Yakima Fold Belt

Yakima Fold Belt
Yakima fold-and-thrust belt
Map showing the location of Yakima Fold Belt
Location South-western part of Columbia Basin (Yakima, Kittitas, Klickitat, Benton, and Grant counties)
Coordinates 46°24′N 120°30′W / 46.4°N 120.5°W / 46.4; -120.5Coordinates: 46°24′N 120°30′W / 46.4°N 120.5°W / 46.4; -120.5
Geology Fold and thrust belt

The Yakima Fold Belt of south-central Washington, also called the Yakima fold-and-thrust belt, is an area of topographical folds (or wrinkles) raised by tectonic compression. It is a 14,000 km2 (5,400 sq mi) structural-tectonic sub province of the western Columbia Plateau Province[1][2][3] resulting from complex and poorly understood regional tectonics. The folds are associated with geological faults whose seismic risk is of particular concern to the nuclear facilities at the Hanford Nuclear Reservation (immediately northwest of the Tri-Cities) and major dams on the Columbia and Snake Rivers.[4]

Location and extent

Lake Keechelus Lake Kachess Lake Cle Elum Cle Elum Ellensburg Quincy Ephrata Moses Lake Othello Yakima Union Gap Wallula Gap The Dalles Hood River Tacoma Tri-Cities Mount Rainier Mount Saint Helens Rock Island Dam Wanapum Dam Priest Rapids Dam Ice Harbor Dam McNary Dam John Day Dam The Dalles Dam Bonneville Dam White River Manastash Ridge Umtanum Ridge Badger Mountain Beezley Hills Saddle Mountains Frenchman Hills Gable Mountain Yakima Ridge #Sedge Ridge Ahtanum Ridge Rattlesnake Hills Snipes Mountain Horse Heaven Hills #Simcoe Mountain #Bickleton Ridge Columbia Hills (Washington) #Paterson Ridge #Red Mountain Olympic-Wallowa Lineament #craton edge #Naneum-Hog Ranch Anticline
Shaded-relief map showing ridges of the Yakima Fold Belt of south-central Washington, mostly between Interstate 90 (red line) and the Columbia River (bottom). Red square in center is the city of Yakima, red rectangle at lower right is the Tri-Cities, red circles are various cities, triangles are the Mount Rainier, Mount Saint Helens, and Mount Adams volcanoes of the Southern Washington Cascades. Purple dashed line marks the approximate location of the Olympic-Wallowa Lineament (OWL), crossing the Columbia River at the Wallula Gap (lower-right). Orange dashed line is approximate location of edge of the North American craton. The smoothness of the central and eastern areas is due to infilling by volcanic flows of the Columbia River Basalts.

The topographical distinctness of the Yakima Folds (see the shaded-relief image) is due to their formation in a layer of lava flows and sedimentary deposits that have filled-in and generally smoothed the topographic surface of a large area of the Columbia Basin. The extent of these lava flows were limited to the west and north by the rising Cascade Mountains and the Wenatchee Mountains. The lava flows extend east well beyond the this image, but the Yakima Folds do not. The northern-most fold seen here[5] (Frenchman Hills) ends at the Potholes Reservoir, another (Saddle Mountains) terminates just south of there, near the town of Othello (red circle). South of the Tri-Cities the rampart of the Horse Heaven Hills extends for a short distance past the Columbia River. The ends of these ridges mark the edge of a block of continental crust (part of the North American craton, indicated by the dashed orange line) that has resisted the tectonic compression that formed the ridges.

The southernmost ridge of the Yakima Fold Belt is the Columbia Hills on the north side of the Columbia River. The pattern of folding continues with the Dalles-Umatilla Syncline just south of the Columbia River, and further into Oregon with the Blue Mountains anticline, which approximately parallels the Klamath-Blue Mountain Lineament that marks the southeastern edge of Siletzia (see geological map, below).

The Yakima Fold Belt is also located on, and the orientation and spacing of some of the Folds influenced by, the Olympic-Wallowa Lineament (OWL), a broad zone of linear topographical features (dashed yellow line) extending from the Olympic Peninsula in northwestern Washington to the Wallowa Mountains in northeastern Oregon.

Geology

It is the central portion of the Olympic-Wallowa Lineament, referred to as the Cle Elum-Wallula deformed zone (CLEW),[6] constising of a series of generally east-trending narrow asymmetrical anticlinal ridges and broad synclinal valleys formed by folding of Miocene Columbia River basalt flows and sediments.[7][2] In most parts of the belt the folds have a north vergence (Columbia Hills' south vergence is an exception) with the steep limb typically faulted by imbricate thrust faults.[2][8] Fold lengths range from 1 km to 100 km with wavelengths from several kilometers to 20 km.[9]

A graben underlies nearly the entire Yakima Fold Belt and has been subsiding since Eocene time, and continues to sink at a slow rate.[10]

A 2011 report found aeromagnetic, gravity, and paleoseismic evidence that the Yakima Fold Belt is linked to active Puget Sound faults.[11]

Geodesy

Geodetic studies of the Oregon Rotation show that Oregon is rotating about a point somewhat south of Lewiston, Idaho compressing the Yakima fold an average of 3 millimeters per year, and the Washington Pacific coast about 7 millimeters per year.[12]

Studies of the motion of the Yakima Fold Belt have been undertaken to evaluate seismic hazards at the Hanford Site.[13]

See also

Notes and sources

Notes

  1. ↑ Barnett et al. 2013.
  2. 1 2 3 Lidke 2002.
  3. ↑ Reidel, Martin & Petcovic 2003.
  4. ↑ Pratt 2012.
  5. ↑ Some researchers include structures north of this image.
  6. ↑ Reidel et al. 1989, p. 248 "The central part of ... [the] Olympic-Wallowa Lineament (OWL) passes through the central Yakima fold belt. This segment of the OWL is referred to as the Cle Elum-Wallula deformed zone (CLEW)..."
  7. ↑ Reidel et al. 1989.
  8. ↑ Reidel 2004, p. 9.
  9. ↑ Reidel, Martin & Petcovic 2003, p. 91.
  10. ↑ Reidel, Martin & Petcovic 2003, p. 95.
  11. ↑ Blakely et al. 2011.
  12. ↑ Wells et al. 2009 "...folding in the embayment is driven by the clockwise rotation of Oregon about a pole near the OR-WA-ID border, compressing Washington against slow-moving Canada. The folds fan westward from this pole of rotation, and shortening increases to the west to about 7.1 mm/yr between Astoria and Penticton, BC. Shortening across the YFB is about 3 mm/yr and decreases eastward to the Idaho border."
  13. ↑ Last et al. 2012.

Sources

Further reading

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