Download MAR110 LECTURE #10 Plate Tectonics Volcanoes

26 September 2007
mar110_L10_PT_volcanoes_26sep07.doc
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MAR110 LECTURE #10
Plate Tectonics Volcanoes
Figure 10.1 Ocean Basin Volcanism
Mid-ocean ridge volcanism produces ocean crust and
occasional volcanic islands which when underwater are
called seamounts. Isolated “hotspots” produce mid-ocean
island chains. In a subduction zone, volcanoes are formed
by the rising of melted lithosphere magma. (ItO)
Figure 10.2 Mid Ocean Ridge Magma
As new crust is formed along the ridge axis the older
crust is pushed to either side forming bands of rock
parallel to the ridge. The upward moving magma in
the rift zone forces its way through the oceanic crust,
forming underwater volcanoes where the magma
breaks through as pillow lava. (?)
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Figure 10.3 Underwater Volcanoes - Seamounts
Underwater volcanoes can be formed in the region of
mid-ocean ridges when mantle magma chambers
remain connected. Once the volcano is carried away
and disconnected it becomes “extinct" and is called a
seamount. (NG)
Guyot or FlatFlat-topped Seamount
Figure 10.4 Volcanic Island Chain Formation
Isolated stationary mantle hotspots can produce
chains of volcanic islands and seamounts in the midocean - like the Hawaiian island chain (right). (ItO,
LEiO)
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Figure 10.5 Hot Spot Island Formation
Isolated stationary mantle hotspots can produce
chains of volcanic islands and seamounts in the
mid-ocean - like the Hawaiian island chain (right).
(ItO, LEiO)
Figure 10.6 Hawaiian Volcanism
The Big Island of Hawaii is the only currently active volcanic island in
the Hawaiian chain. There are three active cones on the island: Mauna
Loa, Kilauea, and Hualalai. Three views of lava flows from Kilauea.
(ItO, NG??)
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Figure 10.7 Subduction Zone Volcanism
A map of the major tectonic plates showing the
types of boundaries and where they may be
found. Red lines indicate areas with significant
subduction zone volcanic activity near or on
land. (LEiO)
Figure 10.8 Juan de Fuca Plate Subduction
The plate subduction in the northeast Pacific
(offshore of Washington and Oregon) generates a
chain of volcanic mountains known as the Cascades.
ashore ,
(NG)
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Figure 10.9 Subduction Zone Volcanism Northeast Pacific
Deep magma chambers - formed by the friction between the
subducting Juan de Fuca plate and the North American plate –
and feed the active volcanoes and spawn earthquakes in the
Cascade Range. An active erupting volcano produces volcanic
“bombs” (small to large pieces of solidified magma) and at
times huge amounts of smoke (fine particles) and somewhat
larger ash which tends to settle back to earth in the region.
Besides slower lava flows, this kind of volcanic action can also
produce superheated, high-speed pyroclastic flows that in turn
can trigger landslides and mudflows. On occasion when the
magma conduits are blocked major explosions can occur like
mt St Helens in the ‘80s.(NG)
Figure 10.10 Subduction Zone Volcanism - Mt St Helens
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Figure 10.11 Mt St. Helens Explosion Impact
Figure 10.12Subduction Zone Volcanism
The friction created when one plates subducts underneath another ,
causes the crustal and lithospheric rocks to melt (i.e. become
magma) creating greater pressure that forces the less dense magma
upward through the denser rock above to form volcanoes at the
surface (ItO?)
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Figure 10.13 Mt Etna Volcanism in the Med
The pressure in the chamber deep in the earth forces the magma
upward to form an active, growing Mt Etna at the surface in sicily,
Italy. (ItO?)
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Figure 10.14 Mt Vesuvius (1663) in coastal Italy. (ItO?)
Figure 10.15 An active Mt Vesuvius Buries Pompeii -79 AD .
(ItO?)
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Figure 10.16 Mummified Remains of
Pompeiian Victims. (NG)
Figure 10.17 A Slumbering Mt Vesuvius hovers high
over Pompeii Ruins . (ItO?)
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Figure 10.18 Santorini . (NH)
Figure 10.18 Krakatoa 1883 . (NH)
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