Week 09 Slopes and Streams, Stream Landscapes PDF

Physical Geography: Slopes and Streams, Stream Landscapes 10/28/2024-10/30/2024 PROFESSOR PETE PULEO 1 Slopes and Streams 2 Learning Objectives Describe the processes responsible for the erosion of slopes by water Explain the concept of sediment yield from...

Physical Geography: Slopes and Streams, Stream Landscapes 10/28/2024-10/30/2024 PROFESSOR PETE PULEO 1 Slopes and Streams 2 Learning Objectives Describe the processes responsible for the erosion of slopes by water Explain the concept of sediment yield from a stream’s drainage basin Analyze the movement of sediment through river systems by processes of erosion, transportation, and deposition Discuss the river as a system 3 Fluvial Related to flowing water (rivers, streams, etc.) 4 Fluvial Processes Water flows from high elevation to low elevation 5 6  Rainsplash Erosion Rain drops dislodge and scatter soils downslope https://eos.com/blog/water-erosion/ 7 Sheet Erosion Runoff channels carve surface soils/sediments Precipitation rate > infiltration rate so water runs across surface 8  Vegetation and Erosion https://graniteseed.com/blog/how-do-plants-help-prevent-erosion/ 9 River System Trunk – Main part of river system (Mississippi River) 10 River System Tributary – Smaller streams feeding into the trunk (unlabeled streams) 11 River System Drainage Basin or Watershed – Full network of trunk and tributaries (green area) 12 Denudation Overall lowering of the landscape elevation from weathering and erosion 13  River Discharge aka streamflow https://www.researchgate.net/figure/Theory-of-Measurement-of- Discharge_fig1_348845081 14  Erosion by Rivers Hydraulic Action – Water dislodging and cracking rock material from valley floor/walls https://www.geo41.com/rivers-matu#river-processes-swiss-maturity 15  Erosion by Rivers Abrasion – Mechanical erosion from rocks and sediment carried by the river scraping against the valley floor/walls https://www.geo41.com/rivers-matu#river-processes-swiss-maturity 16  Erosion by Rivers Attrition – Rocks and sediments hitting each other and breaking into smaller pieces https://www.geo41.com/rivers-matu#river-processes-swiss-maturity 17  Erosion by Rivers Corrosion/Dissolution – Rocks and minerals being dissolved by water (solution on diagram) https://www.geo41.com/rivers-matu#river-processes-swiss-maturity 18 River Sediment Load Dissolved load (not depicted), suspended load, bed load 19  River Sediment Transportation https://www.alevelgeography.com/the-long-profile-changing-processes-types- of-erosion-transportation-and-deposition/ 20  River Sediment Characteristics Transport Capacity – Max amount of sediment a stream can carry at a given discharge (T = Transport Capacity, q = Discharge) https://www.researchgate.net/figure/Measured-sediment-transport-capacity- versus-flow-rate-a-and-measured-sediment_fig2_367407186 21  River Sediment Characteristics Competence – The largest particle size a stream can set in motion https://open.maricopa.edu/physicalgeology/chapter/13-3-stream-erosion-and- deposition/ 22  Sediment Yield Mass of sediment leaving a stream basin per year https://www.researchgate.net/figure/Large-rivers-in-the-world-in-terms-of- suspended-sediment-load-water-discharge-and_tbl1_229151197 23 River Sediment Characteristics Mississippi River - High transport capacity, medium competence 24  Stream Power Stream’s ability to do work (like moving sediments) Increases with discharge and slope https://www.researchgate.net/figure/The-relationship-of-Tc-with-unit-stream- power-on-six-slope-gradients_fig4_318161498 25  Base Level The lowest elevation to which a river can erode Ultimate (sea level) vs. local (elevation of nearby lakes, trunks, etc.) http://www.sepmstrata.org/Terminology.aspx?id=base%20level 26 Rivers and Energy 27 Erosion by Rivers Incision – Downward erosion of stream beds 28 Deposition by Rivers Aggradation – Sediment accumulation raising the level of a river valley’s bed 29 Delta Where a stream reaches a coast or lake, slows down, and deposits sediment in a fan-like shape 30 Alluvial Fan Fan-shaped deposit of sediment Associated with stream power reducing after leaving a confined valley Streams are often seasonal 31 Activity 1 Description Work independently to answer the questions below. Then, discuss your thoughts with a partner. 1) Draw a cross section of a stream. Draw and describe the major types of river erosion (Hint: 4 types). 2) On another stream cross section, illustrate and describe how sediments can move (hint: 4 types) 32 Activity 1 Solution 1) Draw a cross section of a stream. Draw and describe the major types of river erosion (Hint: 4 types). 33 Activity 1 Solution 2) On the same drawing, illustrate and describe how sediments can move (hint: 4 types) 34 Stream Landscapes 35 Learning Objectives Outline the effects of geologic structure, lithology, tectonics, and climate on the patterns of stream erosion Explain the important types of drainage networks and their origin Briefly describe cases in which stream erosion overcomes the control of geologic structure Summarize the major theories of long-term landscape development 36  Factors Influencing Stream Erosion Climate Change Minimum annual streamflow change from 1940-2022 ◦ Precipitation ◦ Temperature ◦ Vegetation type/cover https://www.epa.gov/climate-indicators/climate-change-indicators-streamflow 37 Factors Influencing Stream Erosion Lithology ◦ Resistance to physical weathering ◦ Resistance to chemical weathering ◦ Different slopes ◦ Different erosion rates 38 Factors Influencing Stream Erosion Geologic Structure ◦ Hogback – Relatively steeply dipping ridge from less erodible layer sticking out 39 Factors Influencing Stream Erosion Geologic Structure ◦ Cuesta – Shallow dipping, erosion resistant rock layers forming an asymmetrical ridge 40 Factors Influencing Stream Erosion Geologic Structure ◦ Ridges and valleys 41 Factors Influencing Stream Erosion Geologic Structure ◦ Domes 42 Factors Influencing Stream Erosion Geologic Structure ◦ Faults 43 Factors Influencing Stream Erosion Geologic Structure ◦ Plateaus, Mesa, Buttes from igneous rocks being resistant to weathering 44 Drainage Density Total length of stream channels in a given part of a drainage basin Which has higher drainage density? 45 Drainage Density Total length of stream channels in a given part of a drainage basin Which has higher drainage density? B! 46 Drainage Density Higher drainage density -> higher rate of erosion 47 Drainage Patterns Radial – Radiate outward from a central high point (mountain peak, volcano peak) 48 Drainage Patterns Annular – Around a high point but separated by ridges making the drainage circle the peak 49 Drainage Patterns Trellis – Parallel layers of sloped/folded sedimentary rocks and resistant ridges 50 Drainage Patterns Rectangular – Streams with right angles often associated with faults 51 Drainage Patterns Dendritic – Streams that resemble a tree's branching structure Form on gently sloping, uniform bodies of rock Most common drainage pattern 52 Superimposed Stream Stream maintaining course regardless of underlying structure Forms horizontal surface beds that overlay folded/faulted rock Structural change predates stream 53 Antecedent Stream Stream predating the ridge that it erodes as it is lifted by tectonics Stream predates structural change 54 Stream Piracy The capture of a segment of one stream by another Dashed blue line was former river channel (before piracy) 55  Flood Bankfull – Stream fills largest channel size, frequent, less damage Overbank – Stream overflows its channel, infrequent, more damage https://open.maricopa.edu/physicalgeology/chapter/13-3-stream-erosion-and- deposition/ 56 Recurrence Interval Average time between floods of a given magnitude in a given place 57 Landscape Evolution Theories Major ongoing area of research in geomorphology: how are regional landscapes shaped? The main theories have had mixed success when tested 58 Landscape Evolution Theories William Davis (1850-1934) suggested: Uplift occurred and was followed by erosion and downward slope movement 59 Landscape Evolution Theories Cycle of Erosion ◦ Young – Uplift followed by deep channels and large plateaus ◦ Mature – More extensive channels, steep slopes ◦ Old – Relatively flat plain (peneplain) 60 Landscape Evolution Theories German geographer Walther Penck (1888-1923) suggested: Uplift and weathering occur simultaneously and slopes weather backward, not downward 61 Landscape Evolution Theories Slope Decline (Davis) Slope Retreat (Penck) 62 Activity 2 Description Work independently to list and describe the factors that influence stream erosion. Be as specific as you can. Then, discuss your thoughts with a partner. 63 Activity 2 Solution Work independently to list and describe the factors that influence stream erosion. Precipitation amount influences discharge Temperature and precipitation amount influence vegetation coverage and type which controls how easily soil is eroded Lithology influences resistance to physical weathering and resistance to chemical weathering Geologic structure influences the direction/gradient of slopes and which areas are more susceptible to weathering and erosion 64 Lecture Exam 2 (Weeks 5-9) 65