Chapter 3: Geologic Structure and Landforms
Geologic interpretation of images begins with the identification of lineaments, “regional linear features caused by linear arrangement of regional morphological features such as streams, escarpments, and mountain ranges and tonal features that in many areas are the surface expressions of fractures or fault zones.”[i] The emphasis in this section is on geologic structures and landforms, both of which can be easily identified on air photographs and other images.
The sequence followed here is that often found in geomorphology books. Geologic structures and structurally controlled landforms are illustrated first, followed by images of mass wasting and of the results of the agents of erosion—running water, ground water, ice, wind and the sea. The meandering rivers of southern
3.31: Detail of a Cutoff on the Assiniboine River
This low level photograph was taken 30 years after that in Figure 3.30. It shows the cutoff in figure 3.30 in detail as well as revealing changes that have occurred over the intervening years. The main channel of the
The cutoff has been unfilled by sediment and vegetation 4 but some standing water remains 5. The neck of the abandoned channel that was bare sand in 1951 is now (1981) covered by vegetation, including some trees, probably willows (Salix spp) 6. Both within the cutoff 7 and to the west of it 8, meander scrolls can be seen with trees occupying the ridges and grass the swales in between.
The photograph was taken in the spring before the leaf-on stage for some trees as revealed by their shadows 9, but other with round crowns seem to have some foliage 10.
Figure 3.31: Detail of a Cutoff on the Assiniboine River
Vertical air photograph: 8103 00 098
Flight height: lens focal length:
Date: May 5, 1981
Scale: 1:5,000 (approx.)
Location: Section 25, Township 8, Range 13 WI
Map sheets: 1:250,000 62G Brandon
1:50,000 62G/11 Glenboro