A Brief History of Lake Missoula Bottom Sediment Investigations Before 1970

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• 1899: The earliest mention of lake Missoula sediments I found is in a University of Montana Master's Thesis by Earl Douglass, The Neogene lake beds of western Montana and descriptions of some new vertebrates from the Loup Fork.  On page 4 he noted; There was also a large lake occupying the Bitter Root and Missoula valleys. Though I have not yet visited the region the lake beds are reported by Prof. M. J. Elrod and others farther to the north in the vicinity of Flathead lake. On pages 16-17, Douglass again noted: In the Missoula and Bitter Root valleys on the mountain sides and along the foot hills are level lines to small terraces, evidently shore lines, formed by dashing waves against the mountain side ... The lake beds lie in contact with all the older formations that occur in the western part of the state ...

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• 1910: In his first paper The Glacial Lake Missoula, Pardee stated ... the horizontally bedded clays, sands, and gravels that form the valley terraces or "bench lands," which bear a thin, clayey, fertile soil that as a rule is sharply defined from the underlying gravel and again on page 381, he stated Sediments that settled from this lake are believed to be the main source of the soil referred to on page 378 (sic, page 379)...

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• 1935: The bench-forming sequences of laminated and silt, clay, and minor sand deposits now widely recognized as deposits of Glacial Lake Missoula was informally named the Lake Missoula beds by Langton (1935).

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• 1942: In his now classic paper Unusual Currents in Glacial Lake Missoula, Montana, J. T. Pardee noted that some of deposits associated with the glacial lake are Light-colored varved silt, composed of glacial rock flour derived mostly from the lobes of Cordilleran ice, forms discontinuous terraces 50 to 100 feet high in most of the submerged basins. The silt is confined to the lower parts of the basins and thins out upslope at the height of the terraces which evidently mark its original upper limit.... In the Jocko Basin comparatively small  discontinuous terraces are composed of silt that came from glaciers washed by the arm of the lake in the upper Jocko Valley....Deposition of the silt apparently was limited to the lower parts of the basin ....owing to its higher specific gravity, slowing moving turbid water sinks and flows along the bottom without mixing with the overlying clarified water. In this same publication Pardee reported that no silt was deposited in Camas Prairie.

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• 1959: D. M. Sieja, a graduate student in geology at Montana State University, conducted the earliest known quantitative study of the Lake Missoula bottom sediments in 1959. The main purpose of his study was to document the clay mineralogy of the glacial Lake Missoula varves and to see if the clay minerals changed in quantity vertically in an exposure and laterally from one location to another across the Missoula Valley basin. In his study, Sieja found three varve types: simple, composite, and drainage; however, he made no detailed interpretation for their origin, other than to note that the clays probably settled to the lake floor through calm water, whose source were the Blackfoot and Rattlesnake valley glaciers.

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• 1969: In his last publication The Lake Missoula Floods and the Channeled Scabland,  J Harlen Bretz not only reviewed the outstanding evidence for repeated catastrophic outbursts of Lake Missoula, but also made the following comments about the Lake Missoula sediments: 

As far is known, the glacial lake's sediments are varved and contain randomly distributed, ice floated rock fragments. Future studies will begin with sections in postglacial stream trenches in floors of various lake-occupied valleys.

 

The shallower bays will have had complete emptying with each dam burst and may record currents. All parts of the lake must have been emptied whenever retreat of the Cordilleran ice sheet reestablished the preglacial Clark Fork and Columbia River drainage system and this provided for nonflood erosion of the lake bottom. If, however, an Okanogan lobe still blocks the Columbia, a shrunken remnant of Lake Missoula will linger in the deeper valleys near the site of the dam, and if Upper Grand Coulee's cataract has not yet breached the Columbia's southern wall, a Lake Columbia will extend eastward, possibly past the Colville lobe to join the shrunken Missoula.

 

Reconstruction of the Pend Oreille dam will produce another Lake Missoula and another varved clay deposit. Unconformities will separate every two such units.

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During an episode of glacial retreat and lake drainage, bogs and forests will invade the exposed lake floors. Return of lacustrine conditions will bury peat beds and tree stumps along unconformities. Leaching and oxidation will be added to the record of erosion and plant invasion.

 

Prior to the work I began during the fall of 1969 for my Senior Research paper at the University of Montana under Dr. David Alt, most of the evidence for drainings of glacial Lake Missoula was based on the work of Pardee and Bretz between 1910 and 1969. In contrast as seen from the above summaries, very little research was done within the glacial Lake Missoula basins and even less on the lake bottom sediments.

 

On the following pages I present the findings of my Senior Research Paper and Master's Thesis for the outstanding evidence of repeated lake drainings and subaerial exposure of the Lake Missoula glaciolacustrine sediments based on the study of two well-exposed road cuts at Ninemile Creek and in the Jocko Valley. Since my original study, the Ninemile Creek site has been studied by others (Curry, 1977; Waitt, 1980, 1984, 1985; Levish, 1997; Shaw, et al., 1999, Smith, 2006;  and Hanson, et al., 2012). 

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