Download Presentation

What are volcanoes?
volcanism:any activity that
includes the movement of
magma toward the surface of
the Earth
volcano: place where magma
reaches the surface
MID-OCEAN RIDGE: occurs
where plates are moving apart
•lava flows out smoothly and
fluidly from cracks
SUBDUCTION ZONE: occurs
at subduction boundaries
•usually explosive and erupted
material is mostly lava
HOT SPOTS: areas of volcanic
activity in the middle of a
lithospheric plates
Hawaiian Islands are an example

What are the factors that
determine the violence of the
eruption?
• Composition of the magma
• Temperature of the magma
• Dissolved gases in the magma
What is magma & lava?
magma: liquid, molten rock
underground
lava: magma that reaches the
surface
•
•
the measure of a material's
resistance to flow.
Factors affecting viscosity
- Temperature (hotter magmas are less viscous)
- Composition (silica content)
1. High silica—high viscosity
2. Low silica—more fluid (e.g., basaltic lava)
What are the two types of
lava?
•felsic: much silica, lightcolored, slow moving (continental
crust)
•mafic: low silica, dark-colored,
fast moving (oceanic crust)
Aa Lava
Pahoehoe
Lava
Pahoehoe
Aa
Aa
Pillow lava from Hawaii
How do gases affect magma?
•many magmas contain dissolved
gases that are given off
•water vapor, carbon dioxide
(CO2), sulfur (S)
•magmas with more gases have
more explosive eruptions
What is pyroclastic material?
solid fragments ejected from a volcano
ash (fine, glassy fragments)
lapilli (walnut sized particles)
blocks
(hardened lava)
bombs
(ejected as hot lava)
lapilli
bombs
bombs
blocks
What is the anatomy of
a volcano?
•Vent: opening from which lava
flows
•Crater: funnel-shaped pit or
depression at top of volcano
•Caldera:craters whose walls
have collapsed
What are the 3 different types of
volcanoes?
• Shield
• Cinder Cone
• Composite
•composed of quiet lava flows
•form gently sloping, domeshaped mountain
•basaltic (mafic) magma
largest = Mauna Loa in Hawaii
•Made mostly of tephra and
other rock particle
•Formed from explosive
eruptions
•Not very high, narrow base,
steep sides
•Grantic (felsic) magma
•built up of alternating layers of rock
and lava
•explosive eruptions at first with
tephra, then quiet with lava
•forms large, cone-shaped mountains
•made of grantic and basaltic magma
Mount Fuji
Mount St. Helens Before and
After the May 18, 1980, Eruption
What are Igneous Rock
Structures?
• Intrusions – • Extrusions –
underground surface
rock masses rock masses
What are the different types
of INTRUSIONS?
• 1. Batholiths
– largest igneous intrusions
– Form when huge bodies of magma
cool underground
– Cover 1000 km
Batholith
INTRUSIONS
•2. Laccoliths
– Domelike masses formed
from magma bulging upward
This laccolith in Red and White Mountain, Colorado, is of
Tertiary age. Overlying layers of rock have been eroded.
INTRUSIONS
•3. Dike
– Sheets of igneous rocks
that cut across the rock
layer
Dike
Dike
INTRUSIONS
•4. Sill
– Sheet of hardened magma
that forms between and
parallel to layers of rock
Sill
Sill
INTRUSIONS
•5Stock
– Similar to batholiths but
less than 100 km
What are EXTRUSIONS?
•1. Volcanic neck:
– The plug of hardened magma
left in the vent from which
lava flowed
Volcanic neck:
EXTRUSIONS
•2. Caldera
Aniakchak Caldera formed during an enormous explosive eruption that
expelled more than 50 km3 of magma about 3,450 years ago. The caldera
is 10 km in diameter and 500-1,000 m deep.