Chapter 17 Oceans Cover 70 of Surface Groundwater and the Hydrologic Cycle Vasey s Paradise GCNP Oceans are only 0 025 of Mass Groundwater Groundwater is liquid water that lies in the subsurface in fractures in rocks and in pore space between grains in sedimentary rocks Hydrologic Cycle is the evaporation of water from the oceans transport over the land precipitation and return of the water to the ocean The Hydrologic Cycle x 1000 km3 y Hydrologic Cycle x 1000 km3 y Total ocean mass 1 4 x 1021kg Evaporation 4 3 x 1017 kg y 0 03 y 1 Porosity and Permeability Reservoirs Porosity is the percentage of open space in a rock The reservoir of hydrogen in oxygen minerals is many times that of the oceans Porosity and Permeability Permeability is the ability of fluids to flow through rock Porosity Porosity can be as high as 50 in loose sand to 5 in cemented lithified sandstone to near zero in unfractured igneous rocks Porosity Porosity in close packed identical spheres is about 22 Permeability Permeability depends on the connectivity of the pore space Permeable rocks include sandstone and fractured igneous and metamorphic rocks and karst limestone Impermeable rocks include shales and unfractured igneous and metamorphic rocks 2 The Water Table The Water Table water table is the natural level of liquid ground water in an open fracture or well The water table follows topography The unsaturated zone is the region above the water table The The saturated zone is the region below the water table Unsaturated Zone The unsaturated zone is the region above the water table where pores and fractures are partially filled with water and partly by air The pressure in the unsaturated zone is atmospheric Conditions are usually highly oxidizing due to the presence of free oxygen in the air and highly reactive due to the presence of water Unsaturated Zone The unsaturated zone is the region above the water table where pores and fractures are partially filled with water and partly by air The pressure in the unsaturated zone is atmospheric Conditions are usually highly oxidizing due to the presence of free oxygen in the air and highly reactive due to the presence of water Saturated Zone The saturated zone is the region below the water table where all fractures and pores are filled with water The pressure in the saturated zone is hydraulic that of the overlying water column It increases at the rate of 100 atm km 0 1 atm m At very great depths 2km the pores are sealed and the pressure is that of the overlying rock column 330 atm km Clicker Question That subsurface region above the standing water level water table where the pressure is that of the atmosphere is called the A Saturated zone B Unsaturated zone C Oxidation zone D Reduction zone E Reactive zone 3 Clicker Question That subsurface region above the standing water level water table where the pressure is that of the atmosphere is called the A Saturated zone B Unsaturated zone C Oxidation zone D Reduction zone E Reactive zone Clicker Question That subsurface region below the standing water level water table where the pressure is that of the water column is called the Rock Units of Differing Permeabilities Clicker Question That subsurface region below the standing water level water table where the pressure is that of the water column is called the A Saturated zone B Unsaturated zone C Oxidation zone D Reduction zone E Reactive zone aquifer is a porous and permeable layer through which water can flow easily An Sandstone Alluvium aquitard is a layer that retards the movement of water An Shale Unfractured igneous or metamorphic rock Unusual Conditions perched water table is isolated from the main water table by a layer of impermeable rock A artesian basin is one that is under pressure due to hydraulic head An The artesian aquifer is usually confined between aquitards A Saturated zone B Unsaturated zone C Oxidation zone D Reduction zone E Reactive zone Clicker Question Those rocks that commonly make the best aquifers are A Granite B Schist C Shale D Sandstone E Salt An artesian well is one that will flow without pumping 4 Artesian System Clicker Question Those rocks that commonly make the best aquifers are A Granite B Schist C Shale D Sandstone E Salt Ogallala Aquifer Ogallala Aquifer Depletion Groundwater Irrigation Ogallala Aquifer Depletion Aquifer underlies former dust bowl Aquifer was artesian when first tapped Drilling and pumping greatly increased in last half of 20th century The economy is still largely agricultural Pumping greatly exceeds recharge Aquifer is depleted in some regions and nearly depleted in most of the rest Agriculture will largely cease in 20 years Currently 10 to 15 of US production Clicker Question A groundwater system where the pore pressure exceeds that of the water column to the surface so that water can flow spontaneously to the surface is called A Artesian B Confined C Karst D Depleted E Running 5 Clicker Question A groundwater system where the pore pressure exceeds that of the water column to the surface so that water can flow spontaneously to the surface is called A Artesian B Confined C Karst D Depleted E Running Artesian System Contamination Ogallala Aquifer Texas Ogallala Aquifer Contamination Pantax Site near Amarillo TX Nuclear weapons facility DoE Used TCE was burned in unlined pits Solvents leaked down to aquifer 400ft down What can be done Use surface water Karst Limestone calcite is soluble in water Karst Karst topography refers to a surface topography marked by sinkholes disappearing streams and small closed drainage basins It is an indication of underground drainage in caverns in limestone Limestone Calcite CaCO3 is dissolved by acids in soil and rainwater to form caverns 6 Clicker Question Thunder River Grand Canyon NP Clicker Question The rock type underlying most karst drainage systems is A Sandstone B Shale C Salt D Limestone E Granite Cave Formations The rock type underlying most karst drainage systems is A Sandstone B Shale C Salt D Limestone E Granite Cave Formations Precipitation of calcite from dripping water saturated in calcite gives rise to formations in caverns Stalactites hang from the roof Stalagmites build up on the floor of the cavern Hot Springs and Geysers Hot springs are caused by the outcrop of hot water heated by local igneous activity or by water that is rising from great depths Geysers are caused by hot springs of water at or above the boiling point Geysers occur in active volcanic regions such
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