 19th
Century, when in 1812, Johann Burckhardt visited the Valley surreptitiously dressed as a Bedouin traveler wishing
to sacrifice a lamb at the mountaintop tomb of Aaron. Since the earliest days of
the Nabataean civilization, followed by Roman invaders and partners, then
raided by Crusaders, defended by Sa’aladin, the hidden valley
of Petra was unknown to outsiders. Researchers did not ‘discover’ Petra until the early 1900s,
when historians, geographers and archaeologists extensively studied and
surveyed Petra and its monuments, tombs, buildings, tells, and temples.
Petra is a
crescent-shaped Valley confined by high fault-bound sandstone walls that may
have been the home to more that 50,000 people 2,000 years ago with more than
500 known tombs, structures and monuments. The unique architecture of Petra represents an interesting melding of indigenous Nabataean, Hellenistic, Roman styles, uses and decoration. Since sandstone represents a common
building material and a dominant landscape component across the region and its structures have a known exposure (roughhly 2,000 years old), Petra
represents an ideal outdoor laboratory for sandstone deterioration research since (i) the structures (ie tombs, temples) were carved during known periods, (ii) many of the structures were hewn and have not been moved, (iii) restoration has been recorded and/or is
visible, (iv) the sandstone has been extensively studied and is relatively consistent in lithology. Petra’s two
primary formations are the Cambrian Umm Ishrin and Cambrio-Ordivician Disi
sandstones and represent one of the oldest, most widespread and relatively
unaltered sandstones units on Earth.
Although the PETRA PROJECT was initiated in 1990 with a focus on architectural deterioration and stone decay, over the years it has expanded to included aspects of the cultural and social landscape, and cultural heritage management. Originally the research looked at climatic influences on rock weathering, however it became apparent that visitors were accelerating the rock breakdown faster than nature had in 2,000 years -- humans and their effects were added to the investigation of the architecture and landscape. At first, variations in sandstone lithology were correlated to environmental variables like aspect, moisture, sunlight (insolation), slope, and biotic coverage (lichens, plants). Later, other variables were studied including respiration and humidity from tourists, and visitor frequency across the Valley. Various research components follow that have been investigated so far:
Petra Theater Sandstone Study
This study examined 26 variables related to surface
recession that created a statistical matrix of nearly 14,000 data points
creating the largest sandstone weathering data set known. 526 baseline
recession measurements were taken across the Theater (in a stratified random
scheme) and related to 26 variables that included aspect (220 degrees of coverage), insolation (mjoule/m2/yr), matrix lithologic constituents (calcium, iron, manganese,
silica), clast lithologic components (siliceous, calcareous), lichen genera and coverage, and daily & annual shadowfall.
Sandstone matrix constituents of iron and silica were found
to decrease overall sandstone weatherability, while calcium matrix components
were found to increase deterioration in areas that receive more than 5500
megajoules/square meter/year of solar radiation — a typical southern aspect in
mid-latitude, arid regions. Moreover,
when iron matrix concentrations exceed 4-5% (by weight), original stonemason
dressing marks are still clearly evident, indicating a nearly unweathered state
in 2,000 years. Surface recession rates
for sandstone in the Roman Theater
were determined to range from 15 70mm per millennium on horizontal surfaces to
10 20 mm/millennium on vertical surfaces.
Monument Surface Recession Aspect study
While the Theater study explains significant sandstone
weathering relationships and hierarchies, it created more questions and Petra’s
monuments and quarries afforded new research opportunities. So, quarries and
monuments across Petra - like the
Blocks of Djinn - were studied for surface recession relationships to aspect.
Insolation was found to have the greatest effect on weathering on southwestern
and southeastern aspects (and not southern faces as is often discussed),
indicating that insolation may be most influential in sandstone weathering when
in tandem with increased wetting-drying and/or heating-cooling cycles.
Al-Khazneh and Urn Tomb Anthropogenic Humidity Study
As tourism grew in Petra
and across the Holy Land, studies into anthropogenic
influences on sandstone deterioration are warranted and the Khazneh
(Treasury) and Urn Tomb represent the perfect sites. Over a
five-year study with Arkansas graduate students Mick Frus and Mo Salem, in-tomb humidity
was measured and compared to ambient outside humidity, all related to tomb
visitor numbers. It was found that as
chamber tourists in the Khazneh exceeded 30 persons, relative humidity jumped from 30 to 60%
-- an amount found to accelerate sandstone weathering. These crucial findings have huge policy
repercussions which have led to Khazneh cordons that keep tourists outside the
main chamber. A different circumstance
for tourism but one that will lengthen the life of this magnificent structure
made famous in the film Indiana Jones and the Last Crusade. In addition, it was found that interior surfaces have
dramatically receded due to visitor touching, leaning and rubbing, as much as
40mm in less than 50-100 years (period of increased tourism). This indicates that a 4 by 3 meter wall area
has lost a volume of sandstone of approximately one half cubic meter in these
100 years from 0.5 to 2m above the floor indicating surface recession from
human contact. In the Summer of 2007, similar measurements were taken in the Urn Tomb for further analysis.
Visitor Mapping Project (Synoptic Tourism Cartography)
In the Summer
of 2003, Mo Salem, a graduate student in Geography and Dr. Paradise recorded and assessed each visitor that entered and exited Petra in the hopes of determining tourist movement through the Park. Recording each tourist that entered Petra through the main gate (Bab as-Siq), to then pass the Khazneh and Theater, they mapped the tourists' movements throughout the valley and their use of related infrastructure. Their exit was also recorded as to where they walked, why, and how quickly. This extensive study is invaluable in cultural site management -- determining what resources they use and when, where they are in the Valley and how fast they move, how quickly they leave and by what route is fundamental in management research. Maps were then created for each portion of the Valley and City during various times of the day to determine how many visitors are where and where. This research and mapping project has been studied and utilized in Petra's new Park Management Plan.
Umm Sayhoun Digital Mapping Project
Over the Summer of 2007, graduate student Chris Angel and Dr. Paradise digitally mapped the Bdoul Village of Umm Sayhoun using satellite imaging, flyover photography, ground-level imagery, GIS and computer cartography. Since the village was created in the early 1980s, it is a unique opportunity to assess a new city of 2000 residents since its creation. Aspects of urban morphology, materials and construction, perception of space, and topophilia are addressed. The Bdoul clan of Bedouins were forced to relocate in 1984-1985 when the new designation of the UNESCO title as a World Heritage Site was implemented on the Valley of Petra and its surrounding area -- so how does a previously semi-nomadic clan create a permanent city? This important baseline study has strong implications now that Petra has been designated as the one the NEW SEVEN WONDERS of the WORLD.
So, what have we learned so far in Petra?
in the physical landscape:
* that in architectural deterioration research, the old foci of extrinsic vs. intrinsic
influences has proved significant in Petra;
* the utilization of petrologic microscopy is valuable (i.e. backscatter microprobe, scanning electron, transmission electron);
* that aspect plays an underrated role in the decay of sandstone architecture by
influencing wetting & drying and freezing & thawing cycles;
* that anthropogenic effects on stone decay and environmental
degradation and denudation may be under-evaluated and/or overlooked;
* that high frequency & low magnitude agents (i.e.
particle disaggregation, human foot-tread) may influence sandstone landscape development more than
conventionally accepted episodic occurrences like rockfalls and spalling;
in the cultural landscape:
* that humans represent an underestimated impact influence on sensitive landscapes often representing the most influential single factor;
* the importance of strong and progressive infrastructure on cultural site management and stewardship can never be underestimated or overfunded;
* and that all share-holders (social, environmental, economic, cultural) must be integrated and included in all decision-making policies in effective cultural heritage management.
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For more information on this ongoing project, contact Dr. Tom Paradise at
University of Arkansas, Department of Geosciences
113 Ozark Hall, Fayetteville AR USA 72701
479-575-3159 (telephone), paradise@uark.edu (email)
The Petra Sandstone Deterioration Project has been funded by
a number of agencies including
the US National Science Foundation, USAID,
USIA-USIS, NMERTP, Petra National Trust,
King
Fahd Center
for Middle East & Islamic Studies at the University
of Arkansas,
American Center of Oriental Research (ACOR), and the Hashemite
Kingdom of Jordan.
