Strato
Sponsored Links
This presentation is the property of its rightful owner.
1 / 28

Mt St Helens, 1982 PowerPoint PPT Presentation


  • 95 Views
  • Uploaded on
  • Presentation posted in: General

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

Download Presentation

Mt St Helens, 1982

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


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

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

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


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


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


Volcano Explosive Index (VEI)


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


Pyroclastic Cone: Paricutin, Mexico (1947)


Volcanic Caldera: Crater Lake, OR


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


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


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


Shield Volcano: Kilauea Summit, Hawaii (active)


Loihi Seamount, Hawaii (70 km SE of Kilauea)


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)


Lava flow: Volcano Mayon, Phillippines


Pyroclastic Flows

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


Pyroclastic Flows

Pyroclastic flows in 1997 sweep across the flank of Soufrière

Volcano on Montserrat.


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


Lahars: volcanic mudflows

St Helens

Pinatubo


Famous Active

Volcanoes I

Stromboli

Vesuvius (1944)

Etna (2002)


Explosive Volcanoes, Eruption Columns, and Plumes


Explosive Volcanoes, Eruption Columns and Plumes

  • Eruption Column Anatomy

  • Plume Types

  • Iceland Eruption

  • Historical Catastrophic Eruptions

  • Volcanic Aerosols and Climate


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…)


Famous Active Volcanoes II

Hekla (2000)

Krakatoa

Arenal

Paricutin (1947)


Melting in the Mantle

magma genesis by decompression (pressure reduction) melting

Decompression melting


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…


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


  • Login