Fluvial Processes and Geomorphic Environments

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

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

Braided Stream Platte River near Louisville, NE

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

Ritter et al., 1995

( Ritter, et al., 1995 )

Benoit MS, AR USGS 7.5’ quad

MS River Oxbow Deer Creek Source

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

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

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

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

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

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

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

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

Fill Terrace

Erosional terrace

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

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

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

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

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

Ritter, et al, 1995

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

One Mile Alluvial Fans Stream Terrace

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

( 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 :

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

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

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

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

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

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

( 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

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

( 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”

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