Cataclysmic Late pleistocene flooding from glacial Lake Missoula: A review

Quaternary Science Reviews, Vol. 4, pp. 1-41, 1985.

0277 3791/85 $0.00 + .5(1 Copyright © 1985 Pergamon Press Ltd.

Printed in Great Britain. All rights reserved.

CATACLYSMIC LATE PLEISTOCENE FLOODING FROM GLACIAL LAKE MISSOULA: A R E V I E W

V i c t o r R. B a k e r

Department of Geosciences, University of Arizona, Tucson, Arizona 85721, U.S.A. and Russell C. B u n k e r

Sweet, Edwards and Associates, Inc., 208 Church Street, Kelso, Washington 98626, U.S.A.

Late Wisconsin floods from glacial Lake Missoula occurred between approximately 16 and 12 ka BP. Many floods occurred; some were demonstrably cataclysmic. Early studies of Missoula flooding centered on the anomalous physiography of the Channeled Scabland, which J. Harlen Bretz hypothesized in 1923 to have developed during a debacle that he named 'The Spokane Flood'. Among the ironies in the controversy over this hypothesis was a mistaken view of uniformitarianism held by Bretz's adversaries. After resolution of the scabland's origin by cataclysmic outburst flooding from glacial Lake Missoula, research since 1960 emphasized details of flood magnitudes, frequency, routing and number. Studies of flood hydraulics and other physical parameters need to utilize modern computerized procedures for flow modeling, lake-burst simulation, and sediment-transport analysis. Preliminary simulation models indicate the probability of multiple Late Wisconsin j6kulhlaups from Lake Missoula, although these models predict a wide range of flood magnitudes. Major advances have been made in the study of low-energy, rhythmically bedded sediments that accumulated in flood slack-water areas. The 'forty floods' hypothesis postulates that each rhythmite represents the deposition in such slack-water areas of separate, distinct cataclysmic floods that can be traced from Lake Missoula to the vicinity of Portland, Oregon. However, the hypothesis has numerous unsubstantiated implications concerning flood magnitudes, sources, routing and sedimentation dynamics. There were multiple great Late Wisconsin floods in the Columbia River system of the northwestern United States. Studies of high-energy, high altitude flood deposits are necessary to evaluate the magnitudes of these floods. Improved geochronologic studies throughout the immense region impacted by the flooding will be required to properly evaluate flood frequency. The cataclysmic flood concept championed by J. Harlen Bretz continues to stimulate exciting and controversial research.

2

V.R. Baker and R.C. Bunker

INTRODUCTION The Columbia River system of the northwestern United States (Fig. l) experienced a phase of cataclysmic flooding during Late Wisconsin time that represents the most spectacular phenomenon of the Quaternary (Baker, 1981). Flooding resulted from outbursts of ice-dammed glacial Lake Missoula, from an overspill of Lake Bonneville (Malde, 1968), and probably from j6kulhlaups of other ice-dammed lakes in the Columbia system. A preliminary estimate of the maximum Lake Missoula outflow discharge, close to its breakout point, is 21.3 × 106 m3/sec (Baker, 1973). This is approximately twenty times greater than the average worldwide runoff of 1.1 × 106 m3/sec estimated by Durum et al. (1960). The global significance of the phenomenon is further elucidated by its effects on the abyssal sea floor off the mouth of the Columbia River (Griggs et al., 1970). The history of cataclysmic flood studies for the Columbia River system is one of scientists recognizing anomalous features and developing hypotheses to explain them. Early studies centered on physiographic relationships (Plate 1); the resolution of the cataclysmic flood hypothesis consumed scientific work until the 1960s. Modern studies have pursued the complexities of flood physics and the details of multiple flood stratigraphy.

•VANCOUVER

CANADA ~ WASHINGTON

MONTANA

/

LAKE MISSOULA

GAP

l/

~

/

iF

>

CASCADE RANGE

• BOISE I D A H O

iCRATER LAKE

.~*~

N !

EXPLANATION I PLEISTOCENE FLOODING m LAKES FLOODING FLOOD FLOW DIRECTIONS LATE WISCONSIN ICE •~ OEEP-SEA CHANNELS - - - POLITICAL BOUNDARIES (

NEVADA j

IJ

T. SHASTA

. SEN

50 0

SCALE IO0 I00

150 200 200 km

mi

FIG. 1. Regions of the northwestern United States affected by cataclysmic flooding during the Late Wisconsin.

Cataclysmic Floods from Glacial Lake Missoula

3

Present stratigraphic studies of flooding from glacial Lake Missoula have been immensely stimulated by the hypothesis that the cataclysms were repeated. Waitt (1980, p. 674) interpreted rhythmic beds in the Walla Walla and lower Yakima valleys of south-central Washington as a record ' . . . of about 40 separate Late-Wisconsin catastrophic backfloodi n g s . . . ' . Additional studies of low-energy flood deposits intercalated with glaciolacustrine and subaerial sediments demonstrate multiple floods, which Waitt (1984, p. 46) interprets as evidence of ' . . . regularly recurring, colossal floods from glacial Lake Missoula'. This review will focus on the intriguing evidence for the magnitude and frequency of Late Pleistocene Lake Missoula flooding. It will update an earlier review (Baker and Nummedal, 1978) that focused on process aspects of the problem. However, no review can begin without discussing the rich philosophical and historical tradition of Missoula Flood studies.

THE SPOKANE

FLOOD

DEBATE

The great debate over the origin of the Channeled Scabland has been analyzed in some detail (Baker, 1978a, 1981; Gould, 1980, pp. 194-203). The recounting here will briefly describe the controversy and add some anecdotes that did not appear in earlier reviews. The controversy can be reviewed through its published record, either as an analysis of alternative hypotheses (Table 1) or as the formulation, refinement, and confirmation of a model (Table 2). The focus of the controversy was a region of anomalous physiographic c h a r a c t e r that intrigued Professor J. Harlen Bretz of the University of Chicago. A b o u t 1910 Bretz (pets. cornrnun., 1978) recalled looking at the newly published Quincy topographic map showing a great dry cataract in eastern Washington state. In 1922 he began fieldwork in the region, which he n a m e d 'The Channeled Scabland' (Bretz, 1923a, b). Bretz reminisced on his scabland studies of the early 1920s, as follows: The publication in 1912 of a geomorphic study of 'The Channeled Scabland of the Columbia Plateau' in southeastern Washington state launched a controversy that lasted for decades. A map accompanying the paper depicted a pattern of abandoned erosional waterways, many of them streamless canyons (coulees) with former cataract cliffs and plunge basins, potholes and deep rock basins, all eroded in the underlying basalt of the gently southwestward dipping slope of that part of the Columbia Plateau. The pattern of dry stream ways was described as a network, a plexus, an anastomosis; totally unlike any other drainage pattern on earth. A debacle was asked for, the volume of which filled existing normal stream valleys to overflowing. This great flood spilled over former divides, eroding their summits to complete the network. Associated with the enormously enlarged drainage ways in favorable places were similarly huge mounds of stream gravel which the writer called great river bars. Huge streamrolled boulders occurred in these bars. The boulders were obviously plucked from the columnar basalt bedrock by the postulated high-velocity currents. The term valley would no longer suffice. The abandoned rock-bound former waterways were called channels, and the entire composite was named 'Channeled Scabland.' The total area involved was 18 townships wide by 22 townships long (approximately 40,000 kin2). (Bretz, 1978, p. 1.)

4

V.R. Baker and R.C. Bunker

TABLE 1. Alternative hypotheses for the origin of the Channeled Scabland Hypothesis Glacial Diversion of Columbia River

Glacial Erosion

Cataclysmic Flooding

References

Comments

Symons (1882)

Initiated the concept of glacial diversion of the Columbia River.

Russell (1893), Dawson (1898), Salisbury (1901), Calkins (1905)

Reinforced the concept of glacial diversion of the Columbia River.

Baulig (1913)

Described dry falls, rock basins, and plunge pools of the Channeled Scabland.

Meinzer (1918, 1927)

Ascribed unusual erosion to diversion of river across a steeply dipping basalt surface. See discussion of Bretz (1927a).

McKnight (1927)

Presented diversion of the Columbia River as an alternative to the hypothesis of Bretz (1923b, 1925, 1927a). See discussion by Bretz (1927b).

Oestreich

(1915)

Recognized hanging valleys in the upper Grand Coulee.

Pardee(1922)

Ascribed the Cheney-Palouse scabland tract to glaciation of unusual character.

Hodge (1934, 1940)

Speculative model of complex alternation between ice advances and drainage changes.

Hobbs (1943, 1947)

Attributed scabland to glacial scour by a ~Scabland Glacial Lobe'.

Bretz (1923a, 1923b) Bretz (1925)

Initiated the cataclysmic flood hypothesis.

Bretz (1928a) Proglacial Drainage

Flint (1938) (see also review by Thornbury, 1954)

Attributed scabland relationships in the Cheney-Palouse region to normal proglacial drainage that experienced rapid aggradation followed by incision. See criticisms by Allison (1941) and Bretz et al. (1956).

Other

Alden (1927)

Suggested the possibility of collapsed lava caves resulting in scabland topography.

Keyes(1935)

Ascribed Moses Coulee and the Grand Coulee to erosion by supraglacial streams that developed along the medial axes of waning ice lobes.

CataclysmicFloods from Glacial Lake Missoula

5

Bretz boldly proclaimed the cataclysmic flood origin of the Channeled Scabland in a series of papers during the 1920s. He even named the responsible debacle, the Spokane Flood• His papers presented excellent detailed descriptions of the physiographic relationships in the region, many of which also appear in useful reviews (Bretz, 1928a, 1959). It is important to note that it was the anomalous character of the terrain in southeastern Washington that led Bretz to his famous 'outrageous hypothesis'. 1927 was a key year in the Spokane Flood controversy. Bretz was confronted with righteous indignation by much of the geological community• As stated by Olson: the story of the development of the Channeled Scabland was thought by some to have brushed beyond the dividing line of flaunting catastrophe too vividly in the face of the uniformity that had lent scientific dignity to interpretation of the history of the earth. (Olson, 1969, p. 503.) •

.

.

Although it is now clear that a mistaken view of uniformitarianism (Gould, 1965; Albritton, 1967; Hubbert, 1967) was held by many of his critics, Bretz had to contend with the strong emotions that it engendered. In 1978 he wrote of the experience: Was not this debacle that had been deduced from the Channeled Scabland simply a return, a retreat to catastrophism, to the dark ages of geology? It could not, it must not be tolerated. This, the writer of the 1923 article learned when, in 1927, he was invited to lecture on his finding and thinkings before the Geological Society of Washington, D.C. an organization heavily manned by the staff of the United States Geological Survey. A discussion followed the lecture, and six elders spoke their prepared rebuttals. They demanded, in effect, a return to sanity and Uniformitarianism. The upstart theorist was not upset nor silenced. Despite his knowledge that the country was full of other dissenters to his flood theory, he proceeded to publish more papers on his favorite topic, now named the Spokane Flood. He described other features of the afflicted plateau which he claimed were inexplicable without his flood of glacially derived meltwater. His apostacy would not be corrected as advised by the elders. The one-man rebellion was still alive. (Bretz, 1978, p. 1.) In another description of the Washington meeting, M. King Hubbert (1980, p, 1092) observed, 'the might and majesty of the United States Geological Survey were marshalled in opposition to the flood hypothesis'. Bretz is remembered for his spirited defense of that hypothesis. In accepting the 1979 Penrose Medal of the Geological Society of America, Bretz (1980, p. 1095) said of his major research contribution: 'Perhaps 1 can be credited with reviving and demystifying legendary catastrophism and challenging a too rigorous uniformitarianism'. The profound irony of the whole Spokane Flood controversy is that Bretz's early papers (Bretz, 1923a, b, 1925, 1927a, 1928b) clearly document strict adherence to the principle of methodogic uniformitarianism (Baker, 1981), which is essentially equivalent to Occam's razor (Albritton, 1967). Moreover, a thorough reading of Bretz's papers shows that the cataclysmic flood hypothesis was formulated according to the best tradition of inductive scientific investigation. Bretz clearly followed the method of multiple working hypotheses

6

V.R. Baker and R.C. Bunker

TABLE 2. Development of the cataclysmic flood model for the origin of the Channeled Scabland Phase Discovery

Formulation of the Flood Model

Criticism of the Flood Model

Refinement of the Flood Model

References

Comments

Symons (1882)

First detailed description of Grand Coulee.

Bretz (1919)

Attributed erratic boulders downstream of the Channeled Scabland to marine submergence.

Bretz (1923a)

Described the important physiographic relationships of the Channeled Scabland without claiming a cataclysmic origin.

Bretz (1923b)

Described landforms in the Channeled Scabland which required cataclysmic flooding for their origin, including immense gravel bars and streamlined hills.

Bretz (1924)

Described origin of rock basins by fluvial plucking erosion.

Bretz (1925)

Described the regional relationships for a vast but shortlived cataclysm which he named the 'Spokane Flood'. The flood water spilled across pre-glacial drainage d!vides and affected the Columbia valley downstream of the Channeled Scabland to Portland, Oregon.

Bretz (1927a)

Summarized evidence for the Spokane Flood before a skeptical audience of geologists from the Geological Society of Washington.

Meinzer (1927)

Ascribed scabland erosion to a glacially diverted and swollen Columbia River.

McKnight (1927)

Argued for a glacially diverted Columbia River in a paper criticized by Bretz (1927b).

Gilluly (1927)

Criticized the lack of a documented source for the 'Spokane Flood'.

Bretz (1928a)

Perhaps Bretz's most eloquent summary of his Channeled Scabland hypothesis.

Bretz (1928b)

Answered criticism of flood hypothesis and demonstrated inadequacy of alternatives.

Bretz (1928c)

Described detailed relationships for flood bars.

Bretz (1929)

Described emplacement of flood debris by backflooding of tributaries to scabland channels.

Bretz (1930a)

Ascribed the 'Spokane Flood' to the failure of an ice dam retaining glacial Lake Missoula (Pardee, 1910).

Bretz (1930b)

Described further evidence of backflooding relationships in scabland lributaries.

Bretz (1932a)

Monograph on the Grand Coulee.

Bretz (1932b)

Summary of scabland relationships for the 16th International Geological Congress.

Cataclysmic Floods from Glacial Lake Missoula TABLE 2. (continued) Phase Revisionist Models

Confirmation of the Flood Model

References

Comments

Allison (1933)

Accepted Bretz's cataclysmic flood concept but modified it to include considerable floating ice. Modern studies have confirmed some aspects of Allison's hypothesis that large quantities of ice were included in the flood (Fecht and Tallman, 1978).

Flint (1938)

Ascribed the erosion of the Cheney-Palouse scabland to proglacial streams of 'normal discharge'.

Allison (1941)

Severely criticized Flint's (1938) hypothesis, especially Flint's description of flood bars as normal stream terraces.

Pardee (1940, 1942)

Demonstrated unequivocal evidence for the cataclysmic release of floods from glacial Lake Missoula.

Trimble (1950)

Describe joint control of plucking erosion on the flooderoded divide between the Palouse and Snake Rivers.

Bretz el al. (1956)

Complete refutation of all alternatives to cataclysmic flooding as explanations for the Channeled Scabland.

Bretz (1959)

Detailed review of evidence for the cataclysmic flood model.

e s p o u s e d by his colleague at the University of Chicago, T.C. Chamberlain (1897). H e posed the cataclysmic flood hypothesis with great reluctance, after a b a n d o n i n g all other alternatives as inadequate. In his first reference to a debacle he cautioned: All other hypotheses meet fatal objections. Yet the reader of the following more detailed descriptions, if now accepting the writer's interpretation, is likely to pause repeatedly and question that interpretation. The magnitude of the erosive changes wrought by these glacial streams is nothing short of amazing. (Bretz, 1923b, p. 621.) Bretz persisted in defending his u n p o p u l a r hypothesis because the field evidence would not permit an alternative. Published alternatives (Table 1) have all subsequently been shown to have b e e n based on inadequate field interpretation. Yet, despite his early recognition that L a k e Missoula was the source of the ' S p o k a n e F l o o d ' (Bretz, 1930a), his hypothesis r e m a i n e d controversial (see T h o r n b u r y , 1954, pp. 400-402). Having presented a c o m p l e t e analysis of the p r o b l e m in n u m e r o u s papers to 1932, Bretz left further work to others. T h e most h e r a l d e d alternative to the cataclysmic flood hypothesis was presented by Flint (1938). Flint used a carefully w o r d e d a r g u m e n t and considerable, albeit selective, field data to suggest that the a n a s t o m o s i n g scabland channels were consistent with 'a picture of leisurely streams with n o r m a l discharge' (Flint, 1938, p. 472). Flint traced the scabland fluvial deposits d o w n s t r e a m into the Pasco Basin. There he f o u n d that the deposits c h a n g e d f r o m sand and gravel to silt and fine sand containing erratic stones. H e n a m e d the fine-grained facies the ' T o u c h e r Beds'. The deposits (Plate 2) had

8

V.R. Baker and R.C. Bunker

already been described by Bretz (1928a, pp. 325-328, 1929, pp. 516-536, 1930b, p. 414), who ascribed them to hydraulically ponded flood water; and by Allison (1933), who ascribed them to water ponded by ice jams. The silts are recognized only to a uniform elevation of about 350 m. Stratification ranges from rhythmic parallel bedding to cut-andfill. The included erratic stones are granite and other crystalline rock types. Intense folding, fracturing, and clastic dikes imply slumping and sliding of the water-saturated silt on gentle subaqueous slopes. Flint thought these relationships were most consistent with a large lake, which he proposed was ponded by a landslide dam or glacier ice in the Columbia River gorge. Following Symons (1882) he named this water body Lake Lewis. Finally he proposed that, as Lake Lewis rose behind its dam, the proglacial streams entering it aggraded. Subsequent drainage of the lake resulted in incision by the same streams, leaving remnants of their former fill that Bretz had interpreted as flood bars. Allison (1941) published the first criticism of Flint's fill hypothesis. He noted first that the anastomosing channel patterns and deep rock basins could not have been eroded by 'normal' streams. Second, Allison disputed Flint's correlation of the scabland gravels to the Touchet Beds. He described localities along the Snake River, downstream of the Cheney-Palouse scabland tract, where the 'lacustrine' Touchet Beds overlie coarse flood gravel. Finally, Allison agreed with Bretz that the peculiar streamlined shapes of the scabland gravel deposits (Plate 3) required extraordinary processes, not the activity of Flint's 'leisurely' streams. The return of scientific sentiment to Bretz's hypothesis came through J.T. Pardee's (1940, 1942) revelation that Lake Missoula itself contained evidence of at least one cataclysmic flood release. Pardee (1942) described huge flood bars of current-transported debris (Plate 4) and giant current ripples that indicated a cataclysmic outflow of the lake. Pardee (1942) documented at least one phase of massive lake drainage associated with a maximum water elevation of 1265 m, corresponding to a water depth of 635 m at the ice dam. Pardee also presented evidence for at least one later filling of glacial Lake Missoula to altitude 1079 m, corresponding to a water depth of 449 m at the ice dam. Bretz returned once more for field work in the Channeled Scabland in 1952, and he published a meticulously detailed rebuttal to all criticisms of his flood theory (Bretz et al., 1956). The new study was noteworthy for its identification of numerous examples of giant current ripples on scabland flood bars (Plate 5). With few exceptions studies over the next 25 years generally accepted the cataclysmic flood hypothesis (Table 3). Research since 1956 has had two general themes. Most studies have focused on the stratigraphic details of flood timing, number, and regional correlation (e.g. Richmond et al., 1965; Bretz, 1969; Baker, 1978b; Waitt, 1980, 1984). Another trend has been the quantitative study of flood processes (e.g. Baker, 1973, 1978c). The remainder of this review will focus on the details of these modern studies, particularly the details of Late Quaternary stratigraphy. The 'Spokane Flood Debate' is a striking example of the role of outrageous hypotheses in scientific investigation (Baker, 1978a). It also illustrates a fundamental problem for the

9

Cataclysmic Floods from Glacial Lake Missoula

TABLE 3. Studies of cataclysmic flood features in the northwestern United States, 1956-1981. Additional studies from this period are listed in Table 8

Reference

Region Studied (see Fig. 1)

Comments

Trimble (1963)

Portland, Oregon

Confirmation of Bretz's earlier work on Missoula Flood features.

Fryxell and Cook (1964)

Palouse, Snake, Tucannon valleys

Confirmation of Bretz's work. Identification of slack-water features.

Richmond etal. (1965)

Northwestern U.S.

Discussion of regional Quaternary stratigraphic relationships.

Malde (1968)

Snake River Plain, Idaho

Evidence for the Bonneville Flood.

Bretz (1969)

Northwestern U.S.

Summary of stratigraphic studies to 1969. Evidence for six Late Wisconsin floods.

Hanson (1970)

Moses Coulee, Waterville, Plateau

Geomorphic evidence for cataclysmic flooding of Moses Coulee.

Baker (1971, 1973)

Channeled Scabland

Paleohydraulic flood reconstruction.

Griggs et al. (1970)

Astoria Fan at mouth of Columbia River

Evidence from Pacific Ocean flood for cataclysmic floods down the Columbia River system.

Waitt (1972, 1977a, 1977b)

Columbia River and tributaries from Grand Coulee Dam downstream to Lynch Coulee

Evidence of cataclysmic flooding down the Columbia River system.

Foley (1976), Hammatt (1977)

Snake River Canyon and tributaries

Evidence for two phases of flooding with an interflood phase 13 ka BP.

Moody (1978), Mullineaux et al. (1978)

South-central Washington

Identified 13 ka BP Mount St Helens 'setS' tephra in Touchet Beds.

Baker and Nummedal (1978)

Northwestern U.S.

Collection of review papers, some of which are reprinted in Baker (1981).

Allison (1978)

Williamette valley, Oregon

Considers the Late Wisconsin flooding to have occurred in two phases: an early, prolonged depositional phase of multiple events; and a later, short-lived, erosive flood.

Bjornstad (1980)

Walla Walla River portion of Pasco Basin

Description of Touchet Bed rhythmites separated by a major unconformity.

Bunker (1980)

Badger Coulee portion of Pasco Basin

Interpretation of Mount St Helens set-S tephra as subaerially deposited.

Waitt (1980)

Pasco Basin area

Posed hypothesis that 40 Touchet Bed rhythmites were each emplaced by discrete catastrophic floods in Late Wisconsin time.

Parsons etal. (1981)

Northern Idaho

Hypothesized a sequence of at least five Late Wisconsin cataclysmic floods, each successively smaller, that created outwash terraces 13 ka to 10.85 ka BP.

10

V.R. Baker and R.C. Bunker

scientific community. A fine line may exist between the outrageous hypothesis that goes beyond the bounds of existing theory to explain startling new facts, and the outrageous hypothesis that ignores important facts merely to present speculation as startling new theory. The 'Spokane Flood Debate' contained all too many examples of the latter, but only one for the former. The studies of J. Harlen Bretz stand as a remarkable legacy, not only to the continuing work on flood problems, but to the history of all the earth sciences.

PHYSICS OF M U L T I P L E CATACLYSMIC FLOODS A complete review of cataclysmic flood physics is beyond the scope of this paper. Discussions of Missoula Flood paleohydraulics and sedimentology are given by Baker (1973, 1978c, d, 1981). Rather the emphasis here will be on those aspects of flood physics that relate to the recently posed hypothesis of Waitt (1980, 1984) that about 40 Late Wisconsin cataclysmic floods deluged the environs of the Channeled Scabland. Table 4 summarizes the parameters of glacial Lake Missoula that relate to its potential for cataclysmic failure. Pardee (1942) first estimated the lake's volume, 2167 km 3 at its maximum extent (1265 m elevation). Using a digital terrain model, Singer and Craig (1984) revised this to 2514 km 3 held at the maximum stage of 1265 m. The refilling of glacial Lake T A B L E 4. Physical parameters for the Late Wisconsin Lake Missoula and the flooding of the Pasco Basin ('Lake Lewis') Parameter

Value

Reference

M a x i m u m lake elevation

1265 m

Pardee (1942)

M a x i m u m lake volume

2167 km 3 2184 km 3 2514 km 3

Pardee (1942) Clarke etal. (1984) Singer and Craig (1984)

M a x i m u m water depth at d a m

635 m

Pardee (1942)

Water depth achieved in refilling after cataclysmic outburst (1079 m elevation)

449 m

Pardee (1942)

Volume achieved in refilling to 1079 m elevation

970 km 3

Singer and Craig (1984)

M a x i m u m flooding level of Pasco Basin

350 m

Bretz (1969), Baker (1973), Bunker (1980), Waitt (1980)

M a x i m u m volume of flooding Pasco Basin

1100 km 3

W a i n (1980)

Elevations of rhythmite accumulation in Pasco Basin

180 m to 245 m

Waitt (1980)

Potential flood volume associated with 180 m elevation in Pasco Basin

100 km 3

Craig (1983)

Cataclysmic Floods from Glacial Lake Missoula

11

Missoula after the cataclysmic release that produced the spectacular bedforms reported by Pardee (1942) is estimated to have reached an elevation of 1079 m (Pardee, 1942). The Singer and Craig (1984) model suggests the lake held approximately 970 km -~at that stage. Utilizing data on the advance and retreat of the Cordilleran Ice Sheet and assumptions about the nature of the ice dam (Craig, 1983), Craig and Singer (1984) suggested that Lake Missoula formed and failed repeatedly by flotation of its ice dam. Using Waitt's (1983b) assumption that the ice dam would fail when the lake filled to a critical depth of about 9/lO the ice thickness, Craig and Singer (1984) estimated that 35 j6kulhlaups would be generated. This n u m b e r is consistent with the hypothesis of Waitt (1980). Clarke et al. (1984) developed a computer simulation model of Missoula floods based on glaciological equations governing the enlargement by water flow of a tunnel penetrating the Lake Missoula ice dam. The model is based on observations of j6kulhlaups from modern ice-dammed lakes (Mathews, 1973; Nye, 1976). The model generates outflow hydrographs whose peak discharges range from 2.7 × l0 t' to 14 × 1 0 6 m 3 sec -~. It is interesting that a variety of failures are possible, many of which leave a considerable volume of water in the lake. At the extreme case, collapse of the tunnel roof can lead to the sweeping away of the ice dam and complete drainage of the lake. The Clarke et al. (1984) model predicts j6kulhlaup durations of 8 to 20 days, depending on various physical controls that dictate hydrograph shapes (Fig. 2). Moreover, because an outflow tunnel can close through ice creep within a few days, dam regeneration time is short relative to reservoir filling, Assuming reasonable discharge values, Lake Missoula can be

,5-(a) (b)

~10 O0

I

2

5

4

LLJ rY

'~

(c)

O0

O0

i

4

TIME (hours x I00)

FIG. 2. Idealized hydrographs for large outburst floods from glacial Lake Missoula. (a) Hydrograph at breakout point assuming no tailwater ponding and insignificant lag time of response in lake drainage. (b) Hydrograph at breakout point for opposite assumption to A. (c) Hypothetical inflow hydrograph to a downstream location, such as the Pasco Basin. Multiple peaks are derived from routing effects discussed in text. (a) and (b) are from modeling studies by Clark et al. (1984).

12

V.R. Baker and R.C. Bunker

regenerated to its maximum volume in approximately 100 years. Thus, the 40 Late Wisconsin j6kulhlaups envisioned by Waitt (1980) seem possible. These simulations must be considered hypothetical. Lake Missoula was much larger than any modern analogue, and its ratio of water volume to reservoir depth may have been unique for any example in the geologic record. Major physical extrapolations are required in the above simulations. Moreover, geological evidence is lacking for the exact mechanism of failure. Direct determination of paleoflood discharges from high-water mark indicators was first applied to downstream effects of Lake Missoula flooding by Baker (1973). Critical to that study was the recognition of high-water marks indicating the immense flow depths and steep water-surface profiles that demonstrate cataclysmic discharges and velocities. Such recognition of paleoflood high-water surfaces has become the basis of paleoflood hydrologic analysis for Holocene flood-frequency estimates (Baker e t a l . , 1979, 1983; Kochel and Baker, 1982; Kochel et a l . , 1982). It is important to note that low-level flood deposits, such as bars in main channelways and slack-water accumulations in channelmargin sites, do not directly indicate such a high-water surface and its implication for cataclysmic flow. Baker (1973) used several hydraulic methods of indirect discharge calculation, yielding results shown in Table 5. The methods have a certain imprecision when applied to the immensity of the problem (Baker, 1978c). Recent experience with paleohydraulic calculations for large Holocene floods in bedrock rivers (Webb and Baker, 1984) shows that the slope-area method employed by Baker (1973) overestimates peak discharges by approximately 30%. Better estimates can be obtained with recently developed computerized step-backwater routines (Feldman, 1981). Work on improving the various Missoula Flood flow estimates is in progress.

TABLE 5. Paleohydraulicestimatesof Lake Missoulaflood discharge Location WallulaGap

MaximumDischarge ( m 3 s - l)

Reference

Calculation Procedure

1.9 × 9× 6.3 x

10 6 10 6 10 6

Bretz (1925) Baker (1973) Craig (1983)

ChezyEquation ConstrictedOpeningEquation HEC-2 Procedure

EddyNarrows (Lake Missoula)

10.9 X

10 6

Pardee (1942)

ChezyEquation

RathdrumPrairie (Breakout Point)

21.3 ×

10 6

Baker (1973)

Slope-Area Procedure

Clarke et al. (1984) Clarke et al. (1984)

SimulationModel SimulationModel

OutflowLake Missoula(range)

2.7 x 106 ( l o w ) 14 x 106 (high)

CataclysmicFloodsfrom Glacial Lake Missoula STRATIGRAPHY

13

OF MULTIPLE FLOODS

Flood Facies

Current attempts to define the magnitudes and frequency of various Late Wisconsin floods are complicated by flood deposits occurring as multiple facies throughout the Columbia system. Main-channel deposits include large gravel bars (Plate 4), giant current ripples (Plate 5), transported boulders, and other unequivocal indicators of high-energy conditions associated with cataclysmic flows (Baker, 1973, 1978c, d). However, the best evidence for multiple floods and for their frequency is in slack-water areas, where relatively low-energy conditions prevailed (Plate 2). Such slack-water areas include tributary valleys to the main flood flow paths such as the Tucannon valley (Baker, 1973), Badger Coulee (Bunker, 1980, 1982), Walla Walla valley (Bjornstad, 1980; Waitt, 1980), and the lower Yakima valley (Bunker, 1980; Waitt, 1980). These slack-water areas show somewhat similar proximal-to-distal variation in sediment characteristics. High flow velocities at the proximal end of the Yakima and Walla Walla valleys resulted in transport of gravel and sand. As competence decreased upvalley, i.e. downcurrent for invading flood flows, fine-grained beds were deposited along a distinctive facies tract. Such beds are generally normally graded, fining upwards from gravel and sand to silt. Successive beds have a rhythmic appearance and are termed 'rhythmites'. Their flood origin is evinced by (1) upvalley decreases in grain size, (2) upvalley decreases in bed thickness, (3) sedimentary structures indicating upvalley flow, and (4) ice-rafted non-basalt glacial erratics. These rhythmites are the classic 'Touchet Beds' of Flint (1938) and Allison (1933). Typical rhythmites consist of the following ideal sequence of 'divisions': (1) A basal layer of horizontally laminated very coarse to medium sand. (2) Ripple cross-laminated and climbing ripple cross-laminated coarse to fine sand. (3) Parallel, or horizontal, laminated very fine sand to silt. More proximal rhythmites may have a basal layer of graded, structureless gravel to coarse sand (Baker, 1973). The whole sequence of textures and sedimentary structures is analogous to that of marine turbidites (Bouma, 1962). Following this analogy, the Bouma division names B, C, and D have been applied to the analogous rhythmite divisions (Bunker, 1980; Waitt, 1980). Although the rhythmites are analogous in sedimentary structures to turbidites, some workers in the Columbia Basin have applied the turbidite label to various fine-grained slack-water deposits without a clear idea of the proper and restricted usage of the term 'turbidite'. Turbidites are deposits of turbidity currents, a special type of density current. Turbidity currents result from slumping of bank or delta material, or other sudden influxes of sediment. The sudden sediment influx creates a dense sediment-water mix that is denser than the ambient fluid. Gravity acts on the relative density contrast between the 'cloud' of suspended sediment and ambient fluid, and pulls the 'cloud' downslope as a turbidity current enters a basin, transforming potential energy into kinetic energy. However, rhythmites in backflooded valleys were deposited by flood currents which surged upsiope,

14

V.R. Baker and R.C. Bunker

a n d thus w e r e not n o r m a l t u r b i d i t y currents. Significant h y d r a u l i c h e a d s w e r e p r o b a b l y r e q u i r e d to d r i v e w a t e r scores of k i l o m e t e r s u p v a l l e y . T h e w a t e r surface h a d to slope u p v a l l e y , p e r h a p s r e s e m b l i n g a tidal b o r e . T a b l e 6 lists s o m e s e d i m e n t o l o g i c a l c h a r a c t e r i s t i c s of l o w - e n e r g y s l a c k - w a t e r s e d i m e n t facies o f L a t e W i s c o n s i n M i s s o u l a F l o o d d e p o s i t s .

TABLE 6. Sedimentological characteristics of Touchet Beds and related low-energy Late Wisconsin flood deposits of the northwestern United States. Based on Glenn (1965), Alwin (1970), Bjornstad (1980), Bunker (1980), and Waitt (1980) Depositional Setting

'Slackwater areas" created when floods backflooded up tributary valleys marginal to main floodways or when flood water temporarily ponded upstream of a flow constriction.

Geometry

Laterally extensive drapes over preexisting valley floor topography. Deposits pinch out against valley walls.

Thickness and Bedding

Beds 0.15 to 1.5 m thick. Thickest beds are basal, near tributary valley mouths,.or both. Beds are generally conformable. Proximal, basal beds at tributary valley mouths are commonly discordant locally and amalgamated.

Lithology

Generally quartzose; feldspar and mica also present. Coarser parts of basal or proximal beds commonly enriched in basalt clasts. Dropstones (?) locally present consisting of nonbasalt rock types, such as granite, gneiss, and quartzite.

Sedimentary Structures

Most typically comprising Bouma sequences. Waitt (1980) argues for the presence of interflood sediment as an 'e" division. Beds are normally graded, although some reverse grading occurs. Rhythmic appearance derives from repetition of this sequence bed after bed.

Sediment Size and Texture

Ranging from cobbles to silt. Individual beds grade upward from sand to silt, although proximal, basal beds grade upward from cobble gravel or very coarse sand to fine sand. Distal, topmost beds generally grade upward from fine sand to very fine sand or silt. All beds display moderate to poor sorting.

Rhythmite Genesis B a k e r (1973) briefly i n t r o d u c e d the f l o o d s l a c k - w a t e r s e d i m e n t a r y s e q u e n c e of the T u c a n n o n v a l l e y in s o u t h e a s t e r n W a s h i n g t o n . H e p r e s e n t e d a ' s u r g e ' h y p o t h e s i s for r h y t h m i t e e m p l a c e m e n t in o r d e r to a v o i d the necessity of p o s t u l a t i n g s e p a r a t e f l o o d s for each r h y t h m i t e w h e n c o r r o b o r a t i n g e v i d e n c e of such f l o o d s was lacking. Surging is r e a s o n a b l e to e x p e c t in s c a b l a n d flows b e c a u s e highly u n s t e a d y c o n d i t i o n s m u s t have p r e v a i l e d d u e to s c o u r i n g o f c h a n n e l b e d s , h y d r a u l i c j u m p s , c a t a r a c t recession, etc. ( B a k e r a n d N u m m e d a l , 1978). M o r e o v e r , a l t h o u g h the o u t p u t h y d r o g r a p h of L a k e M i s s o u l a was p r o b a b l y s i m p l e , the c o m p l e x i t y of flow p a t h s in the C h a n n e l e d S c a b l a n d w o u l d surely have r e s u l t e d in a m u l t i p l e - p e a k h y d r o g r a p h at d o w n s t r e a m r e a c h e s (Fig. 2). Such c o n d i t i o n s w o u l d i n d u c e f l u c t u a t i o n s in w a t e r surfaces and s e d i m e n t l o a d i n g in m a i n c h a n n e l s that w o u l d t r a n s l a t e to d e p o s i t i o n a l r e s p o n s e s in b a c k f l o o d e d t r i b u t a r y valleys. I n d e e d , such m u l t i p l e b e d s f r o m a single f l o o d o c c u r even in s l a c k - w a t e r s e d i m e n t s of relatively m o d e s t sized H o l o c e n e f l o o d s ( K o c h e l , 1980; B a k e r et al., 1983). T h e ' s u r g e ' h y p o t h e s i s was p o s e d

Cataclysmic Floods from Glacial Lake Missoula

PLATE 1. Landsat image (E-1039-18143-5) taken on 31 August 1972 showing an area of 185 km × 185 km centered approximately on the Cheney-Palouse scabland tract. The anastomosing pattern of scabland channelways is clearly indicated by the dark patterns of flood-eroded basalt, which stand in contrast to bright areas underlain by loess of the Palouse Formation.

15

16

V.R. Baker and R.C. Bunker

iii

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PLATE 2. Multiple rhythmites of the Touchet Beds exposed at Burlingame Canyon in the Walla Walla valley of southeastern Washington. The 30 m section (base not shown in this photo) consists of 39 counted rhythmites (Waitt, 1980). The top 11 rhythmites, shown here, overlie the Mount St Helens set-S tephra, erupted approximately 13 ka BP.

P L A T E 3. Scabland gravel bar near Wilson Creek, Washington. This bar is relatively small by scabland standards, 1 km long and 25 m high. It is elongated in the paleoflow stream direction downstream from a resistant ledge of basalt in the lower right foreground. The basalt ledge probably induced flow separation in the floodwater, which was approximately 120 m deep in this area. The separation zone then accumulated boulders and gravel that otherwise would have been transported along by the high-velocity floodwater. P L A T E 4. Eddy bar at the mouth of a tributary canyon along the Flathead River near Perma, Montana. This and similar bars formed during the rapid, cataclysmic drainage of Lake Missoula (Pardee, 1942). The low terrace in the foreground is underlain by lake silt of Glacial Lake Missoula. Such silts overlie flood gravel deposited during cataclysmic outbursts of the lake. They indicate that the lake r~robablv reformed numerous times without cataclysmic outflow.

P L A T E 5. Giant current ripples on the great flood bar at Marlin, Washington, in the upper Crab Creek scabland tract. These ripples average 60 m in spacing and 2 m in height. They developed in a region where floodwater was 60 m deep and flowing with a mean velocity of approximately 12 m/s. Larger ripples are associated with flows that were deeper or faster, or both. The giant ripples are composed of gravel and boulders up to 1.5 m in diameter. Nearly 100 sets of giant current ripples are recognized throughout the Channeled Scahland. P L A T E 6. M o u n t St Helens set-S ash tephra (white layer above trowel) at a typical Pasco Basin exposure of Missoula-flood slackwater sediment. T h e tephra occurs in two layers: So (upper) and Sq (lower). T h e stones on the ground surface atop the outcrop are ice-rafted erratics that formed a lag deposit by erosion of the slackwater sediment that originally contained them. T h e scale is 15 cm long.

CataclysmicFloodsfrom Glacial Lake Missoula

19

to show that surges could emplace multiple rhythmites. It remains to be demonstrated whether a single outburst flood would generate one, two, or many slack-water beds because of variable surge effects at various sites in the downstream path of Missoula Flood waters. Waitt (1980, 1984) presented the hypothesis that each rhythmite represents a separate flood, which, in the Walla Walla and Yakima valleys, advanced over dry land. Each rhythmite was succeeded by a nonflood interval decades in length. Moreover, Waitt (1980, 1984) argues that each rhythmite's emplacement was by a cataclysmic flood. This hypothesis was posed as the antithesis of one that ascribes multiple rhythmite beds to surging. Arguments for surge emplacement of rhythmites were presented by Carson et al. (1978) and Bjornstad (1980). Bjornstad (1980) provided abundant evidence of subaqueous conditions for rhythmite emplacement, including soft-sediment deformation structures and load casts. Interestingly the latter do not occur in Waitt's (1980) sections who notes: Rapid accumulation of sand or gravel before dewatering of the underlying silt, moreover, should have caused injection and loading structures in the underlying silt, which generally are absent. (Waitt, 1980, p. 662.) The problem of Touchet Bed emplacement is further complicated by widespread evidence of temporary lacustrine conditions in the distal facies' sites of deposition. The hypothesis of a long-lived regional lake in the Pasco Basin area, named 'Lake Lewis' by various investigators (Allison, 1933; Flint, 1938; Newcomb et al., 1972), seems untenable for reasons discussed by Waitt (1980, pp. 670-1). However, abundant paleontological evidence suggests that relatively persistent lacustrine conditions must have prevailed at least locally during part of the period of Touchet Bed sedimentation (Gustafson, 1976). Waitt (1980, pp. 662-3) reports the presence of freshwater sphaeriid bivalves (Pisidium sp.), gastropods (Valvatata sp., Gyraulus sp., and others), charophytes (Chara sp.), and a fish (?) vertebra in a rhythmite at Mabton, Washington (Locality M, Fig. 3). The fossiliferous bed is the third one below a tephra couplet dated at 13 ka BP (see discussion below). Waitt (1980) presents an environmental interpretation of this assemblage based solely on the charophytes, which live in alkaline waters, probably less than 5 m in depth. A collection from a stratigraphically equivalent bed (third below the tephra couplet) at a nearby locality by one of us (Bunker) yielded an assemblage that also included Pisidiurn sp., Valvatata sp., and Gyraulus sp., but no Charophytes (R.C. Bright, written commun., 1983). The assemblage has several species common to permanent water, including Pisidium variable and Gyraulus parvus. P. variable, known as the 'finger-nail clam', requires fish as an intermediate host for its larval stage (Gustafson, 1976). The entire assemblage indicates clear freshwater, such as a lake, a stream backwater, or a pond, that is permanent and has rooted-aquatic plants (R.C. Bright, written commun., 1983). Based on studies of a similar fossil assemblage in a slightly younger late-glacial lake in the lower Grand Coulee system, Landye (1973) concluded that ponded conditions must have persisted a minimum of 35 years, and probably lasted up to several hundred years.

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t 3 . Generalized location map. Ice-sheet margin and nomenclature based on Wain and Thorson (1983). Numbers refer to locations of radiocarbon dates listed in Table 7 . A - - Arlington, Oregon. B - - Badger Coulee. C P T - - Cheney-Palouse Scabland Tract. G C - - Grand Coulee. G P L - - Glacial Priest Lake. L S - - Little Spokane River Valley. M - - M a b t o n , W a . M C - - Moses Coulee. M S - Missoula. N - - Ninemile Creek Station. P - - P o r t l a n d . P B - - P a s c o B a s i n . Q B - - Q u i n c y B a s i n . S - Seattle. S p - - S p o k a n e . S V - - Sanpoil River Valley. W - - Wenatchee. FIG.

Evidence of subaerial exposure of some Touchet Bed rhythmites is summarized by Waitt (1980) and by Bunker (1982). Burial of both lacustrine and subaerial layers by rhythmites indicates that the low-energy distal slack-water sediments were being emplaced on several kinds of surfaces. At least some rhythmites derive from flood water that invaded ponded water of unknown depth. Tephrochronology

Regional correlation of Late Wisconsin Missoula-flood deposits was made possible by the discovery of Mount St Helens set-S tephra interbedded with flood-slackwater sediment (Moody, 1978; Mullineaux et al., 1978). The tephra generally occurs as a couplet, consisting of two layers (Plate 6) corresponding to layers Sg and So, the most widespread members of the Mount St. Helens 'S' eruption (Mullineaux et al., 1975). The age of the tephra is interpreted from bracketing radiocarbon dates of 13,130 + 350 (W-2983) and 12,120 + 350 (W-3133) BP (Mullineaux et al., 1978). These dates were derived from tephra exposures near the volcano, not from tephra in slack-water sediment. A new radiocarbon date on the Mabton bivalves and gastropods collected by Bunker and described above is consistent with the interpretation of Mullineaux et al. (1978). The date is 13,326 +_ 185 BP (WSU-2714), and thus shows that the third rhythmite below the set-S couplet at Mabton contains organisms that then lived in a permanent body of water.

Cataclysmic Floodsfrom Glacial Lake Missoula

21

Mullineaux et al. (1978) interpreted the association of set-S tephra and the Touchet Beds as indicating an approximate date of 13 ka BP for the last major cataclysmic scabland flood. This hypothesis derives from the assumption that the tephra dates directly its enclosing sediment and, thus, the time of flooding. Alternatively, Bunker (1980, 1982) and Waitt (1980) present sedimentologic and stratigraphic evidence that the set-S tephra was subaerially deposited on a former ground surface atop earlier-deposited flood sediment (Plate 6). Subsequent flooding then buried the tephra. Lovett (1984) presents paleomagnetic evidence supporting this interpretation. Thus, flooding occurred both before and after 13 ka BP. Fryxell (1965) recognized that tephra produced by eruptions of Glacier Peak volcano (Fig. 3) provided an upper limiting age on both cataclysmic flooding and on the retreat of the Cordilleran Ice Sheet from north-central Washington. Recent work shows that the Glacier Peak tephra has two widespread members, layers B and G (Porter, 1978). Radiocarbon dates (Table 7) confirm an age of approximately 11.250 ka BP for the younger layer B (Mehringer et al., 1977; Porter, 1978). The age of the older layer G was considered to be approximately 12 ka BP on the basis of radiocarbon dates (Table 7) cited by Fryxell (1965) and Ives et al. (1967). Recent work by Mack et al. (1983) and Mehringer et al. (1984) has resulted in a reinterpretation of layer G's age, such that it is now considered essentially indistinguishable from the 11,250 BP approximation for layer B. The eruptions were perhaps separated by no more than a few decades (Mehringer et al., 1984). Relationships between the various tephra layers may be used to place constraints on when Lake Missoula flooding terminated. For example, 180 cm of lacustrine clay beneath Glacier Peak tephra at Waits Lake, Colville River valley, was interpreted as indicating that the site was deglaciated by the Colville Lobe of the Cordilleran Ice Sheet 1000 years or more prior to the Glacier Peak eruptions (Mack et al., 1978a). If the ice stagnated prior to recession, deglaciation there would have commenced well before then, i.e. well before 12.250 ka BP. Whatever the interpretation, it seems reasonable that a Lake Missoula could not have been impounded by the nearby Purcell Trench Lobe any later than this same date. Thus, the lake could not be regenerated by ice advance for many centuries after the prominent 13 ka BP marker event of Mount St Helens S-set ash intercalated with flood deposits. To do so would require the Purcell Trench Lobe to be advanced while adjacent lobes were in recession. This does not seem likely given the repeated destruction of its terminus by post-13 ka BP floods, as envisioned by Waitt (1980).

The Forty-Floods Hypothesis

Late Wisconsin lake deposits in the basin of glacial Lake Missoula have been interpreted as recording episodic filling and draining of that basin. Although time-stratigraphic correlation to flood deposits outside the lake basin has not proven feasible, various studies have led to regional event-based correlations and to a synthesis of cataclysmic flood timing (Waitt, 1980, 1983a, 1984; Waitt and Thorson, 1983). L a k e Missoula: Alt and Chambers (1970) and Chambers (1971) interpreted 35 to 40 rhythmic sand-to-silt beds at Ninemile Creek, near Missoula, Montana, as lake-bottom

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sediment of Lake Missoula. Curry (1977) describes other, similar deposits elsewhere in the Lake Missoula basin. Beds typically grade upward from laminated silt and very fine sand to clayey varves. The beds are interpreted as recording 35 to 40 successive drainings and refillings of the lake (Chambers, 1971), the varves representing the minimum number of years before the lake drained. Weathered zones atop 20 or 21 of these beds indicate subaerial exposure of individual beds after successive drainings of the lake (Chambers, 1971). Because the number of varves in any given bed ranges from 9 to 58, Alt and Chambers (1970) inferred periods of a decade to several decades between lake drainings. The deduction that these drainings resulted in cataclysmic floods was made by D. Alt (in Alt and Chambers, 1970) (R.B. Waitt, Jr., 1984, oral commun.).

Flood Deposits: The hypothesis of numerous Late Wisconsin cataclysmic Missoula floods was reformulated by Waitt (1980). Waitt interpreted each of about 40 rhythmites in the Walla Walla valley as the product of a separate flood. The interpretation is based on the following evidence: (1) the local presence atop some rhythmites of sediment of probable interflood eolian and slopewash origin; (2) the Mount St Helens set-S tephra atop one rhythmite; (3) probable bioturbation structures; (4) dispersed animal skeletons; (5) channels of probable subaerial origin atop some rhythmites; and (6) correlation of the roughly 40 flood-slackwater rhythmites studied by Waitt (1980) to sections consisting of approximately 40 beds at Ninemile Creek section in Montana (Alt and Chambers, 1970) and in the Willamette valley, Oregon (Glenn, 1965). Some objections to the above arguments were summarized by Bunker (1982). An important defect in the Waitt (1980) hypothesis is that, while it infers that subaerial exposure succeeded each bed's deposition, evidence of subaerial exposure does not exist atop all rhythmites. Waitt (1980) nonetheless argued that each bed required a separate flood, preferring this explanation to one invoking deposition of the entire sequence within just one flood. However, he ignored a third possible explanation for the data: multiple floods did indeed occur, but one or more of them deposited multiple rhythmites. During the past several years studies in northern Idaho and northeastern Washington have identified sections displaying interbedded Late Wisconsin flood and non-flood sediments (Table 8). Many of these sections show single floodlaid beds of sand and gravel that are intercalated with silt or varved mud deposited in local flood-deposit or ice-dammed lakes. Non-flood beds generally consist of 20 to 55 silt-to-clay varves, although Rigby (1982) reports beds containing up to 60 or 125 varves. Waitt (1983a, b, 1984) and Waitt and Thorson (1983) conclude that the new data confirm the 'forty-floods' hypothesis because they provide clear evidence for significant time breaks between deposition of individual flood beds. Late Wisconsin floods from glacial Lake Missoula are thus interpreted as tens of j6kulhlaups, each succeeded by two to six decades of quiet glaciolacustrine or subaerial environments (Waitt, 1983b, 1984). Waitt (1983b) proposed that glacial Lake Missoula emptied cataclysmically and then refilled every three to six decades. Failure is assumed to have been achieved by floating the glacier dam responsible for impounding the lake. Exponential growth of subglacial drainage tunnels presumably led to cataclysmic lake release (Waitt, 1983a, b). The hydrostatic prerequisites for such j6kulhlaups are assumed to have been repeated tens of times.

Cataclysmic Floods from Glacial Lake Missoula

25

Discussion: Despite the above arguments, the 'forty-floods' hypothesis still leaves many unanswered questions. Atwater (1983, 1984a) and Waitt (1984) assume temporal equivalence of varve sections in northern Idaho and northeastern Washington to rhythmite sections in south-central Washington. However, the necessary time-stratigraphic correlation (Fig. 4) has not yet been demonstrated among the varved Lake Missoula beds (AIt and Chambers, 1971), the interflood lake sediments (Atwater, 1983; Rigby, 1982; Waitt, 1983a), the south-central Washington rhythmites (Waitt, 1980), and the Oregon 'Willamette Silts' (Allison, 1978; Glenn, 1965). No marker beds common to all localities have been identified. Moreover, there is no evidence in flood beds outside the former lakes that intervals of time elapsed between floods comparable to those recorded by the varved sections. It is also possible that some of the floods recorded in various lake sections (Table 5) were confined to those lakes and absorbed by them, as noted by Atwater (1983, p. 1). PATH OF WILLAMETTE SILTS OF NORTHWESTERN OREGON . . . .

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28

V.R. Baker and R.C. Bunker

the base of the section, more varves upwards, and a few varves near the top of the section. Curry interpreted this variation as indicating that the early and late lakes were relatively short-lived in comparison to the middle age of Lake Missoula. Thus, at first the frequency of flood releases decreased while the magnitude of each release increased. A corollary, but opposite, trend existed later in lake history. Waitt (1980) explained these inferred relations by the thickening of successive ice dams during the advancing phase of the Cordilleran Ice Sheet and subsequent thinning of the ice dams during deglaciation. From theoretical modeling of ice-dam failure, Craig and Singer (1984) also recognized an asymmetry in the likely sequence of j6kulhlaup volumes. These predictions require an independent means of verification. Waitt (1980) recognized eleven well-formed rhythmites above the 13 ka BP set-S tephra in several Touchet Bed localities in the Pasco Basin area. The 'forty floods' hypothesis requires a Lake Missoula source for these rhythmites. Indeed hydraulic damming of the Pasco Basin requires an immense flood volume of 220 km 3 merely to pond the necessary water in the Pasco Basin to account for the emplacement of the highest rhythmites (Waitt, 1980, p. 675). A time interval of 30 to 100 years between floods would imply that a selfdumping Lake Missoula must have persisted until perhaps 12.7 to 12 ka BP. This requires Lake Missoula to have formed near the maximum extent of the Purcell Trench Lobe of the Cordilleran Ice Sheet (Waitt and Thorson, 1983), while the well-dated Puget Lobe of the same ice sheet was in full recession (Thorson, 1980). The time problem is further constrained by dating of recession in the Pend Oreille and Kootenai Lobes of the Cordilleran Ice Sheet (Mack et al., 1978b, 1983). Questions also remain concerning the exact number of flood-generated beds. If the 'magic number' of 40 sites throughout the region is thought not to be coincidental, but instead to be the result of genesis by a related chain of events, then each chain produces equivalent responses at various sites of deposition. Measured sections of 62 rhythmites (Bjornstad, 1980) and 89 beds (Atwater, 1984b) are therefore anomalous and require modification of the original hypothesis. Moreover, local unconformities in flood-slackwater sequences (Foley, 1976; Hammatt, 1977; Bjornstad, 1980; Bunker, 1980, 1982) imply relatively long time breaks between some floods. Thus, the somewhat regular timing of floods as proposed by Waitt (1980, 1983b) may be untenable. Finally, it is essential to observe that flood-slackwater sediments, the rhythmites, and various lacustrine beds indicate relatively low-energy depositional environments. As recognized by Waitt (1984), the typical sequence of sedimentary structures in a graded rhythmite is accurately reproduced in a few hours of laboratory flume operation (Ashley et al., 1982). Such a sequence can be produced beneath a meter of water, as in the flume experiments, or beneath hundreds of meters of water, as proposed by Waitt (1980). Thus, individual low-energy flood and lacustrine sequences (Table 8) cannot in themselves indicate cataclysmic flood physics. As pointed out by Waitt (1980), in reference to the Lake Missoula bottom sediments: There is no clear evidence in these sections that the Lakes Missoula discharged truly catastrophically. . . . It is the Touchet Beds in southern Washington which emphasize that most of the roughly 40 Lake Missoula discharges were catastrophic. (Waitt, 1980, p. 674.)

CataclysmicFloodsfrom Glacial Lake Missoula

29

But it is also important to realize that the Touchet Beds are themselves relatively lowenergy sediments. The inference that they were emplaced by cataclysmic floods derives from hypotheses concerning the ponding of proglacial discharges in the Pasco Basin. Waitt (1980) rejects the possibility that the ponding of water in that basin could have been achieved by any other mechanism than the hydraulic damming of catacylsmic flood water. As stated by Waitt: I infer that all the deep pondings in Pasco Basin were short-lived hydraulic lakes. Any hydraulic surges in the basin were within an invading body of floodwater, not in already ponded water suddenly augmented. (Waitt, 1980, p. 670-1.) The above reasoning constitutes an assumption that is implicit in Waitt's hypothesis that low-energy rhythmites can be used to infer massive influxes of flood water to the Pasco Basin, which filled at least once to altitude 350 m and a volume of 1100 km 3 (Waitt, 1980, p. 671). Although rhythmites are best developed at altitudes below 180 m and discernible only to 245 m (Waitt, 1980, p. 672), the addition of 105 m of Pasco Basin ponding to maximum stage (corresponding to 880 km 3 or 80% of the maximum volume) remains to be explained. Demonstrated subaerial exposure of some rhythmites (Waitt, 1980, pp. 662-8; Bunker, 1980, 1982) implies that any volume of ponded water must completely drain after rhythmite emplacement. Waitt (1980, p. 667) further argues as follows: 'If a subaerial environment followed emplacement of the 28th rhythmite, similar environments probably followed emplacement of other rhythmites'. Thus, the 40-floods hypothesis requires a chain of assumptions. If ponding of the Pasco Basin can only have been achieved by hydraulic damming, if each ponding produced a distinct and separate rhythmite, if the subaerial exposure of s o m e rhythmites means that all were so exposed, and if the rhythmites formed under immense depths of water that are not directly indicated by the heights of the deposits themselves, then we are led to accept Waitt's (1980, pp. 672-3) proposed mechanism of rhythmite emplacement, as follows: 'A rhythmite records an upvalley surge of a rapidly deepening flood over dry land, and then hours of hydraulic ponding as the lake deepens, crests, and drains'. Because all rhythmites show sedimentological similarities, all presumably formed by the same chain of events. Low-energy, rhythmically bedded flood deposits have been used to infer the magnitudes of large paleoflood events (Patton et al., 1979; Kochel and Baker, 1982; Kochel et al., 1982; Baker et al., 1983). Indeed, it has proven possible to correlate individual floods along a river and to evaluate the frequency of flooding. However, such studies differ fundamentally from those of Atwater (1984) and Waitt (1980, 1984). In the former case, the highest deposited slack-water sediments are used to establish paleoflood stages and/or hydraulic grade lines for the generating flow events. Hydraulic flow models demonstrate the high discharges associated with water up to (not above) the level of sedimentation. Moreover, even relatively simple rainfall-generated Holocene floods have examples of multiple slackwater sediment units, i.e. two or more rhythmites, emplaced by a single flow event (Baker et al., 1983; Kochel, 1980). The above discussion has shown that there are several assumptions implicit to the 'fortyfloods' hypothesis that require an independent means of verification. The ambiguous

30

V.R. Baker and R.C. Bunker

indications of flood m a g n i t u d e s limit any analysis of Toucher Beds and other low-energy flood deposits in the C o l u m b i a River system. For example, do the eleven rhythmites that overlie the set-S t e p h r a in the Walla Walla and lower Y a k i m a valleys at an altitude of 185 m require eleven very large floods (Waitt, 1980)?

Evidence of Magnitude and Frequency R a t h e r than rely on assumptions to establish flood magnitudes, it would be far m o r e direct to search for high-energy flood deposits, such as b o u l d e r bars, that provide evidence of multiple flooding. S o m e possibilities for such an inventory of high-energy flood events occur in d o w n s t r e a m flood reaches, b e t w e e n W a s h i n g t o n and O r e g o n (Fig. 3). N e a r Arlington, O r e g o n (Locality A , Fig. 3), a flood-gravel bar occurs at altitude 245 m. T h e bar is attached to the d o w n c u r r e n t end of a streamlined hill, in such a position that it could accumulate s e d i m e n t f r o m floods escaping f r o m the Umatilla Basin of north-central O r e g o n (Fig. 5). T h e bar includes multiple flood beds ( B u n k e r , unpubl, data); the set-S tephra lies

SH-C

)

J/~/~"-///f

SH-C

J CHS

J /

TRENCH LOCATION

~y~

CHS

DF

CHS North

DF

J DF

o

1 km

FIG. 5. Geomorphic map of the Arlington region at the western end of the Umatilla Basin, northcentral Oregon. BR - - exposed bedrock of the Columbia River Basalt Group; CHS - - channeled scabland eroded in basalt floor of spill-over channel between Eightmile and Alkali Canyons; DF - channels eroded into the Dalles Formation (of Newcomb, 1969); G - undifferentiated flood-gravel deposits; GB (stipled) - - flood-gravel deposit discussed in text; SH-C - - streamlined hills eroded into conglomerate of the Dalles Formation. Hachured lines represent margins of spillover channel. Arrows show inferred flow directions.

31

Cataclysmic Floods from Glacial Lake Missoula

between the third and fourth beds (Fig. 6). The tephra is enclosed by silt and sand that is distinct from the coarse flood sediment above and below it. The silt and sand are interpreted as eolian sediments deposited subaerially between floods. Thus, one post-set-S flood is indicated. Moreover, a second silt and sand layer between the fourth and fifth flood beds may likewise be of subaerial origin. If so, a second post-set-S flood occurred. The fact that only two post-set-S floods at most are recorded at this relatively high altitude suggests there were relatively few large floods and that the Touchet Bed slack-water sequences located upstream and at lower altitudes may actually record more, but relatively smaller floods. NORTH

SOUTH

MIXED LOESS ~P::'

_~.

. .

.

.

.

.

.

J~'~U~Y~=~

.

.

.

.

.

.

.

.

/MIXED

J"

LOESS

& COLLUVIUM

DALLES FORMATION" - -

.

.

_

_

Im L l m

FIG. 6. Cross section of flood-gravel deposit as exposed in an exploration, now back-filled, trench through Arlington gravel bar (locality shown in Fig. 5). Heavy dashed line indicates the Mount St

Helens set-S tephra. Circled numbers refer to the stratigraphic position of the foreset-like beds; see text for discussion. Presence of sixth foreset-like bed queried because talus obscurred outcrop detail. Dark lens-shaped unit along lower part of inclined contact between beds 4 and 5 is a silt and sand layer of possible subaerial origin; its thickness is exaggerated on the diagram for emphasis. Unit 'A' may be pre-Late Wisconsinan in age, since it is relatively more cemented by calcium carbonate than are upper deposits. In addition, evidence near Portland, Oregon, suggests that even the possible two large post-set-S floods were small by the standards of an earlier Late Wisconsin flood. This earlier flood was responsible for the maximum high-water marks in the Portland area, which reach elevation 120 m (Trimble, 1963). The high-water marks were generated by ponding of a cataclysmic flood behind the narrowing of the Columbia River valley through the Coast Ranges. Flood bedload was deposited in this backwater zone by high-energy water entering the Portland area from the Columbia Gorge. The result was the so-called Portland delta described by Bretz (1925) and Allison (1978). Peat bogs that formed on this deposit indicate nonflood environments prevailed after the particularly deep cataclysmic flood, One bog at an altitude of only 60 m contains basal peat dated at 13,080 + 300 BP (W3404). Mullineaux et al. (1978) indicate that this date provides a younger limit to cataclysmic flooding from glacial Lake Missoula. Their reasoning is that any younger floods were clearly too small to innundate the portions of the Portland delta on which the peat was accumulating. If this stratigraphic interpretation is valid, then the 1l post-13 ka BP floods inferred by Waitt (1980) to derive from glacial Lake Missoula were of relatively small magnitude. Allison (1978) makes similar arguments concerning the sizes of possible floods that reached the Portland area.

32

v.R. Baker and R.C. Bunker

The above studies are preliminary, but they illustrate the obvious need for further work to establish magnitude limits on the various implications of the 'forty floods' hypothesis. Routes of the Late Wisconsin Floods The stratigraphic studies reviewed above do not convey the full complexity of the flood timing problem in the region. In addition to the questions of flood magnitude and frequency we must add questions of flood routing through numerous channelways (Fig. 1). The available radiocarbon dates (Table 7) are sparse for the size of the flooded region. Moreover, they do not permit unique interpretations of flood routing and timing. The chronology of flood episodes that follows is an attempt to distill the most recent literature in a way that is consistent with the radiocarbon constraints. Emphasis is placed on crosscutting relationships in the relatively coarse-grained, high energy, flood facies. A clear sequence of multiple floods can be deciphered in relation to the advance of the Okanogan Lobe (Fig. 3). Relations are well displayed in the vicinity of Wenatchee, Washington. At least one cataclysmic flood affected the Columbia valley at Wenatchee prior to the obstruction of that route by the Okanogan Lobe (Waitt, 1980, 1982). After the Okanogan Lobe had blocked the Columbia's valley during its advance, the Wenatchee area was isolated from upstream floods. Instead, flood water was forced out of the Columbia valley, skirting the Okanogan Lobe to erode Moses Coulee (Hanson, 1970). Where Moses Coulee flood water entered the Columbia valley downstream from Wenatchee, a large flood-gravel bar was built out across the valley (Bretz, 1930b). The bar blocked the Columbia, creating a lake ponded to altitude 260 to 275 m. At least four Moses Coulee floods occurred (Waitt, 1982) as inferred from four upvalley-dipping gravel beds intercalated with thinly bedded silt that accumulated in the floodbar-dammed lake. These floods had to occur before the Okanogan Lobe reached its terminus, because the terminal moraine overlies a flood bar in Moses Coulee (Hanson, 1970; Easterbrook, 1976). The time of arrival of the Okanogan Lobe at its terminus, and thus the minimum age of the Moses Coulee floods, is estimated as before 15 ka to 14 ka BP by analogy with the Puget Lobe, which reached its terminus about 14 ka BP (Waitt and Thorson, 1983). However, it is possible the Okanogan Lobe reached its terminus earlier (Easterbrook, 1976), because it was not influenced by calving into marine water that may have hindered the Puget Lobe's advance (Waitt and Thorson, 1983). Thus, the Moses Coulee floods are interpreted as occurring between 16 ka and 15 ka BP (Waitt, 1982). Once Moses Coulee was blocked by the Okanogan Lobe, floods could only travel via the Grand Coulee, the various eastern scabland tracts, or both. Evidence for flooding at the time the Okanogan Lobe blocked the Columbia River consists of flood-laid beds in glacial Lake Columbia, which formed upstream of the ice dam (Rigby, 1982; Atwater, 1984a; Waitt, 1984). The sizes of these floods are unknown. However, Atwater (1984b) argues that at least 89 regularly recurring floods occurred over a 2000- to 3000-year period between 16 ka to 12.4 ka BP. If the above chronology of the Okanogan Lobe is valid, then the period began after 15 ka BP. Atwater (1984b) uses varve counts to infer that initially the interval between floods was no more than 25-40 years. It quickly reached a maximum of 50-55 years; then it declined slowly to a minimum of 1 to 2 years. Relative magnitude is inferred

CataclysmicFloodsfrom Glacial Lake Missoula

33

from the thickness and grain size of the floodlaid beds. Relative magnitude was greatest for the infrequent floods. Assuming that Lake Missoula was a self-dumping ice-dammed lake, the flood-frequency trends imply that the lake's dam grew more quickly than it shrank. Another major question involves the timing of the retreat of the great upper cataract of the Grand Coulee, whose migration to the vicinity of Coulee Dam (Fig. 1) would have drained the 730-m level of Lake Columbia (Waitt and Thorson, 1983). This would have put an immense flood down the Grand Coulee as Lake Columbia dropped to the 470-m level, the altitude of the intake to the Grand Coulee. This flooding may explain evidence of backflooding into channels leading from the eastern scablands to the Quincy Basin, building gravel bars that block mouths of those channels where they enter Quincy Basin (Bretz et al., 1956). There is excellent field evidence for a phase of large floods associated with the recession of the Okanogan Lobe from the Columbia River valley (Waitt, 1982). These floods seem to have been confined chiefly to that valley. A major flood modified the surface of the Great Terrace, a body of outwash and lake silt that was constructed at the margin of the Okanogan Lobe near Chelan Falls (Fig. 3). That flood occurred before deposition of layer G of the Glacier Peak tephra onto the terrace (Waitt and Thorson, 1983). Two subsequent floods can be interpreted from large flood bars developed adjacent to, but below the Great Terrace (Waitt and Thorson, 1983). These floods are younger than approximately 11.25 ka BP because their depositional surfaces did not accumulate Glacier Peak tephra (Waitt and Thorson, 1983). The above relations have considerable significance because at least the two younger floods cannot have originated from glacial Lake Missoula. As suggested earlier, the upper limiting age for the possible existence of Lake Missoula is approximately 12.25 ka BP, and an argument can be made that the last formation of the lake may have been somewhat older than that. The relatively small size of these floods is also consistent with a non-Missoula source. Clearly the role of other non-Missoula cataclysmic floods needs to be assessed in the complex deglaciation of the Columbia River system. The oldest of the post-Okanogan Lobe floods was certainly cataclysmic. Ice-rafted erratics and upvalley-dipping crossbeds in gravels emplaced up tributaries indicate that this down-Columbia flood was as deep as 400 m at the junction with the Methow River (WaRt, 1977a). These depths require flood water at Coulee Dam (Fig. 3) to have had a surface elevation of 760 m. Waitt (1972, 1977a) suggested that these relations required hydraulic ponding of a Lake Missoula outburst at the Columbia gorge downstream. By assuming a correlation of Okanogan Lobe behavior to that of the Puget Lobe, Waitt (1977b) proposed that this flood occurred about 13.5 to 13 ka BP. In the lower Snake River valley (sites 9 and I0, Fig. 1) set-S tephra occurs in thin-bedded lacustrine silt and alluvium dated at 13 to 14 ka BP (Table 7) (Foley, 1976; Hammatt, 1977). This relation poses some constraints on probable flooding of the Pasco Basin by Missoula floods. Sites at Alpowa Canyon and Steptoe Canyon contain a massive toe bedded floodsedimentation unit older than 14 ka BP. Deposition of this unit was followed by a prolonged period of accumulation of nonflood alluvial fan gravel and colluvium coincident with the

34

V.R. Baker and R.C. Bunker

Mount St Helens set-S eruption. This nonflood phase was followed by a final episode of slack-water sedimentation. The latter is indicated by an undulating mantle of distinctly graded beds similar to the Touchet Bed distal rhythmites described by Waitt (1980). These deposits were probably emplaced by sediment-charged flooding up the Snake River. At Lewiston, Idaho, probable correlative deposits overlie gravel emplaced by a cataclysmic flood down the Snake River (Baker, 1978b, p. 26). The latter flood is probably the Bonneville flood, dated at 15 ka to 13.5 ka BP (Scott et al., 1983). Bonneville Flood flows came down the Snake River, entered the Pasco Basin, and probably contributed to the sequences of flood rhythmites described by Waitt (1980).

DISCUSSION AND CONCLUSIONS The problem of cataclysmic flood features in the northwestern United States has remained a lively controversy through much of this century. It seems certain that the problem will remain an important one into the next century. Future studies must consider the entire region of flooding plus a diversity of landscapes, sedimentary facies, and scientific disciplines. There is an unequivocal need to combine work on the physics of cataclysmic flood processes with detailed sedimentology, stratigraphy, and geochronology. A partial approach to the problem can only be useful when combined with studies from related regions and/or disciplines. The calculation of cataclysmic flood discharges from high-water marks can be improved by new hydraulic flow modeling procedures. The results of new calculations should be compared to glaciological models for Lake Missoula growth and release. Improved studies should be made of the physics of emplacement for both high-energy, main-channel flood deposits and low-energy, slack-water deposits. Periodic j6kulhlaups of glacial lake Missoula were clearly possible in the time interval of approximately 17 ka to 12 ka BP (Table 8). Models of ice dam formation and stratigraphic studies of low-energy flood deposits support this concept. However, it has not yet been demonstrated from evidence of high-energy indicators in the lake basin (Pardee, 1942; Plate 4) that more than one draining of the lake occurred at its maximum volume (Table 4). The 'forty-floods' hypothesis has proven useful in specifying the number and frequency of major flow events through the Columbia River system. However, its corollary assumptions concerning cataclysmic magnitudes for those events and regional correlation of 'cognate' (Waitt, 1980) sedimentation units have yet to be adequately demonstrated. Such assumptions rely on a chain of reasoning that rejects, not one, but innumerable other possibly valid hypotheses. For example, the 'forty-floods' hypothesis holds that each rhythmite in the Walla Walla section (Plate 2) was emplaced by a separate, discrete flood (Waitt, 1980, pp. 661-8); each flood advanced over dry land (Waitt, 1980, p. 672); only separate hydraulic dammings of Wallula Gap could have produced the ponding necessary to emplace each rhythmite (Waitt, 1980, p. 670); each rhythmite can only have been emplaced by a flood emanating from glacial Lake Missoula (Waitt, 1980, pp. 668-71 ; Waitt, 1984, p. 52); individual floodlaid beds in similar stratigraphic sequence can be directly correlated from Montana to Oregon (Waitt, 1984, p. 49); and glacial Lake Missoula must have drained

CataclysmicFloodsfrom Glacial Lake Missoula

35

as a catastrophic j6kulhlaup once every few decades (Waitt, 1984, p. 57). The various ambiguities in regional correlations based on genetic models or on similar-appearing stratigraphic sections will only be resolved by improved time stratigraphy. Given the sparseness of datable materials and the absence of tephra common to all sections, paleomagnetic studies may prove useful. Fine correlations between sections may be possible if base periods of secular variation are short (Barendregt, 1981). Ideally these should be no longer than several decades, the proposed length of time between floods. Thermoluminescence (TL) dating (Wintle and Huntley, 1982) might be attempted, perhaps testing for agreement with sediments containing the Mount St Helens set-S tephra. Improved geochronology for the various flood rhythmite sequences may resolve the question of multiple beds being generated by a single flood. Moreover, if multiple floods are indicated, dating will permit an accurate analysis of flood frequency. The concept of tens of Lake Missoula flooding of the Columbia River should be replaced by one involving a multitude of flood events throughout the Columbia system. Many of these floods, but not all, emanated from glacial Lake Missoula. These events had variable magnitudes, some of which were truly cataclysmic. The floods followed various paths depending on their magnitudes and on the complexities of ice margins and erosional history. Although all converged on the Pasco Basin, they did so from different directions. The floods had frequencies that can be discerned in certain remarkable stratigraphic sections. Unfortunately many of the best sections that indicate the number of events occur at low elevation in low-energy depositional sites that do not directly indicate the magnitudes of each event. Considerable new work is required to accurately specify the magnitudes, frequency, and routing of the Late Pleistocene flooding in the Columbia River system.

ACKNOWLED GEMENTS Research on the Channeled Scabland has been supported over the years by National Science Foundation Grant GA-21478 (1970-71) and by National Aeronautics and Space Administration Grants NSG-7326 (1976-77), NSG-7557 (1979-81) and NAGW-285 (1981-present).

REFERENCES Albritton, C.C. (1967). Uniformity, the ambiguous principle. In: Albritton, C.C. (ed.) Uniformity and Simplicity, pp. 1-2. Geological Society of America Special Paper 89. Alden, W.C. (1927). Discussion: Channeled Scabland and the Spokane Flood. Journal of the Washington Academy of Science, 17, 203. Allison, I.S. (1933). New version of the Spokane Flood. Geological Society of America Bulletin, 44, 675-722. Allison, I.S. (1941). Flint's fill-hypothesis for channeled scabland. Journal of Geology, 49, 54-73. Allison, I.S. (1978). Late Pleistocene sediments and floods in the Willamette valley. The Ore Bin, 40, 177-191, 193-202. Alt, D. and Chambers, R.L. (1970). Repetition of the Spokane Flood. American Quaternary Association, Abstracts of the First Biennial Meeting, Vol. 1, Bozeman, Montana. Alwin, J.A, (1970). Clastic dikes of the Touchet Beds, southeastern Washington. M.S. Thesis, Washington State University, Pullman.

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V.R. Baker and R.C. Bunker

Ashley, G.M., Southard, J.B. and Boothroyd, J.C. (1982). Deposition of climbing-ripple beds - - A flume simulation. Sedimentology, 29, 67-79. Atwater, B.F. (1983). JBkulhlaups into the Sanpoil arm of glacial Lake Columbia, Washington. United States Geological Survey Open-File Report, 83-456. Atwater, B.F. (1984a). Periodic floods from glacial Lake Missoula into the Sanpoil arm of glacial Lake Columbia, northeastern Washington. Geology, 12,464-467. Atwater, B.F. (1984b). Number, frequency, and relative magnitudes of last-glacial floods from Pleistocene Lake Missoula, Montana - - Evidence from the Sanpoil River valley, northeastern Washington. EOS, 65,893. Baker, V.R. (1971). Paleohydrology of catastrophic Pleistocene flooding in eastern Washington, Geological Society of America Abstracts with Programs, 3, 497. Baker, V.R. (1973). Paleohydrology and sedimentology of Lake Missoula flooding in eastern Washington. Geological Society of America Special Publication, 144, 1-79. Baker, V.R. (1978a). The Spokane Flood controversy and the Martian outflow channels. Science, 202, 1249-1256. Baker, V.R. (1978b). Quaternary geology of the Channeled Scabland and adjacent areas. In: Baker, V.R. and Nummedal, D. (eds) The Channeled Scabland, pp. 17-35. National Aeronautics and Space Administration, Washington, D.C. Baker, V.R. (1978c). Paleohydraulics and hydrodynamics of scabland floods. In: Baker, V.R. and Nummedal, D. (.eds) The Channeled Scabland, pp. 59-80, National Aeronautics and Space Administration, Washington, D.C. Baker, V.R. (1978d). Large-scale erosionaland depositional features of the Channeled Scabland. ln: Baker, V.R. and Nummedal, D. (eds) The Channeled Scabland, pp. 17-35. National Aeronautics and Space Administration, Washington, D.C. Baker, V.R. (1981). Catastrophic Flooding: The Origin of the Channeled Scabland. Dowden, Hutchinson and Ross, Stroudsburg, Pennsylvania. Baker, V.R. (1983). Late-Pleistocene fluvial systems. In: Wright, H.E., Jr. (ed.) Late Quaternary Environments of the United States, Vol. 1, Porter, S.C. (ed.) The Late Pleistocene, pp. 115-129. University of Minnesota Press, Minneapolis. Baker, V.R., Kochel, R.C. and Patton, P.C. (1979). Long-term flood frequency analysis using geological data. International Association of Hydrological Sciences Publication, 128, 3-9. Baker, V.R., Kochel, R.C., Patton, P.C. and Pickup, G. (1983). Palaeohydrologic analysis of Holocene flood slack-water sediments. Special Publications of the International Association of Sedimentologists, 6, 229-239. Baker, V.R. and Nummedal, D. (1978). The Channeled Scabland. Planetary Geology Program, National Aeronautics and Space Administration, Washington, D.C. Barendregt, R.W. (1981). Dating methods of Pleistocene deposits and their problems: VI. Paleomagnetism. Geoscience Canada, 8, 56-64. Baulig, H. (1913). Le plateaux de lave du Washington Central et la Grand 'Coulee'. Annals of Geography, 22, 149-159. Bjornstad, B.N. (1980). Sedimentology and depositional environment of the Touchet Beds, Walla Walla River Basin, Washington. Rockwell Hanford Operations Report, RHO-BWI-SA-44, Richland, Washington, 83 pp. Bjornstad, B.N. (1982). Catastrophic flood surging represented in the Touchet Beds of the Walla Walla Valley, Washington. American Quaternary Association, Program and Abstracts of the Seventh Biennial Conference, Seattle, Washington, 72. Black, R.F. (1979). Clastic dikes of the Pasco Basin, southeastern Washington. Rockwell Hartford Operations Report, RItO-BWI-C-64, Richland, Washington. Bouma, A.H. (1962). Sedimentology of some Flysch Deposits. Elsevier, Amsterdam. Bretz, J.H. (1919). The Late Pleistocene submergence in the Columbia Valley of Oregon and Washington. Journal of Geology, 27, 489-505. Bretz, J.H. (1923a). Glacial drainage on the Columbia Plateau. Geological Society of America, 34, 573-608. Bretz, J.H. (1923b). The Channeled Scabland of the Columbia Plateau. Journal of Geology, 31, 617-649. Bretz, J.H. (1924). The Dalles type of river channel. Journal of Geology, 32, 139-149.

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