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White Bluffs overlook (rhythmites exposed by the landslides)

View on map:46.631867°N 119.396063°W

Comments

Many landslides have occured along the bluffs.  Stop 11 in Baker et al. 

" River for ~50 km along the Hanford Reach (Fecht et al., 2004). The 150-m-tall bluffs consist of Miocene–Pliocene Ringold Formation deposits from the ancestral Columbia River and its tributaries (Reidel et al., 1992; Lindsey, 1996). The Ringold Formation accumulated in the Pasco Basin until ca. 3.4 Ma (DOE, 1988). Since then, the Columbia River and Quaternary megaflooding have removed up to 180 m of Ringold deposits from the center of the basin, leaving behind this high erosional escarpment (DOE, 2002). Even here, at this high overview point, the largest Ice Age floods would have been 90 m overhead! Evidence for both modern and ancient landslides is visible from here (Hays and Schuster, 1987; Bjornstad, 2006a). Most landslides along the White Bluffs occur on steep, unstable slopes where water is suddenly added. Recent landslides, beginning in the early 1980s, have resulted from water seeping out of several manmade lakes and unlined canals located just east of the bluffs (Bjornstad, 2006a). Many examples of this type of landslide occur within the Wiehl Ranch landslide complex, which is best seen upriver from here to the northwest. There is evidence immediately below the bluffs for an old landslide (Bjornstad, 2006a). This landslide, with rounded and weathered blocks, likely occurred 14,000–15,000 yr B.P., soon after one of the last Ice Age floods. Unlike modern local landslides, no water is seeping out along the slide, suggesting the water that created this prehistoric slide is no longer present. Another landslide that may be associated with the Ice Age floods can be seen across the river along the north side of Gable Mountain (Fecht, 1978)." 

Description


Missoula Floods

The Missoula Floods (also known as the Spokane Floods or the Bretz Floods) refer to the cataclysmic floods that swept periodically across eastern Washington and down the Columbia River Gorge at the end of the last ice age. The glacial flood events have been researched since the 1920s. These glacial lake outburst floods were the result of periodic sudden ruptures of the ice dam on the Clark Fork River that created Glacial Lake Missoula. After each ice dam rupture, the waters of the lake would rush down the Clark Fork and the Columbia River, flooding much of eastern Washington and the Willamette Valley in western Oregon. After the rupture, the ice would reform, creating Glacial Lake Missoula again.

References

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