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