liBRARY COPY The Catastrophic Late Pleistocene Bonneville Flood in the Snake River Plain, Idaho GEOLOGICAL SURVEY PROFESSIONAL PAPER 596 The Catastrophic Late Pleistocene Bonneville Flood in the Snake River Plain, Idaho By HAROLD E. MALDE GEOLOGICAL SURVEY PROFESSIONAL PAPER 596 A study of colossal features of erosion and deposition produced along the Snake River by sudden overflow of Lake Bonneville UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 -. UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402- Price 70 cents (paper cover) CONTENTS Page Page 1 The canyon below Twin Falls-Continued IntroductionAbstract------------------------------------------- ______________________________________ _ 2 Melon Valley section (mile 162-155) _____________ _ 32 Background of study ___________________________ _ 2 Thousand Springs section (mile 155-151) _________ _ 32 Acknowledgments ______________________________ _ 6 Hagerman Valley (mile 151-141) _________________ _ 32 Summary of flood path _________________________ _ 6 Bliss section (mile 141-121) _____________________ _ 34 Glacial and pluvial stratigraphy ________________ ~_ 7 King Hill basin (mile 121-109) __________________ _ 35 Source--------------------------------------------­ 9 Cove section (mile 109-76) ______________________ _ 37 Age----------------------------------------------- 10 Crane Falls section (mile 76-61) _________________ _ 37 Magnitude of flood _________________________________ _ 11 Grand View basin (mile 61-28) __________________ _ 40 Duration _________________________________________ _ 12 Swan Falls section (mile 28-14) __________________ _ 42 Comparison with last catastrophic flood from glacial Walters basin (mile 14-0)------------------------ 42 Lake Missoula, Mont ____________________________ _ 13 Budget of erosion and deposition ____________________ _ 44 Diagnostic depositional and erosional features _________ _ 13 Discharge as indicated by size of boulders _____________ _ 46 Melon GraveL ________________________________ _ 13 Comparison with historic floods ______________________ _ 47 Lithology _________________________________ _ 13 Reservoir failures ______________________________ _ 47 Physiography _____________________________ _ 17 Gohna Lake, India _________________________ _ 47 Marginal channels _____________________________ _ 18 The Great Indus Flood, India _______________ _ 48 Impounded water ______________________________ _ 18 Flood at Gros Ventre, Wyo _________________ _ 48 Scabland _____________________________________ _ 20 Lake Issyk, U.S.S.R _______________________ _ 48 Path of flood above Twin Falls ______________________ _ 21 St. Francis Dam, Calif ______________________ _ 48 Upper Snake River Plain _______________________ _ 21 Vaiont Reservoir, Italy _____________________ _ 49 Rupert channeL ______________ ----------- ______ _ 22 Floods associated with glaciers __________________ _ 49 Milner reach _____________________________ ------ 23 Jokulhlaups in Iceland _____________________ _ 49 Erosion near Twin Falls ____________________________ _ 25 Various ice-dammed lakes ___________________ _ 50 The canyon below Twin Falls _______________________ _ 30 Summary of historic floods ______________________ _ 51 Weeping Wall section (mile 175-162) _____________ _ 31 References cited ___________________________________ _ 51 ILLUSTRATIONS Page FIGURE 1. Map of northern part of Lake Bonneville and nearby part of Snake River Plain ___________________________ _ 3 2. Map of Snake River below Twin Falls----------------------------------------------------------------- 5 3. Diagram showing profile of Snake River and of Bonneville Flood ________________________________________ _ 8 4. Photograph showing boulders on bar of Melon Gravel near Hagerman ____________________________________ _ 14 5. Photograph showing terminus of gravel bar in Melon Valley _____________________________________________ _ 15 6. Sketch of pit in sandbar of Melon GraveL _________________________________________________________ -- __ 16 7-9. Photographs: 7. Festoon crossbeds in dipping layers of sand _____________________________________________________ _ 17 8. Boulder train on surface of Melon GraveL _______________________________________________ - ____ -_ 17 9. Minor erosional features in basalt scabland _____________________________________________________ _ 20 10. Geologic sketch map of American Falls area ___________________________________________________________ _ 21 11. Topographic map showing dry falls and giant potholes near Eden ________________________________________ _ 23 12. Photograph showing Snake River canyon upstream from Hansen Bridge __________________________________ _ 24 13. Cross sections of Snake River canyon _________________________________________________________________ _ 26 14. Topographic map of Snake River canyon near Twin Falls _______________________________________________ _ 28 15. Photograph showing Snake River canyon downstream from Perrine Memorial Bridge _______________________ _ 30 16. Topographic map of Melon Valley area---------------------------------------------------------------- 33 ~ 7. Geologic sketch of Melon Valley _____________________________________________________________________ _ 34 18. Photograph showing boulders of Melon· Gravel near Banbury Hot Springs ________________________________ _ 34 19. Topographic map of Hagerman Valley ________________________________________________________________ _ 36 20. Topographic map of King Hill basin __________________________________________________________________ _ 38 21. Photograph showing basalt boulders on lava flow near Bancroft Springs ___________________________________ _ 40 III IV CONTENTS Page FIGURE 22. Topographic map of Crane Falls area__________________________________________________________________ 41 23. Topographic map of Walters basin____________________________________________________________________ 43 24. Graph showing volume of Melon Gravel along Snake River______________________________________________ 46 25. Graph showing discharge of some glacier bursts in Iceland_______________________________________________ 50 26. Section of a supra-aquatic delta of sandur type_________________________________________________________ 50 TABLES Page TABLE 1. Topographic relations of mariginal channels______________________________________________________________ 19 2. Discharge capacity of Snake River canyon at selected constrictions_________________________________________ 25 3. Computation of volume of Snake River canyon, Augur Falls (mile 17 5) to Hansen Bridge (mile 1~9) __ _ _ _ _ _ _ _ _ _ _ 45 4. Volume of Melon Gravel above Grand View______________________________________________________________ 45 5. Velocities and discharges indicated by size of boulders in Melon Gravel just below canyon constrictions__________ 46 6. Velocities indicated by size of boulders in Melon Gravel where floodwater was not constricted__________________ 46 7. Flood wave on the Ganges caused by rupture of landslide dam at Gohna, India______________________________ 48 8. Progress of flood wave from St. Francis Dam, CaliL _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 49 \., -' THE CATASTROPHIC LATE PLEISTOCENE BONNEVILLE FLOOD IN THE SNAKE RIVER PLAIN, IDAHO By HAROLD E. MALDE ABSTRACT basalt boulders just below canyon constrictions are commonly A catastrophic flood caused by overflow and rapid lowering larger than 5 feet and can be identified as having come from of Pleistocene Lake Bonneville at Red Rock Pass near Preston, outcrops not more than a few miles upstream. The gravel occurs Idaho, descended Marsh Creek Valley and reached the Snake mainly in wide places along the canyon as groups of bars of River Plain at the site of Pocatello. Large tracts in the upper colossal size that together resemble the greatly magnified bed Snake River Plain were inundated, particularly an area near of a braided stream. In the lower reach of wide segments along American Falls and a basin that surrounds Rupert. Farther the canyon, bouldery flood debris gives way to sandy deposits, downstream, the Snake River CtUlyon that extends 200 miles presumably because of retarded flow. Bars of gravel block the west of Twin Falls was flooded to a depth of 300 feet. Spec­ mouths of some tributary valleys, but at most places the bars tacular erosion in the form of abandoned channels, spillways, stand midway between the canyon walls, from which they are cataracts, nnd scabland identifies the flood path between Ameri­ separated by marginal channels as deep as 150 feet. The con­ can Falls and Twin Falls, and the cnnyon farther west is strewn structional form of these bars is well preserved, and they ap­ with huge boulders-some of them more than 10 feet in diam­ parently have been little modified by erosion since the flood. eter-which are heaped in enormous bars of boulders and sand Fine-grained alluvium formed broad flats in tributary valleys that rise nearly 300 feet above the canyon floor. that were blocked by deposits of Melon Gravel. Other fine­ The Bonneville Flood nlmost certainly wa:s caused by capture grained material was dropped in backwater areas of temporary of the Benr River, which resulted in greatly augmented inflow lakes that filled broad segments of the Snake River canyon to the Bonneville