Download Volcanic Landforms

Volcanic Landforms
Key Idea: The shape of a volcanic
landform is determined by the
materials produced during an eruption.
What are volcanic landforms?
• The term volcano refers not only to a
volcanic vent, but also to the landform that
develops as the materials from a volcanic
eruption harden.
• The shape and structure of a volcano are
determined by the nature of the eruption
and the materials that are ejected during
the volcanic activity.
There are Several Kinds of
Volcanoes:
Mountain like landforms:
• Shield Volcanoes
• Cinder Cones
• Composite Volcanoes
Lava Plateaus-
Shield Volcanoes
• Shield volcanoes ... are built almost entirely of
fluid lava flows. Flow after flow pours out in all
directions from a central summit vent, or group
of vents, building a broad, gently sloping cone of
flat, domical shape, with a profile much like that
a warrior's shield. They are built up slowly by
the accretion of thousands of flows of highly fluid
basaltic (from basalt, a hard, dense dark
volcanic rock) lava that spread widely over great
distances, and then cool as thin, gently dipping
sheets. These are the lest explosive volcanoes.
Shield Volcanoes
Shield Volcanoes
Cinder Cones
• A cinder cone is perhaps the simplest type of
volcano; it forms when molten lava is thrown into
the air from a vent. As it falls, the lava breaks
into fragments that solidify in the air, before
hitting the ground. These fragments accumulate
in a cone shaped mound.
• Cinder cones tend to be smaller than other types
of volcanoes.
• They form in groups, and on the sids of larger
volcanoes.
A Cinder Cone
Another Cinder Cone
Composite Volcanoes
• Sometimes called Stratovolcanoes, Composite
volcanoes form when runny lava escapes through a
fissure and flows a long way. Composite volcanoes are
tall cone-shaped mountains that are typically steeplysided, symmetrical cones of large dimensions. The
essential feature of a composite volcano is a conduit
system through which magma from a reservoir deep in
the earth's crust rises to the surface. The volcano is built
up by the accumulation of material erupted through the
conduit and increases in size as lava, cinders, ash etc.
are added to its slopes.
Composite Volcanoes
• Composite volcanoes erupt in different ways at
different times. These volcanoes are built in
layers by multiple eruptions, sometimes
recurring over hundreds of thousands of years,
sometimes over a few hundred. Andesite
magma (the most common but not the only
magma type), tends to form composite cones.
During some eruptions, cinders, bombs and
blocks form a mountain or add height to one that
earlier volcanic eruptions had built. During other
eruptions, lava flows cement these rocks
together.
Composite Volcanoes
• Most composite volcanoes have a crater
at the summit which contains a central
vent or a clustered group of vents. Lava
either flow through breaks in the crater
wall or from fissures on the flanks of the
cone. Lava, solidified within the fissures,
form dikes that act as ribs which help to
strengthen the cone. They may rise as
much as 8,000 feet above their bases.
Composite Volcanoes
• Some composite volcanoes occur in
chains and are separated by several tens
of kilometers. There are many composite
volcano chains on earth, notably around
the Pacific rim, known as the "Rim of Fir
Composite Volcanoes
• Other examples of composite volcanoes and
their locations are:
• Mount St. Helens - Washington State
• Mount Rainier - Washington State
• Mount Vesuvius - Italy
• Mayon Volcano - Luzon Island, Philippines
• Mount Fuji - Japan
• Mount Cotopaxi - Ecuador
• Mount Shasta - California
• Mount Hood - Oregon
Diagram of a Composite Volcano
Composite Volcanoes
• St. Augustine volcano-Alaska is a composite volcano
Calderas
• A caldera is a very large crater shaped
basin, which forms when the top of the
volcano collapses inward. This happens
when the eruption empties the
underground magma chamber, and leaves
an “empty” space underneath.
Calderas
• Chocosuela caldera-Costa Rica
Lava Plateaus
• Sometimes at plate tectonics boundaries,
there are long, narrow cracks (fissures) in
the crust. Basaltic lave pouring from the
fissure spreads across the land, forming a
lava plateau.
Predicting Eruptions
• Most volcanic eruptions are highly destructive. The
destructive power of the volcano is given by many
factors:
• The gasses can be poisonous
• Hot ashes could kill people in no time (Vesuvius
destroyed two cities by covering them in hot ashes in 79
A.D.; people were burnt alive)
• The lava, or volcanic bombs have also tremendous
destructive power.
• Tsunamis are seismic waves which are created by
powerful earthquakes associated with violent eruptions.
Predicting Eruptions
Facts:
• About 15,000 volcanoes are categorized
as active. Most are located along the Rim
of Fire, in the Pacific Ocean.
• 60 % of Earth’s population live close to the
shore lines, around continents, which
means that many people are at risk.
• Can scientists predict volcanic eruptions?
Can scientists predict volcanic
eruptions?
• Many times it is a possible to predict an eruption.
• For example, in April 1991 Mount Pinatubo (in the
Philippines) started to give signs of activity.
• The scientists set up a station to monitor its activity. They
collected samples of gasses released at the summit of
the mountain, they measured the seismic activity. By
May they detected an increase in sulfur dioxide
emissions, which meant the lava was approaching the
surface.
• In June they noticed that a side of the volcano was
swelling.
• Meanwhile the seismic activity was increasing.
Can scientists predict volcanic
eruptions?
• At Mount Pinatubo all evidence was suggesting
that a large eruption was about to occur.
• Fortunately the scientists and public officials had
worked together to set up a plan for alerting the
population. Eventually, about 200,000 people
have been evacuated.
• The volcano put out huge amounts of lahars
(pyroclasic flows). Thousands of people have
been saved.