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Fluvial Processes and Geomorphic Environments

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Fluvial Processes Erosion headward dissection vertical incision lateral migration Transport bed load suspended load dissolved load Deposition deltas natural levee backswamp alluvial fan

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Fluvial erosion, transport, and deposition by flowing water. des excludes glaciofluvial systems Sediments: coarse to fine grained, commonly stratified; texture and morphology depends upon deposition environment Landscapes: alluvial plain, canyonlands, river valley Landforms: arroyo, flood-plain step, meander, stream terrace Microfeatures: bar, groove, gully

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Braided Stream Platte River near Louisville, NE

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Landscape: flood plain, river valley; Landforms: meanders, oxbow lake, scroll bar ; Laramie R., WY Wysocki

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Ritter et al., 1995

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( Ritter, et al., 1995 )

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Benoit MS, AR USGS 7.5 quad

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MS River Oxbow Deer Creek Source

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Wysocki Holocene clay capped stream terrace (Sharkey soil); Washington Co., MS

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Wysocki Sharkey soil profile ; Washington Co., MS Sharkey Series very fine, Chromic Epiaquert

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Wysocki Natural levee to backswamp transition. Dundee Series Fine Silty Typic Endoaqualf Sunflower Co. MS

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Landscape: river valley; Landforms: scroll bars, oxbows, channelized river ; Miss. R., AR / MS Wysocki

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Landscape: loess-covered till plain; Landform: entrenched stream, meanders; Lincoln, NE Wysocki

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( NASA id 16633 ) Landscapes : river valley, gulf (water) Landforms : delta (birds foot) channel, natural levee Mississippi R., LA (1999; natural color)

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Landform: stream terraces ; Snake R., near Jackson Hole, WY Wysocki

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Landforms: canyon, strath terrace; Black Canyon (Gunnison R.), CO Schoeneberger

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Fill Terrace

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Erosional terrace

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Alluvial Fans Alluvial fans compared to perennial streams cross-sectional profile - longitudinally convex flashy flow system sediment composition: Degree of Sorting - < stream alluvium Degree of Rounding - < stream alluvium Clast supported - > stream alluvium debris / mudflow - common in proximal areas

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Landforms : low mountains, interfluves, alluvial fan, braided river ; Brodeur Peninsula, Baffin Is, Nunavut, CAN ( GSC#2002-205 )

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Insert graphic from Lambert, 1996 ( NM, 2002 ) Landform: alluvial fan; Parent Material: fan alluvium; Organ Mountains, Las Cruces, NM Schoeneberger

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Landform: alluvial fan ; Death Valley, CA. What is the grayer deposit to left?

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Landform: alluvial fan; Cedar Creek Fan MT Ennis, MT USGS 7.5 Quad

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Ritter, et al, 1995

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How do you distinguish a low gradient alluvial fan from a stream terrace?

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One Mile Alluvial Fans Stream Terrace

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active alluvial fan fan remnant ( fan surface abandoned but substantially intact; inset fan-head trenches, terraces) eroded fan remnant ( little fan surface remains; e.g. < 50 % of original fan surface ) eroded fan remnant sideslopes ( no fan surface remains; hillslope elements dominate ) original fan surface Evolutionary stages of alluvial fan landforms ( cross-sectional profiles ) PJS, 2004 Inset fan

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( Peterson, 1981; fig. 3 ) Basic Landform elements of Basin & Range terrain southwestern US A - alluvial fan B - ballenas F - alluvial flat M - mountains (LS) P - fan piedmont (LS) S - fan skirt Y - playa bolson, semi-bolson Landscape :

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A - alluvial fan V - interfan valley P - fan piedmont ( Peterson, 1981; fig. 7 ) Drainageway Types (FFP). 1 - interfan - valley drainageway 2 - fanhead trench 3 - onfan drainageway 4 - interfan-valley drainageway Inset fan fan remnant

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Landscape: bajada in a semi-bolson ; Landforms: ballena, eroded fan remnants, eroded fan-remnant sideslopes, inset fan, terraces ; Organ Mountains., Las Cruces, NM Schoeneberger

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Hillslope Evolution : back wearing side slopes and pedimentation S = ?? a = ?? P = ?? c = ?? ps = ?? ( Peterson, 1981; fig. 16 )

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( Peterson, 1981; fig. 15 ) Hillslope Evolution & Hillslope - Profile Positions: - 2 dimensional - backwearing slope convergence - divide lowering

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( Peterson, 1981; fig. 9 ) p - ( partial ballenas ) s - ( relict summit area )

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Landscape: bajada in a semi-bolson ; Landforms: eroded fan remnants, eroded fan- remnant sideslopes ; Organ Mountains., Las Cruces, NM Schoeneberger

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( adapted from Peterson, 1981; fig. 17 ) c = crest m = summit s = shoulder b = backslope f = footslope t = toeslope x = drainageway Variations of hillslope-profile positions in southwestern US Landscapes

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Landscape: bajada ; Landform: eroded fan remnants, inset terraces ; Tortugas Mtn. view (Organ Mountains., Las Cruces, NM ) Schoeneberger

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( Peterson, 1981; fig 11 ) 1 - original fan surface 2 - first gullying sequence ( or its remnants of pediments, footslopes ) 3 - second gullying sequence ( or its remnants of pediments, footslopes ) 4 - third gullying sequence ( or its remnants of pediments, footslopes ) Landscape Evolution : Typical Erosion Sequences of Fan Piedmonts Generalized (Erosional) Evolution of Divides a relict fan-piedmont surface (1) b - asymmetric, relict fan piedmont surface and new, encroaching pediments c - ridgeline remnants of pediments 2 & 3 d - late stage erosion of c

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Landform : slot canyon Escalante Natl. Mon., UT Schoeneberger slot canyon A long, narrow, deep and tortuous channel or drainageway with sheer rock walls eroded into sandstone or other sedimentary rocks, especially in the semi-arid western USA (e.g. Colorado Plateau); subject to flash flood events; depth to width ratios exceed 10:1 over most of its length and can approach 100:1; commonly containing unique ecological communities distinct from the adjacent, drier uplands. NSSH