1. Forces of Change Formula: + = The Earth’s Builders and Landscapers!!!!!!

2. Main Idea: Together with the internal forces of plate tectonics, the external forces of weathering and erosion are constantly changing the appearance of the earth’s surface.

3. Landscaping the Earth: Weathering and Erosion

4. Weathering –process that breaks down rock into smaller pieces Two ways:  physical (or mechanical) weathering – when physical processes break apart rocks  chemical weathering – occurs when changes are made to the chemical make-up of rocks that cause them to break apart

5. Physical Weathering Examples:  frost wedging – where water seeps into cracks of rocks and freezes; ice expands causing the rock to split  tree roots grow through cracks of rocks eventually forcing rocks apart

6. Chemical Weathering Examples:  underground caves form when carbon dioxide combines with water and dissolves limestone  oxidation - rocks that contain iron can rust just like iron does; as the rust expands, it helps to break up rock

34. Erosion – the transporting of weathered material from one place to another Three Agents of Erosion:  Water  Wind  Ice

35. WATER: Nature’s Scouring Pad RIVERS:  most important agent of erosion  rainfall/snowmelt forms into creeks, streams, and/or rivers carrying rocks, pebbles, and sediment  source: beginning of river  mouth: where it empties  tributary: river that feeds into another river  abrasion – when rivers cut and scour the landscape into channels and V-shaped valleys as they carry weathered material  sometimes valleys are carved even further to form high, steep walls called canyons  muddy water is a sign that erosion is taking place b/c that means that bits of rock and soil are in the water  deposition of sediment from moving water can result in: - alluvial fans at mountain bases - alluvial fans at mountain bases - deltas at mouths of rivers - deltas at mouths of rivers

63. Water Continued…. WAVES: Waves crashing against shores can:  change shape of coastlines  build up and tear down beaches  reduce the coastline (coastal erosion)  form caves and arches  pound rocks into sand

70. WIND Nature’s Sandblaster  Wind is capable of carrying dust, sand, soil, and volcanic ash  Wind sculpts or “sand-blasts” land surfaces into very unusual formations  Wind forms sand dunes because unlike water and ice, sediment can be moved uphill or downhill ….constantly moving and changing shape  Dunes are found along coastlines, deserts, lakes, and rivers  Beach dunes attract vegetation. This helps to reduce coastal erosion, but protective dunes are often damaged or destroyed due to human development and weather-related occurrences.  Barrier islands are islands that have dunes that help to protect inland areas from coastal erosion

84. GLACIERS: Nature’s Bulldozers  ice sheets or caps - vast glaciers that covered large portions of the earth’s surface during the last ice age.  What’s left of these ice caps still exist and cover much of Antarctica, Greenland, and the Arctic Ocean  mountain glaciers – form when fallen snow accumulates in mountain tops year after year eventually turning into ice; once heavy enough, gravity pulls these glaciers downhill  all glaciers move slowly picking up soil, rocks, boulders, trees, etc.  Glaciers carve out U-shaped valleys (Yosemite)  Glaciers gouge out basins that eventually become lakes (Great Lakes and Lakes of Canada)  As glaciers begin to retreat (melt), they deposit boulders, rocks, soil, and sediment called moraine.

109. Weathering and Erosion Miscellaneous  Effects of weathering and erosion can create spectacular scenery which many governments protect as national parks and other federally protected lands  Every physical land feature on earth was formed by the combination of plate tectonics and weathering and erosion…..so, don’t forget the formula!!!  Unfortunately, humans speed up these naturally occurring effects at alarming rates with dire consequences. Examples include: - acid rain - poor farming practices - deforestation - urbanization - strip mining - building levees!!!!