Science of volcanology

We can start with broad questions about volcanism in general. These are important for understanding the exact nature of related geohazards and the associated risks and possible mitigation steps.

• What are the compositional variations and physical properties of lavas?
• How do you melt rocks to make magma that erupts as lava?
• What are the sources of magma?
• What are types of volcanic eruptions?

Shield vs. Composite Volcanoes (Stratovolcanoes)

There are two fundamentally different types of volcanic constructs with contrasting behavior, shield volcanos and stratovolcanos:

• shield volcanos: basaltic, low angle slopes and often very large, quieter eruptions, small summit calderas, example Hawaiian islands.
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  • Example above is of the small Belknap shield volcano that is part of the Cascade chain of volcanism. The foreground is relatively young basalt lava flow. Below is a small image of the top of the Mauna Loa shield volcano. Note the low angle slopes Image source USGS website: http://pubs.usgs.gov/gip/volc/types.html
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• strato or composite volcanos: andesitic, high angle slopes, sometimes very large calderas, potential for very devestating eruptions, example Mt. Fuji.
  • The example below is of Mount Rainier with Tacoma in the foreground. Ancient lahars from Mount Ranier can be found beneath the outskirts of Tacoma. Image source: http://vulcan.wr.usgs.gov/Volcanoes/Rainier/images.html
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  • Comparison above of shield versus composite volcanos. Image source: http://vulcan.wr.usgs.gov/Glossary/VolcanoTypes/Graphics/graphic_shield_vs_composite_volcano.html
• What factor helps explain the traits of these two different types of volcanic constructs?
• Composite volcanos can build up ( a constructive phase) and then literally blow themselves apart (a destructive phase).
  • large calderas and very extensive ash beds are the remanants of such catastrophic eruptions. Calderas are depressions where a very explosive eruption ejected material and formed a depression. Since they are depressions lakes often form in them.
  • The classic historic example is Krakatoa (more on that later).

USGS map of Yellowstone volcanic center. Yellowstone does not look like a volcano, yet there are volcanic rocks and hotsprings everywhere, and geophysically we can detect the magma underneath it. It is a super volcano with very large caldera complexes. The purple and green lines mark the edges of the calderas from the most recent explosive eruption, and older ones. Image source: USGS U.S. Geological Survey Fact Sheet 2005-3024 2005 - https://pubs.usgs.gov/fs/2005/3024/images/fs2005-3024_fig_03_large.jpg (accessed 11/13/2017).

What plate settings do different types of volcanism occur in?

Iceland - land of fire and ice, and lots of basalt

View of Mount Hecla in the background (low white ridge) taken during 1986 UNO field trip to Iceland. Mt Hecla is one of the most active volcanic constructs in Iceland (most recent flows in 1970s), and is also the site of descent into the interior in Jules Verne's Journey to the Center of the Earth.

Iceland is an anomalous emergent portion of a seafloor spreading ridge, so basalt dominated. Map below shows the position of the active rift and related volcanoes (as red triangles). Image from USGS website: http://pubs.usgs.gov/gip/dynamic/understanding.html

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  • Image from NASA Visible Earth of Iceland. Click on it for the larger image. Source: http://visibleearth.nasa.gov/view_rec.php?id=4702
• case history of Heimay eruption. Images below of houses destroyed by 1973 Heimay flow and air fall material from USGS web site: http://pubs.usgs.gov/gip/heimaey/
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  • USGS website on lava cooling operations at Heimay: http://pubs.usgs.gov/of/1997/of97-724/index.html
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• fire + ice (eruptions under and into glaciers) = jokulhaups (discussed earlier), more explosive eruptions and ash clouds.
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  • April-May 2010 eruptions of Eyjafjallajökull. Image source USGS site - https://www.usgs.gov/media/images/eyjafjallaj-kull-eruption , accessed 11/14/2017 (Credit: Oddur Sigurðsson, Iceland Meteorological Office. Public domain.)
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  • The greyish coloration distinguishes the ash cloud from the 2010 eruption (April 15th) from normal water vapor clouds. As weather positions shifted the ash cloud shifted with them. Satellites help keep track of such ash clouds so that planes can avoid them. Abundant ash clouds closed northern European air traffic a times. This and a suite of ash cloud pictures form the eruption at https://www.nasa.gov/topics/earth/features/iceland-volcano-plume-archive1.html (accessed 11/14/2017).
• hot springs and geothermal energy.

• Volcano World - Oregon State University.
• Cascades Volcano Observatory (USGS).

Next lecture outline on volcanos.