Aerial photography at the Fort Lawrence National Historic Site of Canada

The advantages of gaining a good aerial view of the ground had been long appreciated by archaeologists as a high viewpoint permits a better appreciation of fine details and their relationships within the wider site context.

 Aerial photography is one of the best ways of understanding archaeological landscapes, because it reveals and makes sense of features which are too faint, too large or too discontinuous to be appreciated at ground level. Archaeological features may also be more visible from the air than on the ground. Tiny differences in ground conditions caused by buried features can be emphasized by a number of factors and then viewed from the air:

  • Slight differences in ground levels will cast shadows when the sun is low and these can be seen best from an aeroplane. These are referred to as shadow marks.
  • Buried ditches will hold more water and buried walls will hold less water than undisturbed ground, this phenomenon, amongst others, causes crops to grow better or worse, taller or shorter, over each kind of ground and therefore define buried features which are apparent as tonal or colour differences. Such effects are called cropmarks.

  • Frost can also appear in winter on ploughed fields where water has naturally accumulated along the lines of buried features. These are known as frostmarks.
  • Slight differences in soil colour between natural deposits and archaeological ones can also often show in ploughed fields as soilmarks.
  • Differences in levels and buried features will also affect the way surface water behaves across a site and can produce a striking effect after heavy rain.
  • Images can be taken in the near infra-red part of the spectrum revealing details which are otherwise invisible.

At the Fort Lawrence National Historic Site of Canada, aerial photography allows, among other things, a better understanding of the landscape disturbances that have affected the archaeological remains on the site.

The Fort Lawrence, built in 1750, was a four pointed star-shaped construction located on the ridge immediately east of the Missaguash River.

In 1968, the archaeologist Pierre Nadon located the Fort Lawrence remains between the Canadian National Railway tracks, the Fort Lawrence Road and a few farm buildings.

 

These remains are visible on aerial photographs preceding the construction of a barn in 1991. As a reference point, notice the location of the farm buildings and the road.  The outline of Fort Lawrence appears through cropmarks.

On this next aerial view, the location of Fort Lawrence still appears visible through faint shadow marks.

In 1991, the ground was leveled to allow the construction of a barn on the Fort Lawrence location.

The ground levelling and the construction of the barn revealed numerous artifacts through a one day salvage excavation initiated by the Nova Scotia government. Nowadays, the precise location of the remains of Fort Lawrence is only vaguely known and archaeologists of the Beaubassin and Fort Lawrence Public Archaeology Experience aim to determine it through excavations and analysis of aerial views.

This next aerial view is more recent and shows what is currently believed to be the location of the Fort Lawrence remains.  As you can observe, the 1991 barn would now cover part of the remains of the fort.

In summary, for the Fort Lawrence National Historic Site, aerial photography represents a very useful tool for archaeologists to understand the processes, natural and human, that have shaped the landscape. Light Detection And Ranging (LiDAR) is also a technology which helps archaeologists in their work. This technology allowed the detection of a low-relief 18th Century British siege trench at the Fort-Beauséjour/Fort-Cumberland National Historic Site. To know more, follow this link: http://www.geosynoptics.ca/beasejour.pdf

References:

The first section of this article is part of the Wikipedia article called Aerial Archaeology. Here are the references cited in this article:

Bourgeois, J. and Meganck, M. (eds.) (2005). Aerial Photography and Archaeology 2003. A Century of Information. Archaeological Reports Ghent University 4. Ghent: Academia Press. ISBN 90-382-0782-4

Brophy, K. and Cowley, D. (eds.) (2005). From the air: understanding aerial archaeology. London: The History Press Ltd. ISBN 0-7524-3130-7

Riley, D. N. (1987). Air photography and archaeology. Univ of Pennsylvania. ISBN 0-8122-8087-3

Wilson, D. R . (2000). Air photo interpretation for archaeologists, London: The History Press Ltd. (2nd edn.). ISBN 0-7524-1498-4

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