Transcript volcanic islands

Classification of Ocean Floor
Deep Ocean Basins
Deep-Ocean Basins
Features of the deep ocean floor:
 Oceanic Ridges
 Hydrothermal Vents
 Trenches
 Island Arcs
 Abyssal Plains
 Abyssal Hills
 Seamounts
 Volcanic Islands
 Guyots
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Deep-Ocean Basins
An oceanic ridge is a mountainous chain of
young, basaltic rock at an active spreading center
of an ocean.
•Long, underwater mountain ranges.
•The largest tectonic feature on the earth.
•More than 1500 km wide, 64,000 km (40,000
miles) long.
•Rises 2-3 km (up to 2 mi) high above the
abyssal plain.
•Has a central rift valley.
•Composed of basalt rocks.
•Faulted with strike-slip (transform) faults.
•Shallow earthquakes occur along central rift.
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Deep-Ocean Basins
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Deep-Ocean Basins
Hydrothermal vents are sites where superheated
water containing dissolved minerals and gases
escapes through fissures or vents.
Usually associated with mid-ocean ridges
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Deep-Ocean Basins
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Deep-Ocean Basins
Trenches are long, narrow, deep depressions in the
ocean floor with steep sides caused by the
subduction of a converging ocean plate.
Trenches are the deepest places on Earth.
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Deep-Ocean Basins
Island Arcs, chains of volcanic
islands and seamounts, are usually
found parallel to the edges of ocean
trenches
•Found along ocean-ocean
convergent boundaries
As two oceanic plates converge, an
island arc is formed by volcanic
activity.
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Deep-Ocean Basins
Abyssal Plain -Very flat area of the ocean floor at
the edge of the continental rise.
•Average depth is about 4-6 km (2.5-4 mi).
•Covered by a layer of sediment, mostly <1 km
thick.
•The flattest areas on the planet.
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Deep-Ocean Basins
Abyssal hills are small, extinct volcanoes or rock
intrusions found between the continental margins
and oceanic ridges.
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Deep-Ocean Basins
Seamounts are volcanic projections from the
ocean floor that do not rise above sea level
(underwater volcanoes).
•Associated with hot spots and mid-ocean ridges
If seamounts break the surface of the ocean, they
create volcanic islands
•The biggest mountain on earth is Mauna Loa
(Hawaii).
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Deep-Ocean Basins
•Over time, wave & wind action erodes the peak of
a seamount or volcanic island to form a flat-topped
tablemount or guyot.
•Guyots were once volcanic peaks above sea level.
They were eroded by wave action as they sank
beneath the surface of the water.
•As seamount or guyot is being eroded, it is also
being moved away from the ridge or hotspot.
•Hot Spots: Surface expression of plumes of
magma rising from a stationary source of heat in
the mantle.
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A volcanic island chain can form when a plate passes
over a hot spot.
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Hawaiian Islands-Emperor Seamount
Chain
• A hotspot in the middle
of the Pacific plate
creates a volcano.
• Pacific Plate is moving
northwest.
• As the plate moves, a
new island forms & is
active.
• Result: a chain of
extinct volcanoes that is
progressively older
away from the hotspot
Over time…
• In the future, the HI island
chain will subduct into the
Aleutian Trench as new
• There is a “bend” in
islands form.
the HI island chain:
1. The Pacific Plate used • There is a new island about
1 km below the surface
to move north and
called Loihi.
changed directions to
move northwestward
OR
2. the hotspot could have
changed locations.
Coral Reef
Development
• Darwin noticed on his
voyage on the HMS Beagle
that coral reefs developed
around sinking volcanic
islands.
• Corals form in shallow,
warm, tropical seawater.
• Temperature, salinity, and
turbidity of the water have
to be just right.
• The coral polyp (animal)
secretes limestone, which
serves as the skeleton that
new polyps grow on to
build the coral reef.
Fringing Reef
• Corals develop around
a landmass.
• If it’s on a hotspot
(active volcano), lava
can destroy corals.
When the volcano
becomes inactive and
subsides, corals
develop toward barrier
stage.
Moorea, French Polynesia
Barrier Reef
• When the island
subsides, or sea level
rises, corals will
continue to build
upward and form a
circular reef.
• Water in between the
reef and island/land is
called the lagoon.
• If land subsides or sea
level rises faster than
the coral can grow, than
it will die off.
Great Barrier Reef, Australia
Tuanake, French Polynesia
Atoll
• When the island is
completely submerged
and conditions are right
for the coral, all that will
be visible on the surface
is the coral reef.
• If enough coral debris builds up, a narrow island can
be large enough to allow habitation.
A pie chart showing the distribution of Earth’s solid surface.
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