Transcript Groundwater
Groundwater BIG Idea: • Precipitation and infiltration contribute to groundwater, which is stored in underground reservoirs until it surfaces as a spring or is drawn from a well. Infiltration: • process of water moving into the soil/ground • to penetrate, enter or gain access I. Water Beneath the Surface Groundwater: underground water that fills almost all of the pores in rock and sediment Aquifer: a body of rock that can store water and also let water flow through Think of an AQUIFER as a… • large, horizontal sponge that absorbs and transports water along its length A. Rock Properties that Affect Groundwater Porosity Permeability Porosity: percentage of open spaces in a rock or sediment 1. FACTORS THAT INFLUENCE POROSITY: (a) SORTING: amount of uniformity in particle size HIGH pore space LOW pore space (b) SHAPE: rounder particles = more porous (c) PACKING: loosely packed = more porous 2. Permeability: how freely water flows through open spaces in a rock (the pores must be connected) Impermeable – water can NOT flow through Can something be porous but impermeable? • The cork end is red because the grape juice went into it. Does this mean it is porous? • If you turn the bottle upside down will it leak? Is the cork permeable? B. Zones of Groundwater 1. Zone of Saturation: the layer of ground where all the pores are filled with water. 2. Water Table: upper surface of the zone of saturation 3. Zone of Aeration: upper region, where water is both in the soil and seeping down to the water table. Zone of Aeration ► • Capillary Action: ability of water to rise UP the soil. • particle size = greater capillarity Smaller Capillary Fringe: middle layer, between the water table and the zone of aeration. C. MOVEMENT OF GROUNDWATER • Depends on: 1. Permeability of the aquifer • ↑ permeability = ↑ velocity 2. Gradient of the water table • Gradient = steepness of the slope • ↑ gradient = ↑ velocity II. Wells and Springs • Water Table: upper layer of rocks with all pores filled with water. A. Ordinary Well: A hole dug below the water table which fills up with water. Cone of Depression: lowered area of the water table due to pumping B. Artesian Wells: water flows freely with no pumping • Underground water under pressure (between two impermeable rock layers) rises to the surface • Water is naturally filtered as it passes through porous rock and seeps to surface III. Groundwater and Chemical Weathering A. Caverns: rocks rich in calcite (limestone) slowly dissolved by carbonic acid. • Hard water = many dissolved minerals (Ca, Mg, Fe) • Soft water = few dissolved minerals Luray Caverns, VA • Formation of a Cave 1. Stalactites: water with dissolved calcite runs from a cave’s ceiling and solidifies downward. 2. Stalagmites: calcite rich water drips on the cave’s floor and builds upward. If the two connect, then it forms a column. 3. Natural Bridge: when the roof of a cavern collapses in several places leaving an archshaped rock. B. KARST TOPOGRAPHY • regions where chemical weathering by groundwater is now visible at the surface • regions where it is humid and there are limestone formations near the surface • Virginia, Kentucky, Tennessee, Indiana, and Florida have Karst Topography 1. Sinkholes (the main feature of Karst Topography) How do sinkholes form? • Rain seeps through soil and absorbs carbon dioxide and reacts with decaying vegetation • Acidic water is created • Water moves through spaces and cracks underground • Limestone is slowly dissolved, creating network of cavities and voids • Pores and cracks enlarge • Land surface above collapses or sinks 2. Streams that disappear in the ground Like Lewis Creek in Staunton 3. Caverns and Caves •