agents of erosion are...

Geologic Processes & Freshwater Resources •  Earth’s agents of erosion are constantly

changing Earth’s surface.

Agents: – Wind – Water –  Ice – Gravity

Geologic Processes & Freshwater Resources •  These changes can happen slowly- Creep.

Example of slump

Geologic Processes & Freshwater Resources

Avalanche Slump

Creep Flow Rockslide

Gravity and water content determine the type of sudden movement (often called mass movement or mas wasting) that occurs.

Geologic Processes & Freshwater Resources Porosity – The amount of pore space between particles of sediment.

Permeability – The ability of water to flow/permeate/percolate through the soil or rock.

CHAPTER HOME CHAPTER

SECTION OUTLINE

VOCABULARY 12.4 Hydrologic Cycle 12 Weathering, Soil, and Erosion

soil fertility

soil depletion

salinization

soil_savvy video

Distribution of Earth’s Water

Zone of aeration

Capillary fringe

Zone of saturation

Impermeable layer

Zone of aeration

Zone of saturation

Water table


Geologic Processes & Freshwater Resources •  Groundwater containing carbonic acid dissolves

limestone, forming caverns and features of karst topography.

Limestone Cave Formation

1. Rainwater containing carbonic acid seeps into the ground.

2. Limestone dissolves, forming underground caves.

3. Below the water table, the cave is filled with water.

•  Ground water is found beneath the soil mantle in rock fractures and sediment formations. Large units that yield water to wells are called aquifers. The annual recharge to the groundwater system from precipitation ranges from 8 inches in western Virginia to 10 inches in the Coastal Plain. About 2 million Virginians, or 34%, depend entirely on wells for drinking water.


Threats to Groundwater •  Sediments - from soil erosion •  Urban and suburban stormwater flows - from storm

events •  Phosphates and nitrates - from agricultural sources •  Improperly treated sewage - from overflows during storm

events, or from failing septic systems •  Industrial wastes such as acids, oils, and grease - from

factories and other industrial facilities •  Acids and leachates - from abandoned mines and dumps •  Encroaching salt water - from the ocean into groundwater

supplies •  Herbicides and pesticides - from water and sediments

running off the land


River Systems


•  Rivers move at different velocities based the the angle of the land and volume of water.

•  Rivers cut paths through the rock called channels.


Surface Water

•  Over time the river starts to wander from side to side.

•  This is called a meandering river


Surface Water

•  A very mature river may meander so much, loops connect, cutting off pre-existing sections of the river forming oxbow lakes.


Stages of River Development ! Youthful Stream ! Mature Stream ! Old Age Stream


Geologic Processes & Freshwater Resources •  Youthful rivers form steep-sided canyons and

V-shaped valleys. The lowest level to which a river can erode its bed is called its base level

Meanders


Meander



floodplain

Valley wall

Oxbow lake

Meander

Meander •  The Pearl

River meanders nearly a full loop in Mississippi. USA.


Meandering River


•  The tumbling waters cut away the shale and sandstone layers until the undermined top layer collapses, thus maintaining the vertical face of the Falls.


Niagara Falls from above


Flood Plain •  Flood-plain zoning, which places

restrictions on the use of land on flood plains, can reduce the cost of flood damage. Local governments may pass laws that prevent uncontrolled building or development on flood plains to limit flood risks and to protect nearby property. Landowners in areas that adopt local ordinances or laws to limit development on flood plains can purchase flood insurance to help cover the cost of damage from floods.


Deposition of Sediment


Rivers Deposit Sediments


Rivers Cary Sediment •  Flowing water transports gravel,

rocks, and boulders downstream by rolling or sliding them along the bottom of the streambed.

•  Small grains of sand and gravel can bounce along the bottom in a series of jumps.

•  Smaller sand, silt, and clay particles are transported in suspension. The particles move downstream suspended in the turbulent water, giving the water a muddy appearance.

•  Dissolved rock materials (not visible) move downstream in solution.


Deposition - Deltas •  Deltas are accumulations

of sediments that form where rivers empty into bodies of quieter water. When flowing water enters a lake or ocean basin, its speed slows. The slower water drops its sediments to the bottom of the basin and they accumulate to form a delta.


Deposition – Alluvial Fans •  An alluvial fan forms

on land where a river emerges from a mountainous area and flows out onto a more gently sloping plain

•  They typically form when there is a sharp change in slope.


The Watersheds of VA

Glencoe- Watershed

What is the largest watershed in VA?

Chesapeake Bay Watershed

Maryland

Delaware

New York

District of Columbia

Virginia

West Virginia

Pennsylvania

Water from these 6 states is drained into the Bay: Virginia Maryland West Virginia Delaware New York Pennsylvania

The water from over 50 rivers empties into the Bay. Can you name the 5 major rivers that flow into the bay?

Susquehanna River

Potomac River

Rappahannock River

York River

James River

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