What can damage archeological resources?
Portions of a 2,900-year-old pack basket found in a snowfield at Olympic National Park. (NPS)
Sites continue to be affected by tranformations of their physical surroundings. The degree to which archeological materials are preserved will vary greatly. Physical decay effects archeological materials exposed to elements such as extremes of hot or cold, wind, rain, snow, water, ice, or seismic activity (McIntosh 1999:88). Mechanical deterioration due to climate and human and animal activity determines material preservation, as do chemical processes. Soil composition can spur material decomposition. Biological deterioration results from the action of plants and animals, insects, fungus, and other microorganisms (Hester et al. 1997:134). Humans also damage archeological resources, intentionally or through cumulative use in the course of regular activity.
Mechanical deterioration includes breakage, abrasion, and disassembly resulting from ground pressure, frost wedging, and even careless archeology (Hester et al. 1997:134). Climatic conditions such as extremes of hot and cold, wind, rain, snow, water or ice and seismic activity affect material preservation. Material decomposition is most rapid in tropical climates and less a factor in arid or frozen climates. Human activities, including construction, artifact reuse and careless archeology also break and otherwise damage archeological materials.
For your information
Lessons on Future Soil Use
This article demonstrate the “Archeological records contain advice aplenty for modern man and his use of the land.”
Chemical deterioration occurs as the result of various amounts of moisture, acids, and bases in the soil (Hester et al. 1997:134). Soil composition—particularly the amounts of acid and alkaline—greatly affects the condition of material remains, not only at an archeological site but also in the laboratory and storage facility. Bone and glass are poorly preserved in acidic soils, yet some organic remains may be preserved therein. In alkaline soils, organic remains decay rapidly, although bone is preserved and may become semifossilized. Insoluble salts encrusted on pottery, bone, stone and metals may damage them. Wood may be preserved in alkaline waterlogged conditions and seawater (McIntosh 1999:88). Proximity to copper, though, helps preserve organic materials.
For your information
of Deterioration, Enemies of Preservation
This web site describes and pictures agents of deterioration—different things that can harm or degrade an object.
Fragments of a deteriorated textile uncovered at Canyon de Chelly National Monument show signs of biological deterioration. (Harpers Ferry Center, NPS)
Biological deterioration results from the action of plants and animals, insects, fungus, and other microorganisms. Organic materials such as soils, plants, wood, bone, leather, shell, and stone are broken down over time. Sometimes archeologists cannot tell whether materials were damaged by humans, animals, or natural forces.
Humans also damage archeological resources. As discussed in previous sections, unpermitted disturbance of subsurface archeological resources is illegal on federal land. Looters, pothunters, and metal detectorists can damage archeological sites by digging for artifacts. More innocent activities by people can also damage resources. Hikers' footsteps or hands brushing across rockfaces, for example, can have cumulative impacts on archeological resources. Interpretation can help NPS staff, particularly law enforcement, communicate appropriate behaviors to the public.
Archeologists working at Wyoming's Warren Air Force Base estimate that burrowing rodents and squirrels turn over 15-20 percent of the surface soil in a single season. More deeply burrowing rodents are estimated to bring 7,200-14,000 kg/ha of subsoil to the surface annually. These activities have a significant effect on smaller archeological objects, displacing them from their stratigraphic contexts.
Use What You Know: Assess Your Knowledge (#3 of 9)
- What kinds of factors impact the preservation and maintenance of archeological contexts?
- What can't archeology tell us, and why might this information be important for your visitors to understand?
- What is archeological context? Why is it important?
- Where would you find examples of archeological resources in your park (don't forget collections!)?