Internal/External Forces Unit 1: Basics of Geography Internal Forces ○ Tectonic plates: enormous moving pieces that form the earth’s crust- continually being reshaped ○ Earthquakes/Volcanoes ○ Move 1 of 4 ways: ○ Spreading ○ Subduction (dive under another plate) ○ Collision ○ Sliding past each other Internal Forces ○ 3 types of boundaries that mark plate movements: 1. Divergent boundary- plates move apart/spread (b/w Saudi Arabia and Egypt) 2. Convergent boundary- plates collide (India crashing into Asia) 3. Transform boundary- plates slide apart (San Andreas Fault) Internal Forces ○ Folds/Faults- 2 plates meet- folding and cracking of rock -Occurs very slowly -Sometimes rock not flexible, cracks cause a fault ○ Earthquakes- Plates grind/slip past each other, causing an earthquake ○ Seismograph detects earthquakes ○ Focus- where an earthquake begins ○ Epicenter- point directly above the focus Internal Forces ○ Landslides, displacement of land, fires (broken gas lines) collapsed buildings ○ Aftershocks and smaller magnitude earthquakes ○ Richter Scale- 2 usually not noticed; 4.5 makes the news ○ Major is 7 or more- Largest reported 8.9 Kermadec Islands, So. Pacific Internal Forces ○ Tsunami- Giant wave in ocean caused by an earthquake up to 450 mph and 50-100 ft. waves ○ 2004 Tsunami hit Dec. 26 Indonesia, Thailand, Sri Lanka, Somalia ○ Waves about 33 feet high ○ 4th largest in world since 1900….9+ more than 150,000 casualties ○ Volcanoes- Found along tectonic plate boundaries -Magma, gases, and water from the lowest of the crust collect in underground chambers -Magma that reaches the earth’s surface is called lava Internal Forces □ Most dramatic volcano action-eruption- hot lava, gases, ash, dust, rocks explode out of vents in the earth’s crust (often a hill or mountain is formed by lava □ Volcanoes can be active for many years than stop. Can be inactive and become active. □ Ring of Fire- Zone around the rim of the Pacific Ocean- location of the vast majority of active volcanoes Internal Forces ○ 8 major tectonic plates meet in zone. Volcanic action and earthquakes occur frequently. ○ Hot spots- Hot springs and geysers- water heats up and rises to surface ○ Yellowstone- Old Faithful External Forces ○ Weathering- physical and chemical processes that change the characteristics of rock on or near the earth’s surface. Occurs slowly. ○ Creates sediment- smaller and smaller pieces of rock, mud, sand, or silt ○ Mechanical weathering- breaks rock into smaller pieces (construction, drilling, blasting, frost, plant roots External Forces ○ Chemical weathering- Decomposition (break up) Rock is changed into a new substance as a result of interaction b/w elements in the air. ○ Erosion- Weathered material is moved by the action of wind, water, ice or gravity. Glaciers, waves, blowing winds cause erosion; reshapes landforms ○ Water forms a delta (river enters ocean) Waves form beaches External Forces ○ Wind- transports/deposits sediment- sand dunes, rocks, loess (loh-uhs) are wind blown silt/clay sediment ○ Glaciers- large, long lasting mass of ice; cut valleys into the land; rocks left behind may form a ridge or hill; may be tunnels inside or under glacier ○ Soil- weathered rock, organic matter (humus), air, and water External Forces ○ Soil factors: Determine type of vegetation ○ Parent material- chemical composition of original rock ○ Relief- steeper slopes are eroded easily and do not produce soil quickly ○ Organisms- help loosen soil/supply nutrients ○ Climate- hot/cold wet/dry ○ Time- amount of time to produce soil varies (avg 2.5 cc/century).