Weathering, Soil, Erosion, Groundwater, & Surface Water Chapters 10, 11, & 12

Mechanical (Physical Weathering) Breaking down rocks by physical means, like ice, wind, water, gravity, and plants/animals Ice wedging occurs when water squeezes into cracks in rocks, freezes, expands, and cracks the rock open Plant roots also act like ice…they wedge themselves into cracks, splitting the rock apart Abrasion occurs when rocks and sediment grind against each other, wearing away the exposed surfaces. This can happen with wind and water.

Grave stone attacked by acid rain Chemical Weathering Breaking down rocks by changing their chemical composition Major agents are water, acids, and air When carbon dioxide and water combine, they form carbonic acid, which is found in precipitation (acid rain) Acids are also found in the roots of decaying plants and lichens (fungi and algae) The oxygen in the air also chemically changes iron and turns soil a reddish color (oxidation) Lichens Grave stone attacked by acid rain

The Result of Weathering is…SOIL!!!!! Soil is a mixture of pieces of broken down rocks and organic matter The organic material in soil is called humus Soil forms in layers, called horizons. Thickness and presence of horizons depends on climate. “O” horizon: decomposed plant and animal matter or humus “A” horizon: also called topsoil, very dark in color and lots of humus “B” horizon: also called subsoil, is lighter than A and may have parts of A contained in it through leaching “C” horizon: partly weathered bedrock or parent material Profile showing the horizons Actual soil profile

What is Karst? Cave Sinkhole Natural Bridge, VA Karst topography is a landscape created by acidic groundwater dissolving sedimentary rock such as limestone. Abundant in the Valley & Ridge province. Caves: Natural cavities beneath the surface of the earth, created by groundwater dissolving rock. Sinkholes: Rounded depressions in the landscape. Sinkholes are often collapsed caves and can be quite deep, or they can be shallow holes. Sinkholes collect surface water running off the surrounding land, and the runoff goes directly into the groundwater. Natural bridges: Arches that are the remnants of collapsed caves, usually fairly short. Cave Sinkhole Natural Bridge, VA

The Water Cycle (Hydrologic Cycle) The cycling of water from the ocean, to the atmosphere, into and on the ground, and back to the oceans again Evaporation: changing from the liquid to gaseous state Condensation: changing from the gaseous to liquid state through cooling (clouds) Precipitation: when clouds are fully saturated, they give back extra water through rain and snow Runoff: water that remains on the surface in rivers and streams Infiltration: water that soaks into the soil and added to the water table Transpiration: water vapor given back to the atmosphere through photosynthesis in plants

Groundwater Permeability is a measure of the ability of a rock or sediment to transmit water or other liquids. Water does not pass through impermeable materials. Porosity is the available pore spaces in rocks that can store water. Mixtures of sediments, such as gravel and sand, are the most porous and can hold the most water. A good aquifer is both porous AND permeable. Zone of Aeration Water Table Zone of Saturation

Permeability and Porosity A substantial amount of water is stored in permeable soil and rock underground. Earth’s fresh water supply is finite. Water is continuously being passed through the water cycle. Human activities, such as waste disposal, can pollute groundwater supplies.

Rivers & Estuaries Estuaries, like the Chesapeake Bay, are areas where fresh and salt water mix, producing variations in salinity and high biological activity. Four major regional watershed systems in Virginia lead to the Chesapeake Bay: Potomac-Shenandoah, Rappahannock, York, James Two major watersheds drain into the North Carolina Sounds: Chowan and Roanoke Two major watersheds lead to the Gulf of Mexico via the Ohio River: New and Tennessee James River drains most of the surface water in Virginia

Erosion Video