ORIGINAL SOURCE: SITES.TENAFLY.K12.NJ.US/~PLOBOSCO/
Volcanoes
Slide 2
Volcanoes and Earths Moving Plates Objectives: To describe how
volcanoes can affect people. To discuss the conditions that cause
volcanoes. Identify the relationship between volcanoes and Earths
moving plates.
Slide 3
Volcanoes A volcano is an opening in the Earth that erupts
gases, ash and lava. Kilauea is the worlds most active
volcano.
Slide 4
Lava When the magma reaches the surface, it is called lava. The
place in the Earths surface through which magma and other materials
reach the surface is called a volcano. In some places, lava can
build up to form a cone-shaped mountain. The opening from which
lava erupts is the vent. Volcanoes often have more than one
vent.
Slide 5
Formation of a Volcano The opening where lava flows out is a
vent. The steep walled depression around the vent is a crater.
Slide 6
Volcanoes Volcanoes can be both destructive and constructive
forces.
Slide 7
Destructive Effects of Eruptions Lava destroys everything in
its path. Ash can cause lung damage. If ash and debris run down the
side of the mountain, this is called a pyroclastic flow.
Temperatures in this flow can be hot enough to ignite wood.
Sulfurous gases can mix with water vapor and form acid rain that
kills plants and animals.
Slide 8
Constructive Effects of Eruptions The soil formed from
volcanoes is very fertile and will eventually lead to abundant
plant growth. The sulfur in volcanic vents along the ocean floor
allow life to exist without sunlight Volcanoes recycle earths
minerals
Slide 9
Where do Volcanoes occur? Volcanoes form along divergent plate
boundaries, convergent boundaries and hot spots.
Slide 10
Divergent Plates Volcanoes often form where plates are moving
apart, such as the Surtsey in Iceland. Iceland is located on the
Mid Atlantic Ridge.
Slide 11
Convergent Plate Boundaries Soufriere Hills On the Island of
Monserrat is an example of a volcano that formed when one plate
slide under another and melted. The magma was forced up and formed
a volcano.
Slide 12
Hot Spots Some volcanoes form over hot spots in the mantle.
These are not on a plate boundary but in the center of a plate. The
Hawaiian Islands formed over a hot spot in the Pacific Plate.
Slide 13
Types of Volcanoes Objectives: To discuss how explosiveness of
a volcano is related to the silica and water content. To discuss
the three types of volcanoes.
Slide 14
Magma Deep within the Earth, under tremendous pressure and at
great temperatures, rock exists as a hot liquid called magma. This
molten rock is found in pockets called magma chambers.
Slide 15
What Controls Eruptions? Eruptions are controlled by 1) the
amount of trapped gas and the water vapor 2) how much silica is
present in the magma
Slide 16
Trapped Gas As magma reaches the surface, it is under less
pressure. Gas can escape. Gas escapes easily during quiet
eruptions. If gas build up to high pressure this will cause an
explosive eruption.
Slide 17
Amount of Water Vapor The magma at some convergent boundaries
contains a lot of water vapor. This is because oceanic plate
material and some of its water slide under other plate material at
some convergent plate boundaries. The trapped water vapor in the
magma can cause explosive eruptions.
Slide 18
Viscosity of Magma Magma is divided into two major types:
silica rich and silica poor The greater the silica content, the
more viscous or thick the magma.
Slide 19
Basaltic Magma Magma that is low in silica is called basaltic
magma. It is fluid and produces quiet flows such as those at
Kiluea. Basaltic lava flows under water produce pillow lava
formations.
Slide 20
Basaltic Lava Pahoehoe (p-hoi-hoi) forms a smooth, billowy,
ropelike surface. Aa, flows at a lower temperature, is stiff and
slow moving. https://encrypted-
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Slide 21
Andesitic Magma Andesitic magma is more rich in silica than
basaltic magma but it has less silica than granitic magma. It forms
at convergent boundaries where one plate slides under the other. It
is more explosive than basaltic magma. Krakatau was mainly
andesitic in composition. The word andesitic comes from the Andes
Mountains.
Slide 22
Granitic Magma This type of lava is light in color. This lava,
has high water content and high silica content. Light-colored lava
causes explosive eruptions. Silica hardens in the vents and form
rocks. Steam and new lava build up under the rocks. When the
pressure becomes great, a violent explosion occurs. When this type
of lava cools on the surface it forms the igneous rock, rhyolite,
which resembles granite.
Slide 23
Gaseous Lava When lava that contains large amounts of gases,
such as steam and carbon dioxide, hardens it forms rocks with many
holes in them, due to the gas bubbles. Pumice and scoria are
igneous rocks formed from this type of lava.
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Slide 24
3 Types of Volcanoes Different types of volcanic eruptions form
different types of volcanoes. Cinder cones Shield volcanoes
Composite volcanoes
Slide 25
Cinder Cones They are steep sided cones of basaltic fragments
and are smaller and simpler than composite volcanoes. Streaming
gases carry liquid lava blobs into the atmosphere that fall back to
earth around a single vent to form the cone. The volcano forms when
ash, cinders pile up around the vent to form a circular or oval
cone. Most common kind of volcano https://encrypted-
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http://www.k12.hi.us/~kapunaha/student_projects/volc_blowout/cinder_cone_volcano.htm
Slide 26
Tephra Explosive eruptions throw lava and rock high into the
air. Bits of rock or solidified lava dropped from the air are
called tephra. The smallest particles are called volcanic dust.
(less than 0.25 mm) Volcanic Ash ( 0.25 -5mm) falls to the Earth
and forms small rocks. Cinder (5mm-a few cm) Volcanic bombs (a few
cm to several meters) are molten and harden as they travel through
the air.
Slide 27
Paricutin Volcano in Mexico
http://4.bp.blogspot.com/-x6k8MObhuIg/T0vD-
JmMSxI/AAAAAAAAGv8/myMqukEGkwk/s1600/paricutin.jpg
Slide 28
Shield Volcanoes Volcanoes composed of quiet flows are called
shield volcanoes. Because it is runny, the lava flows over a large
area. After several eruptions, a dome-shaped mountain is formed
such as Mauna Loa (4km over sea level) in the Hawaiian
Islands.
Slide 29
Mauna Loa, Hawaii Earths Largest Volcano
http://hvo.wr.usgs.gov/maunaloa/4303062_M.jpg
http://hvo.wr.usgs.gov/maunaloa/
Slide 30
Flood Basalts Basaltic lava can also flow onto Earths surface
through large cracks called fissures. This type of eruption forms
flood basalts Columbia Plateau was formed as the lava spread out
over the ground.
Slide 31
Composite Volcanoes (Stratovolcano) Most deadly Volcanoes built
up of alternating layers of rock particles and lava are called
composite volcanoes. During the formation of a composite volcano, a
violent eruption first occurs, hurling volcanic bombs, cinder and
ash out of the vent. Then a quiet eruption, produces lava flow that
covers the rock particles. Lower slope is gentle, but they rise
steeply toward the summit
Slide 32
Composite Volcano (Stratovolcano)
Slide 33
Mount Vesuvius (near Naples, Italy)
http://www.history.com/topics/pompeii/videos
Slide 34
Mount St Helens http://dsc.discovery.com/tv- shows/discovery-
presents/videos/understanding- volcanoes-mt-saint-helens.htm
Slide 35
Krakatau One of the most violent eruptions in recent times
occurred on an island in the Sunda Straits neat Indonesia in 1883.
36,000 people were killed. The island fell into the magma chamber.
http://www.history.com/s hows/how-the-earth-was-
made/videos/the-krakatoa- volcano#the-krakatoa- volcano
http://www.history.com/s hows/how-the-earth-was-
made/videos/the-krakatoa- volcano#the-krakatoa- volcano
Slide 36
Igneous Rock Features Objectives To describe intrusive rock
features. To explain how a volcanic neck and a caldera form.
Slide 37
Predicting Volcanoes There are four indicators of volcanic
activity: Rising magma (increase in electric current) Seismic
activity (tremors) Ground deformation Changes in gases (carbon
dioxide and sulfur dioxide)
Slide 38
Instruments used to Detect Volcanic Activity Tiltmeters are
sensors that use laser beams to help create map of the physical
changes in the earths surface that rising magma causes. Scientists
also measure the levels of gases escaping, such as carbon dioxide
and sulfur dioxide. Gravimeters measure the electrical currents
given off by magma. An increase indicates a rise in the level of
magma The most recent development uses satellites to detect heat
from the gases released by volcanoes. The satellite Landsat uses
infrared sensors.
Slide 39
Limits of Seismography in Detecting Volcanic Activity
Seismographs cannot determine magma height, depth or how fast the
magma is rising.
Slide 40
Crater There is often a funnel-shaped pit or depression at the
top of a volcanic cone. This pit is called a crater. If the crater
becomes very large as a result of the collapse of its walls, it is
called a caldera. A caldera may also form when the top of a volcano
explodes or collapses.
Slide 41
Volcanic Crater
Slide 42
Intrusive Igneous Rock Features Most magma never reaches the
surface. Much of it hardens in the earth. Sometimes the hardened
magma becomes exposed at the surface. These rock bodies are called
intrusive igneous rock features. Examples are batholiths, sill,
dikes and volcanic necks.
Slide 43
Batholiths The largest intrusive igneous rock bodies are called
batholiths. They form when magma bodies that are being forced
upward cool and solidify before reaching the surface.
Slide 44
Yosemite National Park The granite domes of Yosemite National
Park are exposed batholiths.
Slide 45
Sills and Dikes Magma sometimes squeezes into cracks below the
surface. Magma that cuts across rock layers and hardens is called a
dike. Magma that is forced into a crack parallel to the rock layers
and hardens is a sill.
Slide 46
Volcanic Neck When a volcano stops erupting, magma will harden
inside the vent. Erosion wears away the outside of the volcano and
the solid igneous rock in the vent remains. Ship Rock in New Mexico
was formed this way.
Slide 47
Calderas Sometimes after an eruption, the top of a volcano can
collapse. This produces a large depression called a caldera. Crater
Lake in Oregon is a caldera that filled with water and is now a
lake.
Slide 48
Volcanic Activity Volcanoes are rather unpredictable. Some
erupt regularly, others have not erupted in modern history.
Scientists classify them as active, dormant or extinct.
Slide 49
Active Volcanoes An active volcano is one that erupts whether
continually or periodically such as Mount Katmai in Alaska and
Mount St. Helens in the Cascade Range.
Slide 50
Dormant Volcano A volcano that has been known to erupt within
modern times but is now inactive is classified as a dormant
volcano. Mount Rainier in Washington state is an example of a
dormant volcano in the United States. Scientists can be wrong.
Mount St. Helens was considered to be dormant but erupted after
long periods of inactivity.
Slide 51
Extinct Volcano A volcano not known to have erupted within
modern history is classified as an extinct volcano. They have been
worn away almost to the level of their magma chamber.
Slide 52
Volcano and Earthquake Zones Most major earthquakes and
volcanic eruptions occur in three zones of the world. Scientists
believe that there is a great deal of movement and activity in the
Earths crust in these three zones.
Slide 53
Ring of Fire One major earthquake and volcano zone extends
nearly all the way around the edge of the Pacific Ocean. This zone
goes through New Zealand, the Philippines, Japan, Alaska and along
the western coasts of North and South America. The San Andreas
fault is part of this zone.
Slide 54
Ring of Fire
Slide 55
Mediterranean Zone A second Major earthquake and volcano zone
is located near the Mediterranean Zone and extends across Asia into
India. Many countries in the zone, including Italy, Greece and
Turkey, have violent earthquakes. Many volcanic eruptions also
occur in this zone.
Slide 56
Mid-Atlantic Ridge Zone The third major earthquake and volcano
zone extends through Iceland and to the middle of the Atlantic
Ocean. Under the ocean, there is a long range of volcanic mountains
called the Mid-Atlantic Ocean Range. Scientists believe that the
volcano and earthquake activity are due to the formation of new
parts of the Earths crust along the ridge. The volcanic island of
Iceland is part of this zone.