Download Shield Volcano

Volcanoes
Volcano Stats
• Definition of Volcano
– Mountain that forms when molten rock
(magma) is forced to the Earth’s surface
• Number of active volcanos = ? 1,300 –
1,500
– 20 erupting right now
(50-60/year) (160/decade)
• Number of volcanologists = 1,500
Why Volcanoes Occur?
• Temperatures in the mantle are hot
enough to melt rock into magma.
• Less dense than the solid rock around it,
magma rises and some of it collects in
magma chambers.
• As the magma rises, pressure decreases
allowing trapped gasses to expand and
propel the magma through openings in the
Earth’s surface causing an eruption.
• Erupted magma is called lava.
What causes volcanoes?
What causes volcanoes?
Hot Spots
Where Volcanoes Form
• Tectonic Plate Boundaries!!!
~75% world’s active volcanoes in Ring of Fire
Highlight the
places where
volcanoes
form on the
map in your
notes! Also,
answer the 1st
question as to
why
volcanoes
form here!
Magma vs. Lava
• Magma is molten rock beneath the
surface.
• Lava is erupted magma. There are 2
types of lava:
– A a (ah ah) is largely solidified
rock that gets pushed forward.
– Pahoehoe (pah hoy hoy) is flowing
“liquid” with a ropy, billowy surface
What Erupts from a
Volcano?
Blocky lava
Lava can be
thick or thin.
Pahoehoe
Aa
Pillow lava
Volcanic Eruptions
• Effusive Eruptions - outpouring of lava without
significant explosive eruption
• Explosive Eruptions - gas-driven explosions
that propels magma and tephra (small fragments
of material)
The Composition of Magma Determines
whether it is explosive or not!
• High water content
– More likely to be
• High
!!!
content
– More likely to be
– Why?
!!!
• Silica has a thick, stiff consistency
– Flows slowly
– Tends to harden in the volcano’s vent
What Erupts from a Volcano?
Pyroclastic material
• Rock fragments created by
eruptions.
• Magma explodes from volcano and solidifies in the air.
• Existing rock is shattered by powerful eruptions.
• Pyroclastic flows are the most dangerous type of
eruption because they are very hot and travel very
fast.
Volcanic bombs
Volcanic blocks
Volcanic ash
Types of Lava Flows
•Lava flows are superheated streams of
molten rock that flow at 1 – 50 mph.
•Pyroclastic flows are avalanches of hot
ash, rock fragments, and gases that flow at
speeds greater than 100 mph.
•Landslides are avalanches of rock, snow
and ice on slopes of volcanoes (loosened
and tumbling due to seismic activity).
•Lahars (mud flows) are a mixture of
volcanic ash and water (like wet concrete)
How do volcanoes affect the Earth?
Flows and Fallouts
• hot ash can flow really
quickly
•Knock down buildings
•Dam rivers (flooding/drought)
•Kill crops and livestock
Climatic Changes
•Ash & Gases can block sunlight
•Drop average global temperature
noticeably
Types of Volcanoes
Shield volcano
Cinder cone volcano
Composite volcano
On the chart in
your notes, draw a
sketch of each
volcano, and
describe what it
looks like in the top
row! 
Shield Volcano
• Shield volcanoes are broad, gently sloping volcanic
mountains (What does it look like?)
• Shield volcanoes are slowly formed by layer over layer
of solidified lava, and formed by effusive eruptions of
fluid lava. (How is it formed?)
• Shield Volcanoes have effusive eruptions that are low
in silica –flows easily and spreads out in thin layers
(Describe the eruption)
Shield Volcano
Example: Mauna, Loa
Takes up much of the Hawaiian Island
2 ½ miles, 13,678 ft. high
Composite Volcano
• Composite volcanoes are formed from both explosive and effusive
eruptions, and are built from layers of lava and rock fragments. (How
does it form?)
• Composite volcanoes have very violent eruptions with viscous lava
flows & layers of tephra, or rock fragments (Describe the eruption)
Composite Volcano
Example:
Mt. Saint
Helens,
Washington
Cinder Cone Volcano
• Cinder cones are the smallest volcanoes (< 500 ft),
formed by explosive eruptions of explosive lava, and can
form near other volcanoes (How does it form?)
• Blown violently into the air, the erupting lava breaks
apart into fragments called cinders that fall and
accumulate around the vent. (Describe the eruption)
• Cinder cones are easily eroded. They have short life
spans as gas causing violent eruptions is quickly
depleted.
Cinder Cone Volcano
Example:
Paricutin,
Mexico
How do volcanologists predict
eruptions?
• Measuring Small Quakes
– Before eruption, increase in number & intensity
• Measuring Slope
– Bulges may form with magma (tiltmeter)
• Measuring Volcanic Gases
– Outflow of volcanic gases
• Sulfur dioxide, carbon dioxide
• Measuring Temperature from Orbit
– Measure changes in temperature over time