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Lecture 5
Volcanism
Physical Geology
Lecture Outline
I
II
A)
B)
C)
III
IV
V
VI
Characteristics of Volcanoes
Types of Volcanoes
Shield Volcanoes
i.
ii.
iii.
Description
Composition
Eruption Features
i.
ii.
iii.
iv.
Description
Composition
Eruption Features
Distribution
i.
ii.
iii.
Description
Composition
Eruption Features
Composite Volcanoes
Cinder Cones
Lava Floods
Submarine Eruptions
Living with Volcanoes
Conclusions
Physical Geology
Characteristics of Volcanoes
Vent
Fumarole
Crater
Caldera
Volcanic Domes
Physical Geology
Characteristics of Volcanoes
Vents and Fumaroles
vent : the opening at
the earth's surface
through which
volcanic materials
are extruded.
fumarole : a hole or vent from which volcanic
fumes or vapors issue.
Physical Geology
Characteristics of Volcanoes
Craters
crater : a basin-like rimmed structure at the
top or on the flanks of a volcanic cone;
it is formed by explosion or collapse
Mt Erebus, Antarctica
Halemaumau, Hawaii
Mt Poas, Coast Rica
Physical Geology
Characteristics of Volcanoes
Calderas
Aniakchak, Alaska
caldera : a large basin-shaped
volcanic depression, more or less
circular. the diameter of which is
many times greater than that of the
included vent or vents, irrespective
of the steepness of the walls or the
form of the floor.
Kaguyak, Alaska
Crater Lake, Oregon
Physical Geology
Characteristics of Volcanoes
Caldera Formation
Physical Geology
Characteristics of Volcanoes
Volcanic Dome
volcanic (lava) dome: steep-sided mound
built by magma too viscous to flow far
from vent before crystallizing and cooling.
Physical Geology
Types of Volcanoes
Shield Volcanoes
Composite Volcanoes
Cinder Cones
Physical Geology
Types of Volcanoes
Shield Volcanoes
o
Slope: Gentle (2-10 )
Height: up to 10 km
Composition: Flow layers
Basaltic
Eruption: Effusive
Low-Viscosity Lava
A'a
Pahoehoe
Flank Eruptions
Other Characteristics:
Lava Ponds and Tubes
Spatter Cones
Mauna Loa, Hawaii
Physical Geology
Types of Volcanoes
Shield Volcanoes
Physical Geology
Types of Volcanoes
Shield Volcanoes
pahoehoe
a'a
Physical Geology
Types of Volcanoes
Shield Volcanoes
lava tube : a hollow space beneath the surface of a
solidified lava flow, formed by the
withdrawal of molten lava after the
formation of a surficial crust
spatter cone: A low steep-sided
cone of spatter built by lava
fountains along a fissure or
around a vent
Physical Geology
Types of Volcanoes
Composite Volcanoes
o
Slope: < 33
Height: 1000 - 4000 m
Composition: Layers of pyroclastic fragments
and lava flows
Andesitic
Eruption: Explosive
Other Characteristics:
Magma blocks conduit
Glowing clouds
Mt St Helens and Mt Ranier
Physical Geology
Types of Volcanoes
Composite Volcanoes
Mount St. Helens
May 18, 1980
8:32:00 a.m. The bulging north flank that geoscientists had
watched develop since March is intact. It had clearly grown by
450 feet in some areas, and by late April was estimated to be
growing at five feet a day.
8:32:10 a.m. A 5.1 magnitude earthquake about 1 mile
beneath the mountain causes the north flank to slide. Tendrils
of steam burst from the mountain, releasing pressure bottled
up in magma below.
8:33:00 a.m. A cubic mile of mountain gives way, traveling at
70 to 150 mph, and superheated rocks in the volcano's core
are suddenly exposed, shooting a lateral blast of gas north,
incinerating everything in its path. Huge glaciers on the
mountain's peak melt instantly.
8:33:20 a.m. The blast is over but the mountain begins to
pulverize as the eruption vents its full fury, sending a thick, 3mile-wide ash cloud 80,000 feet into the sky.
http://seattlepi.nwsource.com/mountsthelens/grapherupt.shtml
Physical Geology
Types of Volcanoes
Composite Volcanoes
Physical Geology
Types of Volcanoes
Composite Volcanoes
http://www.3dnworld.com
Physical Geology
Types of Volcanoes
Composite Volcanoes
Physical Geology
Types of Volcanoes
Cinder Cones
o
Slope: Steep (33 )
Height: < 300 m
Composition: Pyroclastic fragments
Various
Eruption: Explosive
Other Characteristics:
Short-lived
Paricutin, Mexico
Cinder Cone,Mauna Kea, Hawaii
Physical Geology
Lava Floods
Physical Geology
Lava Floods
The Columbia Plateau
Physical Geology
Submarine Eruptions
Kavachi, Solomon Islands
Physical Geology
Submarine Eruptions
The Mid-Ocean Ridge
Physical Geology
Volcanic Hazards