EAR 105 1st EditionLecture 9Outline of Last Lecture I. Review of TerminologyII. WeatheringIII. SoilExam # 1Outline of Current Lecture IV. Mass WastingV. Running WaterCurrent LectureIV. Soil Erosion Mass Wasting- Soil is essential to life on Earth- Removal of vegetation endangers soil, therefore food supply on Earth- Slope, climate, and composition determine a soil’s propensity to erode.- Erosion is catalyzed by water, wind, and iceo Water erosion- rain, flowing water. The latter accounts for 2/3 of erosion of Earth’s soilo Wind erosion- occurs in arid regions like deserts- Soil erosion and sedimentation can cause reservoirs to fill with sediment and contamination by pesticides and fertilizers- Water as an erosive agent:o After rain, sheet flow= water flowing over the land, some percolates into the ground, some is run-ofo Run-of channeling rills gullies “before even arriving at a proper stream”o Soil washes away when it is not protected by vegetation- Controlling soil erosion:o Leave steep slopes undisturbedo Terrace crop plantingo Grassed waterwayso Tree windbreak barriers- Mass Wasting: the downslope movement of rock, regolith and soil under the direct influence of gravity. Factors: composition, speed, trigger, and outcome (type of landscape modifications)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- It is triggered by:o Saturation- ideally, has some but not too much Destroys particle cohesion Water adds weighto Overly steep slopes Unconsolidated particles assume a stable angle of repose—diferent depending on material Materials include: debris, mud, earth, rock Movement of material; fall, slide (movement along defined plane), flow (movement along viscous fluid)o Mast Wasting Forms: slump- rapid movement along a curved surface. Occurs along overly steep slopes Debris flows- rapid flow of debris with water Often confined to channels Debris flows- composed mostly of volcanic materials are called lahars Earth flows- moving fast, very saturated Creep- slow movement of soil and regolith downhill- Causes fences and utility poles to tilt- J-shape tree trunks- **Creep is catalyzed by freeze-thaw cycles Solifluction; pertains to permafrost, not important for this classV. Running Watero 2.5% of Earth’s water is fresho 1.3% of that water is on the surfaceo 20.1% of it is in lakeso 73.1% is in snow and iceo .46% is in lakeso .44% are split between the atmosphere & the biosphere- Hydrologic Cycleo Processes of condensation, evaporation, precipitation- All rivers have drainage basinso A drainage basin is the land area that contributes water to a river systemo A divide separates drainage basinso Tributaries are streams that feed into other streamso Trunk streams receive water from all of the outer tributarieso The mouth or the outlet defines the area in which the water flows out to the oceano Put simply: rainwater falls on ground, some becomes run-of, some percolates as groundwater.o The lakes in the US form a huge network of rivers with their own drainage basins that eventually link up at the Mississippi River- There are three zones in a river system: production, transport, and deposition- Production relates to sediment erosion (via running water)- Transport relates to the carrying sediment through the trunk stream- Deposition relates to the area near the mouth, where sediment is finally settled- **Networks of streams form distinctive patterns—they vary b yterrain- Four common drainage patterns:o Dendritic- most important for EAR 105. Looks like a tree to a branch to a trunk Develops on relatively uniform surface materialso Rectangular- develops along margins of highly jointed bedrock o Radial- form on isolated volcanic cones or domes in radial patterno Trellis- develop in areas of alternating weak and resistant bedrock- Streamflow- i.e. velocity of watero Gradient- slope of streamo Channel characteristics: [shape, size, roughness]o Discharge- i.e. the volume of water flowing in the stream- generally expressed as cubic feet per second Discharge increases with declination- Geologists draw longitudinal profiles of streams.o Chart of distance and elevation patterns in a given stream- Erosion= Transportation of a stream’s loado Load types: Dissolved: Invisible Suspended: Silt, clay Bed load:, boulders, sand, gravelo Keep in mind that increase in velocity of stream flow allows for the carrying of heavier particles that make up the streams bed
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