History and Dynamics of Glaciation in the Northern Yellowstone National Park Area

Fl Introduction . 2 Previous work . 4 Acknowledgments . 5 Physical features relevent to glaciation . 5 Regional topography . 5 Bedrock type and distribution . 5 Climate . 5 Effect of geothermal features on glaciation . 7 Patterns of ice accumulation, movement, and ablation . 7 Major ice sources and drainageways . 8 Interaction between glaciers from different sources through time . 8 Discussion of methods . 9 Indicators of age . 10 Soil development. 10 Obsidian hydration . 10 Determining direction of glacial flow . 11 Erratics . 11 Rat tails . 11 Striations . 11 Striations and polish on bedrock protuberances . 11 Polish on treads and not on risers . 11 Low-angle friction cracks . 11 Reconstruction of the ice surface . 12 The Bull Lake-Pinedale paradigm. 14 Outline of pre-Bull Lake surficial deposits . 15 Bull Lake Glaciation . 15 West Yellowstone Basin . 15 Relative-age criteria. 19 Discussion of age assignment. 23 Glaciers on western Mount Cowen. 25 Bull Lake deposits within the area covered by Pinedale ice . 26 Northern Yellowstone outlet glacier . 26 Northern Yellowstone National Park . 27 Transport of Beartooth erratics southward past the Washburn Range . 27 Pinedale Glaciation . 30 Ice accumulation prior to full-glacial conditions . 30 Glaciers from the Beartooth uplift. 30 Local icecap on the Washburn Range . 31 Icecaps on the Yellowstone plateau and Gallatin Range. 31 Full-glacial conditions . 31 Terminal area of the northern Yellowstone glacier. 31 Pinedale outwash fan and ice-marginal channel. 31 End moraines . 33 Northern Yellowstone outlet glacier from its terminus to Gardiner. 34 Icecap sources feeding the northern Yellowstone outlet glacier. 36 Gallatin Range icecap . 36 Plateau icecap between the Gallatin and Washburn Ranges . 38 Pinedale Glaciation Continued Plateau icecap overriding the Washburn Range and Specimen Ridge . F39 Beartooth uplift icecap . 40 Ice in the upper Lamar drainage basin. 43 Age of high-level scour features . 45 Ice divides and flow away from the northern Yellowstone glacier . 46 Gallatin Range. 46 Glaciation south of the Gallatin Range . 46 Obsidian-sand outwash plain . 48 East-west icecap axis above the Obsidian Cliff flow . 51 Ice divide south of the Washburn Range . 52 Ice divide in the upper Lamar drainage . 52 Ice divide on the Beartooth uplift. 53 Ice divide between Soda Butte and Clarks Fork glaciers . 53 Changing glacial dynamics during waning glacial conditions . 53 Simple upvalley recession. 53 Gallatin Valley glacier . 53 Glaciers in the valleys of Cougar, Maple, and Grayling Creeks . 55 Phase relations between areas feeding the northern Yellowstone outlet glacier in pre-Deckard Flats time. 55 Backfill in Tom Miner Basin . 55 Other tributary glaciers north of Yellowstone National Park . 56 Ice in central northern Yellowstone National Park . 57 Deckard Flats readjustment. 57 Yellowstone valley . 57 Glaciers from the Gallatin Range . 58 Glaciers from the Beartooth uplift. 59 Plateau icecap south of the Washburn Range . 60 Recession following the Deckard Flats readjustment . 60 Age of the Deckard Flats readjustment. 61 Late Pinedale advance or standstill. 61 Gallatin Range glaciers . 63 Icecap on the Beartooth uplift. 63 Recession from the late Pinedale position . 63 Gallatin Range glaciers . 63 Glaciers from the Beartooth uplift. 63 Age-limits of the late Pinedale advance or standstill. 64 Late Pinedale and younger floods . 65 Glacial dynamics inferred from geologic studies . 68 Comparison of Bull Lake and Pinedale Glaciations . 68 Quantitative evaluation of the reconstructed icemass . 69 Basal shear stress . 69 Basal shear stress and alternate glacial reconstructions . 72 Equilibrium-line altitude. 74