Mantle Plumes and Ocean Islands

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Mantle Plumes and Ocean Islands

• What is a mantle plume?
• What is a hotspot track?
• How does age vary along a hotspot track?
• How are many ocean islands formed?
• What is an atoll and how do they form?

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Ocean Islands and Mantle Plumes
volcanic island chain
ocean crust
mid-ocean ridge
trench
island arc
cont.crust
mantle
670 km
D
core
After Kellogg et al., 1999
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Hotspots and plate tectonics

• Hotspots are stationary and have abundant
  volcanic activity
• The lithospheric plate moves over the hotspot
• Creates a row of volcanoes progressively older
  toward one end.

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What is a plume?
Davies (1995)
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Plumes in Mars and Venus?

• Olympus Mons on Mars is the largest volcano in
  the Solar System
• three times higher than Earths highest mountain
• volume over fifty times than Earths largest
  volcano

• Sif Mons is one of over 1600 volcanoes and
  volcanic features on Venus
• this volcano is 2 km high and 300 km across

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Galapagos Archipelago

• From 1831 to 1836 Charles Darwin (a geologist)
  served as an unpaid naturalist on a science
  expedition aboard HMS Beagle
• This voyage and the visit to the Galapagos
  helped him formulate the theory of evolution and
  natural selection, as well as atoll formation.

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Stages of coral reef development

• If in tropical shallow water, coral reefs can
  form on the tops of volcanoes
• Fringing reef
• Barrier reef
• Atoll

Figure 2-30
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Atoll and barrier reefs in the Society Islands
Figure 2-32
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Tectonic setting
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Seismic network
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Galapagos platform
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Galápagos volcanoes
Cerro Azul Sep 98
Genovesa
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Getting around the islands
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Installing high frequency stations

• 5 high-frequency stations
• telemetry signal is transmitted to central
  station at Puerto Ayora

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Installing broadband stations
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Example seismograms
P
S
R
L
Teleseismic event
Local events
P
P
S
S
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Results from body wave tomography
Nazca plate motion
Depth (km)
North-South
West-East
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Deformation from InSar 1992-1999
Sierra Negra volcano
92-97 97-98 98-99
Darwin volcano
Mogi model depth 3km
Amelung et al., 2000