Constructive & Destructive Forces on Landforms 5-3.1

Two Types of Forces Destructive Forces: processes that destroy landforms. 2 types: Slow (weathering) and Fast (Erosion) Ex. landslides, volcanic eruptions, earthquakes, floods Constructive forces: forces that build up an existing landform or create a new one. Caused by: water, gravity, wind and glaciers. Ex: deposition, landslides, volcanic eruptions, floods

Weathering Weathering Pictures Weathering: a slow, destructive force that breaks rocks into smaller pieces called sediments. Can by physical (mechanical) or chemical. Keywords: wear down, break apart

Mechanical weathering: the breaking of rock into smaller pieces by forces due to gravity, ice, plant roots, or other physical forces.

Mechanical Weathering: Rock is physically broken into smaller pieces Small pieces have same composition as the original rock Very slow

Mechanical Weathering: Caused by…(Agents) Freezing and Thawing Release of Pressure Growth of Plants Animals Abrasion – Grinding away of rock by other rock particles that are carried by water, ice, wind, or gravity

Chemical Weathering: the changing of materials in a rock by chemical processes. Rock particles have different mineral make-up than original rock

Chemical Weathering: Caused by…(Agents) H2O  MOST important Oxygen (O2) Carbon Dioxide (CO2) Living organisms Acid Rain  very rapid

Agent Type Description Mechanical Rock particles wear away rock Chemical Forms from coal, oil, and gas burning Freezing/Thawing Breaks rock by ice wedging Carbon Dioxide Forms carbonic acid in water Weathers marble and limestone Burrowing in the ground breaks rock Plant growth Roots pry apart cracks in rock Living Organisms Produce weak acid that weathers rock Oxygen Causes rust on some rock Sun or forest fire causes rock to crack

Rates of Weathering: Type of rock Climate Minerals that make up the rock determine how fast it weathers Climate Occurs faster in wet climates & at high temperatures

Erosion Grand Canyon Video Erosion: the destructive movement of materials away from one place by wind, water, ice and gravity. Wave Erosion- caused by water Wind Erosion (Dust Storm)

Landslides Landslides: occur when gravity quickly pulls rock and dirt downhill.

Floods Floods: a great flow of water over an area that is usually dry land.

Erosion & Deposition Deposition: the placing of materials in a new place (constructive force). Ex. Sandbars

Water Erosion & Deposition River Delta- Deposits of sediment at the mouth of the Mississippi River creating new land called a delta.

Wind Erosion & Deposition Sand Dunes- sand is moved by wind Desert Sand Dunes Ocean Sand Dunes

Mass Movement: Caused by gravity Process that moves sediment downhill 4 types Landslide - Slump Mudslide - Creep

Landslide: Most destructive When rock & soil slide quickly down a steep slope

Mudflow: Rapid downhill movement of H2O, rock, and soil Often occurs after heavy rains

Slump: A mass of rock & soil suddenly slips down a slope (in a large mass/clump)

Creep: Very slow downhill movement of rock & soil

Volcanic Eruptions Volcano: an opening in the Earth’s crust through which steam, lava and ashes erupt. Cause both destructive and constructive changes to landforms.

Mount St. Helens Mount St. Helens Video Saint Helen’s Before Saint Helen’s After

Volcanoes can be constructive, but also destructive…

Earthquakes Earthquakes: the shaking of Earth’s surface caused by the release of energy along a fault. San Andreas Fault, California

Effects of Weathering on Mountain Ranges Moraine Lake, Rocky Mountains (younger mts.) Appalachian Mountains Older mountains Effects of weathering Rounding, softening of edges