Environmental Engineering Reference
In-Depth Information
Interpretative Factors
Rock masses have characteristic features, as deposited, which result in characteristic land-
forms that become modified by differential weathering. Deformation and rupture change
the rock mass, which subsequently develops new landforms. Some relationships between
morphological expression, structure, and lithology are given in Figure 6.1.
Interpretation of these characteristic geomorphological expressions provides the basis
for identifying rock type and major structural features. The more significant factors pro-
viding the interpretative basis are landforms (surface shape and configuration), drainage
patterns, and lineations.
Lineations
are weakness planes intersecting the ground surface and providing strong
rectilinear features of significant extent when emphasized by differential weathering. The
causes include faults, joints, foliations, and bedding planes of tilted or folded structures.
Stream Forms and Patterns
Significance
Rainfall runoff causes erosion, which attacks rock masses most intensely along weakness
planes, resulting in stream forms and patterns that are strongly related to rock conditions.
Costal plains
Horizontal strata
Folds
Domes
Homogeneous crystalline masses
Fault blocks
Complex structures
Volcanoes
FIGURE 6.1
Diagrams showing effect of varying geologic structure and lithology on morphology of landscapes. (From A. N.
Strahler,
Physical Geology,
Wiley, Inc.; from Thornbury, W. D.,
Principles of Geomorphology,
Wiley, New York, 1969.)
