Lake Missoula Research Articles

Lake Missoula and Its Floods

The city of Spokane lies astride the Spokane River, some 40 miles from its origination near Coeur d’Alene, Idaho. The convention center and hotel, site of the 65th annual meeting of SRM, are located right along the river, creating a beautiful and even idyllic setting. These qualities make it even harder to imagine a long-ago day when a miles-wide wall of water, measuring as much as 500 feet high, bore down on this site. Hours before, a great ice dam on glacial Lake Missoula (present-day Clark Fork River) had failed. The dam was as much as 2,500 feet in height, impounded a lake up to 2,000 feet deep, extended east in the intermontane valleys for 200 miles, and covered some 3,000 square miles. It probably contained over 500 cubic miles of water, approximating half the volume of Lake Michigan. It is now generally agreed that catastrophic fl oods, in accordance with prevailing ice age conditions, repeatedly issued from Lake Missoula, probably on the order of several tens of times. Geologists estimate that the latest and last of the fl oods occurred about 13,000 years ago, creating the observable effects on the ground today, while largely obscuring the effects of earlier fl oods. Most students of the fl oods support that this particular event and its effects should be named “Bretz’s Flood” after the early geologist J Harlen Bretz, who fi rst recognized in 1919 the effects of catastrophic fl ooding on the Columbia drainage of southeastern Washington, as well as the Columbia River Gorge, the Portland-Vancouver Basin, and the Willamette Valley of Oregon. Over the 2 million years of the last ice age, four major glaciations advanced into what is now the northwestern United States. The last of these, the Wisconsin glaciation, left clear evidence of its effects, while likely obscuring most of the evidence of earlier fl ooding. It is near-certain, however, that each of the many fl oods inundated thousands of square miles in what is now central and southeastern Washington to depths of hundreds of feet. Later study also showed that the many fl oods likely shared the same provenance, that is, the same cause and effect. Piecing together the available evidence, it appears that the full glacial climate was cold and dry, with strong winds that redistributed soil materials to the southeastern quadrant of the Columbia Basin. These processes created what is today called the Palouse, an area of wind-deposited silts (loess) over the underlying basalt that had literally oozed out of the earth over previous untold centuries. The winds created dune-like deposits of variable orientation and depth that today make up fertile farmland in southeastern Washington and adjacent Idaho. Bretz’s Flood followed the path of the many earlier fl oods and recreated the effects over thousands of square miles in the Columbia Basin. These can briefl y be considered in four major categories: 1) the channeled scablands, 2) the river canyon, 3) the Grand Coulee, and 4) Lake Lewis.

A Seismic Landstreamer Survey at the Hanford Site, Washington, U.S.A

Research Article| August 01, 2011 A Seismic Landstreamer Survey at the Hanford Site, Washington, U.S.A EMMA R. HYDE; EMMA R. HYDE Search for other works by this author on: GSW Google Scholar MARVIN A. SPEECE; MARVIN A. SPEECE 1. Corresponding author email: mspeece@mtech.edu Search for other works by this author on: GSW Google Scholar CURTIS A. LINK; CURTIS A. LINK Search for other works by this author on: GSW Google Scholar TED R. REPASKY; TED R. REPASKY Search for other works by this author on: GSW Google Scholar MICHAEL D. THOMPSON; MICHAEL D. THOMPSON Search for other works by this author on: GSW Google Scholar STEVEN F. MILLER STEVEN F. MILLER Search for other works by this author on: GSW Google Scholar Environmental & Engineering Geoscience (2011) 17 (3): 227–239. https://doi.org/10.2113/gseegeosci.17.3.227 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation EMMA R. HYDE, MARVIN A. SPEECE, CURTIS A. LINK, TED R. REPASKY, MICHAEL D. THOMPSON, STEVEN F. MILLER; A Seismic Landstreamer Survey at the Hanford Site, Washington, U.S.A. Environmental & Engineering Geoscience 2011;; 17 (3): 227–239. doi: https://doi.org/10.2113/gseegeosci.17.3.227 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyEnvironmental & Engineering Geoscience Search Advanced Search Abstract The Hanford Nuclear Reservation, located in south-central Washington, U.S.A., is the site of a large-scale and ongoing environmental cleanup effort, which includes the remediation of radionuclide- and chemical-contaminated groundwater. Identification of preferential pathways for groundwater contaminant flow near the top of the Columbia River Basalt Group is critical for the groundwater cleanup effort. High-resolution shallow seismic surveys were conducted using a 96 channel landstreamer with gimbaled geophones on the Hanford Central Plateau near the Gable Gap area of the Hanford Nuclear Site. A primary goal of the surveys was to demonstrate the feasibility of using a landstreamer to image the top of the basalt. We were able to collect an average of 606 m of profile line at 2 m station spacing per day, for a total of 12,722 m. The survey successfully imaged the top of the basalt and demonstrated that a landstreamer with gimbaled geophones can provide quality seismic data in this area. We found that the top of the basalt ranged in depth from 30 to 100 m deep, and it displays a rugose character caused by faults and erosion from turbulent flood waters of ice-age floods originating from Glacial Lake Missoula or from later ancestral Columbia River flooding. Erosional features present in the basalt might provide an avenue for mixing of water between the supra-basalt and the basalt-confined aquifers, and faults might provide pathways for groundwater flow. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pre-and post-Missoula flood geomorphology of the Pre-Holocene ancestral Columbia River Valley in the Portland forearc basin, Oregon and Washington, USA

Geomorphic landscape development in the pre-Holocene ancestral Columbia River Valley (1–5km width) in the Portland forearc basin (~50km length) is established from depositional sequences, which pre-date and post-date the glacial Lake Missoula floods. The sequences are observed from selected borehole logs (150 in number) and intact terrace soil profiles (56 in number) in backhoe trenches. Four sequences are widespread, including (1) a vertically aggraded Pleistocene alluvial plain, (2) a steep sided valley that is incised (125–150m) into the Pleistocene gravel plain, (3) Missoula flood terraces (19–13ka) abandoned on the sides of the ancestral valley, and (4) Holocene flooding surfaces (11–8ka) buried at 70–30m depth in the axial Columbia River Valley. Weathering rims and cementation are used for relative dating of incised Pleistocene gravel units. Soil development on the abandoned Missoula flood terraces is directly related to terrace deposit lithology, including thin Bw horizons in gravel, irregular podzols in sand, and multiple Bw horizons in thicker loess-capping layers. Radiocarbon dating of sand and mud alluvium in the submerged axial valley ties Holocene flooding surfaces to a local sea level curve and establishes Holocene sedimentation rates of 1.5cmyear−1 during 11–9ka and 0.3cmyear−1 during 9–0ka. The sequences of Pleistocene gravel aggradation, river valley incision, cataclysmic Missoula flooding, and Holocene submergence yield complex geomorphic landscapes in the ancestral lower Columbia River Valley.

Lake Missoula and Its Floods

Lake Missoula and Its Floods

Isotopically‐depleted late Pleistocene groundwater in Columbia River Basalt aquifers: Evidence for recharge of glacial Lake Missoula floodwaters?

Late Pleistocene outburst flooding of ice‐dammed glacial Lake Missoula, and possible discharge from the Cordilleran Ice Sheet (CIS), catastrophically altered the northwestern United States landscape, yet little is known about potential infiltration of flood waters into the subsurface. This study provides compelling evidence for the presence of late Pleistocene CIS‐related recharge waters in the Columbia River Basalt Aquifers (CRBAs) in central Washington. CRBA groundwaters with corrected 14C ages from 15.7 and 33.3 k yrs BP (during periods of flood events) have anomalously low δ18O values (−18.9 to −17.6‰), compared to late Pleistocene soil waters (−16.1 to −13.4‰) and modern precipitation in the region (average −15.9‰), consistent with CIS‐related meltwater recharge. These results have implications for our understanding of megaflood phenomena on earth and Mars.

Paleohydraulic reconstruction of the largest Glacial Lake Missoula draining(s)

Glacial Lake Missoula (GLM) was the source of Earth’s largest known peak flood discharges onto the Channeled Scabland, northwestern United States. The original studies of GLM were based on geomorphological mapping of lake sediments and shorelines. More recently, studies have emphasized the computational fluid dynamics of downstream megaflood routing and characteristics in the Channeled Scabland and adjacent areas. However, actual details of the lake-draining processes GLM have received little scientific attention. In this paper, we employ two-dimensional hydraulic modelling to understand the paleoflow conditions for different scenarios of draining GLM at its highest stands. Values are calculated for three GLM drainage hydrographs (2.6; 13; 17 × 10 6 m 3 s −1) that previous studies had estimated for outlet flows. Consistent with regional mapping and with the original interpretation of fluvial geomorphology by other studies, the modelling shows that lake silt sequences in the gorges of GLM must postdate the most highly energetic outburst events from the lake. This is because the flows generated in the lake by megaflood outflows are sufficiently energetic to erode any accumulated silt deposits. In contrast, the gravels underlying the silts in these zones include boulder-sized clasts, large-scale cross stratification, and 70–100 m-high bars forms, all of which indicate very high-energy flood flow conditions. The modelling also shows that the paleohydraulic conditions which developed in the lake basin during the largest megaflood outflows would be capable of accounting for the observed bedrock scour at Rainbow Lake Pass, various “high eddy deposits” (eddy bars of flood gravel) in gorges, and the “giant ripple marks” (subaqueous gravel dunes) that were classically described in the 1940s. Previous studies interpreted the glacial lake silt/rhythmites and related deposits, such as the Ninemile Section, as evidence for numerous fillings and drainings of GLM. Our modelling suggests that these inferred events must have been relatively low in energy and magnitude relative to the earlier outburst(s) that emplaced the flood gravels, subaqueous gravel dunes, and scabland-like erosion surfaces.

Lake Missoula and the Scablands, Washington, USA

Gigantic floods that, for just a few days, had flow rates many times greater than the combined flows of all the other rivers of the world put together. Sounds ridiculous, and it's almost inconceivable, but it's real, and it all happened at the end of the last Ice Age. The water came from Lake Missoula, which exists no more, but the effects are still to be seen in the landscapes, most notably in the vast scablands of eastern Washington.

Simulations of cataclysmic outburst floods from Pleistocene Glacial Lake Missoula

Using a flow domain that we constructed from 30 m digital-elevation model data of western United States and Canada and a two-dimensional numerical model for shallow-water flow over rugged terrain, we simulated outburst floods from Pleistocene Glacial Lake Missoula. We modeled a large, but not the largest, flood, using initial lake elevation at 1250 m instead of 1285 m. Rupture of the ice dam, centered on modern Lake Pend Oreille, catastrophically floods eastern Washington and rapidly fills the broad Pasco, Yakima, and Umatilla Basins. Maximum flood stage is reached in Pasco and Yakima Basins 38 h after the dam break, whereas maximum flood stage in Umatilla Basin occurs 17 h later. Drainage of these basins through narrow Columbia gorge takes an additional 445 h. For this modeled flood, peak discharges in eastern Washington range from 10 to 20 × 10 6 m 3 /s. However, constrictions in Columbia gorge limit peak discharges to 6 m 3 /s and greatly extend the duration of flooding. We compare these model results with field observations of scabland distribution and high-water indicators. Our model predictions of the locations of maximum scour (product of bed shear stress and average flow velocity) match the distribution of existing scablands. We compare model peak stages to high-water indicators from the Rathdrum-Spokane valley, Walulla Gap, and along Columbia gorge. Though peak stages from this less-than-maximal flood model attain or exceed peak-stage indicators along Rathdrum-Spokane valley and along Columbia gorge, simulated peak stages near Walulla Gap are 10–40 m below observed peak-stage indicators. Despite this discrepancy, our match to field observations in most of the region indicates that additional sources of water other than Glacial Lake Missoula are not required to explain the Missoula floods.

The Channeled Scabland: A Retrospective

The Channeled Scabland of east-central Washington in the United States is a complex of anastomosing rock-cut fluvial channels, cataracts, loess islands, rock basins, broad gravel deposits, and immense gravel bars. In the 1920s, J Harlen Bretz demonstrated that the Channeled Scabland formed by cataclysmic erosion and deposition from Pleistocene megaflooding derived from the margins of the Cordilleran Ice Sheet, particularly glacial Lake Missoula in western Montana and northern Idaho. Studies of this region and the high-energy flood processes that generated it are stimulating (a) discoveries of similar megaflood-related landscapes around the world and on Mars, (b) enhanced understanding of the processes involved in the fluvial erosion of bedrock, and (c) the use of paleoflood indicators for understanding the magnitudes and frequency of flooding.

Pleistocene megafloods in the northeast Pacific

Massive discharges of freshwater from the glacial lake Missoula to the northeast Pacific Ocean are thought to have sculpted the Channeled Scablands of eastern Washington and debouched via the Columbia River near 46°N. The dynamics and timing of these events and their impact on northeast Pacific circulation remain uncertain. Here we date marine records of anomalous freshwater inputs to the ocean based on freshwater diatoms, oxygen isotopes in foraminifera, and radiocarbon data. Low-salinity plumes from the Columbia River reduced sea-surface salinities by as much as 6 psu (practical salinity units) more than 400 km away between 16 and 31 cal (calendar) ka B.P. Anomalously high abundances of freshwater diatoms in marine sediments from the region precede generally accepted dates for the existence of glacial Lake Missoula, implying that large flooding or freshwater routing events were common during the advance of the Cordilleran Ice Sheet and that such events require multiple sources.

The Spokane Flood debates: historical background and philosophical perspective

Abstract The 1920s–1930s debates over the origin of the ‘Channeled Scabland’ landscape of eastern Washington, northwestern USA, focused on the cataclysmic flooding hypothesis of J Harlen Bretz. During the summer of 1922, Bretz began leading field parties of advanced University of Chicago students into the region. In his first paper, published in the Bulletin of the Geological Society of America , Bretz took special care not to mention cataclysmic origins. However, in a subsequent paper in the Journal of Geology , to the editorial board of which he had recently been added, Bretz formally described his hypothesis that an immense late Pleistocene flood, which he named the ‘Spokane Flood’, had derived from the margins of the nearby Cordilleran Ice Sheet. This cataclysm neatly accounted for numerous interrelated aspects of the Channeled Scabland landscape and nearby regions. Nevertheless, the geological community largely resisted Bretz's hypothesis for decades, despite his enthusiastic and eloquent defence thereof. Resolution of the controversy came gradually, initially through the recognition by J. T. Pardee of a plausible source for the flooding: ice-dammed Pleistocene glacial Lake Missoula in northern Idaho and western Montana. Eventually, by the 1960s, the field evidence for cataclysmic flooding became overwhelming, and physical processes were found to be completely consistent with that evidence. The controversy is of philosophical interest in regard to its documentation of the attitudes of geologists toward hypotheses, which illustrate aspects of geological reasoning that are distinctive in degree from those of other sciences.

Cataclysmic Scabland flooding: Insights from a simple depth-averaged numerical model

This work presents numerical assessments of possible routing paths for the reported late Pleistocene Missoula floods, which involved Earth's largest known peak discharges of freshwater. For our numerical model, we adopt the diffusion wave approximation of the shallow-water equation with the empirical Manning coefficient. This simplification is required because (1) most previous studies are one-dimensional or analytical studies based on simple equations, so that our two-dimensional expansion is a natural step towards more sophisticated models; (2) a simple model can easily incorporate the effect of complicated topography; and (3) lower computational costs permit a broader exploration of parameters. Important and new insights obtained from this work include: (1) numerically, we confirm the presence of the Cordilleran Ice Sheet at the time of the Missoula floods; (2) floods with relatively small peak discharges cannot inundate some major reaches, including the Cheney Palouse Scabland Tract; (3) deposits indicative of multiple floods are mostly confined in the locations that can be inundated by relatively lower peak flood discharges; and (4) although Lake Missoula glacial lake failure scenario can reasonably reproduce extensive water coverage, the best fit result to the geological evidence of flooding is obtained when the total water volume is three times larger than that estimated for Glacial Lake Missoula. The above results do not negate previous works, but indicate the need for further detailed field investigation and more sophisticated modeling in order to pursue further understanding of the complex behavior of megaflooding in the Channeled Scabland.

Stratigraphic evidence for multiple drainings of glacial Lake Missoula along the Clark Fork River, Montana, USA

Glacial Lake Missoula, a source of Channeled Scabland flood waters, inundated valleys of northwest Montana to altitudes of ∼ 1265 m and to depths of >600 m, as evidenced by shorelines and silty lacustrine deposits. This study describes previously unrecognized catastrophic lake-drainage deposits that lie stratigraphically beneath the glacial-lake silts. The unconsolidated gravelly flood alluvium contains imbricated boulder-sized clasts, cross-stratified gravel with slip-face heights of 2–> 35 m, and 70- to 100-m-high gravel bars which all indicate a high-energy, high-volume alluvial environment. Gravel bars and high scablands were formed by catastrophic draining of one or possibly more early, high lake stands (1200–1265 m). Most glacial-lake silt, such as the Ninemile section, was deposited stratigraphically above the earlier deposits, represents a lower lake stand(s) (1050–1150 m), and was not deposited in lake(s) responsible for the highest discharge events. The glaciolacustrine silt-covered benches are incised by relict networks of valleys formed during the drainage of the last glacial lake. Significant erosion associated with the last lake draining was confined to the inner Clark Fork River canyon.

Hydro plant planned for British Columbia

Immense late Wisconsin floods from glacial Lake Missoula drowned the Wenatchee reach of Washington's Columbia valley by different routes. The earliest debacles, nearly 19,000 cal yr BP, raged 335 m deep down the Columbia and built high Pangborn bar at Wenatchee. As advancing ice blocked the northwest of Columbia valley, several giant floods descended Moses Coulee and backflooded up the Columbia past Wenatchee. Ice then blocked Moses Coulee, and Grand Coulee to Quincy basin became the westmost floodway. From Quincy basin many Missoula floods backflowed 50 km upvalley to Wenatchee 18,000 to 15,500 years ago. Receding ice dammed glacial Lake Columbia centuries more—till it burst about 15,000 years ago. After Glacier Peak ashfall about 13,600 years ago, smaller great flood(s) swept down the Columbia from glacial Lake Kootenay in British Columbia. The East Wenatchee cache of huge fluted Clovis points had been laid atop Pangborn bar after the Glacier Peak ashfall, then buried by loess. Clovis people came five and a half millennia after the early gigantic Missoula floods, two and a half millennia after the last small Missoula flood, and two millennia after the glacial Lake Columbia flood. People likely saw outburst flood(s) from glacial Lake Kootenay.

Hydro plant planned for British Columbia

Immense late Wisconsin floods from glacial Lake Missoula drowned the Wenatchee reach of Washington's Columbia valley by different routes. The earliest debacles, nearly 19,000 cal yr BP, raged 335 m deep down the Columbia and built high Pangborn bar at Wenatchee. As advancing ice blocked the northwest of Columbia valley, several giant floods descended Moses Coulee and backflooded up the Columbia past Wenatchee. Ice then blocked Moses Coulee, and Grand Coulee to Quincy basin became the westmost floodway. From Quincy basin many Missoula floods backflowed 50 km upvalley to Wenatchee 18,000 to 15,500 years ago. Receding ice dammed glacial Lake Columbia centuries more—till it burst about 15,000 years ago. After Glacier Peak ashfall about 13,600 years ago, smaller great flood(s) swept down the Columbia from glacial Lake Kootenay in British Columbia. The East Wenatchee cache of huge fluted Clovis points had been laid atop Pangborn bar after the Glacier Peak ashfall, then buried by loess. Clovis people came five and a half millennia after the early gigantic Missoula floods, two and a half millennia after the last small Missoula flood, and two millennia after the glacial Lake Columbia flood. People likely saw outburst flood(s) from glacial Lake Kootenay.

120 MW hydro plant planned for British Columbia

Immense late Wisconsin floods from glacial Lake Missoula drowned the Wenatchee reach of Washington's Columbia valley by different routes. The earliest debacles, nearly 19,000 cal yr BP, raged 335 m deep down the Columbia and built high Pangborn bar at Wenatchee. As advancing ice blocked the northwest of Columbia valley, several giant floods descended Moses Coulee and backflooded up the Columbia past Wenatchee. Ice then blocked Moses Coulee, and Grand Coulee to Quincy basin became the westmost floodway. From Quincy basin many Missoula floods backflowed 50 km upvalley to Wenatchee 18,000 to 15,500 years ago. Receding ice dammed glacial Lake Columbia centuries more—till it burst about 15,000 years ago. After Glacier Peak ashfall about 13,600 years ago, smaller great flood(s) swept down the Columbia from glacial Lake Kootenay in British Columbia. The East Wenatchee cache of huge fluted Clovis points had been laid atop Pangborn bar after the Glacier Peak ashfall, then buried by loess. Clovis people came five and a half millennia after the early gigantic Missoula floods, two and a half millennia after the last small Missoula flood, and two millennia after the glacial Lake Columbia flood. People likely saw outburst flood(s) from glacial Lake Kootenay.

Extensive Deposits on the Pacific Plate from Late Pleistocene North American Glacial Lake Outbursts

Abstract One of the major unresolved issues of the Late Pleistocene catastrophic‐flood events in the northwestern United States (e.g., from glacial Lake Missoula) has been what happened when the flood discharge reached the ocean. This study compiles available 3.5‐kHz high‐resolution and airgun seismic reflection data, long‐range sidescan sonar images, and sediment core data to define the distribution of flood sediment in deepwater areas of the Pacific Ocean. Upon reaching the ocean at the mouth of the Columbia River near the present‐day upper continental slope, sediment from the catastrophic floods continued flowing downslope as hyperpycnally generated turbidity currents. The turbidity currents resulting from the Lake Missoula and other latest Pleistocene floods followed the Cascadia Channel into and through the Blanco Fracture Zone and then flowed west to the Tufts Abyssal Plain. A small part of the flood sediment, which was stripped off the main flow at a bend in the Cascadia Channel at its exit point f...

Paleomagnetic and tephra evidence for tens of Missoula floods in southern Washington

Paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from Glacial Lake Missoula, Montana, entered Washington’s Yakima and Walla Walla Valleys during the last glaciation. In these valleys, the field evidence for hiatuses between floods is commonly subtle. However, paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at Zillah, Touchet, and Burlingame Canyon display consistent secular variation that correlates serially both within and between sections. The secular variation may further correlate with paleomagnetic data from Fish Lake, Oregon, and Mono Lake, California, for the interval 12,000‐17,000 14 C yr B.P. Deposits of two successive floods are separated by two tephras derived from Mount St. Helens, Washington. The tephras differ in age by decades, indicating that a period at least this long separated two successive floods. The beds produced by these two floods are similar to all of the 40 beds in the slack-water sediment sequence, suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years.

Number and size of last-glacial Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon

Field evidence and radiocarbon age dating, combined with hydraulic flow modeling, provide new information on the magnitude, frequency, and chronology of late Pleistocene Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon. More than 25 floods had discharges of 1.0 106 m3/s. At least 15 floods had discharges of 3.0 106 m3/s. At least six or seven had peak discharges of 6.5 106 m3/s, and at least one flood had a peak discharge of 10 106 m3/s, a value consistent with earlier results from near Wallula Gap, but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near Crown and Mitchell Points in the Columbia River Gorge. Stratigraphy and geomorphic position, combined with 25 radiocarbon ages and the widespread occurrence of the ca. 13 ka (radiocarbon years) Mount St. Helens set-S tephra, show that most if not all the Missoula flood deposits exposed in the study area were emplaced after 19 ka (radiocarbon years), and many were emplaced after 15 ka. More than 13 floods perhaps postdate ca. 13 ka, including at least two with discharges of 6 106 m3/s. From discharge and stratigraphic relationships upstream, we hypothesize that the largest flood in the study reach resulted from a Missoula flood that predated blockage of the Columbia River valley by the Cordilleran ice sheet. Multiple later floods, probably including the majority of floods recorded by fine- and coarse-grained deposits in the study area, resulted from multiple releases of glacial Lake Missoula that spilled into a blocked and inundated Columbia River valley upstream of the Okanogan lobe and were shunted south across the Channeled Scabland.

Glacial Lake Missoula and Its Humongous Floods. By David Alt. Missoula, Mont.: Mountain, 2001. 208 pages, 58 colored maps and illustrations, 45 black‐and‐white photographs. $15.00 paper.

<i>Glacial Lake Missoula and Its Humongous Floods</i>. By David Alt. Missoula, Mont.: Mountain, 2001. 208 pages, 58 colored maps and illustrations, 45 black‐and‐white photographs. $15.00 paper.