Missoula Floods Research Articles

Magnetostratigraphic evidence from the Cold Creek bar for onset of ice-age cataclysmic floods in eastern Washington during the Early Pleistocene

This study provides a detailed magnetostratigraphy of sediments composing the Cold Creek cataclysmic flood bar in the Pasco Basin, Washington. Our interpretation suggests onset of Missoula floods or similar events prior to 1.1 myr, later than previously suggested by Bjornstad et al. [Bjornstad, B.N., Fecht, K.R., Pluhar, C.J., 2001. Long history of pre-Wisconsin, Ice Age cataclysmic floods: evidence from southeastern Washington State. Journal of Geology 109 (6), 695–713]. Nonetheless these data suggest that Channeled Scabland features formed over a much longer timespan than commonly cited, that continental ice sheets of the early Pleistocene reached as far south as those of the late Pleistocene, and that similar physiography existed in eastern Washington and perhaps Montana to both generate and route Missoula-flood-like events. This study adds paleomagnetic polarity results from 213 new samples of silts and sands derived from nine new drill cores penetrating the Cold Creek cataclysmic flood bar to our previous database of 53 samples from four boreholes, resulting in a much more robust and detailed magnetostratigraphy. Rock magnetic studies on these sediments show pure magnetite to be the predominant remanence-carrying magnetic mineral, ruling out widespread remagnetization by secondary mineralization. The magnetostratigraphy at eastern Cold Creek bar is characterized by a normal polarity interval bracketed by reversed polarities. Equating the normal zone with the Jaramillo subchron (0.99–1.07 myr) affords the simplest correlation to the magnetic polarity timescale. Western Cold Creek bar was likely deposited during the Brunhes chron (0–0.78 myr) since it exhibits mainly normal polarities with only two thin reversed-polarity horizons that we interpret as magnetic excursions during the Brunhes.

Simulating the evolution of coastal morphology and stratigraphy with a new morphological-behaviour model (GEOMBEST)

A new morphological-behaviour model is used to simulate evolution of coastal morphology associated with cross-shore translations of the shoreface, barrier, and estuary. The model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales (order 10 3 years), as well as shorter time scales applicable for long-term coastal management (order 10 1 to 10 2 years). Changes in sea level, and sediment volume within the shoreface, barrier, and estuary, drive the model behaviour. Further parameters, defining substrate erodibility, sediment composition, and time-dependent shoreface response, constrain the evolution of the shoreface towards an equilibrium profile. Results from numerical experiments are presented for the low-gradient autochthonous setting of North Carolina and the steep allochthonous setting of the Washington shelf. Simulations in the Currituck region of North Carolina examined the influence of sediment supply, substrate composition, and substrate erodibility on barrier transgression. Results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible, sand-rich substrate exists. Simulations of the Washington coast, 20 km north of the Columbia River, confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution. Results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the Columbia River attributed to the Missoula floods. This was followed by a period where little or no sediment was added (12 400–9100 BP) and a third period when most sediment was added to the shelf (9100 BP to present) from the Columbia River. Comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates. Shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation, with the sensitivity increasing as substrate slope decreases.

Genetic Analysis of Interior Pacific Northwest Oncorhynchus mykiss Reveals Apparent Ancient Hybridization with Westslope Cutthroat Trout

Seventeen populations of Oncorhynchus mykiss were analyzed for mitochondrial haplotype diversity through either polymerase chain reaction–restriction fragment length polymorphism analysis or mitochondrial DNA sequencing. Six new mitochondrial haplotypes were observed among these populations, five in steelhead and one in Harney Basin rainbow trout. Although no distinct patterns were observed between steelhead and rainbow trout with mitochondrial DNA sequencing, Harney Basin rainbow trout populations from southeastern Oregon exhibited a high frequency of a unique new haplotype designated MYS22. Fourteen of 17 individuals within the Harney Basin rainbow trout populations possessed this haplotype. Additionally, the mitochondrial DNA haplotypes of six westslope cutthroat trout O. clarki lewisi were observed among 90 steelhead from the Tucannon River, Washington, a river in which no native or introduced cutthroat trout have been documented. Analysis of other introduced hatchery and wild stocks of steelhead and rainbow trout from throughout the interior Pacific Northwest revealed only rainbow trout and steelhead mitochondrial haplotypes. Analysis of 90 wild Tucannon River steelhead using 16 nuclear DNA markers detected only one individual with a single nuclear allele consistent with westslope cutthroat trout, although the marker may be a rare rainbow trout or steelhead nuclear allele. This suggests that a hybridization event of ancient origin probably occurred within the Tucannon River basin. This hybridization event may have occurred between Tucannon River steelhead and a now extinct native population of westslope cutthroat trout that probably arrived as a result of late Wisconsin glacial outburst floods (Missoula Floods) occurring 19,000–10,000 years before the present.

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.

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.

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.

Computer modelling of the water resurge at a marine impact: the Lockne crater, Sweden

Abstract When a cosmic impact occurs at sea, the resulting crater can form completely in the water mass or extend into the seafloor. At intermediate to great water depths, the collapse of the water cavity generates a forceful resurge of water along the seafloor towards the central part of the crater. The erosive effects as well as certain conspicuous deposits from resurge flows are known from several craters. This study uses numerical modelling to estimate the magnitude of the resurge in the case of the 455 Myr old marine-target Lockne impact crater, Sweden. The water depth at the Lockne target site was at least 200 m, possibly even as great as 1 km. Field evidence show that the resurge was strong enough to erode gullies hundreds of metres wide, tens of metres deep, and kilometres long. With computer modelling we studied the behaviour of the flow to get a notion of its magnitude. The calculations required simplification of the reality. We used a fixed seafloor topography and pure water. A rim in the water mass is expected but was neglected in the calculations. The simplification likely led to underestimation of the magnitude of the resurge. The effect of different target water depths was studied. At 200-m target water depth, about 1.2×10 11 m 3 of water were needed to fill the Lockne crater, including the water cavity. This took about 2200 s. It has been suggested that the main gully formation occurs when the resurge passes the inner rim of the crater. That phase lasts for about 700 s. With a 500-m target water depth, these processes are 3–4 times faster. The erosive force of the flow (i.e. unit stream power) is 1.9×10 5 (Wm −2 ) in the 200-m water depth model. This is of the same magnitude as the Lake Missoula Flood, the greatest catastrophic flooding known on Earth. At 500-m target water, the unit stream power is a magnitude greater.

Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River

Research Article| May 01, 1999 Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River Charlotte A. Brunner; Charlotte A. Brunner 1Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi 39529, USA Search for other works by this author on: GSW Google Scholar William R. Normark; William R. Normark 2U.S. Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Gian G. Zuffa; Gian G. Zuffa 3Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Francesca Serra Francesca Serra 3Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40127 Bologna, Italy Search for other works by this author on: GSW Google Scholar Author and Article Information Charlotte A. Brunner 1Department of Marine Science, University of Southern Mississippi, Stennis Space Center, Mississippi 39529, USA William R. Normark 2U.S. Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, California 94025, USA Gian G. Zuffa 3Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40127 Bologna, Italy Francesca Serra 3Dipartimento di Scienze della Terra e Geologico-Ambientali, Università di Bologna, Via Zamboni 67, 40127 Bologna, Italy Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1999) 27 (5): 463–466. https://doi.org/10.1130/0091-7613(1999)027<0463:DSSROT>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Charlotte A. Brunner, William R. Normark, Gian G. Zuffa, Francesca Serra; Deep-sea sedimentary record of the late Wisconsin cataclysmic floods from the Columbia River. Geology 1999;; 27 (5): 463–466. doi: https://doi.org/10.1130/0091-7613(1999)027<0463:DSSROT>2.3.CO;2 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 SocietyGeology Search Advanced Search Abstract New results from Ocean Drilling Program Site 1037 and U.S. Geological Survey high-resolution seismic-reflection profiles confirm the great thickness, fast deposition rate, distant source, and convolute path of turbidites that fill the Escanaba Trough, the rift valley of the southernmost segment of the Gorda Ridge. Accelerator mass spectrometry 14C measurements provide the first direct dating of the Escanaba Trough turbidites, demonstrating an average deposition rate faster than 10 m/k.y. between 32 and 11 ka and as fast as 15 m/k.y. during the oxygen isotope stage 2 lowstand. In the upper 60 m of sediment, the petrology of turbidite sand beds, which are as much as 12 m thick, show that the dominant source for the turbidites is from the Columbia River, which is more than 800 km to the north, rather than from the much closer rivers of northern California. New high-resolution seismic-reflection profiles show that, except for areas of very recent volcanism, the entire Escanaba Trough below 3200 m water depth is floored by the turbidite sequence that was cored in the upper 60 m at Site 1037B. The ages of the upper 120 m of turbidites correspond with the ages of channeled scabland deposits associated with latest Quaternary jokulhlaups from glacial Lake Missoula. The age and source characteristics suggest that these megaturbidite beds in Escanaba Trough are most likely deposits formed by hyperpycnally generated turbidity currents as the largest of the Lake Missoula floods entered the sea. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Report on the Sixtieth Annual Meeting

REPORT ON THE SIXTIETH ANNUAL MEETING Spokane, Washington September 10-13, 1997 After 3 years of whining by our California colleagues about the lack of an annual meeting invitation by a “northern institution,” East­ ern Washington University stepped boldly into the breach and hosted the 1997 convocation at the Ridpath Hotel in beautiful downtown Spokane. Although the bright promise of financial support by the university failed to materialize (owing to a severe fiscal crisis—sound familiar?) and APCG members from more southerly latitudes stayed away in droves, the meeting was an experiential—if not financial— success. A grand total of 104 registrants overcame the limitations of time and distance to participate: 59 full registrations, 35 students, and 10 spouse/others. The meeting kicked off on Wednesday night with a reception featuring Washington wines, cheeses, fruits, and vegies, followed by a stirring opening address by Phil Wagner, professor emeritus at Simon Fraser University, whose topic was “Borders” (and not just the ones on the ground...). Thursday was devoted entirely to field work, as EWU geographers and planners spent the day introducing APCG members to the highlights of the Inland Empire. Dick Winchell led an all-day trip to the Colville Indian Reservation and Grand Cou­ lee Dam, while Susan Bradbury and Linda Yeomans burrowed through the urban delights of central Spokane. Dale Stradling’s group explored the geomorphology of Spokane County’s Channelled Scablands , and once again Dale’s powerful description of the prehistoric Lake Missoula Flood caused him to have to deny having been an eyewitness to the events. Bob Quinn and Mike Folsom led two sepa­ rate wetlands excursions, both of which focused on ecological and growth management issues. The field experiences were capped on Thursday night with an outdoor salmon barbeque at Riverfront Park. 187 188 APCG YEARBOOK • VOLUME 60 • 1998 A total of 44 papers were presented— 17 of them by students— during the day on Friday and on Saturday morning, ranging across the entire spectrum of geographical topics. A President’s Plenary Session on “GIS and Cartography” was hosted by President Joan Clemons on Saturday, featuring cartographic luminaries Michael Goodchild, Nick Entrikin, and Stacy Warren. Portland State Univer­ sity geographers also organized a panel on “Teaching Geography in the Changing University,” which was well attended. Other highlights of APCG ’97 included the Womens Network Luncheon, the Depart­ ment Chairs Luncheon, and of course, the Friday night Presidential Banquet. Joan Clemons’ presidential address, “Emerging from Sew­ age and Waste: The Postmodern Landscape,” was a fascinating and beautifully illustrated exploration of topics not ordinarily dealt with right after dinner. While attendance at this year’s meeting was significantly down, owing perhaps more to core-periphery issues than to the attractive­ ness of the host city, some interesting patterns nonetheless emerged. As usual, California led the roster with 35 participants, followed by Oregon and Washington with 22 each. These were followed by Brit­ ish Columbia with seven, Arizona with four, Nevada with two, and Alaska with one. Incidentally, the return of our Canadian colleagues to the APCG fold after a long absence is to be noted. Most major research universities in the APCG turf zone were represented; even the University of Washington managed to send four graduate stu­ dents after being savaged in this report so often over the past decade! (We can only wonder how much closer to Seattle we would have to hold the meeting to get a faculty member...). The mileage award this year was a tie between Roger Pearson of Alaska-Fairbanks and Jim Nemeth of Toledo. While it would be nice to conclude that the 1997 Spokane meet­ ing was a big moneymaker for the APCG, it simply could not happen with such a small attendance, an urban hotel venue, and a lack of host university financial support. Looking on the bright side, a great Annual Meeting Report 189 time was had by all, new friendships were formed and old ones re­ newed, and we all learned something...and that’s what it’s all about. Dan Turbeville Eastern Washington University ...

Energy Expenditure and Geomorphic Work of the Cataclysmic Missoula Flooding in the Columbia River GGorge, USA

Cataclysmic releases from the glacially dammed Lake Missoula, producing exceptionally large floods, have resulted in significant erosional processes occurring over relatively short time spans. Erosional landforms produced by the cataclysmic Missoula floods appear to follow a temporal sequence in many areas of eastern Washington State. This study has focused on the sequence observed between Celilo and the John Day River, where the erosional features can be physically quantified in terms of stream power and geomorphic work. The step-backwater calculations, in conjunction with the geologic evidence of maximum flow stages, indicate a peak discharge for the largest Missoula flood of 10 ×10 6 m 3 s -1 . The analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross-section. The nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations. Therefore, the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes. The critical stream power required to initiate erosion varied for the different landforms of the erosional sequence, ranging from 500 W m -2 for the streamlined hills, up to 4500 W m -2 to initiate processes producing inner channels. Erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion. In fact, despite the multiple outbursts which occurred during the late Pleistocene, only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work. © 1997 by John Wiley & Sons, Ltd.

Tephrochronologic Constraints on the Late Pleistocene History of the Southern Margin of the Cordilleran Ice Sheet, Western Washington

An ash layer that appears geochemically correlative with Mt. St. Helens tephra set S occurs in a sequence of Pleistocene lake sediments in the Ohop Valley of the southern Puget Lowland, below Vashon till deposited during the maximum late Pleistocene advance (Fraser Glaciation) of the Puget Lobe of the Cordilleran Ice Sheet. The Puget Lobe reached its maximum southern extent ca. 14,000–14,500 yr B.P., and at least part of set S is evidently somewhat older. Previous radiocarbon and thermoluminescence dates for set S have ranged from 13,000 to 16,000 yr B.P.Geochemically correlative deposits of set S tephra occur in slackwater sediments coeval with the Missoula Floods in eastern Washington, produced by jökulhlaups through the Purcell Trench Lobe of the Cordilleran Ice Sheet. These relationships suggest that advances of glacier lobes on the southern margin of the Cordilleran Ice Sheet were nonsynchronous, as the Pucell Trench lobe east of the Cascade Range advanced to its maximum southern extent prior to the time of the eruption of set S, before the Puget Lobe west of the Cascades reached its maximum southern extent.

Catastrophic flood sediments in Chryse Basin, Mars, and Quincy Basin, Washington: Application of sandar facies model

Viking visible and thermal infrared observations and terrestrial catastrophic flood deposits provide clues to identify the outflow channel sediments that went into Chryse Basin on Mars. On Earth, sandar (outwash plains formed by coalescence of many jökulhlaup floods) are described in terms of three laterally adjacent facies: proximal, midfan, and distal. The Missoula Flood sediments deposited in Quincy Basin, Washington, comprise a miniature analog of Chryse Basin. The terminology and general characteristics of the sandar facies model are applied to Quincy Basin, although the depositional environment and clast sizes are somewhat different (higher‐energy flood, larger clasts, subaqueous rather than subaerial deposition). For example, the Ephrata Fan (a deposit of boulders, cobbles, and pebbles) forms the midfan facies analog; a downfan sandy deposit (reworked into a dune field) comprises the distal facies analog. In Chryse Basin the midfan is defined by a heterogeneous rocky (0–25%), intermediate‐albedo (0.21–0.26), intermediate thermal inertia (260–460 J m−2 s−0.5 K−1) surface, while the distal facies has a low albedo (0.14–0.16) and higher thermal inertia (340–700 J m−2 s−0.5 K−1). The Chryse midfan unit has rocks and windblown dust exposed at the surface. The sand of the distal facies in Chryse/Acidalia is reworked by the wind, as in Quincy Basin. The Viking 1 and Mars Pathfinder landing sites are located on the midfan unit. Observations that can be made at the Mars Pathfinder site might help in reevaluating whether or not Viking 1 landed on outflow channel sediments.

Geochemical Estimates of Paleorecharge in the Pasco Basin: Evaluation of the Chloride Mass Balance Technique

The Pasco Basin in southeastern Washington State provides a unique hydrogeologic setting for evaluating the chloride mass balance technique for estimating recharge. This basin was affected by late Pleistocene catastrophic floods when glacial dams in western Montana and northern Idaho were breached. It is estimated that multiple Missoula floods occurred between ∼13,000 and 15,000 years B.P. and reached a high water elevation of ∼350 m. These floods removed accumulated chloride from the sediment profile, effectively resetting the chloride mass balance clock at the beginning of the Holocene. The rate of chloride accumulation qCl in the sediments was determined by two methods and compared. The first method measured qCl by dividing the calculated natural fallout of 36Cl by a measured ratio of 36Cl/Cl in the pore water, while the second method used the total mass of chloride in the profile divided by the length of time that atmospheric chloride had accumulated since the last flood. Although the two methods are based on different approaches, they showed close agreement. In laboratory studies the sediment to water ratio for chloride extraction was sensitive to the grain size of the sediments; low extraction ratios in silt loam sediments led to significant underestimation of pore water chloride concentration. Br/Cl ratios were useful for distinguishing nonatmospheric (e.g., rock) sources of chloride. Field studies showed little spatial variability in estimated recharge at a given site within the basin but showed significant topographic control on recharge rates in this semiarid environment. An extension of the conventional chloride mass balance model was used to evaluate chloride profiles under transient, time‐varying annual precipitation conditions. This model was inverted to determine the paleorecharge history for a given soil chloride profile, and the parameters of the root extraction model required to estimate paleoprecipitation

Buried carbonate paleosols developed in Pliocene-Pleistocene deposits of the Pasco Basin, south-central Washington, U.S.A.

Abstract Carbonate-rich paleosols represent a small volume of material at the Hanford Site in south-central Washington state, U.S.A., but their position below highly permeable Missoula-flood deposits and above the water table makes them an important component of contaminant remediation plans. Previous work indicated that these buried carbonate paleosols constitute a relatively continuous, low-permeability paleosurface. The distribution of the Pliocene-Pleistocene deposits containing the paleosols depends in part on erosion of the underlying Miocene-Pliocene fluvial/lacustrine Ringold Formation and post-depositional erosion by the catastrophic Missoula floods. The character of the ‘caliche’ layer(s), as determined from cores, varies across the study area: from 0–20 m in thickness; at depths of 20 m in the south, to 65 m in the northwest; bounded above and below by irregular surfaces with as much as 25 m relief; and in general co-varies in number of carbonate layers with the thickness of the deposits. These carbonate layers reflect the geomorphology and hydrology existing during the time they developed. I interpret these carbonate layers as paleosols but recognize morphologic features that indicate modification may have occurred after initial development at the surface. These include the absence of associated soil horizons; no apparent decrease in carbonate content with depth in some of the carbonate layers; and unusual Bk horizon fabrics (including crystalline or popcorn-like forms). These features and fabric differences influence potential flow pathways of waste fluids.

Cosmogenic 3He and 21Ne age of the Big Lost River flood, Snake River Plain, Idaho

The Big Lost River flood in southeastern Idaho occurred 20,500 calibrated yr B.P., on the basis of dates derived from cosmogenic 3 He and 21 Ne measurements of samples from flood-deposited boulders and from scour features. This date corresponds to a date of 16,900 14 C yr B.P. and is close in age to several other cataclysmic flood events in western North America; it may mark evidence for widespread warming at the end of the Pleistocene in western North America. The Big Lost River flood was smaller than some other late Pleistocene floods, such as the Bonnevi1le flood and the Missoula floods; thus, some samples exposed after the flood had significant amounts of cosmogenic 3 He and 21 Ne that was acquired before the flood occurred.

Sedimentary effects of cataclysmic late Pleistocene glacial outburst flooding, Altay Mountains, Siberia

Pleistocene glacial outburst floods were released from ice-dammed lakes of the Altay Mountains, south-central Siberia. The Kuray-Chuja lake system yielded peak floods in excess of 1 × 106 m3 s−1 and as great as 18 × 106 m3 s−1. The phenomenally high bed shear stresses and stream powers generated in these flows produced a main-channel, coarse-grained facies of coarse gravel in (1) foreset-bedded bars as much as 200 m high and several kilometers long, and (2) degradational, boulder-capped river terraces. Giant current ripples, 50 to 150 m in spacing, composed of pebble and cobble gravel, are locally abundant. The whole sedimentary assemblage is very similar to that of the Channeled Scabland, produced by the Pleistocene Missoula Floods of western North America.

Missoula flood dynamics and magnitudes inferred from sedimentology of slack-water deposits on the Columbia Plateau, Washington

Sedimentological study of late Wisconsin, Missoula-flood slack-water sediments deposited along the Columbia and Tucannon Rivers in southern Washington reveals important aspects of flood dynamics. Most flood facies were deposited by energetic flood surges (velocities > 6 m/sec) entering protected areas along the flood tract, or flowing up and then directly out of tributary valleys. True still-water facies are less voluminous and restricted to elevations below 230 m. High flood stages attended the initial arrival of the flood wave and were not associated with subsequent hydraulic ponding upslope from channel constrictions. Among 186 flood beds studied in 12 sections, 57% have bioturbated tops, and about half of these bioturbated beds are separated from overlying flood beds by nonflood sediments. A single graded flood bed was deposited at most sites during most floods. Sequences in which 2-9 graded beds were deposited during a single flood are restricted to low elevations. These sequences imply complex, multi-peaked hydrographs in which the first flood surge was generally the largest, and subsequent surges were attenuated by water already present in slack-water areas. Slack-water-sediment stratigraphy suggests a wide range of flood discharges and volumes. Of >40 documented late Wisconsin floods that inundated the Pasco Basin, only about 20 crossed the Palouse-Snake divide. Floods younger than the set-S tephras from Mount St. Helens were generally smaller than earlier floods of late Wisconsin age, although most still crossed the Palouse-Snake divide. These late floods primarily traversed the Cheney-Palouse scabland because stratigraphy of slack-water sediment along the Columbia River implies that the largest flood volumes did not enter the Pasco Basin by way of the Columbia River.

Magnitudes and implications of peak discharges from glacial Lake Missoula

New field evidence and discharge calculation procedures provide new estimates of maximum late Pleistocene glacial Lake Missoula flood discharges for two important reaches along the flood route. Within the Spokane Valley, near the point of release, the peak discharge probably exceeded 17 ± 3 million m3 sec-1. Downstream at Wallula Gap, a major point of flow convergence, peak discharge was about 10 ± 2.5 million m3sec-1. Flow duration was on the order of several days. These are the largest known terrestrial fresh-water flows. Consideration of these discharge values constrains models for the failure of glacial Lake Missoula. The maximum discharges estimated here are larger than theoretical and empirical predictions of maximum subglacial jokulhlaup-style releases for Lake Missoula. We postulate, consistent with geological relations in the glacial Lake Missoula basin and in the Channeled Scabland, that the largest late Wisconsinan Missoula Flood resulted from a cataclysmic failure of the impounding ice dam of glacial Lake Missoula. This large release may have been the result of a complete rupture of the ice dam. Subsequent multiple flows of lesser magnitude may have resulted from repeated subglacial releases from the lake.