Talk:Touchet Formation

Untitled
This is my first nomination of an article as a Good Article. Please grade vigorously. Thanks - Williamborg (Bill) 23:03, 6 September 2009 (UTC)

Star category rating
Somebody ought to put a "Star" category rating on this article, ..with Nobody, ..Anywhere, ...and Anyhow having anything to say about it, except other ideas for improvements, additions, or other connected-ness to other articles. (a comment from the extremeSW SonoranDesert of SWestern Arizona).. -Mmcannis 13:58, 13 January 2007 (UTC)

Bretz’s cataclysmic flood
In the summer of 1922, and for the next seven years, Bretz conducted field research of the Columbia River Plateau. He had been interested in unusual erosion features in the area since 1910 after seeing a newly published topographic map of the Potholes Cataract. Bretz coined the term Channeled Scablands in 1923 to describe the area near the Grand Coulee, where massive erosion had cut through basalt deposits. Bretz published a paper in 1923, arguing that the channeled scablands in Eastern Washington were caused by massive flooding in the distant past. This view, which was seen as arguing for a Catastrophic explanation of the geology, was against the prevailing view of uniformitarianism, and Bretz's views were initially discredited. The Geological Society of Washington, D.C invited the young Bretz to present his previously published research at a January 12, 1927 meeting where several other geologists presented competing theories. Another geologist at the meeting, J.T. Pardee, had worked with Bretz and had evidence of an ancient glacial lake that lent credence to Bretz's theories. Bretz defended his theories and this kicked off an acrimonious forty year debate over the origin of the Scablands. Both Pardee and Bretz continued their research over the next 30 years, collecting and analyzing evidence that led him toidentify Lake Missoula as the source of the Spokane Flood and creator of the Channeled Scablands.

Wiatt’s multiple flood hypothesis
Wiatt extended Bretz argument, arduing for a sequence of multiple floods — 40 or more. Wiatt's proposal was based mainly on analysis from glacial lake bottom deposits in Ninemile Creek and the flood deposits in Burlingame Canyon. HIs most compelling argument was that the Touchet bed deposits from two successive floods were found to be separated by two layers of volcanic ash (tephra) with the ash separated by a fine layer of windblow dust deposits, located in a thin layer located between sediment layers ten rhythmites below the top of the Touchet beds (see picture). The two layers of volcanic ash are separated by 1-10 cm of airborne nonvolcanic silt. The tephra is comprised of Mount St. Helens ash that fell in eastern Washington. By analogy, since there were 40 layers with comparable characteristics at Burlingame Canyon, Wiatt argued they all could be considered to have similar seperation in deopsition time.

Continuing controversy
The controversy whether the Channeled Scabland landforms were formed mainly by multiple periodic floods or by a single grand-scale cataclysmic flood from late Pleistocene Glacial Lake Missoula or from an unidentified Canadian source continued through 1999. Shaw’s team reviewed the sedimentary sequences of the Touchet beds and concluded that the sequences do not automatically imply multiple floods separated by decades or centuries. Rather, they proposed that sedimentation in the Glacial Lake Missoula basin was the result of jökulhlaups draining into Lake Missoula from British Columbia to the north. Further, Shaw’s team proposed the scabland flooding might have partially originated from an enormous subglacial reservoir that extended over much of central British Columbia, particularly including the Rocky Mountain Trench, which may have discharged by several paths including one through Lake Missoula. This discharge, if occurring concurrently with the breach of the Lake Missoula ice dam, would have provided significantly larger volumes of water. Further, Shaw and team proposed that the rhythmic Touchet beds are the result of multiple pulses, or surges, within a single larger flood.

In 2000, Komatsu’s team simulated the floods numerically with a 3-dimensional hydraulic model. They based the discharge rate from the Spokane Valley–Rathdrum Prairie immediately downstream of Glacial Lake Missoula on a number of previous estimates which placed the maximum discharge of 17 × 106m3/s and total amount of water discharged (2184 km3) equal to the maximum estimated volume of Lake Missoula. Neglecting erosion effects, their simulated water flow was based on modern-day topography. Their major findings were that the calculated depth of water in each flooded location except for the Spokane Valley–Rathdrum Prairie was shallower than the field evidence showed. For example, their calculated water depth at the Pasco Basin–Wallula Gap transition zone is about 190 m, significantly less than the 280–300 m flood depth indicated by high-water marks. They concluded that a flood of ~106m3 could not have made the observed high-water marks.

In comment on the Komatsu analysis, Atwater’s team observed that there is substantial evidence for multiple large floods, including evidence of mud cracks and animal burrows in lower layers which were filled by sediment from later floods. Further, evidence for multiple flood flows up side arms of Glacial Lake Columbia spread over many centuries have been found. They also pointed out that the discharge point from Lake Columbia varied with time, originally flowing across the Waterville Plateau into Moses Coulee but later, when the Okanagon lobe blocked that route, eroding the Grand Coulee to discharge there as a substantially lower outlet. The Komatsu analysis does not evaluate the impact of the considerable erosion observed in this basin during the flood (or floods) – hence the assumption that the flood hydraulics can be modeled using modern-day topography is an area which warrants further consideration – earlier narrower constrictions at places such as Wallula Gap and through the Columbia Gorge could be expected to produce higher flow resistance and correspondingly higher floods.

The current understanding
The dating for Wiatt’s proposed separation of layers into sequential floods has been supported by subsequent paleomagnetism studies, which supports a 30-40 year interval between depositions of Mount St. Helens’ ash, and hence flood events, but do not preclude an up to 60 year interval. Offshore deposits on the bed of the Pacific at the mouth of the Columbia River include 120 meters of material deposited over a several thousand year period that corresponds to the period of multiple scabland floods seen in the Touchet Beds. Based on Wiatt's identifiecation of 40 floods, this would give an average separation between floods of 50 years.

Although these sources provide support for temporal separation of floods, they do not definitively identify the source of water for the floods, which remains an open question.


 * This is great stuff but is clearly a new article. I would welcome a single paragraph summarizing this, as it seems to be very important, with a link to the new main article. I also think there must be other articles on catastrophic floods on wikipedia that this text could go into so best to check around before creating one. Polargeo (talk) 07:05, 17 November 2009 (UTC)


 * Turned out to be a very fascinating topic, but you are right - the bulk of this belongs somewhere else. I'll do some research and figure out where it goes - perhaps the Missoula Floods article - perhaps a new article. Also need to do more research to understand the current literature, since it appears the two schools may still be debating whether the floods all originated from Glacial Lake Missoula or some originated from Candadian sources. Thanks - Williamborg (Bill) 15:47, 17 November 2009 (UTC)
 * In fact I think this does need to be included for GA so we are not there yet but as I mentioned definitely only a summary paragraph with a link to the major article and not in its full detail here. Also answering Awickert's points (not necessarily incorporating them all) before rating as GA. This is near to being GA so I will keep it on hold but I don't want to do this indef. Polargeo (talk) 16:30, 17 November 2009 (UTC)
 * I agree with Polargeo; the material that Williamborg put together here is fantastic (and was fantastically-quickly assembled) but the majority should go somewhere else. This is a very interesting topic in North American geology, so maybe we could even create some kind of template box to link the related articles together. I have not finished combing through the article for GA-status, but it seems to be very close if not already there. Awickert (talk) 02:38, 18 November 2009 (UTC)
 * Added to the Missoula Flood discussion. Williamborg (Bill) 03:21, 10 July 2011 (UTC)