Volcanic hazards

Environmental Geology lecture outline:

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.

Shield vs. Composite Volcanoes (Stratovolcanoes)

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

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

Photo of a geysir in Iceland, with a jet of steam just erupting through the overlying water and initiating an eruption. This feature erupted about every 5 minutes. Note the light colored cinter around that represents silica precipitating out of the hot waters. This activity is fed by magma and hot volcanic rocks at depth. Iceland takes good advantage of this geothermal energy source.
Related web Resources:

Next lecture outline on volcanos.

© Harmon D. Maher Jr.. This page may be used for non-profit educational purposes. For any other use please contact me.

H.D. Maher Jr., 3/6/2017

Return to Environmental Geology course index.

Return to Harmon's home page.