DOCSLIB.ORG

Rates and Mechanisms of Bedrock Incision and Strath Terrace Formation in a Forested Catchment, Cascade Range, Washington

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Rates and Mechanisms of Bedrock Incision and Strath Terrace Formation in a Forested Catchment, Cascade Range, Washington Geological Society of America Bulletin, published online on 8 January 2016 as doi:10.1130/B31340.1 Bedrock incision and strath terrace formation in a forested catchment Rates and mechanisms of bedrock incision and strath terrace formation in a forested catchment, Cascade Range, Washington Brian D. Collins1,†, David R. Montgomery1, Sarah A. Schanz1, and Isaac J. Larsen2 1Department of Earth and Space Sciences and Quaternary Research Center, University of Washington, Seattle, Washington 98195-1310, USA 2Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003-9297, USA ABSTRACT strath abandonment corresponds with histor- pension), macro-abrasion (fracturing of the bed- ical anthropogenic removal of fluvial wood, rock into pluckable or entrainable sizes through Measurements of channel bed and bank suggesting that the relative abundance of flu- the collision with particles in transport), pluck- incision into bedrock coupled with mapping vial wood may influence episodes of vertical ing (hydraulic removal of blocks), dissolution, and radiocarbon dating of strath terraces in bedrock incision by affecting the retention of and cavitation (Whipple et al., 2000). The domi- the West Fork Teanaway River, Washington, alluvium on streambeds. nance and efficacy of an erosional process in a provide insight into rates and mechanisms natural channel depend in part on lithology, joint of river incision and strath terrace forma- INTRODUCTION spacing, fractures, and bedding planes (Whipple tion in a forested landscape. The West Fork et al., 2000). Physical and chemical weather- drains 102 km2 of the slowly exhuming Bedrock incision by rivers drives the topo- ing can greatly enhance erosional processes southeastern North Cascade Range, and it graphic evolution of mountain landscapes and (Howard, 1998; Whipple et al., 2000; Stock is rapidly eroding its bed and creating strath can leave a morphologic signature in the form of et al., 2005; Hancock et al., 2011; Han et al., terraces in its lower reach. Minimum vertical strath terraces, which provide important records 2014; Small et al., 2015) by increasing rough- incision, measured annually relative to nails for interpreting tectonic and climatic history ness (Hancock et al., 1998; Huda and Small, embedded in the streambed, was greater in the (Pazzaglia, 2013). Because of bedrock incision’s 2014) and decreasing rock strength and thereby seasonally exposed, weathering-dominated, importance, it has been the subject of a number of enhancing susceptibility to abrasion, expanding high-flow channel (mean = 10.9 mm yr–1) theoretical and experimental (see review by Lamb fractures along which blocks are removed by than in the perennially wet, abrasion-domi- et al., 2015) and field studies (e.g., Hancock et al., plucking (Hancock et al., 1998; Whipple et al., nated, low-flow channel (3.8 mm yr –1), docu- 1998; Tinkler and Parish, 1998; Whipple et al., 2000), and comminuting rock into smaller frag- menting unsteady lowering of the channel 2000; Hartshorn et al., 2002; Stock et al., 2005; ments (Stock et al., 2005). margin. Ages of radiocarbon-dated materials Johnson et al., 2010; Lamb and Fonstad, 2010; The efficacy of at least some erosional and from alluvium on strath terraces, 0.1 m to Cook et al., 2013; Inoue et al., 2014). However, weathering processes is also influenced by the 5.4 m above the water surface, suggest three few studies have linked incisional processes with thickness of alluvial cover. For example, labora- episodes of strath abandonment at maximum lateral planation of straths or their subsequent tory experiments predict maximum abrasion ages of ca. A.D. 830, A.D. 1560, and A.D. 1890, incision and stranding as strath terraces (e.g., of streambeds having partial bedrock exposure and average incision rates of 1.3 mm yr–1, Montgomery, 2004; Finnegan and Balco, 2013; associated with intermediate sediment supplies 1.4 mm yr –1, and 7.4 mm yr –1 for the oldest to Johnson and Finnegan, 2015). Here, in a field that provide the “tools” for abrading the bed youngest surfaces, respectively. Weathering- study of a river that is rapidly eroding its bed without protecting the bed from abrasion (Sklar promoted vertical incision in the high-flow and creating strath terraces, we measured annual and Dietrich, 2001). While most applications of channel provides a mechanism for “top- vertical and lateral incision to address theoretical this concept to interpreting river incision his- down” rapid lateral strath planation in which and laboratory predictions on the relative roles tories have focused on regional- or basin-scale scour of alluvium on incipient strath terraces of erosion and weathering processes in shaping influences on stream power or the supply and incorporates the surface into the high-flow channels (e.g., Hancock et al., 2011; Small et al., caliber of sediment (e.g., changes to base level, channel, allowing rapid removal of bedrock 2015). We then coupled these measurements climate, or tectonic uplift rates), reach-scale weathered during wetting and drying cycles. with incision rates determined from strath ter- processes that control the routing or retention Relationships among channel width, channel races using radiocarbon dating, and we propose of sediment in channels, such as landslides that confinement by bedrock terrace risers, mod- a mechanism of rapid strath planation and how form temporary dams in rivers, could control eled bankfull shear stress, and alluvial bed it may, by adjusting channel morphology, inter- rates of bedrock incision by altering the dis- cover suggest that rapid channel widening nally limit incision. tribution of alluvial and bedrock reaches (e.g., could also internally limit vertical incision Ouimet et al., 2007). In forested regions, such by slowing incision as shear stresses decline Background a mechanism could also be provided by in- and more alluvium is retained on the bed. channel wood accumulations, which can trans- The timing of the most recent (ca. A.D. 1890) Bedrock channels erode by processes that form channels from bedrock to alluvial by alter- include abrasion (removal of rock by impact ing the balance between sediment transport and †[email protected] from saltating particles in the bed load or in sus- supply (Montgomery et al., 1996). GSA Bulletin; Month/Month 2015; v. 1xx; no. X/X; p. 1–18; doi: 10.1130/B31340.1; 15 figures; 6 tables.; published online XX Month 2015. For permission to copy, contact [email protected] Geological Society of America Bulletin, v. 1XX, no. XX/XX 1 © 2016 Geological Society of America Geological Society of America Bulletin, published online on 8 January 2016 as doi:10.1130/B31340.1 Collins et al. Cross-channel variation in processes and than, 2002; Finnegan et al., 2007; Spotila et al., et al., 2014). However, Gallen et al. (2015) rates of bedrock incision shapes channel cross- 2015) or susceptibility to weathering (Hancock recently proposed this effect could, in many riv- sectional and planform geometry, which in turn et al., 2011; Johnson and Finnegan, 2015), and ers, be the result of a systematic bias introduced controls hydraulics and the distribution of ero- thus the efficacy of lateral strath planation of by use of the modern streambed as the datum for sive power across the channel (for review, see bedrock channels (Montgomery, 2004; García, measuring terrace heights. Hancock et al., 2011). Differential incision rates 2006; Wohl, 2008). Channel planform may in a channel’s low-flow and high-flow bed (in also influence rates and patterns of lateral ero- Approach this paper, we use “low-flow channel” inter- sion; Finnegan and Balco (2013) suggested that changeably with “channel thalweg” and “high- a braided channel is more likely to accomplish To investigate how different erosional pro- flow channel” interchangeably with “channel lateral planation because the channel is more cesses operate in space and time to vertically margins”) can result from differences in weath- prone to incise laterally along both margins, and horizontally incise rivers and create straths, ering (Stock et al., 2005; Hancock et al., 2011; rather than just one margin. we undertook a field study of a rapidly incis- Small et al., 2015) or from whether cover or Incision and terrace creation have long been ing river in a region with slow rock uplift and tool effects dominate (Turowski et al., 2008). recognized as inherently unsteady (Gilbert, no known active faulting, the forested West Differences in rock erodibility can also be a 1877; Mackin, 1937; Bull, 1990) due to tempo- Fork Teanaway River in the southeastern North primary influence on the shape of river longi- ral variation in uplift (e.g., Pazzaglia and Gard- Cascades of Washington State (Fig. 1). Previ- tudinal profiles (Duvall et al., 2004; Allen et al., ner, 1993; Schoenbohm et al., 2004), base-level ously, we reported 1 yr average bedrock inci- 2013). Locally rapid incision is often associ- fall, and knickpoints that propagate upstream sion from the study site (Stock et al., 2005). ated with knickpoints that propagate upstream (e.g., Harvey and Wells, 1987; García et al., Here, we report direct field measurements of or that initiate in steeper, smaller-drainage- 2004, Bishop et al., 2005), or climate-forced vertical bed incision and lateral bank reces- area parts of a channel network (Crosby and variations in the relative supply of water and sion measured relative to nails in the riverbed Whipple, 2006). However, several field studies sediment (e.g., Pazzaglia and
Load more

Recommended publications
  • Proceedings of the Indiana Academy of Science
    Origin of the Mitchell Plain in South-Central Indiana 1 Richard L. Powell, Indiana Geological Survey The pre-karst surface of the southern part of the Mitchell Plain was leveled by surface streams of late Tertiary age that headed on the plain or within the Norman Upland and flowed through re-entrant valleys in the Crawford Upland into the pre-Pleistocene Ohio River. The karst features and subterranean drainage characteristic of the Mitchell Plain developed as a lower base level was established by rejuvenation during the late Tertiary or early Pleistocene. These ancient stream routes were first noticed on the Corydon West, Depauw, Fredericksburg, Hardinsburg, Leavenworth, Mauckport, Milltown, and New Amsterdam topographic quadrangles, which cover part of the Mitchell Plain and the Crawford Upland. The ancient stream courses are represented by three kinds of topographic features which are well shown on these maps : hanging dry valleys, bedrock terraces, and abandoned meander loops. The topographic features were checked on aerial photographs and in the field to determine their geologic characteristics. The fossil drainage system studied occupies part of the present drainage basins of Blue River, Indian Creek, and Buck Creek, which are tributaries of the Ohio River (fig. 1). This combined drainage area Figure 1. Map of south-central Indiana showing- the location of drainage features. includes approximately 900 square miles mostly in Crawford, Harrison, and Washington Counties. This drainage basin includes parts of three physiographic units: the Norman Upland, the Mitchell Plain, and the Crawford Upland (2). The Norman Upland is upheld by resistant shales and siltstones of early Mississippian age, which form an eastward facing cuesta that is called the Knobstone Escarpment.
    [Show full text]
  • Timescale Dependence in River Channel Migration Measurements
    TIMESCALE DEPENDENCE IN RIVER CHANNEL MIGRATION MEASUREMENTS Abstract: Accurately measuring river meander migration over time is critical for sediment budgets and understanding how rivers respond to changes in hydrology or sediment supply. However, estimates of meander migration rates or streambank contributions to sediment budgets using repeat aerial imagery, maps, or topographic data will be underestimated without proper accounting for channel reversal. Furthermore, comparing channel planform adjustment measured over dissimilar timescales are biased because shortand long-term measurements are disproportionately affected by temporary rate variability, long-term hiatuses, and channel reversals. We evaluate the role of timescale dependence for the Root River, a single threaded meandering sand- and gravel-bedded river in southeastern Minnesota, USA, with 76 years of aerial photographs spanning an era of landscape changes that have drastically altered flows. Empirical data and results from a statistical river migration model both confirm a temporal measurement-scale dependence, illustrated by systematic underestimations (2–15% at 50 years) and convergence of migration rates measured over sufficiently long timescales (> 40 years). Frequency of channel reversals exerts primary control on measurement bias for longer time intervals by erasing the record of observable migration. We conclude that using long-term measurements of channel migration for sediment remobilization projections, streambank contributions to sediment budgets, sediment flux estimates, and perceptions of fluvial change will necessarily underestimate such calculations. Introduction Fundamental concepts and motivations Measuring river meander migration rates from historical aerial images is useful for developing a predictive understanding of channel and floodplain evolution (Lauer & Parker, 2008; Crosato, 2009; Braudrick et al., 2009; Parker et al., 2011), bedrock incision and strath terrace formation (C.
    [Show full text]
  • Experimental Evidence for Fluvial Bedrock Incision by Suspended and Bedload Sediment Joel S
    Experimental evidence for fl uvial bedrock incision by suspended and bedload sediment Joel S. Scheingross1*, Fanny Brun1,2, Daniel Y. Lo1, Khadijah Omerdin1, and Michael P. Lamb1 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA 2Geosciences Department, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France ABSTRACT regime, the saltation-abrasion model was re- Fluvial bedrock incision sets the pace of landscape evolution and can be dominated by cast (by Lamb et al., 2008) in terms of near-bed abrasion from impacting particles. Existing bedrock incision models diverge on the ability of sediment concentration rather than particle hop sediment to erode within the suspension regime, leading to competing predictions of lowland lengths (herein referred to as the total-load mod- river erosion rates, knickpoint formation and evolution, and the transient response of orogens el). The saltation-abrasion and total-load mod- to external forcing. We present controlled abrasion mill experiments designed to test fl uvial els produce similar results for erosion within incision models in the bedload and suspension regimes by varying sediment size while holding the bedload regime, but within the suspension fi xed hydraulics, sediment load, and substrate strength. Measurable erosion occurred within regime the total-load model predicts nonzero the suspension regime, and erosion rates agree with a mechanistic incision theory for erosion erosion rates that increase with increasing fl uid by mixed suspended and bedload sediment. Our experimental results indicate that suspen- bed stress, leading to contrasting predictions sion-regime erosion can dominate channel incision during large fl oods and in steep channels, for landscape evolution, especially during large with signifi cant implications for the pace of landscape evolution.
    [Show full text]
  • Experimental Study of River Incision: Discussion and Reply Discussion
    Experimental study of river incision: Discussion and reply Discussion G. H. DURY Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, Wisconsin 53706 While introducing their experiments on river incision into bed existing streams and ancestral larger streams have proved equally rock, Shepherd and Schumm (1974) claimed that the morphologic capable of developing pool-and-riffle sequences in bed rock. details of interfaces between alluvium and bed rock are essentially Although far more abundant evidence would, of course, be wel- unknown. They referred to highs and lows shaped in bed rock as come, it seems reasonable to suggest that the morphologic details possible analogues of the riffles and pools of alluvial rivers but re- of the alluvium/bedrock interface beneath underfit streams are far garded the longitudinal profiles of bedrock streams as effectively from being essentially unknown. On the contrary, those details unstudied (see their p. 261). The clear implication is that interfaces have been deliberately and extensively studied. Similarly, it would and profiles have not been deliberately investigated. Both here and appear that somewhat more than a little is known of the longitudi- in their review of opinions about the inheritance or noninheritance nal profiles of bedrock streams. Australian serials, especially those of incised meanders (266—267), they overlooked a considerable with a geographical title, might perhaps be regarded as not particu- body of published research and commentary. larly accessible sources, except that Schumm was attached to the The question of the possible inheritance of incised meanders Department of Geography in the University of Sydney, Australia, at from an ancient flood plain at high level has been debated over the about the time when the Colo and Hawkesbury Rivers were being years, the debate involving numbers of workers on the European investigated from that department as a base.
    [Show full text]
  • Channel Morphology and Bedrock River Incision: Theory, Experiments, and Application to the Eastern Himalaya
    Channel morphology and bedrock river incision: Theory, experiments, and application to the eastern Himalaya Noah J. Finnegan A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Washington 2007 Program Authorized to Offer Degree: Department of Earth and Space Sciences University of Washington Graduate School This is to certify that I have examined this copy of a doctoral dissertation by Noah J. Finnegan and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Co-Chairs of the Supervisory Committee: ___________________________________________________________ Bernard Hallet ___________________________________________________________ David R. Montgomery Reading Committee: ____________________________________________________________ Bernard Hallet ____________________________________________________________ David R. Montgomery ____________________________________________________________ Gerard Roe Date:________________________ In presenting this dissertation in partial fulfillment of the requirements for the doctoral degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of the dissertation is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Requests for copying or reproduction of this dissertation may be referred
    [Show full text]
  • River Incision Into Bedrock: Mechanics and Relative Efficacy of Plucking, Abrasion and Cavitation
    River incision into bedrock: Mechanics and relative efficacy of plucking, abrasion and cavitation Kelin X. Whipple* Department of Earth, Atmospheric, and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Gregory S. Hancock Department of Geology, College of William and Mary, Williamsburg, Virginia 23187 Robert S. Anderson Department of Earth Sciences, University of California, Santa Cruz, California 95064 ABSTRACT long term (Howard et al., 1994). These conditions are commonly met in Improved formulation of bedrock erosion laws requires knowledge mountainous and tectonically active landscapes, and bedrock channels are of the actual processes operative at the bed. We present qualitative field known to dominate steeplands drainage networks (e.g., Wohl, 1993; Mont- evidence from a wide range of settings that the relative efficacy of the gomery et al., 1996; Hovius et al., 1997). As the three-dimensional structure various processes of fluvial erosion (e.g., plucking, abrasion, cavitation, of drainage networks sets much of the form of terrestrial landscapes, it is solution) is a strong function of substrate lithology, and that joint spac- clear that a deep appreciation of mountainous landscapes requires knowl- ing, fractures, and bedding planes exert the most direct control. The edge of the controls on bedrock channel morphology. Moreover, bedrock relative importance of the various processes and the nature of the in- channels play a critical role in the dynamic evolution of mountainous land- terplay between them are inferred from detailed observations of the scapes (Anderson, 1994; Anderson et al., 1994; Howard et al., 1994; Tucker morphology of erosional forms on channel bed and banks, and their and Slingerland, 1996; Sklar and Dietrich, 1998; Whipple and Tucker, spatial distributions.
    [Show full text]
  • VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION in the CRETACEOUS Mcdermott MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO
    VOLCANIC INFLUENCE OVER FLUVIAL SEDIMENTATION IN THE CRETACEOUS McDERMOTT MEMBER, ANIMAS FORMATION, SOUTHWESTERN COLORADO Colleen O’Shea A Thesis Submitted to the Graduate College of Bowling Green State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August: 2009 Committee: James Evans, advisor Kurt Panter, co-advisor John Farver ii Abstract James Evans, advisor Volcanic processes during and after an eruption can impact adjacent fluvial systems by high influx rates of volcaniclastic sediment, drainage disruption, formation and failure of natural dams, changes in channel geometry and changes in channel pattern. Depending on the magnitude and frequency of disruptive events, the fluvial system might “recover” over a period of years or might change to some other morphology. The goal of this study is to evaluate the preservation potential of volcanic features in the fluvial environment and assess fluvial system recovery in a probable ancient analog of a fluvial-volcanic system. The McDermott Member is the lower member of the Late Cretaceous - Tertiary Animas Formation in SW Colorado. Field studies were based on a southwest-northeast transect of six measured sections near Durango, Colorado. In the field, 13 lithofacies have been identified including various types of sandstones, conglomerates, and mudrocks interbedded with lahars, mildly reworked tuff, and primary pyroclastic units. Subsequent microfacies analysis suggests the lahar lithofacies can be subdivided into three types based on clast composition and matrix color, this might indicate different volcanic sources or sequential changes in the volcanic center. In addition, microfacies analysis of the primary pyroclastic units suggests both surge and block-and-ash types are present.
    [Show full text]
  • Floodplain Geomorphic Processes and Environmental Impacts of Human Alteration Along Coastal Plain Rivers, Usa
    WETLANDS, Vol. 29, No. 2, June 2009, pp. 413–429 ’ 2009, The Society of Wetland Scientists FLOODPLAIN GEOMORPHIC PROCESSES AND ENVIRONMENTAL IMPACTS OF HUMAN ALTERATION ALONG COASTAL PLAIN RIVERS, USA Cliff R. Hupp1, Aaron R. Pierce2, and Gregory B. Noe1 1U.S. Geological Survey 430 National Center, Reston, Virginia, USA 20192 E-mail: [email protected] 2Department of Biological Sciences, Nicholls State University Thibodaux, Louisiana, USA 70310 Abstract: Human alterations along stream channels and within catchments have affected fluvial geomorphic processes worldwide. Typically these alterations reduce the ecosystem services that functioning floodplains provide; in this paper we are concerned with the sediment and associated material trapping service. Similarly, these alterations may negatively impact the natural ecology of floodplains through reductions in suitable habitats, biodiversity, and nutrient cycling. Dams, stream channelization, and levee/canal construction are common human alterations along Coastal Plain fluvial systems. We use three case studies to illustrate these alterations and their impacts on floodplain geomorphic and ecological processes. They include: 1) dams along the lower Roanoke River, North Carolina, 2) stream channelization in west Tennessee, and 3) multiple impacts including canal and artificial levee construction in the central Atchafalaya Basin, Louisiana. Human alterations typically shift affected streams away from natural dynamic equilibrium where net sediment deposition is, approximately, in balance with net
    [Show full text]
  • Classifying Rivers - Three Stages of River Development
    Classifying Rivers - Three Stages of River Development River Characteristics - Sediment Transport - River Velocity - Terminology The illustrations below represent the 3 general classifications into which rivers are placed according to specific characteristics. These categories are: Youthful, Mature and Old Age. A Rejuvenated River, one with a gradient that is raised by the earth's movement, can be an old age river that returns to a Youthful State, and which repeats the cycle of stages once again. A brief overview of each stage of river development begins after the images. A list of pertinent vocabulary appears at the bottom of this document. You may wish to consult it so that you will be aware of terminology used in the descriptive text that follows. Characteristics found in the 3 Stages of River Development: L. Immoor 2006 Geoteach.com 1 Youthful River: Perhaps the most dynamic of all rivers is a Youthful River. Rafters seeking an exciting ride will surely gravitate towards a young river for their recreational thrills. Characteristically youthful rivers are found at higher elevations, in mountainous areas, where the slope of the land is steeper. Water that flows over such a landscape will flow very fast. Youthful rivers can be a tributary of a larger and older river, hundreds of miles away and, in fact, they may be close to the headwaters (the beginning) of that larger river. Upon observation of a Youthful River, here is what one might see: 1. The river flowing down a steep gradient (slope). 2. The channel is deeper than it is wide and V-shaped due to downcutting rather than lateral (side-to-side) erosion.
    [Show full text]
  • Stream Visual Assessment Manual
    U.S. Fish & Wildlife Service Stream Visual Assessment Manual Cane River, credit USFWS/Gary Peeples U.S. Fish & Wildlife Service Conasauga River, credit USFWS Table of Contents Introduction ..............................................................................................................................1 What is a Stream? .............................................................................................................1 What Makes a Stream “Healthy”? .................................................................................1 Pollution Types and How Pollutants are Harmful ........................................................1 What is a “Reach”? ...........................................................................................................1 Using This Protocol..................................................................................................................2 Reach Identification ..........................................................................................................2 Context for Use of this Guide .................................................................................................2 Assessment ........................................................................................................................3 Scoring Details ..................................................................................................................4 Channel Conditions ...........................................................................................................4
    [Show full text]
  • Part 629 – Glossary of Landform and Geologic Terms
    Title 430 – National Soil Survey Handbook Part 629 – Glossary of Landform and Geologic Terms Subpart A – General Information 629.0 Definition and Purpose This glossary provides the NCSS soil survey program, soil scientists, and natural resource specialists with landform, geologic, and related terms and their definitions to— (1) Improve soil landscape description with a standard, single source landform and geologic glossary. (2) Enhance geomorphic content and clarity of soil map unit descriptions by use of accurate, defined terms. (3) Establish consistent geomorphic term usage in soil science and the National Cooperative Soil Survey (NCSS). (4) Provide standard geomorphic definitions for databases and soil survey technical publications. (5) Train soil scientists and related professionals in soils as landscape and geomorphic entities. 629.1 Responsibilities This glossary serves as the official NCSS reference for landform, geologic, and related terms. The staff of the National Soil Survey Center, located in Lincoln, NE, is responsible for maintaining and updating this glossary. Soil Science Division staff and NCSS participants are encouraged to propose additions and changes to the glossary for use in pedon descriptions, soil map unit descriptions, and soil survey publications. The Glossary of Geology (GG, 2005) serves as a major source for many glossary terms. The American Geologic Institute (AGI) granted the USDA Natural Resources Conservation Service (formerly the Soil Conservation Service) permission (in letters dated September 11, 1985, and September 22, 1993) to use existing definitions. Sources of, and modifications to, original definitions are explained immediately below. 629.2 Definitions A. Reference Codes Sources from which definitions were taken, whole or in part, are identified by a code (e.g., GG) following each definition.
    [Show full text]
  • Experiments on Patterns of Alluvial Cover and Bedrock Erosion in a Meandering Channel Roberto Fernández1, Gary Parker1,2, Colin P
    Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2019-8 Manuscript under review for journal Earth Surf. Dynam. Discussion started: 27 February 2019 c Author(s) 2019. CC BY 4.0 License. Experiments on patterns of alluvial cover and bedrock erosion in a meandering channel Roberto Fernández1, Gary Parker1,2, Colin P. Stark3 1Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at 5 Urbana-Champaign, Urbana, IL 61801, USA 2Department of Geology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA 3Lamont Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA Correspondence to: Roberto Fernández ([email protected]) Abstract. 10 In bedrock rivers, erosion by abrasion is driven by sediment particles that strike bare bedrock while traveling downstream with the flow. If the sediment particles settle and form an alluvial cover, this mode of erosion is impeded by the protection offered by the grains themselves. Channel erosion by abrasion is therefore related to the amount and pattern of alluvial cover, which are functions of sediment load and hydraulic conditions, and which in turn are functions of channel geometry, slope and sinuosity. This study presents the results of alluvial cover experiments conducted in a meandering channel flume of high fixed 15 sinuosity. Maps of quasi-instantaneous alluvial cover were generated from time-lapse imaging of flows under a range of below- capacity bedload conditions. These maps were used to infer patterns
    [Show full text]