Passive Systems

Example 2 – Structurally Controlled Geomorphic Features

The following examples demonstrate how exposed and obscured/buried structures may be identified by their surface expression; most notably in the way they may influence geomorphic features. The three examples shown below show Landsat imagery and their respective interpretation.

1. Truncated fold in the Wind River Basin, Wyoming. The imagery illustrates how abrupt changes in channel and stream valley width and disturbed local drainage may indicate the presence of geological structure. Note how the stream on the right side of the imagery joins the main drainage valley at a relatively obtuse angle.
    
2. Buried fold of the Pearsall oil field in southern Texas. In this example, the Pearsall buried structure forms structurally-controlled drainage features similar to the previous example. Most notable are the cone-shaped river valley that crosses the structure, and the structurally-controlled stream following the northern portion of the buried fold.
   
   
3. Obscured normal faults of the Mexia-Talco fault system in eastern Texas. Local deflections in channel orientations are a good indication of structurally-controlled features. The vegetation patterns in the imagery also highlight the extent of the faulting.

CS Cone shaped valley; SS Subsequent stream; DD Structurally controlled drainage divides; HV Heavy vegetation cover; SD Slope direction; BS Breached structure; DS Deflected stream

[click to enlarge]

Example 1 – Ouachita Mountains, Oklahoma.

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