Lecture 5
Volcanism
Lecture Outline
I Characteristics of VolcanoesII Types of Volcanoes
A) Shield Volcanoesi. Descriptionii. Compositioniii. Eruption Features
B) Composite Volcanoesi. Descriptionii. Compositioniii. Eruption Featuresiv. Distribution
C) Cinder Conesi. Descriptionii. Compositioniii. Eruption Features
III Lava FloodsIV Submarine EruptionsV Living with VolcanoesVI Conclusions
Physical Geology
Characteristics of Volcanoes
Vent
Fumarole
Crater
Caldera
Volcanic Domes
Physical Geology
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.
Characteristics of VolcanoesVents and Fumaroles
Physical Geology
Mt Poas, Coast Rica
Mt Erebus, Antarctica
Halemaumau, Hawaii
crater : a basin-like rimmed structure at the top or on the flanks of a volcanic cone; it is formed by explosion or collapse
Characteristics of VolcanoesCraters
Physical Geology
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.
Aniakchak, Alaska Kaguyak, Alaska
Crater Lake, Oregon
Characteristics of VolcanoesCalderas
Physical Geology
Characteristics of VolcanoesCaldera Formation
Physical Geology
volcanic (lava) dome: steep-sided mound built by magma too viscous to flow farfrom vent before crystallizing and cooling.
Characteristics of VolcanoesVolcanic Dome
Physical Geology
Shield Volcanoes
Composite Volcanoes
Cinder Cones
Types of VolcanoesPhysical Geology
Mauna Loa, Hawaii
Slope: Gentle (2-10o)Height: up to 10 kmComposition: Flow layers
BasalticEruption: Effusive
Low-Viscosity LavaA'aPahoehoe
Flank EruptionsOther Characteristics:
Lava Ponds and TubesSpatter Cones
Types of VolcanoesShield Volcanoes
Physical Geology
Types of VolcanoesShield Volcanoes
Physical Geology
a'a
pahoehoe
Types of VolcanoesShield Volcanoes
Physical Geology
spatter cone: A low steep-sided cone of spatter built by lava fountains along a fissure or around a vent
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
Types of VolcanoesShield Volcanoes
Physical Geology
Mt St Helens and Mt Ranier
Slope: < 33o
Height: 1000 - 4000 mComposition: Layers of pyroclastic fragments
AndesiticEruption: ExplosiveOther Characteristics:
Magma blocks conduitGlowing clouds
and lava flows
Types of VolcanoesComposite Volcanoes
Physical Geology
Mount St. HelensMay 18, 1980
Types of VolcanoesComposite Volcanoes
Physical Geology
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, 3-mile-wide ash cloud 80,000 feet into the sky.
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.
8:32:10 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.
8:32:00 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.
http://seattlepi.nwsource.com/mountsthelens/grapherupt.shtml
Types of VolcanoesComposite Volcanoes
Physical Geology
Types of VolcanoesComposite Volcanoes
Physical Geology
http://www.3dnworld.com
Types of VolcanoesComposite Volcanoes
Physical Geology
Paricutin, Mexico
Slope: Steep (33o)Height: < 300 mComposition: Pyroclastic fragments
VariousEruption: ExplosiveOther Characteristics:
Short-lived
Cinder Cone,Mauna Kea, Hawaii
Types of VolcanoesCinder Cones
Physical Geology
Lava FloodsPhysical Geology
Lava FloodsThe Columbia Plateau
Physical Geology
Kavachi, Solomon Islands
Submarine EruptionsPhysical Geology
Submarine EruptionsThe Mid-Ocean Ridge
Physical Geology
Volcanic HazardsPhysical Geology