Where water and land meet- the margins

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Where water and land meet- the margins
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Continental Margins

• Two types
• Active (pacific) margins boundary with much
  geologic activity (earthquakes, volcanoes), plate
  boundaries, subduction, narrow
• Passive (Atlantic) margins boundary with little
  geologic activity

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Margin Features

• Continental shelf extremely flat extension of
  continents under the oceans surface
• Continental break edge of the shelf
• Continental slope from the edge of the break,
  depth increases rapidly
• On active margin, slope usually leads into trench
• On passive margin, slope fans onto the
  continental rise (gently sloping region toward
  the ocean basin) submarine canyons are also
  found on passive margins (primarily from coastal
  river currents)

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Sea floor features

• Abyssal plain flat area of ocean basins
• Abyssal hills small hills, grouped, primarily
  Atlantic
• Trenches
• Ridges
• Seamounts mountains that were once volcanoes
• Guyots volcanoes that have had their tops
  sheared off by erosion
• Atolls center of volcano gone but outer ring
  left

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Volcanic Island Arcs

• Usually form when plates converge
• Two types
• Continental Cascades, Andes
• Oceanic Japan, Philippines, most of Aleutians

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• Process of subduction forms arc

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Atolls
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Hydrothermal Vents

• Superheated, mineral-rich water
• Forms smokers/chimneys
• Very biologically active in a very harsh habitat
• Cracks in plate allow water to get superheated
• Plate boundaries, hot spots

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Schematics of a Hydrothermal vent
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