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SHAPING EARTH’S SURFACE
CHAPTER 4 LESSON 2 SHAPING EARTH’S SURFACE
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4.2 INFORMATION
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EARTHQUAKES The vibration caused by the rupture and sudden movement of rocks along a break or a crack in Earth’s crust
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EARTHQUAKES An earthquake can occur at a fault
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FAULT a crack or a fracture in Earth’s crust along which movement occurs.
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FAULT Because of the convection currents beneath tectonic plates, forces build up along faults at plate boundaries
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FAULT RUPTURES When a fault ruptures, Earth’s crust moves along the fault, causing an earthquake
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FAULT RUPTURES Most earthquakes occur at plate boundaries
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MAGNITUDE The size of an earthquake
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MAGNITUDE Magnitude is determined by how much energy is released during the earthquake.
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FAULTS A plate boundary involves more than one fault
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FAULTS AND SUBDUCTION Faults are largest where one plate subducts into the mantle, and the strongest and most damaging earthquakes occur there
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MOVEMENT ALONG FAULTS The movement of crust along faults can make mountains, valleys, and other landforms
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TRANSFORM BOUNDARY Blocks of crust move horizontally past each other at a transform boundary
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MID-OCEAN RIDGES Mid-ocean ridges form at divergent boundaries between oceanic plates
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SUBDUCTION ZONE At a convergent boundary with a subduction zone, the plate that does not subduct deforms and crumples as the two plates push toward each other.
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SUBDUCTION ZONE
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NO SUBDUCTION ZONE At a convergent boundary without a subduction zone, the edges of both tectonic plates become crumpled and deformed.
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NO SUBDUCTION ZONE
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B. VOLCANOES
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MAGMA molten rock stored beneath Earth’s surface
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LAVA Magma that erupts onto Earth’s surface
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VOLCANO vents in Earth’s crust through which molten rock flows
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CONVERGENT BOUNDARY Most volcanoes form at convergent plate boundaries
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CONVERGENT BOUNDARY At some convergent boundaries, one plate subducts another plate
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MAGMA RISES Magma formed from the subducted plate then rises toward the surface and forms volcanoes on the plate that does not subduct
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LINE OF VOLCANOES A line of volcanoes forms parallel to the plate boundary directly above the plate that subducted
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VOLCAOES FORM QUICKLY Mountains can form over millions of years, but volcanoes can form in hundreds to thousands of years
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VOLCANIC ERUPTIONS Volcanoes erupt in two ways
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LAVA FLOWS 1 - In a lava flow, lava can flow over Earth’s surface before cooling, hardening, and becoming solid rock.
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ASH ERUPTIONS 2 - Sometimes, volcanoes can erupt explosively, as happened at Mount St. Helens in 1980.
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ASH ERUPTIONS Tiny pieces of glass made from solidified lava are called ash and can be blown high into the atmosphere
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C. OCEAN BASINS
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LAVA FORMS NEW CRUST At convergent plate boundaries and divergent plate boundaries, lava hardens and forms new crust
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LAVA FORMS NEW CRUST At an oceanic divergent plate boundary, newly formed crust is added to the edges of the plates as new ocean crust
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MID-OCEAN RIDGES Long, narrow mountains formed by magma at divergent boundaries
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MID-OCEAN RIDGES Three-quarters of all lava erupts at mid-ocean ridges
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MOUNTAINS FORM Most mountains form near plate boundaries because folding and crumpling usually occur at the edges of plates
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MOUNTAIN RANGES Large mountain ranges form when two continents collide at a convergent plate boundary.
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HIMALAYAS The Himalayas are the world’s largest and highest mountain range, and they are still growing
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