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Volcanic Landforms:

Objectives:

    1.    Compare and contrast the landforms that result from volcanic activity.

    2.    Hypothesize how predicting eruptions and emergency preparedness can reduce loss of life and loss of property.

Key Terms:

    shield volcano    cinder cone    composite volcano    lahar    caldera    lava plateau

Volcanoes come in three basic forms.  The type of volcano is determined by the magma composition, shape and structure.

Forms:

1)  Shield Volcano

Primarily basaltic lava - low viscosity

Quiet eruptions

Magma spreads in smooth layers

Very broad at the base - can be very tall (Mauna Loa 9170m)

ex: Kilauea, Diamond Head

(www.gpc.peachnet.edu/~janderso/ images/mons.gif)

 

(USGS - Kilauea 2-18-03)

2)  Cinder Cone Volcano

Explosive eruptions  

Rhyolitic & Andesitic magma

Throws lava high in the air

The lava forms into tephra as it cools - usually hardens before it hits the ground

Forms a steep small structure called a cinder cone  

Generally form in groups or by the base of larger composite volcanoes

Pu`u `O`o cone, Kilauea Volcano, Hawaii(www.aqd.nps.gov/grd/usgsnps/ volcano/24ds064_L.jpg)

(volcanoes.usgs.gov/.../Photoglossary/ 30424305-084_large.JPG)

U.S. Geological Survey, Home page

3)  Composite Volcano

Alternates between Shield and Cinder Cone stages

Violent eruptions followed by lava and pyroclastic flows build up around the vent

Has eruptions followed by long dormant periods - during this time gas and magma reaccumulate in the magma chamber

Andesitic and Granitic magma

Mt. St. Helens  

Steam plume, May 19, 1982(USGS - Mt. St Helens)

Photo of MSH from Johnston Ridge(USGS - Mt. St Helens)

Igneous Land Forms:

Dike - vertical igneous intrusions into formed rock

(www.landsat4u.com/Merchant/ Contact2.jpg)

Sill - horizontal igneous intrusions into formed rock

Laccoliths - thick magma hardens into a dome under rock before reaching the surface.  They are usually very large and are exposed after long periods of erosion.

volcano.und.nodak.edu/.../north_america/ bear_butte.html

Volcanic necks - Magma that has hardened in the neck of the volcano can be exposed after many years of erosion.

(geoweb.tamu.edu/faculty/herbert/ bigbend/ig/b19b.jpg)

Batholith - The largest of the intrusive structures.  Formed from the solidification of magma chambers.

(seis.natsci.csulb.edu/.../ Intrusive_soCal_batholith.jpeg)

Caldera - the eroded base of a volcano
Sometimes formed when magma in the chamber is released collapsing the sides forming a large crater.
ex: Crater lake

(www.educeth.ch/stromboli/glossary/ icons/caldera.jpg)

Lahar - a mixture of pyroclastic flow and snow

results in a massive mud flow

Dark lahar (USGS - Lahars - Mt. St. Helens)

Schoolhouse nearly buried by lahar deposits from Mount Pinatubo, 
            Philippines(USGS- Mt. Pinatubo)

Sediment-clogged Abacan River, Philippines(USGS- Mt. Pinatubo)

 

Lava Plateau 

Created as cracks in tectonic plates expose the asthenosphere.  
Massive amounts of basaltic lava from the fissure spread over the land

(geog.tamu.edu/.../ Edge%20of%20Columbia%20Basalt%20flow.jpg)

 

 

Last modified: October 20, 2003