Earth as a System The hydrologic cycle  Illustrates the circulation of Earth's water supply  What processes make up the water cycle?

The hydrologic cycle

Sources of Earth’s water

GROUNDWATER  Largest freshwater reservoir for humans  Geological roles An erosional agent in the formation of Sinkholes Caverns Equalizes stream flow and surface water

North Avenue – Escalade ???

Cave with stalagmites, stalactites

Groundwater model ms/groundwater/ ms/groundwater/

Features associated with subsurface water

Water beneath the surface (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

Water beneath the surface (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

Water beneath the surface (groundwater)  Distribution and movement of groundwater Distribution of groundwater Porosity Percentage of pore spaces Determines how much groundwater can be stored Permeability Ability to transmit water through connected pore spaces Aquitard – an impermeable layer of material Aquifer – a permeable layer of material

Water beneath the surface (groundwater)  Features associated with groundwater Springs Hot springs Water is 6-9ºC 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

Water beneath the surface (groundwater)  Features associated with groundwater 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

Formation of a cone of depression in the water table

An artesian well resulting from an inclined aquifer

Water beneath the surface (groundwater)  Environmental problems associated with groundwater Treating it as a nonrenewable resource Land subsidence caused by its withdrawal Contamination

Water beneath the surface (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

Water beneath the surface (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 )

Dripstone formations in Carlsbad Caverns National Park

Water beneath the surface (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 topography

Infrared image of karst topography in central Florida