Sculpting the Earth’s Surface

1. Sculpting the Earth’s Surface Running Water And Groundwater

2. The Hydrologic Cycle • Water Basics • Sea water 97.2% • Fresh Water 2.8% • Polar ice & glaciers 2.15% • Groundwater 0.62% • Lakes and Rivers 0.01%

3. The Hydrologic Cycle • The Three Fates of Precipitation • Infiltration • The movement of water into rocks or soil through cracks and pore spaces • Runoff • Water that flows over the land • Transpiration/Evapotranspiration • the release of water vapor to the atmosphere by plants

5. The Hydrologic Cycle • Infiltration capacity of the soil is controlled by: • Intensity and duration of rainfall • Soil saturation • Soil texture • Slope of the land • Nature of the vegetative cover

6. Main Sources of Water • Surface Water • Lakes, rivers, reservoirs • Ground Water • In the Earth, flows through fractures and pores

7. Surface Water • Streamflow • Factors that determine velocity • Gradient, or slope • Channel characteristics • Shape • Size • Roughness • Discharge – volume of water flowing in the stream (generally expresses as cubic feet per second)

8. Surface Water • Most important agent sculpturing Earth’s land surface • Begins as sheetflow • Sheetflow develops into tiny channels called rills • Eventually flows into streams, rivers & lakes

9. Profile of a Stream

10. Upstream Higher velocity Smaller discharge Smaller channel Downstream Lower velocity Greater discharge Larger channel Surface Water - Streams Upstream-downstream characteristics

11. Local and Ultimate Base Level

12. Surface Water - Streams • Erosion = transportation of sediments • AKA load • Dissolved load • Suspended load • Bed load

13. Surface Water - Streams • Erosion = transportation of sediments • Load is related to a stream's • Competence - maximum particle size • Capacity - maximum load • Capacity is related to discharge

14. Surface Water - Streams • Deposition • Caused by a decrease in velocity • Competence is reduced • Sediment begins to drop out

15. Surface Water - Streams • Stream sediments • Known as alluvium • Well-sorted deposits

16. Surface Water - Streams • Features produced by deposition • Deltas • Natural levees • Back swamps • Yazoo tributaries

17. Surface Water – Streams • River Erosion • Vertical erosion • Upstream portion • Produces deep, V-shaped valleys with rapids • Lateral erosion • Downstream portion • produces broad valleys, flood plains, and meandering streams

18. Meanders

19. Oxbow Lakes

21. Surface Water – Stream Valleys • Drainage basins and patterns • A divide separates drainage basin • Types of drainage patterns

22. Surface Water – Stream Valleys • Flood Plains • Periodic floods deposit rich soils • Agricultural production on floods plains is followed by urbanization • Natural levees • Forms as floods deposit coarse detritus near the river • Naturally constraint the river except in the larger floods

23. Surface Water – Flooding • Floods and flood control • Floods are the most common geologic hazard • Causes of floods • Weather • Human interference with the stream system

24. What is Groundwater? • Water found in the pores and fractures of soil and bedrock • Largest reservoir of fresh water • Tends to be less polluted than surface water

25. What is Groundwater? • An important erosional agent • Groundwater is often mildly acidic • Contains weak carbonic acid • Forms caverns at or just below the zone of saturation • Karst topography on the surface

26. Groundwater Terminology

27. Groundwater Terminology • How does water get from the stream to the water table? • Gaining streams – gain water from the inflow of groundwater through the streambed • Losing streams – lose water to the groundwater system by outflow through the streambed • Interactions - A combination of the first two

28. Groundwater Movement & Storage • Factors • Porosity • Percentage of total volume of rock or sediment that consists of pore spaces • Determines how much groundwater can be stored • Variations can be considerable over short distances • Permeability • The ability of a material to transmit a fluid

29. Groundwater Movement & Storage • Factors (continued) • Specific retention • The portion whish is retained as a film on particles, rock surfaces, and pore spaces • Specific yield • The portion which will drain under gravity • In general, • Porosity = Specific retention + Specific yield

31. Groundwater Movement & Storage • Factors (continued) • Aquifer - A zone of Earth material capable of supplying groundwater at a useful rate from a well

32. Groundwater Movement & Storage • Factors (continued) • Aquitard - A zone of Earth material that holds water but cannot transmit it fast enough to pump from a well

33. Getting Groundwater Out of the Ground • Extraction Methods • “Natural” Methods • Springs, Hot Springs, & Geysers

34. Getting Groundwater Out of the Ground • Extraction Methods (continued) • Man-made Methods • Wells

35. Getting Groundwater Out of the Ground • Artesian well/spring • A situation in which groundwater under pressure rises above the level of the aquifer • Types of artesian wells • Nonflowing – pressure surface is below ground level • Flowing – pressure surface is above the ground • Not all artesian systems are wells, artesian spring also exist

37. Getting Groundwater Out of the Ground • Problems with groundwater removal • Non-renewable resource • Subsidence • Contamination

38. Sources of Contamination • Natural Sources • Biologic activity / organisms • Bacteria and viruses • Naturally occurring elements • Uranium, radium, arsenic, and fluoride • Often naturally occurring in rock formations

39. Geologic Work of Groundwater • Groundwater dissolves rock • Groundwater is often mildly acidic • Contains weak carbonic acid • Forms when rainwater dissolves carbon dioxide from the air and from decaying plants • Carbonic acid reacts with calcite in limestone to form calcium bicarbonate, a soluble material • Forms caverns at or just below the zone of saturation

40. Geologic Work of Groundwater • Caverns • Composed of dripstone (travertine) • Calcite deposited as dripping water evaporates • Collectively, they are called speleothems • Includes: • Stalactites (hanging from the ceiling) • Stalagmites (form on the floor of a cavern)

41. Geologic Work of Groundwater • Karst topography • Landscapes that to a large extent have been shaped by the dissolving power of groundwater • Some common features include • Irregular terrain • Sinkhole or sinks (formed by groundwater slowly dissolving the bedrock often accompanied by collapse) • Striking lack of surface drainage (streams)

42. Karst Topography

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