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What is a Volcano? A volcano is an opening in the Earth that erupts gases, ash, and lava. Volcanic mountains form when layers of lava, ash, and other material build up around these openings.
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Volcanoes and Earths Moving Parts What is a Volcano? A volcano
is an opening in the Earth that erupts gases, ash, and lava.
Volcanic mountains form when layers of lava, ash, and other
material build up around these openings. Kilauea is the worlds most
active volcano.
It has been erupting for centuries although not explosively. Its
lava moves very slowly. Iceland is also famous for its active
volcanoes
Iceland is also famous for its active volcanoes.It sits on an area
where the Earths plates move apart. ( a boundary). How do volcanoes
form? Deep inside the earth, heat, and pressure cause rock to melt,
forming magma (liquid rock). Magma is forced upward because it is
less than the rock above it, so it is forced toward the Earths
surface. After thousands or millions of years, the magma reaches
the Earths surface and flows out of an opening called a vent.
volcano Where do volcanoes occur?
Divergent plate boundaries Convergent plate boundaries Hot spots
-Hawaii What controls eruptions?
Some eruptions are quiet while others are explosive. Two factors
control if an eruption is quiet or explosive. One factor is the
amount of water vapor and trapped gases in the magma.
The second factor is the viscosity of the magma how quickly or
slowly the magma flows (determined by how much silica is present).
Basaltic Magma is relatively low in SILICA has a low
viscosity.
It is fluid and produces quiet, non-explosive eruptions (like those
at Kilauea.) Kilauea Explosive Eruptions Silica-rich or GRANITIC
magma produces explosive eruptions. It has a high viscosity.This
magma sometimes forms where the Earths plates are moving together
where one plate slides under another (AKA ) Shield Volcanoes Cinder
Cone Volcanoes Composite Volcanoes
Forms of Volcanoes Shield Volcanoes Cinder Cone Volcanoes Composite
Volcanoes Shield volcanoes are volcanic mountains built up by the
eruption of fluid, basaltic lava flowing out of a central vent.
They have broad bases with very gentle slopes, and are the largest
volcanoes on Earth. The volcano gets its name from its resemblance
to the slightly domed shape of a warrior's shield. Shield volcanoes
do not erupt violently
Shield volcanoes do not erupt violently. Rather, fluid, basaltic
lava erupts onto the surface and flows freely across the ground for
great distances forming a broad cone. Lava tubes can form beneath
the surface of the lava flow which allows the lava to flow for tens
of kilometers (miles) without cooling. Each successive flow
increases the size of the shield volcano. Sheild volcanoes have
magma with a low viscosity. Hot Spots Weak areas in the earths
crust where magma plumes punch through. Volcanoes eventually form
islands chains like the Hawaiian Islands. Cinder cone
volcanoesconsist of steep, loosely packed material. Cinder Cone
Cinder Cone Cinder cones are the simplest type of volcano
Cinder cones are the simplest type of volcano. They are built from
particles and blobs of congealed lava (tephra) ejected from a
single vent. As the gas-charged lava is blown violently into the
air, it breaks into small fragments that solidify and fall as
cinders around the vent to form a circular or oval cone. Most
cinder cones have a bowl-shaped crater at the summit and rarely
rise more than a thousand feet or so above their surroundings.
Cinder cones are numerous in western North America as well as
throughout other volcanic terrains of the world. Cinder cone
volcanoes have lava with high viscosity. Composite Volcano
Structure of a Composite Volcano Composite volcanoes are also known
as strata volcanoes.
They have alternating layers of tephra and lava. They have a
mountainous form, and usually form at subduction zones. Mount St.
Helens is a composite volcano. The End