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Palouse Falls Fracture Zone

View on map:46.658417°N 118.233678°W

Comments

From this vantage point you can see how the Palouse river takes right angle terms following what is believed to be a fracture pattern.  Stop 2 in Prtichard and Cebula.

"The long straight line of the Palouse River followed by the sharp changes of course near the Palouse Falls has been attributed to stream capture for decades (e.g., Trimble, 1950). The straight portion of the Palouse River upstream of the falls has an orientation of 338°, which is similar to Devil’s Canyon (340°) and H U Coulee (340°). The three coulees are all ~6.5 km (4 miles) long. At each of the coulees, there are a number of other fractures ranging in orientation from ~292° to 356° and lengths of 170 m to over 4 km (558 ft to 2.5 miles). However, the Palouse River Canyon differs from the other coulees due to the dense number of fractures that force the river to make numerous sharp turns (Fig. 14), and occasionally small waterfalls, which is what we see at this stop. Baker (1978) suggested that the fractures may have originated from axial cleavage, or fracturing at the crest, trough, and/or inflection lines of the gentle folds in the area, which are likely associated with the Yakima Fold Belt (e.g., Reidel et al., 2013a).  Griggs (1976), Reidel et al. (2013a), and Hatch et al. (2014) suggest that they are associated with regional strike-slip, or lateral, faults in the underlying basement. Figure 15 shows that most of the 90 measured fractures are oriented between 300° and 310° (and to a lesser extent between 290° and 300°), which correlates well with the dextral motion on the Olympic-Wallowa lineament (308°), Lewis and Clark fault zone (300°), and other strike-slip faults in the Yakima Fold Belt (Hammond, 2013; Blakely et al., 2014). Other common fracture orientations in the Palouse Falls fracture zone are between 320° and 330° and are similar to the shortening axis estimated by Hammond (2013) for deformation related to the Yakima Fold Belt. Reidel et al. (2003 and 2013a) present the Olympic-Wallowa lineament as a thrust-dominated system. Though there are some conflicting interpretations of fault motion, the above studies agree that the region is undergoing N-S shortening, which is likely re-activating faults in the basement." 

Description


Stream capture

Stream capture, river capture, or stream piracy is a geomorphological phenomenon occurring when a stream or river drainage system or watershed is diverted from its own bed, and flows instead down the bed of a neighbouring stream. This can happen for several reasons, including:

References

  • http://en.wikipedia.org/wiki/Stream capture
  • Page 85 - Pritchard, C. J. and Cebula, L., 2016, Geologic and anthropogenic history of the Palouse Falls area: Floods, fractures, clastic dikes, and the receding falls: Geological Society of America Field Guide 41, p. 75-92.
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