Transcript Chapter 8 Section 2 Types of Volcanoes

Chapter 8 Section 2
Types of Volcanoes
Key Concept: Tectonic plate
motions can result in volcanic
activity at plate boundaries.
Volcanoes
How do volcanoes work?
• Heat and pressure cause rocks to melt and form magma.
• Magma needs to get out, too much pressure!!!!!!
• Rise in temperature or drop in pressure causes magma to form
faster.
How do volcanoes work?
• Magma is forced onto
Earth’s surface.
• It dries and hardens,
this happens many
times over thousands
of years.
• Eventually a mountain
called a volcano is
formed.
Parts of a Volcano
• Most volcanoes share a
specific set of features.
• The magma that feeds the
eruptions pools deep
underground in a structure
called a magma chamber.
• At Earth’s surface, lava is
released through openings
called vents.
• Flowing lava in the interior
travels through long, pipelike
structures known as lava
tubes.
Where do most volcanoes occur?
• Volcanoes occur at
both divergent and
convergent
boundaries and also
at hot spots.
Why do we have different types of
Volcanoes?
• The process of magma formation is
different at each type of plate boundary.
• Therefore, the composition of magma
differs in each tectonic setting.
• Tectonic settings determine the types of
volcanoes that form and the types of
eruptions that take place.
Volcanoes at Divergent Boundaries
• At a divergent boundary, the lithosphere becomes
thinner as two plates pull away from each other.
• A set of deep cracks form in an area called a rift zone.
• Hot mantle rock rises to fill these cracks.
• As the rock rises, a decrease in pressure causes hot
mantle rock to melt and form magma.
• The magma that reaches Earth’s surface is called lava.
Basaltic magma rises to Earth’s surface through these
fissures and erupts nonexplosively
Types of volcanoes
Types of volcanoes
• Shield volcano: usually form at hot spots,
from non explosive eruptions
• Cinder cone volcano: form from explosive
eruptions, very steep.
• Composite volcano: form from both
explosive and non explosive eruptions.
Shield volcano
•
•
•
•
Form from many layers of “runny” lava.
Very wide, not to steep.
Biggest type of volcanoes
Tallest mountain in the world is Mauna Kea
(measures from sea floor to top)
• non explosive eruptions
Mauna Kea, Hawaii
Cinder cone volcano
• Smallest type of volcano
• Most common
• Made from pyroclastic material (material
shot out of a volcano)
• Form a large crater
• Explosive!
Paricutin, Mexico
Composite volcano:
• Eruptions alternate between explosive and
non-explosive.
• Sometimes they have runny lava layers,
other times the have pyroclastic materials
form layers.
• Have a wide base and steep sides.
• Have a crater
• Mount Fuji
Mount Fuji
2 Types of eruptions
• Explosive: volcanoes
that build enough
pressure to blow its
top, sending
pyroclastic material
into the air.
• Non explosive: Build
only enough pressure
to allow lava to run
down its sides.
Non explosive eruption
• Mafic: refers to rocks and magma rich in
iron and magnesium.
• This type of lava that is very runny.
• As magma nears the surface there is little
pressure, causing gasses escape easily.
• Magma low in Silica have quiet eruptions
Explosive eruptions
• Felsic: means magma with high silica and
feldspar content.
• Felsic magma traps water and gas
bubbles, which leads to lots of pressure.
• Silica acts like a cork
• Explosive eruptions are caused by a build
up of high pressure.
• Convergent zones contain lots of water,
therefore have explosive eruptions.
Pyroclastic materials
• Material that is thrown into the air during
an explosion.
• Volcanic bombs: large blobs of magma
that harden in the air.
• Lapilli: pebble size rocks
• Volcanic ash: tiny powder like material
Four types of lava
• Aa: lava that is thick and sharp
• Pahoehoe: lava that forms thin crust and
wrinkles
• Pillow lava: lava that erupts under water,
has a round shape
• Blocky lava: cooler, lava that does not
travel far from eruption, jagged when it
dries.
Aa
• lava that is thick and sharp
Pahoehoe:
• lava that forms thin
crust and wrinkles
Pillow lava
• lava that erupts under
water, has a round
shape
Blocky lava
• cooler, lava that does
not travel far from
eruption, jagged when
it dries.