DOCSLIB.ORG

Spatial and Temporal Patterns of River Incision and Terrace Deposition in Response to Climate and Tectonics in Southern Taiwan

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Spatial and Temporal Patterns of River Incision and Terrace Deposition in Response to Climate and Tectonics in Southern Taiwan Utah State University DigitalCommons@USU All Graduate Theses and Dissertations Graduate Studies 5-2021 Spatial and Temporal Patterns of River Incision and Terrace Deposition in Response to Climate and Tectonics in Southern Taiwan Dominique M. Shore Utah State University Follow this and additional works at: https://digitalcommons.usu.edu/etd Part of the Geology Commons Recommended Citation Shore, Dominique M., "Spatial and Temporal Patterns of River Incision and Terrace Deposition in Response to Climate and Tectonics in Southern Taiwan" (2021). All Graduate Theses and Dissertations. 8070. https://digitalcommons.usu.edu/etd/8070 This Thesis is brought to you for free and open access by the Graduate Studies at DigitalCommons@USU. It has been accepted for inclusion in All Graduate Theses and Dissertations by an authorized administrator of DigitalCommons@USU. For more information, please contact [email protected]. SPATIAL AND TEMPORAL PATTERNS OF RIVER INCISION AND TERRACE DEPOSITION IN RESPONSE TO CLIMATE AND TECTONICS IN SOUTHERN TAIWAN by Dominique M. Shore A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Geology Approved: _______________________ ____________________ Tammy M. Rittenour, Ph.D. Brian J. Yanites, Ph.D. Major Professor Committee Member ____________________ ____________________ Patrick Belmont, Ph.D. D. Richard Culter, Ph.D. Committee Member Interim Vice Provost of Graduate Studies UTAH STATE UNIVERSITY Logan, Utah 2021 Copyright © Dominique M. Shore 2021 All Rights Reserved ABSTRACT Spatial and Temporal Patterns of River Incision and Terrace Deposition in response to Climate and Tectonics in Southern Taiwan by Dominique M. Shore, Master of Science Utah State University, 2021 Major Professor: Tammy M. Rittenour, Ph.D. Department: Geology The incision of bedrock rivers is often thought of as a detachment limited system reflecting the underlying tectonics. Recent studies have shown sediment supply also plays a crucial role in understanding landscape response to uplift, and can obscure tectonic forcings. This thesis investigates river incision patterns across a steep gradient of topography and accumulated uplift in southern Taiwan to better understand the role of climate and tectonics in landscape development. Taiwan is a young island undergoing rapid, southward propagating uplift resulting from the oblique collision of the Philippine Sea Plate and Eurasian Plate. Rapid uplift coupled with a warm, wet climate heavily influenced by the East Asian Summer Monsoon (EASM) allows processes of erosion to occur quickly resulting in a steep, dynamic landscape. Age control from luminescence dating and field measurements were used to determine timing of terrace deposition and rates of river incision along the southern 100 km of Taiwan. Preliminary terrace deposition ages ranging from late-Pleistocene to late- iv Holocene reveal periods of regional terrace deposition around 1, 11, 18, 28, and 40 ka. Periods of terrace deposition coincident with precession-driven cyclicity of the EASM during the Holocene and Pleistocene. Periods of terrace deposition also correlate with periods of increased hillslope erosion recorded in Holocene mass-wasting records from central and southern Taiwan. Results suggest that climate-driven changes in sediment supply are able to obscure tectonic drivers of incision on short-term timescales (100-103 yrs). Preliminary incision rates range from 6 ± 2.6 to 0.2 ± 0.1m/kyr with an average of 2.4 ± 1.2 m/kyr. Incision rates increase northward along with hillslope denudation rates until a critical hillslope threshold is met ~80 km northward at which point hillslope denudation decreases and rates of incision continue to increase. Northward increasing rates of denudation mirroring the assumed pattern of uplift suggest that that tectonics is the primary driver of river incision on longer-term scales (103-106 yrs). The influence of climate on shorter timescales suggests that caution should be taken in using short-term incision rates to understand underlying geomorphic response to tectonics in Taiwan. (107 pages) v PUBLIC ABSTRACT Spatial and Temporal Patterns of River Incision and Terrace Deposition in response to Climate and Tectonics in Southern Taiwan Dominique Shore Geologists often look at the Earth’s surface to understand the underlying processes that cause mountain formation. As tectonic forces drive uplift of Earth’s surface, processes of erosion transport sediment to lower elevations. Climate can play a large role in landscape formation as well as increased precipitation, accelerating rates of erosion. Rivers leave markers of landscape evolution through terrace landforms, former river floodplains that are left behind when rivers incise into a valley. To better understand landscape response to uplift, this research investigated the initial linkages between uplift, hillslope erosion (mass wasting) and river incision. At some point, it is thought that these three will be in equilibrium. Taiwan is a young mountain range making it the ideal setting to capture landscape development in the initial stages of uplift. I compare rates of river incision to rates of hillslope erosion and timing of terrace deposition to understand the links between erosion, tectonics and climate in the beginning stages of mountain building. This thesis uses luminescence to provide age control for the last time sediment was exposed to light to determine when river terraces formed. Field mapping and observations allowed us to measure the height between terraces to quantify the rate at which streams incised. The results from this study show that the rivers of southern Taiwan are incising on average at a rate of 2.4 ± 1.2 meters per thousand years (m/kyr) vi with rates ranging from 6 ± 2.6to 0.2 ± 0.1 m/kyr. River incision rates and hillslope erosion (denudation) rates increase northward with drainage development suggesting that rates of erosion are primarily linked to tectonic forces on medium to longer-term scales (1,000-1,000,000 years) . Regional periods of terrace development occurred at 1, 11, 18, 28, and 40 ka. Periods of terrace development align with periods of increased East Asian Summer Monsoon (EASM) intensity chronicled in paleoclimate records. The EASM is the dominate weather pattern that delivers moisture to East Asia affecting 1/3 of global populations. Terrace deposits recording EASM intensity extends the record of landscape response to climate in Taiwan and reveals that climate signals can obscure tectonic forces on short-time scales (100 – 103 yrs). vii ACKNOWLEDGMENTS I would like to thank sincerely the National Science Foundation, Geological Society of America, and USU Geology Department for their generous funding and support of this research project. I would also like to acknowledge the enormous help of Carlie Ideker, Michelle Nelson, Harriet Cornachione, Natalie Tanski, and Maggie Erlick of the USU Luminescence Laboratory for their endless help and support. I am grateful for my committee members, Dr. Brian Yanites and Dr. Patrick Belmont for their advisement and time spent editing my thesis. I am grateful to Dr. Chia-Yu Chen, Dr. Bruce Shyu, Eva Yin, Clark DeLisle and others for their assistance in the field in southern Taiwan. I am especially grateful to my advisor, Dr. Tammy Rittenour. She gave me the opportunity to attend USU and receive an advanced degree in Geology studying the fascinating landscape of Taiwan through a research assistantship and tuition waivers. She spent numerous hours editing my writing, discussing my data with me and writing references. I am so grateful for her patience through challenging times and working with me to finish my thesis after I began working in Montana. In addition to scholarly support, I would like to give thanks to my friends and parents who helped me push through challenging times and finish my thesis. The numerous biking, skiing, and fishing breaks provided much-needed breaks. I cannot express how much the support of my parents, Jill Woodhouse, Jack McLaren, and Oscar S.S. Shore meant to me. Thank you all for you unwavering and constant support. Dominique M. Shore viii CONTENTS ........................................................................................................................... Page ABSTRACT ...................................................................................................................... iii PUBLIC ABSTRACT .........................................................................................................v ACKNOWLEDGMENTS ................................................................................................ vii CONTENTS .................................................................................................................... viii LIST OF TABLES ...............................................................................................................x LIST OF FIGURES ........................................................................................................... xi CHAPTER 1 - INTRODUCTION .............................................................................................. 1 CHAPTER 2 - SPATIAL AND TEMPORAL PATTERNS OF RIVER INCISION IN SOUTHERN TAIWAN .......................................................................................................... 3 ABSTRACT .......................................................................................................... 3 INTRODUCTION ................................................................................................
Load more

Recommended publications
  • 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]
  • 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]
  • Sequence Stratigraphy Ofholocene Incised-Valley Fills and Coastal Evolution in the Gulf of Cadiz (Southern Spain)
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by EPrints Complutense Sequence stratigraphy ofHolocene incised-valley fills and coastal evolution in the Gulf of Cadiz (southern Spain) Cristino J. Dabriol, Cari Zazo2, Javier Lario2, Jose Luis Goy3, Francisco J. Sierro3, Francisco Borja4, Jose Angel Gonzalez3 & Jose Abel Flores3 1 Departamento de Estratigrafia and Instituto de Geologia Econ6mica-CSIC, Universidad Complutense, 28040 Madrid, EspafJa (e-mail: [email protected]); 2Departamento de Geologia, Museo Nacional de Cien­ cias Naturales-CSIC, 28006 Madrid, EspafJa ([email protected]); 3Departamento de Geologia, Fac­ ultad de Ciencias, Universidad, 37008 Salamanca, EspafJa ([email protected], [email protected], an­ [email protected], [email protected]); 4Area de Geografia Fisica, Facultad de Humanidades, Universidad, 21007 Huelva, EspafJa (fbO/[email protected]) Key words: estuarine deposits, Flandrian transgression, Late Pleistocene, radiocarbon data, spit barriers Abstract This first sedimentary interpretation of two incised-valley fills in the Gulf of Cadiz (southern Spain), which accumulated during the last fourth-order eustatic cycle in response to fluvial incision, changes of sea level, and correlative deposition, relates the filling of the estuarine basins and their barriers with four regional progradation phases, HI to H4. The cases studied are the wave-dominated Guadalete, and the mixed, tide and wave-dominated Odiel-Tinto estuaries. The sequence boundary is a type-l surface produced during the low stand of the Last Glacial period ca. 18 000 14C yr BP No fluvial lowstand deposits were found in the area. Due to rapid transgression the valley fills consist of transgressive and highstand sediments.
    [Show full text]
  • Avulsion Dynamics in a River with Alternating Bedrock and Alluvial Reaches, Huron River, Northern Ohio (USA)
    Open Journal of Modern Hydrology, 2019, 9, 20-39 http://www.scirp.org/journal/ojmh ISSN Online: 2163-0496 ISSN Print: 2163-0461 Avulsion Dynamics in a River with Alternating Bedrock and Alluvial Reaches, Huron River, Northern Ohio (USA) Mark J. Potucek1,2, James E. Evans1 1Department of Geology, Bowling Green State University, Bowling Green, OH, USA 2Arizona Department of Water Resources, Phoenix, AZ, USA How to cite this paper: Potucek, M.J. and Abstract Evans, J.E. (2019) Avulsion Dynamics in a River with Alternating Bedrock and Alluvi- The Huron River consists of alternating bedrock reaches and alluvial reaches. al Reaches, Huron River, Northern Ohio Analysis of historical aerial photography from 1950-2015 reveals six major (USA). Open Journal of Modern Hydrolo- gy, 9, 20-39. channel avulsion events in the 8-km study area. These avulsions occurred in https://doi.org/10.4236/ojmh.2019.91002 the alluvial reaches but were strongly influenced by the properties of the up- stream bedrock reach (“inherited characteristics”). The bedrock reaches Received: December 19, 2018 Accepted: January 20, 2019 aligned with the azimuth of joint sets in the underlying bedrock. One inhe- Published: January 23, 2019 rited characteristic in the alluvial reach downstream is that the avulsion channels diverged only slightly from the orientation of the upstream bedrock Copyright © 2019 by author(s) and channel (range 2˚ - 38˚, mean and standard deviation 12.1˚ ± 13.7˚). A Scientific Research Publishing Inc. This work is licensed under the Creative second inherited characteristic is that avulsion channels were initiated from Commons Attribution International short distances downstream after exiting the upstream bedrock channel reach License (CC BY 4.0).
    [Show full text]
  • A 184-Year Record of River Meander Migration from Tree Rings, Aerial Imagery, and Cross Sections
    Geomorphology 293 (2017) 227–239 Contents lists available at ScienceDirect Geomorphology journal homepage: www.elsevier.com/locate/geomorph A 184-year record of river meander migration from tree rings, aerial MARK imagery, and cross sections ⁎ Derek M. Schooka, , Sara L. Rathburna, Jonathan M. Friedmanb, J. Marshall Wolfc a Department of Geosciences, Colorado State University, 1482 Campus Delivery, Fort Collins, CO 80523, USA b U.S. Geological Survey, Fort Collins Science Center, 2150 Centre Avenue, Building C, Fort Collins, CO 80526, USA c Department of Ecosystem Science and Sustainability, Colorado State University, 1476 Campus Delivery, Fort Collins, CO 80523, USA ARTICLE INFO ABSTRACT Keywords: Channel migration is the primary mechanism of floodplain turnover in meandering rivers and is essential to the Channel migration persistence of riparian ecosystems. Channel migration is driven by river flows, but short-term records cannot Meandering river disentangle the effects of land use, flow diversion, past floods, and climate change. We used three data sets to Aerial photography quantify nearly two centuries of channel migration on the Powder River in Montana. The most precise data set Dendrochronology came from channel cross sections measured an average of 21 times from 1975 to 2014. We then extended spatial Channel cross section and temporal scales of analysis using aerial photographs (1939–2013) and by aging plains cottonwoods along transects (1830–2014). Migration rates calculated from overlapping periods across data sets mostly revealed cross-method consistency. Data set integration revealed that migration rates have declined since peaking at 5 m/ year in the two decades after the extreme 1923 flood (3000 m3/s).
    [Show full text]
  • Alluvial Cover Controlling the Width, Slope and Sinuosity of Bedrock Channels
    Earth Surf. Dynam., 6, 29–48, 2018 https://doi.org/10.5194/esurf-6-29-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Alluvial cover controlling the width, slope and sinuosity of bedrock channels Jens Martin Turowski Helmholtz-Zentrum Potsdam, German Research Centre for Geosciences GFZ, Telegrafenberg, 14473 Potsdam, Germany Correspondence: Jens Martin Turowski ([email protected]) Received: 17 July 2017 – Discussion started: 31 July 2017 Revised: 16 December 2017 – Accepted: 31 December 2017 – Published: 6 February 2018 Abstract. Bedrock channel slope and width are important parameters for setting bedload transport capacity and for stream-profile inversion to obtain tectonics information. Channel width and slope development are closely related to the problem of bedrock channel sinuosity. It is therefore likely that observations on bedrock channel meandering yields insights into the development of channel width and slope. Active meandering occurs when the bedrock channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments.
    [Show full text]
  • Causes and Consequences of Meandering in Bedrock Rivers
    UNIVERSITY OF CALIFORNIA SANTA CRUZ CAUSES AND CONSEQUENCES OF MEANDERING IN BEDROCK RIVERS: HOW INTERACTIONS BETWEEN ROCK PROPERTIES AND ENVIRONMENTAL CONDITIONS SHAPE LANDSCAPES A dissertation submitted in partial satisfaction of the requirements for the degree of DOCTOR OF PHILOSOPHY in EARTH SCIENCE with an emphasis in GEOLOGY by Kerri N. Johnson March 2016 The Dissertation of Kerri N. Johnson is approved: _______________________________ Professor Noah J. Finnegan, Chair _______________________________ Professor Andrew T. Fisher _______________________________ Dr. Amy E. East _______________________________ Tyrus Miller Vice Provost and Dean of Graduate Studies Copyright © by Kerri N. Johnson 2016 Chapter 1 is used here within the copyright terms of the Geological Society of America P.O. Box 9140, Boulder, CO 80301-9140 USA (http://www.geosociety.org) Table of Contents Title Page i Copyright Page ii Table of Contents iii Table of Figures iv Abstract v Dedication vii Acknowledgments viii Introduction 1 Chapter 1: A lithologic control on active meandering in bedrock channels 4 Chapter 2: Precipitation patterns control chemical weathering and therefore bedrock channel sinuosity in the Kohala Basalts, Hawai’i 15 Chapter 3: Autogenic Reorganization of Drainage Networks and Erosion Patterns from Bedrock River Meandering in the Oregon Coast Range 34 Conclusion 56 Bibliography 58 iii Table of Figures Chapter 1 Figure 1 5 Figure 2 5 Figure 3 6 Figure 4 7 Figure 5 8 Figure 6 9 Figure 7 10 Figure 8 11 Figure 9 12 Figure 10 13 Table 1 11 Chapter 2 Figures 1-6 28-33 Chapter 3 Figures 1-9 46-53 Table 1 54 iv CAUSES AND CONSEQUENCES OF MEANDERING IN BEDROCK RIVERS: HOW INTERACTIONS BETWEEN ROCK PROPERTIES AND ENVIRONMENTAL CONDITIONS SHAPE LANDSCAPES Kerri N.
    [Show full text]
  • Sediment Supply Controls Equilibrium Channel Geometry in Gravel Rivers
    Sediment supply controls equilibrium channel geometry in gravel rivers Allison M. Pfeiffera,1, Noah J. Finnegana, and Jane K. Willenbringb aDepartment of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064; and bScripps Institution of Oceanography, University of California, San Diego, CA 92037 Edited by Thomas Dunne, University of California, Santa Barbara, CA, and approved January 26, 2017 (received for review August 3, 2016) τp In many gravel-bedded rivers, floods that fill the channel banks stress ( bf ) may be a criterion to which all gravel rivers must τp create just enough shear stress to move the median-sized gravel conform (8). The critical Shields stress ( c) describes the amount particles on the bed surface (D50). Because this observation is com- of stress needed to initiate median grain motion, normalized for mon and is supported by theory, the coincidence of bankfull flow the grain size, and is generally between 0.03 and 0.08 (9). The and the incipient motion of D has become a commonly used τp 50 bankfull Shields stress ( bf ) describes the stress acting on the bed assumption. However, not all natural gravel channels actually con- during bankfull flow, and (at the reach scale) is approximated as form to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sed- τp = ρ ðρ ρÞ [1] bf Rbf S s- D50, iment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to 3 where ρ is the density of water (1,000 kg/m ), ρs is the density of explore the hypothesis that sediment supply drives the magnitude sediment, Rbf is the bankfull hydraulic radius, and S is the channel of bankfull shear stress relative to the critical stress required to slope (note that all Shields stresses referred to herein apply to D ).
    [Show full text]
  • Sediment and Rock Strength Controls on River Incision Into Bedrock
    Sediment and rock strength controls on river incision into bedrock Leonard S. Sklar William E. Dietrich Department of Earth and Planetary Science, University of California, 307 McCone Hall, Berkeley, California 94720-4767, USA ABSTRACT Recent theoretical investigations suggest that the rate of river incision into bedrock depends nonlinearly on sediment supply, challenging the common assumption that incision rate is simply proportional to stream power. Our measurements from laboratory abrasion mills support the hypothesis that sediment promotes erosion at low supply rates by pro- viding tools for abrasion, but inhibits erosion at high supply rates by burying underlying bedrock beneath transient deposits. Maximum erosion rates occur at a critical level of coarse-grained sediment supply where the bedrock is only partially exposed. Fine-grained sediments provide poor abrasive tools for lowering bedrock river beds because they tend to travel in suspension. Experiments also reveal that rock resistance to ¯uvial erosion scales with the square of rock tensile strength. Our results suggest that spatial and tem- poral variations in the extent of bedrock exposure provide incising rivers with a previously unrecognized degree of freedom in adjusting to changes in rock uplift rate and climate. Furthermore, we conclude that the grain size distribution of sediment supplied by hill- slopes to the channel network is a fundamental control on bedrock channel gradients and topographic relief. Keywords: rivers, sediment supply, grain size, erodibility, landscape evolution, erosion. INTRODUCTION ly the role of sediment supply, grain size, and similar to Gilbert's qualitative hypothesis. Our The topography of mountainous landscapes rock strength in controlling bedrock erosion model also predicts a nonlinear dependence of is created by the interaction of rock uplift and rates.
    [Show full text]