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Mt St Helens, 1982 PowerPoint PPT Presentation


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Strato volcano. Mt St Helens, 1982. Global Volcano Distribution (active & dormant). Volcanism on the Earth: I. Some important Terms: magma : molten (or partially molten) rock and dissolved gas volcanoes: vents in the crust where magma reaches the surface

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Mt St Helens, 1982

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Mt st helens 1982

Strato volcano

Mt St Helens, 1982


Mt st helens 1982

Global Volcano Distribution

(active & dormant)


Mt st helens 1982

Volcanism on the Earth: I

  • Some important Terms:

  • magma: molten (or partially molten) rock and dissolved gas

  • volcanoes: vents in the crust where magma reaches the surface

  • lava: magma and condensed H2O ejected from a volcano as liquid

  • pyroclastics: magma ejected as solids – ash, pumice, bombs, cinders…


Mt st helens 1982

Types of Volcanic Eruptions

  • pyroclastic falls: airborne ash and rock fragments

  • pyroclastic flows: avalanches of heated rock and gas mixtures

  • lahars: mudflows made of ash and rainwater

  • lava flow compositions: basalt, andesite, rhyolite

  • basaltic flow styles : pahoehoe (billowy) & aa (blocky)

  • strato volcano

  • shield volcano

  • fissure eruption

  • pyroclastic cone

Types of Volcano Edifices


Mt st helens 1982

Historically Important Eruptions

  • Vesuviusce79 - ash fall destroyed Pompeii

  • 1815 Tambora -- pyroclastic flow ~ 300,000 fatalities

  • 1883 Krakatau -- pyroclastic flow + tsunami

  • 1902 Pelee -- famous pyroclastic flow

  • 1980 St. Helens

  • 1991 Pinatubo -- largest eruption of 20th century; global climate effects; forecasted


Mt st helens 1982

Volcano Explosive Index (VEI)


Mt st helens 1982

Historical Example by VEI

VEI Volume (km^3) Eruption

0 Effusive Masaya (Nicaragua), 1570

>0.00001 Poás (Costa Rica), 1991

2 >0.001 Ruapehu (New Zealand), 1971

3 >0.01 Nevado del Ruiz (Colombia), 1985

4 >0.1 Pelée (West Indies), 1902

>1 Mount St. Helens (United States), 1980

>10 Krakatau (Indonesia), 1883

>100 Tambora (Indonesia), 1815

>1000 Yellowstone (United States), Pleistocene


Mt st helens 1982

Pyroclastic Cone: Paricutin, Mexico (1947)


Mt st helens 1982

Volcanic Caldera: Crater Lake, OR


Mt st helens 1982

Shield Volcano: Mauna Kea, Hawaii (last eruption: 4000 bce)


Mt st helens 1982

Caldera with pyroclastic cones: Haleakala, Maui (last eruption: 1700 ce)


Mt st helens 1982

Shield Volcano: Mauna Loa, Hawaii (last eruption 1800 ce)


Mt st helens 1982

Shield Volcano: Kilauea Summit, Hawaii (active)


Mt st helens 1982

Loihi Seamount, Hawaii (70 km SE of Kilauea)


Mt st helens 1982

Basaltic Lava Flows, Kilauea

eruption temperature ~ 1200 C

Low silica, low viscosity

low crystal content

relatively low gas content

(not explosive)

pahoehoe (gas poor)

aa (somewhat higher gas content)


Mt st helens 1982

Lava flow: Volcano Mayon, Phillippines


Mt st helens 1982

Pyroclastic Flows

Ash clouds rise above a pyroclastic flow traveling down the flank of Mayon Volcano, Philippines, September 12, 1984


Mt st helens 1982

Pyroclastic Flows

Pyroclastic flows in 1997 sweep across the flank of Soufrière

Volcano on Montserrat.


Mt st helens 1982

Pyroclastic Fall: Erosional dissection of an ash deposit from the 1991 Pinatubo eruption, Philippines


Mt st helens 1982

Lahars: volcanic mudflows

St Helens

Pinatubo


Mt st helens 1982

Famous Active

Volcanoes I

Stromboli

Vesuvius (1944)

Etna (2002)


Mt st helens 1982

Explosive Volcanoes, Eruption Columns, and Plumes


Mt st helens 1982

Explosive Volcanoes, Eruption Columns and Plumes

  • Eruption Column Anatomy

  • Plume Types

  • Iceland Eruption

  • Historical Catastrophic Eruptions

  • Volcanic Aerosols and Climate


Mt st helens 1982

Anatomy of an Explosive Volcanic Eruption

Neutral buoyancy level

Umbrella

Turbulent Gravity Current

Turbulent convective plume

Pumice & ash fallout

Jet phase

Surface vent

conduit

Fragmentation & ex-solution

Magma chamber

Silicate liquids & solids + volatiles (CO2, H2O, SO2…)


Mt st helens 1982

Famous Active Volcanoes II

Hekla (2000)

Krakatoa

Arenal

Paricutin (1947)


Mt st helens 1982

Melting in the Mantle

magma genesis by decompression (pressure reduction) melting

Decompression melting


Mt st helens 1982

Subduction Zone - Island Arc Volcanism

  • Volcanoes located ~ 200 km behind deep sea trench

  • Andesite (silica-rich) composition

  • Often explosive

  • Magma produced by subducted volatiles (melting point reduction)

  • Examples (abundant): Cascade Volcanoes, Aleutians, Andean & Central American Volcanoes…


Mt st helens 1982

Hotspots: long-lived mid-plate volcanic centers

  • tracks defined by island chains

  • regular age progression

  • tracks indicate plate motion

  • nearly stationary mantle heat source (thermal plume)

  • examples: Hawaii (best), Yellowstone, Iceland…

  • mostly basaltic volcanism

  • decompression melting starting ~ 100 km depth


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