Thomas R. Paradise

Geomorphology's role in the study of weathering of cultural stone

Abstract Great monumental places—Petra, Giza, Angkor, Stonehenge, Tikal, Macchu Picchu, Rapa Nui, to name a few—are links to our cultural past. They evoke a sense of wonderment for their aesthetic fascination if not for their seeming permanence over both cultural and physical landscapes. However, as with natural landforms, human constructs are subject to weathering and erosion. Indeed, many of our cultural resources suffer from serious deterioration, some natural, some enhanced by human impact. Groups from the United Nations to local civic and tourism assemblies are deeply interested in maintaining and preserving such cultural resources, from simple rock art to great temples. Geomorphologists trained in interacting systems, process and response to thresholds, rates of change over time, and spatial variation of weathering processes and effects are able to offer insight into how deterioration occurs and what can be done to ameliorate the impact. Review of recent literature and case studies presented here demonstrate methodological and theoretical advances that have resulted from the study of cultural stone weathering. Because the stone was carved at a known date to a “baseline” or zero-datum level, some of the simplest methods (e.g., assessing surface weathering features or measuring surface recession in the field) provide useful data on weathering rates and processes. Such data are difficult or impossible to obtain in “natural” settings. Cultural stone weathering studies demonstrate the importance of biotic and saline weathering agents and the significance of weathering factors such as exposure (microclimate) and human impact. More sophisticated methods confirm these observations, but also reveal discrepancies between field and laboratory studies. This brings up two important caveats for conservators and geomorphologists. For the conservator, are laboratory and natural setting studies really analogous and useful for assessing stone damage? For the geomorphologist, does cultural stone data have any real relevance to the natural environment? These are questions for future research and debate. In any event, cultural stone weathering studies have been productive for both geomorphologists and conservators. Continued collaboration and communication between the geomorphic, historic preservation, archaeological, and engineering research communities are encouraged.

SANDSTONE WEATHERING THRESHOLDS IN PETRA, JORDAN

From ongoing research examining weathering rates and mechanisms in the Paleozoic sandstones of Petra, Jordan, two possible thresholds have been identified. From a carved Roman Theater built under Vitruvian standards during the first century A.D., a two-meter sampling scheme was used to measure the presently weathered surfaces from a hypothetical false datum determined through originally documented Roman engineering and construction canon. Some 526 depth measurements were made on vertical and horizontal surfaces and correlated to the intrinsic variables of sandstone matrix-to-clast ratios, overall densities, matrix chemistry (Si, Ca, Fe, Al concentrations), and to the extrinsic accumulated annual insolation receipt (mega-joules/m2). When matrix iron concentrations exceeded 2%, an abrupt decrease in overall weatherability is indicated until weathering is found to have decreased below measurable limits at 4%. It is speculated that matrix iron acts as a sandstone-clast binding agent, reducing clast disaggrega...

Defining tafoni: Re-examining terminological ambiguity for cavernous rock decay phenomena

Cavernous rock decay processes represent a global phenomenon, ubiquitous to all environments, with the viewable-in-landscape form usually being the final descriptor (e.g. “alveoli”), sometimes alluding to the specific decay process (e.g. “pitting”), other times not (e.g. “honeycombing”). Yet, definitive terminology remains inconsistent, usually owing to variability in dimension, morphometry, distribution, and/or academic lineage. This lack of an established lexicon limits scientific collaboration and can generate scientific bias. With no official consensus on appropriate distinctions, researchers and scientists must either be familiar with all the possible terminology, or know the apparent distinction between “forms”—which can seem arbitrary and, even more frustrating, often differs from researcher to researcher, scientist to scientist. This article reviews the historical and contemporary progression of scientific inquiry into this decay—and, arguably, erosional—feature to identify lexical inconsistencies and promote a singular unifying term for future scholars. Ultimately, the authors support using “tafoni” (singular: “tafone”) as the non-scalar universal term—the form created by numerous processes involved in cavernous decay features—and strongly suggest researchers adopt the same vernacular in order to promote collaboration.

Sandstone architectural deterioration in Petra, Jordan

Publisher Summary Petra, Jordan was an extensively occupied city during the Nabataean and Roman eras. Incorporating Hellenistic, Assyrian, Egyptian, and Roman architectural motifs and techniques, the Nabataeans created an architecture style that was both derivative and unique. However, its architecture is deteriorating because of weathering processes. The weathering influences have been separated into two distinctive categories: those affected by the characteristics of the stone itself or intrinsic effects (i.e. lithologic constituents, fractures), and those affected by external influences or extrinsic effects (i.e. climate, human contact). This chapter describes the weathering causes, effects, and rates of deterioration in the Roman Theater, Anjur Quarry, and Al-Khazneh. Through these three research sites, the following conclusions regarding the complex dynamics of sandstone weathering in Petra were drawn: (1) The Roman Theater study confirms the importance of rock chemistry and composition in interpreting deterioration mechanisms, (2) Research at the quarry of Anjur establishes the role of sunlight in the acceleration of weathering and architectural decay, and (3) Measurements of the inner chamber walls and the human-induced humidity in Al-Khazneh demonstrates the effect of tourism on accelerating stone deterioration. Therefore, examinations of both intrinsic and extrinsic conditions are vital to the preservation and conservation of the unique architecture and history of Petra.

Architecture and Deterioration in Petra: Issues, Trends, and Warnings

The ruined city of Petra is situated in a deep valley, surrounded by steep, impassable sandstone walls and winding gorges, within the arid expanse of Jordan’s great southern desert. However, it is the spectacular architecture rather than its beautiful setting that has drawn international attention and visitors since it was first “discovered” and described to the Western world by Burckhardt JL (1835) North Am Rev 40(87):477–510. Although its structures and archaeological evidence indicate occupation in the Petra area since 7,000 BCE, it was its Nabataean occupants and Roman clients that gave Petra notoriety, then and now. These residents worked the valley walls into simple, elaborately carved tombs and spaces, hewn directly from the reddish brown and yellowish sandstone cliffs; many exceed 50 m in height. Since the construction 2000 years ago, natural and anthropogenic forces have been working to weather this delicate and unique sandstone and limestone architecture.

Islam and earthquakes: seismic risk perception in a Muslim city

In the Qur’an, earthquakes are separated from other natural hazards in meaning, significance, and risk perception: this can be attributed to their focus in surah “al‐Zalzala” (99th). In 2002, more than 250 earthquake survivors and residents were surveyed and interviewed across Agadir, Morocco 40 years after the 1960 tremor left 15,000 dead and 25,000 injured. This study was conducted to obtain perceptions of quake recurrence, construction standard policies, seismology and local planning strategies. It was found that younger persons (<25yo) were likely to believe that brick, mortar and cement structures were always safer (and stronger). Television‐viewers were less knowledgeable about earthquakes, while most aspects of seismology were more widely understood by this group, suggesting that TV can be an efficient, mass education tool. Less educated respondents attributed earthquakes to divine retribution. Questions concerning quake recurrence caused an prevalent refusal to answer, commonly with the relpy of A...