Download Volcanoes

Volcanoes
Erupting with fun!
Magma vs. Lava
• Magma is liquid rock produced under the Earth’s surface
but Magma becomes Lava as soon as it leaves the Earth
and flows outside.
Lava
Magma
Magma
Magma can form under three conditions:
1. If rock temperature rises above its melting point then it
will melt into magma
2. Rock can melt when too much pressure is removed from
rock that is above its melting point
3. The addition of fluids, such as water, may lower the
melting point of some rock and cause it to melt
Volcanism
• Volcanism is any activity that includes the movement
of magma onto Earth’s surface
• A volcano is a vent or fissure in Earth’s surface
through which magma and gases are expelled
Location and Formation Of Volcanoes
Most volcanoes
occur in convergent
and divergent
boundaries of
tectonic plates
A major zone of active volcanoes is located in the
“Pacific Ring of Fire” which is also a major earthquake zone
Locations of Volcanoes
Some tectonic boundaries include:
• Subduction Zones
• Mid-Ocean Ridges
• Hot Spots
Subduction Zones
A subduction zone is where one tectonic
plate moves under another
Mid-Ocean Ridges
• A long, undersea
mountain chain that has
a steep, narrow valley at
its center.
• Forms as magma rises
from the asthenosphere
• Creates new ocean floor
as tectonic plates move
apart (sea floor
spreading)
Hot Spots
• Areas of volcanism within the interiors of lithospheric
plates
• The Hawaiian Islands were created by a hot spot
• See HOT demo!
Types of Volcanic Eruptions
• Quiet volcanoes have mafic magma which is
rich in magnesium and iron. Mafic magma is
dark in color with runny lava
• Explosive volcanoes have felsic magma
which is rich in light-colored silicate
materials and is thick and sticky.
Compare water boiling (quiet volcano) to thick
spaghetti sauce boiling (explosive volcano)
Pyroclastic
Materials
• “Pyro” means fire
• Pyroclastic materials include
fragments of rock that form
during volcanic eruptions
Types of Pyroclastic Materials
(from smallest to largest
1. Volcanic dust
2. Volcanic ash
3. Lapilli—means little stones…they
normally fall near the vent
4. Volcanic bombs—clots of lava
that are thrown out of the
volcano & become round or
spindle shaped as they go
through the air
5. Volcanic blocks—solid rock that
is blasted through the
vent…some are as big as a
house!!
Read “What Volcanoes Can
Produce”
Types of Volcanoes
1.
2.
3.
4.
Shield volcanoes
Cinder Cones
Composite Volcanoes (Stratovolcanoes)
Calderas
Shield Volcanoes
• Wide base
• Gently sloping sides
• Forms from quiet eruptions
Cinder Cone Volcanoes
• Steep slopes
• Form from explosive eruptions and are
made of pyroclastic materials
Composite Volcanoes
(Stratovolcanoes)
• Made with alternating layers of hardened lava flows and
pyroclastic materials
• This type of volcano alternates quiet and explosive
eruptions
Calderas
• This type of volcano is created when the magma chamber
below a volcano empties and the cone collapses
• The collapse leaves a large basin-shaped depression (crater)
• Some calderas eventually fill with water to become lakes
Read “What Are Volcanoes?”
and answer questions