Download Causes of Volcanic Eruptions

Objectives
• Describe the formation and movement of
magma.
• Explain the relationship between
volcanoes and plate tectonics.
• Summarize the methods scientists use to
predict volcanic eruptions.
I. The Formation of Magma
A. Pressure and
Temperature Rock melts
when its temperature
increases or when the
pressure on the rock
decreases.
B. Magma Formation in the
Mantle Because the
temperature of the mantle
is fairly constant, a
decrease in pressure is
the most common cause
of magma formation.
http://www.geology.wisc.edu/courses/g115/volcano/images/voldgm.gif
II. Where Volcanoes Form
A. Location The locations of volcanoes give
clues about how volcanoes form. The next
slide shows the locations of major
volcanoes around the world.
B. Plate Boundaries About 80% of active
volcanoes on land form where plates
collide, and about 15% form where plates
separate.
The Location of Major Volcanoes
III. When Tectonic Plates Separate
A. Divergent Boundaries At a divergent
boundary, tectonic plates move away from each
other.
B. Mid-Ocean Ridges Form at Divergent
Boundaries Most volcanic activity on Earth
occurs at mid-ocean ridges. The next slide
shows how magma forms at divergent
boundaries such as those found along midocean ridges.
How Magma Forms at a Divergent
Boundary
IV. When Tectonic Plates Collide
A. Convergent Boundary A convergent boundary
is a place where tectonic plates collide.
B. Subduction Produces Magma As the
descending oceanic crust scrapes past the
continental crust, the temperature and pressure
increase. This causes the water contained in the
oceanic crust to be released. The water mixes
with the mantle rock, which lowers the rock’s
melting point, causing it to melt into magma.
This process is illustrated on the next slide.
How Magma Forms at a
Convergent Boundary
V. Hot Spots
A. What Are Hot
Spots? Hot spots are
volcanically active
places on the Earth’s
surface that are far
from plate boundaries.
B. What Do Hot Spots
Form? A hot spot
often produces a long
chain of volcanoes.
VI. Predicting Volcanic Eruptions
A. Measuring Small Quakes and Volcanic
Gases Most active volcanoes produce small
earthquakes as the magma within them moves
upward. Also the ratio of certain gases may be
important in predicting eruptions.
B. Measuring Slope and Temperature As
magma moves upward prior to an eruption, it
can cause the Earth’s surface to swell. Also,
infrared satellite images record changes in the
surface temperature. If the site is getting hotter,
the magma below is probably rising.
http://www.cnn.com/2012/08/30/us/wussupervolcanoes-yellowstone/index.html
http://www.msnbc.msn.com/id/49037141/ns/
technology_and_science/t/yellowstonessupervolcano-where-lava-likely-erupt/