Earth as a System: The Hydrologic Cycle Illustrates the circulation of Earth’s water supply Most water is in the oceans

Earth as a System: The Hydrologic Cycle Processes involved in the water cycle Precipitation Evaporation Infiltration Runoff Transpiration

The Hydrologic Cycle

Running Water Drainage basin Divide Land area that contributes water to a river system Divide Separates drainage basins

Mississippi River Drainage Basin

River Systems Three zones Sediment production Sediment transport Sediment deposition

Drainage Patterns Networks of streams form distinctive patterns Drainage pattern varies by terrain Four common drainage patterns Dendritic Rectangular Radial Trellis

Drainage Patterns

Running 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)

Running Water Upstream-downstream changes Profile Cross-sectional view of a stream From head (source) to mouth Profile is a smooth curve Gradient decreases from the head to the mouth Factors that increase downstream Velocity Discharge

Channel Changes from Head to Mouth

Running Water Upstream-downstream changes Profile Factors that increase downstream Channel size Factors that decrease downstream Gradient or slope Channel roughness

Longitudinal Profile of a Stream

Work of Running Water Erosion Transportation Transported material is called the stream’s load Dissolved load Suspended load Bed load

Potholes Due to Erosion

Work of Running Water Transportation Load is related to a stream’s Competence – maximum particle size Capacity – maximum load Capacity is related to discharge

Work of Running Water Transportation Deposition Stream sediments Caused by a decrease in velocity Competence is reduced Sediment begins to drop out Stream sediments Known as alluvium Well-sorted deposits

Work of Running Water Transportation Features produced by deposition Deltas – exist in ocean or lakes Natural levees – form parallel to the stream channel Area behind the levees may contain back swamps or yazoo tributaries

Stream Channels Bedrock channels – cut into strata Alluvial channels – loosely consolidated sediment

Stream Channels Meandering streams – move in sweeping bends Braided streams – complex network of channels

Braided Stream

Shaping Stream Valleys Base level Lowest point a stream can erode to Two general types Ultimate – sea level Temporary or local Changing causes readjustment of the stream – deposition or erosion

Base Levels

Shaping Stream Valleys Valley sides are shaped by Weathering Overland flow Mass wasting Characteristics of narrow valleys V-shaped Downcutting toward base level Incised meanders

Shaping Stream Valleys Characteristics of narrow valleys Features often include Rapids Waterfalls Characteristics of wide valleys Stream is near base level Downward erosion is less dominant Stream energy is directed from side to side

V-shaped Valley of the Yellowstone River

Erosional Floodplain Development

Shaping Stream Valleys Characteristics of wide valleys Floodplain Features often include Meanders Cutoffs Oxbow lakes

Meander Loop on the Colorado River

Floods and Flood Control Floods are the most common geologic hazard Causes of floods Weather Human interference with the stream system

Floods and Flood Control Engineering efforts Artificial levees Flood-control dams Channelization Nonstructural approach through sound floodplain management

Mississippi River Flood of 1993

Groundwater: Water Beneath the Surface Largest freshwater reservoir for humans Geological roles As an erosional agent, dissolving by groundwater produces Sinkholes Caverns An equalizer of stream flow

Groundwater Distribution and movement of groundwater Distribution of groundwater Belt of soil moisture Zone of aeration Unsaturated zone Pore spaces in the material are filled mainly with air

Groundwater Distribution and movement of groundwater Distribution of groundwater Zone of saturation All pore spaces in the material are filled with water Water within the pores is groundwater Water table – the upper limit of the zone of saturation

Groundwater Features

Groundwater Distribution and movement of groundwater Distribution of groundwater Porosity Percentage of pore spaces Determines storage of groundwater Permeability Ability to transmit water through connected pore spaces Aquitard – an impermeable layer of material Aquifer – a permeable layer of material

Groundwater Features associated with groundwater Springs Hot springs Water is 6–9° C (10–15° F) warmer than the mean air temperature of the locality Heated by cooling of igneous rock Geysers Intermittent hot springs Water turns to steam and erupts

Old Faithful Geyser in Yellowstone National Park

Groundwater Features associated with groundwater Wells Artesian wells Pumping can cause a drawdown (lowering) of the water table Pumping can form a cone of depression in the water table Artesian wells Water in the well rises higher than the initial groundwater level

Cone of Depression Formation

Artesian Systems

Groundwater Environmental problems associated with groundwater Treating it as a nonrenewable resource Land subsidence caused by its withdrawal Contamination

Subsidence

Groundwater Geologic work of groundwater Groundwater is often mildly acidic Contains weak carbonic acid Dissolves calcite in limestone Caverns Formed by dissolving rock beneath Earth’s surface Formed in the zone of saturation

Groundwater Geologic work of groundwater Caverns Features found within caverns Form in the zone of aeration Composed of dripstone Calcite deposited as dripping water evaporates Common features include stalactites (hanging from the ceiling) and stalagmites (growing upward from the floor)

Groundwater Geologic work of groundwater Karst topography Formed by dissolving rock at, or near, Earth’s surface Common features Sinkholes – surface depressions Sinkholes form by dissolving bedrock and cavern collapse Caves and caverns Area lacks good surface drainage

Development of Karst Landscape