Le Crotoy (Somme). In the dried-out crops of grain, we can see a protohistoric circular ditch, as well as a number of light areas, which are the result of natural periglacial phenomenon.
 
Same site, after removal of the plant layer. We can easily see the pebbles that have come to the surface, ringed with dark patches (silt pockets).
 
Pitfalls and confusions
The work of nature, or of human beings?
page 1page 2page 3page 4page 5page 6page 7
Le Crotoy (Somme). In the dried-out crops of grain, we can see a protohistoric circular ditch, as well as a number of light areas, which are the result of natural periglacial phenomenon.

Same site, after removal of the plant layer. We can easily see the pebbles that have come to the surface, ringed with dark patches (silt pockets).

Cross-section view of the same site. At the base, the alluvia are perfectly horizontal. But the great cold of the last glaciation has pushed them vertically up for more than two meters.
From the air, how can you distinguish the work of the human hand from the work of nature?

"Geometry is the language of human beings"
as Le Corbusier so aptly put it

Indeed, natural phenomena that appear in aerial photographs are not really geometric, whether these are recent occurrences such as erosion marks, or fossils such as the lines of ancient rivers, outcroppings of geological strata, patterns of diaclases, silt and wind-born sediment deposits, and periglacial structures such as at Crotoy (Somme). It is like mushroom caps, which are never perfectly circular.


 
 
Cross-section view of the same site. At the base, the alluvia are perfectly horizontal. But the great cold of the last glaciation has pushed them vertically up for more than two meters.


Top
page 1page 2page 3page 4page 5page 6page 7