HUMAN IMPACTS ON THE INTERPRETATION OF LINEAR GEOLOGICAL FETURES

The interpretation of linear features on imagery - regardless of scale or resolution - becomes a more complicated task in areas that have long human histories. Lineations are linear patterns observed on imagery that represent fracture patterns. The fractures may be either joints or faults. Each lineation does not necessarily represent an individual fracture, and typically, represents a zone of fractures. Lineations include, but are not limited to, straight stream segments, linear alignments of natural vegetation, aligned topographic features, and linear changes in image tone and/or texture. Any feature thought to be a lineation should be one of a group of parallel features. Each group may consist of different types of features.

It is often useful to obtain information about the history and culture of an area, particularly if human occupancy has occurred over millennia. Man-made, or man-influenced, linear features may be present and should not be delineated as lineations. For example, Bronze Age field boundaries (reaves) on Dartmoor in southwest England extend for great distances across the landscape, and unless one knew such features existed, they would surely be delineated as lineations: reaves are long, linear, and parallel, and tend to cross the landscape regardless of the terrain in the same manner as lineations. Another example that could cause confusion is the straight nature of streams in tropical regions where rice is grown in paddies. Because the fertile land is in the valleys, people in past centuries have often moved the streams that formed the valleys into linear structures along the valley sides. These features can easily be confused with natural linear patterns. Skill and experience is thus required to delineate the lineations; the greater the skill, experience, and knowledge of the human history of the area, the more complete and accurate the delineation will be.