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Lesson 4.4 - A Watery Landscape

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  • Why is the ocean floor not flat?
    Because of rising and falling crust, much like land on Earth's surface.
  • Why can magma reach the surface at plate boundaries more easily?
    Because there are gaps and weak spots in the crust where plates meet.
  • What happens to magma when it hits ocean water?
    It cools quickly and hardens, forming new rock.
  • How deep is the Mariana Trench?
    It is more than six-and-a-half miles (around 10.5 kilometers) deep.
  • T/F:All islands form at the edges of tectone plates.
    False
  • FITB: The ocean floor is over two _______________ deep on average.
    miles
  • FITB: Mid-ocean ridges are created when __________ rises between tectonic plates.
    magma
  • What causes Earth's plates to move
    The pressure from seafloor spreading at mid-ocean ridges.
  • How do volcanoes contribute to island formation?
    Volcanoes release magma that hardens and builds up until it forms islands.
  • FITB: Volcanoes under the ocean usually __________ instead of exploding.
    ooze
  • How is a mid-ocean ridge formed?
    They are formed where magma steadily rises through the spaces between the tectonic plates.
  • FITB: The Hawaiian Islands were formed by underwater ____________________.
    volcanoes
  • FITB: The Galapagos Islands were formed from peaks of an undersea _______________.
    ridge
  • What do mid-ocean ridges resemble in shape?
    They resemble the seams on a baseball.
  • Where is the Mariana Trench located?
    It is located in the Pacific Ocean, south of Japan.
  • Why does the crust under the oceans allow magma to reach the surface more easily?
    Because it is thinner than the crust on land.
  • What is subduction?
    It's when one tectonic plates moved under another, creating deep ocean trenches.
  • T/F: Mid-ocean ridges can form islands when their peaks rise above sea level.
    True
  • Why are the Hawaiian Islands unusual in terms of how they were formed?
    Because they were formed by undersea volcanoes and they are not located at a tectonic plate boundary.
  • T/F: Magma cool faster on land than in the ocean.
    False.
  • FITB: Earth's crust is ______________ under the oceans than on land.
    thinner
  • What causes the formation of Islands like the Galapagos?
    The peaks of undersea mountains fridges rise above the water's surface.
  • FITB: When magma cools in the ocean, it forms new _______________.
    rock
  • Describe how undersea volcanoes behave different than land volcanoes?
    Undersea volcanoes usually do not explode; instead, magma oozes out due to high pressure.
  • What happens when tectonic plates collide?
    One plate slides under the other in a process called subduction.
  • How is Mauna Kea taller than Mount Everest?
    When measures from its base on the ocean floor, it is taller than Everest is from sea level.
  • Why doesn't magma from undersea volcanoes usually explode?
    Because the pressure from the water above prevents explosive erruptions.
  • FITB: Subduction happens when one tectonic plate _________ under another.
    slides
  • The ______________ ______________ is the deepest part of Earth's crust.
    Mariana Trench
  • What is seafloor spreading?
    It is the process where magma add new material to mid-ocean ridges, pushing tectonic plates apart.
  • How does seafloor spreading affect Earth's tectonic plates?
    It causes them to move around the planet and sometimes collide.
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