Download Chapter 2, Section 2

Chapter 2, Section 2
“Forces of Change”
Earth’s Structure
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Surface: changes constantly
Wind, water, volcanoes, earthquakes
3 layers:
Core: inner (solid-iron and nickel) and outer
(liquid-melted iron and nickel)
Mantle-releases 80% of heat generated from
interior Earth
Crust-rocky shell---broken into slabs of rock
(plates)---float on melted layer of upper
mantle
Structure…
• Landmasses once part of Pangaea
• Millions of years: broken apart---continental drift
• Moving: created continents, oceans, and
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mountain ranges
Movement: slow (4 inches a year)
Spread apart---magma---pushed up from mantle
Bump together---forms trench
Plate tectonics---causes?
– Heat rising from earth’s core-creates slow-moving
currents---shifts plates around
Internal Forces of Change
1. mountains-colliding of plates
2. Subduction-sea plate becomes molten material--3.
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becomes magma-forms volcanic mountains
Accretion---movement levels off seamounts---piles up
debris in trenches
Spreading---allows magma from within earth to come
between plates-builds undersea volcanoes
FoldsFaults-San Andreas Fault (CA)---folded land cannot be
bent any further---crust cracks/breaks
San Andreas Fault
Earthquakes
• Sudden, violent movements of plates along fault
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line
Shaking changes surface
Occur where different plates meet one another
Tension builds up---stain becomes too intense--rocks snap and shift---ground trembles
Cities along Ring of Fire---zone of earthquake
and volcanic activity surrounding Pacific Ocean
Ring of Fire---compare to pg. 39
Volcanic Eruptions
• Mountains formed by lava or magma that breaks
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through earth’s crust
Rise along plate boundaries
Rocky plate-melts as it goes into hot mantle
Molten rock too thick-flow is blocked-pressure
builds
Some areas are hotter than others----hot spots
may create geysers or hot springs (Old Faithful)
Yellowstone National Park--Old Faithful
External Forces of Change
1. Weathering
*physical---when large landmasses of rock are
physically broken down
*chemical---changes chemical makeup of rocks
2. Wind Erosion
*involves movement of dust, sand, and soil
*plants help protect land
*Great Plains---1930s
External…
3. Glacial erosion
*form over long periods of time
*weight causes movement-pick up rock and soil
*change landscape
*melt-leave behind moraines
*two types: 1-sheet 2-mountain
4. Water Erosion
*fast-moving water-greatest cause of erosion
*begins when water flows off land downhill in streams
*oceans---waves pound cliffs, etc