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Volcanic Eruptions Pages 325-330
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I read in the text …
(Evidence/quotes from the text)
Types of eruptions
Quiet- Oceanic volcanoes commonly form
from mafic magma. Mafic lava is rich is
magnesium and iron and is usually dark in
color. Because of mafic magma’s low
viscosity, gases can easily escape. Eruptions
from oceanic volcanoes, such as those in
Hawaii, are usually quiet.
Explosive-Felsic lavas of continental
volcanoes, such as Mount St. Helen, tend to
be cooler and stickier. Felsic lava is rich in
light color silicate materials. Felsic lava also
contain large amount of trapped gases, such
as water vapor and carbon dioxide. When a
volcano erupts, the gases in lava escape and
send molten and solid particles shooting into
the air. Felsic lava trends to explode and
throw pyroclastic material into the air.
Types of Volcanoes (Name and describe)
1. Shield cones- cones that are broad at
base and have gently sloping sides. Formed
from quiet eruptions. Hawaiian islands are
example
2. Cinder cones- has very steep sides and
are rarely a few hundred meters high. Form
from explosive eruptions of pyroclastic
material.
3. Composite Cones- Made of alternating
layers of hardened lava flows and pyroclastic
materials. Quiet flows cover the sides of the
cone. Explosive eruptions deposit pyroclastic
material around the vent. The explosive is
then again followed by a quiet to form large
volcanic moutains.
Viscosity – is the resistance to flow and
affects the force behind a volcanoes eruption.
Pahoehoe- Mafic lava that cools rapidly to
form a crust on surface of the flow. If the lava
continues to flow after crust forms, it
wrinkles the crust to form this type of rock
called pahoehoe. It is smooth with a ropy
texture.
Aa- If the crust deforms rapidly or grows to
thick to wrinkle, the surface breaks into
jagged chunks to from aa. This texture is
formed from differences in gas content and
the rate and slope of lava flow.
Blocky- type of lava has a higher silica
content than aa lava does, which makes
blocky lava more viscos than aa lava. The
high viscosity causes the cooled lava at the
surface to break into large chunks, while the
lava underneath continues to flow . This
gives the lava a blocky appearance.
Pyroclastic Material (What is it and how is it
classified?) consists of fragments of rock that
form during a volcanic eruption. It is
classified according to size of material
_
1.Vocanic Dust- less than .25mm diameter
2. Vocanic Ash- less than 2mm diameter
3.Lapilli- less than 64 mm. means little
stones.
4.volcanic bombs- clots of red hot lava,
spindle or round shaped
5.volcanic blocks – large pieces of solid rock ,
can be the size of a house
Name____________________
Date ____________________
Video____________________
Class ____________________
Volcanic Eruptions Pages 325-330
I read in the text…
I read in the text …
(Evidence/quotes from the text)
Caldera (Define and example)It is when a
magma chamber empties and the volcanic
cone collapses to leave a large , basin shaped
depression called a caldera. Mount Mazama
in Oregon erupted and formed a caldera that
later filled with water and is now called
Crater Lake.
3 Steps to forming a caldera
1. A cone forms from volcanic eruptions
2. Eruptions partially empty the magma
chamber
Predicting Volcanic Eruptions
Earthquake Activity is the most important
warning signal of a volcanic eruption.
Growing pressure on surrounding rocks
from rising magma creates small earth
quakes. Increase in strength and frequency
can signal that an eruption is about to occur.
3. The top of the cone collapses to inward to
form a depression called a caldera.
Patterns in Activity the upward movement
of magma may cause the surface of the
volcano to bulge outward. Scientist also
compare past behavior to from previous
measurements to current daily
measurements
SUMMARY: (2 TO 3 sentences)
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