By: Jenny Griffes and Holly Kreutzer

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Plate Tectonics of the Hawaiian Islands

• By Jenny Griffes and Holly Kreutzer

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Plate Tectonics

• Continental lithospheric plates are about 50 km
  thick
• Most of worlds active volcanoes are along
  boundaries between shifting plates
• Intra-Plate Volcanoes
• -form roughly linear chains

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Plate Motion

• The plate moves W / NW at approx. 5-10 cm per
  year (rate depends on where you are on the plate)
• About 43 million years ago, there was a global
  reorganization of plate motions, which changed
  the direction of the plate
• The westerly turn might have been due to the
  collision of India with Asia (which was at about
  the same time)
• The earlier rate was about 6 cm / year before the
  shift

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Plate Motion

• Sudden jerks in the plate create new volcanoes by
  moving the current volcano out of the way to
  create a new one.
• On the other hand, when the plate is moving
  slowly, it just enlarges the current volcano
  (like the Big Island)

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Hot spot theory

• Hot spot theory was thought up by J. Tuzo Wilson
  in 1963
• Suspected by ancient Hawaiians long before who
  saw difference in erosion, soil formation and
  vegetation
• Oldest volcanic rocks of Kauai (most NW island)
  are dated to about 5.5 million years and deeply
  eroded
• Oldest rocks of the Big Island are approx. 0.7
  million years old

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How Hot Spots Work

• Pacific Ocean is mostly floored by a single
  tectonic plate moving over the asthenosphere
• Plate moves over a fixed hotspot, and deeper in
  the earth where the magma forms, a new volcano
  can push through to make a new island
• As the plate moves, the old volcano stops
  erupting and a new one forms

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• As they age, the plate upon which they sit cools
  and subsides
• This combined with the erosion of the islands
  once active volcanism stops, leads to shrinking
  and eventual submergence below the ocean surface

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and more on how Hot Spots work

• Magma is formed in the mantle and comes through
  crust where it is called lava
• If in the ocean, it cools and forms a volcanic
  island
• Takes many eruptions to raise level of volcano to
  oceans surface (millions of years)
• Usually in the middle of the plate and in ocean
• Plate moves over stationary hot spot to form
  chain of volcanoes
• Hot spots persist for 10 Ma - 100 Ma or more

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The Chain Gang

• The past 70 million years have left a long trail
  over the Pacific floor
• Hawaiian Ridge to Emperor Seamount chain extends
  6,000 km from Big Island to Aleutian Trench off
  Alaska
• Hawaiian Islands are only a small part of the
  chain
• - many are submerged already
• Chain is composed of more than 80 volcanoes
• More than 3,200 km from the nearest plate boundary

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Emperor and Hawaiian Chain

• Emperor Seamounts and Hawaiian islands are en
  echelon volcanoes
• Arose along the same hot spot in linear
  progression
• Stretches from Kuril-Aleutian Trench conjunction
  southward
• - changes direction at 33 N and 171 E to
  the SE

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• This is known from the Deep Sea Drilling Program
  (DSDP)
• Project started in 1964 and concluded in 1965
• Confirmed ocean beds were young, the sea floor
  spread, and plate tectonics did exist
• How?
• Several sediment cores where taken near the
  Emperor Seamounts and Hawaiian Islands
• Cores contained similar materials in similar
  compositions
• Showed that the seamounts and islands had
  decreasingly younger ages

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Size of Hot Spot
Size of the Hot Spot

• The size of the Hawaiian hot spot is not know
  precisely, but it presumably is large enough to
  encompass the currently active volcanoes of Mauna
  Loa, Kilauea, Loihi, and, possibly, also Hualalai
  and Haleakala. Some scientists have estimated the
  Hawaiian hot spot to be about 200 miles across,
  with much smaller vertical passageways that feed
  magma to the individual volcanoes.

• The size of the Hawaiian hot spot is not know
  precisely, but it presumably is large enough to
  encompass the currently active volcanoes of Mauna
  Loa, Kilauea, Loihi, and, possibly, also Hualalai
  and Haleakala. Some scientists have estimated the
  Hawaiian hot spot to be about 200 miles across,
  with much smaller vertical passageways that feed
  magma to the individual volcanoes.

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Loihi

• Hawaiian Islands are part of a chain 3,045 miles
  long spanning from Hawaii to the Emperor Seamount
  chain to the northwest
• Chain starts with Loihi seamount (3,000 ft below
  sea level)
• 4,000 earthquakes in summer of 1996
• 60,000 years before it becomes an island

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Seamounts and Guyots

• Seamounts are isolated volcanic mounts scattered
  around the ocean floor
• Most common in Pacific
• Generally rise more than 1,000m above sea-floor,
  forming islands
• When Plate tectonic motion moves a
  seamount-formed island away from mid-ocean ridge,
  the ocean crust sinks and pulls island beneath
  surface
• These submerged, flat-topped seamounts are called
  guyots

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Conclusion
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Fun Facts

• Hawaiian Ridge from Big Island to Midway is
  approx.. the distance from Washington D.C. to
  Denver (2,600 km)
• Amount of lava in chain is at least 750,000 cubic
  km which could blanket CA with lava 1.5 km thick
• Tectonics is from the Greek work construction