GEOG 100 lecture 10--Water Resources (ground water and ice)
Chapter 8: The Hydrosphere Water and Ice: Underground and on the Surface
The Global Water Budget• Earth has a global water budget—if water is lost in one place or in one form, it is moved to another place or another form• The total amount of water (in whatever form) varies from place to place, but stays constant over the planet as a whole
Subjects you’ll be studying in thissegment:• Underground water – Groundwater – Hydrothermal sources• Ice on the surface – Permafrost – Glaciers• Water on the surface – Lakes – Swamps and Marshes
Where is all of Earth’s water found?• Oceans = 97.2%• Glaciers = 2.0%• Underground sources (aquifers, underground pools & groundwater) = 0.5%• Lakes (half saline, half fresh) = 0.2%• Pore spaces in soil (“soil water”) = 0.04%• Atmospheric water, streams, living things = 0.01%
The Hydrologic Cycle• The hydrologic cycle is the planetary circulation of water within and between the different sources of water on Earth—it is a closed system.• The power source behind the hydrologic cycle is the radiant energy of the sun.
Residence Time• The amount of time a given amount of water may remain in a particular segment of the hydrologic cycle is its residence time.• Residence time can vary from hours (evaporation followed by a thundershower), to millions of years (trapped in deep aquifers)
Underground Water• Small portion of Earth’s total water (0.5%)• Significant source of water for humans• But how did it get there?
Surface and Sub-surface Water:Into and Under the Ground• Precipitation adds to the surface soil water belt• Water not taken up by plants and soil flows downward under the influence of gravity• Once saturation is reached, water flows laterally (sideways), following topography— this movement is called subsurface flow
Subsurface Flow• At the base of a slope or at a surface depression that is lower than the water table, subsurface flow may reemerge (return flow).
Percolation• The downward flow of water through pore spaces in soil or rock under the influence of gravity is called percolation (just like water percolating through coffee grounds)• Different types of subsurface material will hold or pass water through in different ways.
Porosity and Permeability• Porosity—A measure of the total volume of pore spaces through which liquids or gases can pass, in relation to the total volume of solid ground material – Sand and sandstone have coarse grains and open textures, making them very porous – The more porous the material, the more water it can hold (like a sponge)
Porosity and Permeability• Permeability—How easily soil, rock fragments, or solid rock allow water to enter and pass through (how easily does the water flow?) – Dry clay is very porous (lots of spaces between particles for holding water) – Once water is added, clay particles hold the water very tightly (water is held but can’t flow through) – Clay is very porous, but not permeable—it is impermeable
Hydrologic Zones• Zone of Aeration—The soil water belt; this zone is not completely saturated—some pore spaces are filled with air, some with water.• This is where infiltration and percolation happen—water is just passing through.
Hydrologic Zones• Zone of Saturation—All pore spaces in rock or sediment filled with water – The top of the zone of saturation (groundwater layer) is called the water table – The shape of the water table follows topography —it is highest where elevations are highest and lowest in areas of low elevation – This groundwater flows slowly toward depressions or lower elevations • Note: Groundwater is NOT an underground stream!
Hydrologic Zones• Zone of Saturation – Effluent condition—The water table is higher than a surface depression; groundwater flows out onto the surface – Influent condition—The water table is lower than a surface depression; water in the depression (a stream or a lake) seeps downward until it reaches the groundwater layer
Hydrologic Zones• Zone of Confined Water— separated from the zone of saturation by an impermeable layer, called an aquiclude• This underground water storage layer is called an aquifer• Artesian well—A well drilled into the aquifer that is lower than the top of the water table and flows to release pressure, without any pumping
Hydrologic Zones• Waterless Zone—A few miles down, the pressure too great; pore spaces collapse and water can’t flow
Groundwater Management• A lack of careful management can endanger humans, wildlife, and vegetation• Depletion and contamination are serious threats to global health and well-being• Competition and conflicts over adequate, clean water supplies may become the dominant issue, world-wide.
Groundwater Management:Issues • Removal of groundwater faster than natural recharge can replace it may lead to a depleted and unusable water source • The case of the Ogallala Aquifer
Groundwater Management:Issues • As water is removed from the groundwater layer, it doesn’t drop the water level uniformly across the surface of the water table • An area of empty pore spaces surrounds the well in a cone shape. This cone-shaped lowering of the water table is called a cone of depression.
Groundwater Management: Issues• When pore spaces are left unrecharged, they collapse and the ground sinks. This ground subsidence can be significant and environmentally destructive.
The Case of Venice, Italy The worst acqua alta in memory, the one that truly woke Venetians up to how bad things could get, occurred on November 3, 1966. The high tide that swept into all corners of the city that night lasted an astonishing 22 hours (typical high tides last six).
Groundwater Management:Issues • Contamination of groundwater – Percolation through compromised landfills and waste dump sites carrying pollutants into groundwater sources – Surface and buried pollutants seeping into groundwater from industry and energy sources – Seepage from septic systems – Seawater intrusion into coastal groundwater sources turning them saline and undrinkable
Hydrothermal Activity• Occurs where underground water comes into contact with magma sources• Temperatures as high as 400ºF; water remains liquid because of the extreme pressure of the rocks above• Heated water dissolves minerals, especially silica, which are carried away and deposited on the surface
Hydrothermal Features• Hot springs – Heat is dissipated evenly as the water rises to the surface, so it flows slowlyMorning Glory Pool, Yellowstone N.P.
Hydrothermal Features• Geysers – Heat is not lost, so that water shoots rapidly to the surface as if exploding Old Faithful, Yellowstone N.P.
Hydrothermal Features • Fumaroles (steam vents) – Above the water table, so little water is present; only steam and volcanic gases are released from surface cracks and fissuresGreen Dragon Fumarole,Yellowstone N.P.
Surface Water: Ice• Permafrost—Permanently frozen ground water; any subsoil that stays frozen for two consecutive years is considered permafrost
Melting permafrost is a serious problemYukon, Canada The Alaska Pipeline Pipeline in northern Russia • Building foundations cracking as surface turns to mud, broken pipelines, etc. (This is why the Alaska Pipeline sits above ground) • Release of heat-trapping methane – http://www.youtube.com/watch?v=B36EoEuKjVg&feature=player_embedded
Surface Water: Glaciers Extent of ice sheets during last glacial maximum (the last Ice Age)
Surface Water: Ice• Glaciers – Large, moving mass of ice, forming on or adjacent to a land surface through the accumulation and consolidation, under pressure, of snow falling at higher elevations – The ice mass moves outward and downward from the zone of accumulation to lower elevations – Glaciers are in constant motion
Glaciers• Constant motion scrapes away surface material wherever the glacier is flowing
Glacial Moraines in Northern U.S.• Glacial till (scraped material) is trapped and transported by moving ice, then deposited at the end and sides of the glacier in a chaotic jumble – The Great Plains, U.S. and Michigan
Glaciers• Two types of glaciers – Alpine glaciers (mountain glaciers or valley glaciers) • Form in mountain valleys – Continental glaciers (ice sheets) • A continuous mass of thick ice moving outward in all directions from the center of accumulation • So large that they bury the entire landscape – Greenland and Antarctica
What will happen when theworld’s glaciers melt?• Melting sea ice is increasing temperatures in the Arctic Ocean, reducing albedo and creating a positive feedback loop that is increasing warming – Melting of sea ice will not raise sea level – Melting of ice on land, which then flows to sea, has already significantly raised sea level (low- lying islands disappearing, coral forests “drowning”) • Greenland’s ice sheets melting completely would raise sea level by 6 m (~18 feet)
Lakes• A body of water surrounded by land (no size definition)• Many lakes, esp. in dry regions, are ephemeral (dry for part of the year)• Water balance maintained by sfc. inflow and/or springs beneath the sfc.• Drainage can occur by stream, or into the subsurface where aquacludes are not present• Movement of water is always downward in elevation toward the ocean
Lakes• Lakes can be created by glaciation, crustal activity, volcanism, sinkhole collapse, etc.• The destiny of most lakes is infilling by sediments or destruction by humans
An alkali dust storm building along the shores of Owens Lake, CASalts blowing acrossPaoha Island, MonoLake, CA 53
Swamps and Marshes Marshes—dominated by grasses/rushes shallow enough for plants to grow• Associated with coastal plains (like the area surrounding S.F. and S.P. Bays), broad river valleys, and recently glaciated areas• May be an intermediate Swamps—plant growth dominated by trees stage during the infilling of a lake
Surface Water: Streams• Runoff—water that flows downslope along the surface is called overland flow – Runoff that flows downslope in sheets, where the ground surface is slick or solid and water can’t infiltrate easily is called sheet flow• If runoff occupies a narrow channel confined by its banks, it is a stream or river• Rivers and Streams flow to lowest possible elevation, powered by: Gravity!