How did the archaeological material end up under ground in the first place?

There are many possibilities in answer to this question ranging from natural processes to human activities.

For example, when inhabitants abandon a dwelling or a house, it gradually collapses; the roof caves in and the walls start to sag and crumble. Plants, living creatures, wind, rain, snow, frost, or intense sunlight all contribute to degeneration. The gradual accumulation of soil from the decay of vegetation gradually rises above ground level, and the last remnants of the house eventually become buried under a layer of soil that is slowly deepening.

Site of Mohenjodaro, India, a part of the 'Indus Civilization'

Different natural forces may be involved in burying archaeological sites. Soil that has eroded from higher ground can be deposited or archaeological sites can be buried from soil, wind or floods. In a desert, for example, the site may be covered by wind blown sand and debris.

In other instances natural disasters may cause the archaeological remains to become immersed. Ash and lava flows from volcanic eruptions can overtake sites as in the case of Pompeii, which was buried from ash by Mt. Vesuvius. A very good example of how a local site became buried comes from the Ozette site on the northwest coast of Washington, United States. Around 1750, a huge mudslide buried part of a whale hunting settlement. The village remained buried for over 200 years, but descendants from the Ozette area had kept the memories of their ancestors alive through oral tradition.

The ‘man’ factor

Nature is not the only thing that conceals the proof of previous human settlement. Abandoned buildings are often demolished and any useful materials are removed. New buildings may be constructed on top of the old debris, sometimes using any salvageable remains from the previous building.

Coppergate Site (York, England), the layers of soil that have built up show the different eras (strata) of human occupation at the site

Through this system of destruction and renewal, settlements gradually rise above the earliest level of occupation. Sometimes this factor can cause astonishing results. One example comes from the Near East, where an archaelogical site occupied for thousands of years has become a gigantic mound built upon the decayed remains of previous mud and brick dwellings.

Ditches, post-holes pits, and foundation trenches are among the most common archaeological finds. Floors that were originally laid at ground level as well are common survivors over the years.

Powerful natural and man made forces of destruction

It is often the same natural processes that preserve an archaeological site that demolishes them. For instance, historic sites that are located on top or on the side of a hill fall prey to erosion, mudslides, and landslides over the years. Flooding and the actions of glaciers can have similar effects.

Although nature has a great deal to do with the destruction of archaeological and historic sites, modern technology plays a much larger role. Agricultural machinery penetrates deeper into the soil than traditional farm implements. Road construction and other industrial advances are equally destructive.