Groundwater

1
Groundwater

• groundwater precipitation that infiltrates the
  ground 22 of the worlds freshwater
• Porosity is the percentage of pore space in a
  material, represents the amount of water rocks
  can hold
• Permeability is the ability of rocks to transmit
  fluids
• Aquifers porous and permeable layers of rock
  that can hold and transmit groundwater
• aquicludes shales and many crystalline rocks act
  as boundaries for aquifers also called aquitards

2
The Water Table

• Porous zones in the subsurface can be
  characterized by whether their pore space contain
  mostly air or water
• zone of aeration contains mostly air in its pore
  spaces, some water adheres to particles as
  suspended water
• zone of saturation contains mostly water in its
  pore spaces
• The surface separating the two zones is the water
  table

3
The Water Table

• The water table usually mirrors surface
  topography, but varies along with precipitation
  rates and permeability
• capillary fringe an thin, irregular layer where
  groundwater moves upward into the zone of
  aeration due to capillary action (surface
  tension)
• GROUNDWATER MOVES FROM ZONES OF HIGH PRESSURE TO
  ZONES OF LOW PRESSURE at rates that vary from
  250 m per day to cm per year

4
Springs and wells

• Groundwater is discharged from an aquifer
  naturally into streams, rivers, lakes and swamps
• springs occur where groundwater percolates down
  to an impermeable layer and flow laterally until
  it intersects the surface
• Well a hole dug that penetrates the water table,
  water flows into the cavity and fills it to the
  level of the water table

5
Springs and wells

• Pumping water from a well may result in a zone of
  depression, a localized lowering of the water
  table caused by removing water at a rate greater
  than the maximum inflow allowed by permeability
• Artesian wells are natural or manmade wells where
  water gushes to the surface under pressure
  caused by confinement of a tilted aquifer by
  impermeable beds

6
Sinkholes and Karst topography

• Karst topography regions characterized by caves,
  springs, sinkholes, solution valleys and
  disappearing streams
• Karst topography occurs in areas with large
  amounts of limestone in the subsurface
  dissolution occurs as carbonic acid in
  groundwater reacts with limestone
• Sinkholes depressions formed as underlying rock
  is dissolved by seeping water, or by cave roof
  collapse

7
Sinkholes and Karst topography

• Sinkholes are common in Kentucky and Florida,
  where they can be the often unexpectedly occur,
  especially during drought periods as the water
  table drops
• Disappearing streams are streams which empty into
  sinkholes, they may reemerge in elsewhere as a
  spring
• Caves are defined as naturally occurring
  subsurface openings that are connected to the
  surface and are large enough for a person to
  enter a large cave is a cavern

8
Caves and cave structures

• Caves form as groundwater percolates through
  carbonate rocks and dissolves and enlarges
  fractures and openings, often forming a complex
  interconnecting system
• 17,000 known U.S. caves Mammoth Cave, KY
  Carlsbad Cave, NM
• As groundwater falls, dripstone structures can
  form as groundwater saturated with dissolved
  carbon ions drips into the now air filled caves
  and precipitates some of the calcite

9
Caves and cave structures

• stalactites are icicle-shaped dripstone
  structures that hang from cave ceilings
• stalagmites are the deposits formed on the cave
  floor by mineral laden dripping groundwater
• columns are formed as stalagmites and stalactites
  meet rows of stalactites may form a drip curtain
  and layers of calcite deposited by sheet flow
  along the cave flow can form travertine terraces

10
Human Impact on Groundwater

• Groundwater accounts for 20 of all water used in
  the U.S.
• Unwise use of this valuable resource can damage
  or deplete groundwater reservoirs
• Some of the problems related to groundwater use
  include
• overpumping-lowering the water table
• saltwater incursion
• subsidence
• contamination

11
Hydrothermal Activity

• Hydrothermal Activity refers to water heated by
  geological processes such as proximity to
  intrusive magmatic bodies
• fumeroles vents where steam and gases are
  discharged
• hot springs discharge hot water (gt 37oC, temp of
  the human body)
• geysers hot springs that intermittently eject
  hot water and steam