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Video on Youtube:
Volcano Eruption – The Eruption of Mount St Helens 1980
22 minutes
VOLCANOES
Pipe
Central vent
Lava flows
Side vent
...accumulating on
the surface to form
a volcano.
Lavas erupt through
a central vent and
side vents,...
Magma
chamber
Lithosphere
...rises through the
lithosphere to form
a crustal magma
chamber.
Magma, which
originates in the
asthenosphere...
Central vent
Flank
eruption
Shield volcanoes
are built up by the
accumulation of
thin basaltic flows.
Lava flow
10 km
Magma
reservoir
Most commonly found in Hawaii – Mafic lava flows out and runs
parallel to oceans (not the triangle type of some other volcanoes)
Mauna Loa
(Hawaii)
Lava dome
Crater
Volcanic domes are
bulbous masses of
felsic lava, which are
so viscous that they
pile up over the vent.
Similar to Mt St Helens – The lava is so viscous that they end up
piling up and then later blow all in one time.
Mount St. Helens
(Washington)
Central vent filled
with rock fragments
Cinder-cone volcanoes
are made of layers of
ejected material that
dip away from the crater
at the summit. The vent
is filled with fragmental
debris.
Successive layers of
ejected material
Cerro Negro
(Nicaragua)
Central vent filled
from previous eruption
Radiating dikes
Stratovolcanoes are
built from alternating
layers of pyroclastic
material and lava flows.
Riblike dikes strengthen
the cone.
Pyroclastic layers
Lava flows
Alternating layers of pyroclastic and lava
Mount Fuji
(Japan)
Craters are found
at the summits of
most volcanoes.
Mt. Etna
(Sicily, Italy)
Mount Mazama created Crater Lake in Oregon
Calderas result when
a violent eruption
empties a magma
chamber, which
collapses, leaving a
large, steep-walled
basin.
Crater Lake (Oregon)
STAGE 1
Fresh magma triggers
an eruption of lava and ash.
Mt. Mazama
STAGE 2
Eruption continues, and the magma
chamber becomes partly depleted.
STAGE 3
The mountain summit collapses
into the empty chamber.
STAGE 4
A lake forms in the caldera.
Crater Lake
Highly fluid basalt erupting
from fissures…
…forms widespread layers
rather than mountains.
Earlier flows
Cinder
cones
Lava
Fissures
At ocean-ocean convergent
Magmas formed at ocean-continent
boundaries, magmas give rise to
convergences give rise to volcanoes
volcanic island arcs erupting
erupting andesitic lavas.
basaltic and andesitic lavas.
Continental volcanic belt
Active
volcano
Island arc
over hot spot
Extinct volcano
Mid-ocean ridge
Hot
spot
Plate separation at a
mid-ocean ridge results
in basaltic volcanism.
Plate motion over hot spots
creates midplate chain of basaltic
volcanic islands.
Mantle
plume
Continental
crust
Continental
mantle
lithosphere
The Pacific Plate has
moved northwest
over the Hawaiian
hot spot…
…resulting in a
chain of volcanic
islands.
The ages of the
mountains suggest
plate movement of
about 100 mm/yr…
Older extinct
volcanoes
Direction
of plate
movement
Hot-spot
volcano
ASIA
Emperor
Seamounts
Midway
NORTH
AMERICA
Hawaii
Equator
PACIFIC OCEAN
Tahiti
Hot-spot
Galápagos
Islands
64.7 Ma
56.2
Midway 27.7
55.4
55.2
Direction
48.1
of plate
39.9
movement
43.4
42.4
Nihau 5.5
Kilauea 0
Hawaii hot spot
A sharp change in direction
has been dated at about
43 Ma.
1.8 2.0 0.8 Ma
PACIFIC OCEAN
Montana
Yellowstone
Caldera Chain
Washington
Oregon
California
Idaho
Nevada
Hot
spot
4.3
15.5
13.8
Wyoming
Utah
13.7
16.1
13.8 12.5
15.6 14.7
11
Yellowstone
National
6.6 Park
6.2
10.3
The North American Plate
is moving southwest over
the Yellowstone hot spot.
1.8 2.0 0.8 Ma
Hot
spot
4.3
15.5
13.8
13.7
16.1
13.8 12.5
15.6 14.7
11
Yellowstone
National
6.6 Park
6.2
10.3
10 things you didn’t know about volcanoes
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Instability at
the core-mantle
boundary
causes a mantle
plume to arise.
Basaltic magma
penetrates the
lithosphere and
erupts as flood
basalts.
Flood basalts
Lithosphere
Mantle
Outer core
Plume head
Core-mantle
boundary
The plume
tail may form
a hot-spot
volcano.
Continued plate
movement
creates a hotspot volcano
chain.
Hot-spot volcano
Plate movement
Plume tail
Extinct
volcano
Active
volcano