Water Erosion and Deposition Chapter 9 Water Erosion and Deposition

Surface Water Runoff – rainwater that flows across Earth’s surface; amount of runoff is affected by several factors Amount of rain that falls Length of time the rain falls Steepness of the slope, of the land Amount of plants, vegetation

Surface Water Erosion – the wearing away of soil and rock by water Rill erosion – during a heavy rain, a small stream forms and carries away soil, creating a groove called a channel. Gully erosion – heavy rains remove large amounts of soil and sediment from a rill channel, forming a gully.

Surface Water Sheet erosion – sheets of water flowing across the land pick up and carry away sediments Stream erosion – water in a stream picks up sediments from the bottom and sides of its channel, making the channel deeper and wider

Surface Water River system – the network of groundwater and streams that come together to form a river Drainage Basin – the area of land from which a stream or river collects runoff Mississippi River drainage basin – the largest in the United States

Surface Water Stages of stream development Young streams – flow swiftly through a steep vally May have whitewater rapids and waterfalls Erodes the stream bottom faster than the sides

Surface Water Mature stream – flows more smoothly through its valley Stages of stream development Mature stream – flows more smoothly through its valley Erodes more on its sides Curves are called meanders Carves a broad, flat valley floor called a floodplain

Surface Water Stages of stream development… continued Old stream – flows slowly through a floodplain it has carved

Surface Water Flooding – when too much water enters a river system, it overflows its banks Dams – Built to control the flow of water downstream Levees – mounds of earth built along the sides of a river to prevent flooding

Surface Water Deposition – when water slows down, its drops, or deposits, the sediments it is carrying. Delta – formed by sediments that are deposited as water empties into an ocean or lake Alluvial fan – fan-shaped area formed by sediments deposited as water empties from a mountain valley onto a flat open plain

Groundwater Groundwater – water that soaks into the ground and collects in the pores of the rock underlying the soil 14% of all freshwater exist as groundwater Soil and rock are permeable if water can pass through the pore space. Example: sandstone Soil and rock are impermeable if water cannot pass through them. Example: Granite

Groundwater Aquifer – a layer of permeable rock that lets water move freely Zone of saturation: the area where all pores in the rock are filled with water Water Table – upper surface of the zone of saturation

Groundwater Water Table Many people get their water from groundwater through wells Groundwater flows into a well, and a pump brings it to the surface. Good wells extend deep into the zone of saturation, past the water table. Wells can dry up during seasons or if demand is too high

Groundwater Water table… continued Artesian wells – water rises to the surface under pressure Springs – the water table is so close to the surface that water flows out. Geyser – a hot spring that erupts periodically, shooting water and steam into the air

Groundwater The work of groundwater Groundwater mixes with carbon dioxide to form carbonic acid. Acidic groundwater moves through cracks in limestone, dissolving the rock Gradually, the cracks in the rock enlarge until a cave is formed

Groundwater Stalactites – calcium carbonate deposit that hangs from the cave’s ceiling Stalagmites – calcium carbonate deposit that forms on a cave’s floor

Groundwater The work of groundwater… continued If underground rock is dissolved near the surface, a sinkhole forms

Groundwater Subsidence – the sinking of land caused by the excessive withdrawal of groundwater

Ocean Shoreline Shoreline forces – three major forces constantly change the shape of the shoreline. Waves pound against shores, breaking rocks into smaller pieces Move large amounts of sediments Collide with the shore at angles, creating longshore currents, which act like rivers of sand in the ocean Currents move sediments along the shoreline Tides carry sediments out to sea and bring in new sediments

Ocean Shoreline Rocky shorelines – steep shorelines Rocks and cliffs are the most common features Softer rocks erode away before harder rocks, leaving islands of harder rocks

Ocean Shoreline Sandy beaches – gently sloping shorelines Beaches – deposits of sediments that are parallel to the shore Made of rock and shell fragments Fragile because longshore currents constantly carry sand down the shore to form barrier islands, spits, sand-bars, and baymouth bars

Ocean Shoreline Sandy beaches… continued Barrier islands – fragile sand deposits that parallel the shore but are separated from the mainland