Download Volcanoes!

Volcanoes!
Pg222-235
Quick Review
• magma-?
• lava-?
• Can be explosive
• Can be nonexplosive
• lava flows
• lava fountains
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Molten rock explodes into air
Hardens
Circle the globe for years
Larger pieces fall closer
Cross-section of a volcano
What makes a volcano more explosive?
Water
• Dissolves in the magma
(turns into gas because of
high temps.)
• Gases need more room
• Pressure builds up
• (like shaking a can of pop)
Silica
• Is thick, flows slowly
• Plugs the vent
• Build-up of pressure/gases
Mt. Vesuvius 79AD
People of Pompeii
Types of Lava
Aa
Pahoehoe
Flows slowly, like wax
dripping on a candle
Glassy surface with
wrinkles
Stiffer lava
Pours out quickly
with brittle crust,
jagged surface
Lava underneath
keeps moving
Pillow Lava
Forms underwater
Blocky Lava
Cool, stiff, can’t travel far, oozes
Pyroclastic Material
Magma explodes and cools in the air
Existing rock is shattered by eruptions
Volcanic Blocks
Volcanic Bombs
Large blobs of magma,
harden in the air
Largest pieces,
solid rock
Lapilli
“little stones”
Pebble-like
bits of magma
Volcanic Ash
Gases and stiff magma
expand, walls of gas
bubbles explode into
tiny slivers
Too much Ash
• Can block the sun for days=
lower Earth’s temperature
• Mix with water= like wet cement
• Collapse buildings, dam rivers
• Can be a good fertilizer (in
moderation)
Types of Volcanoes
Composite Volcano
Cinder Cone Volcano
Moderately explosive
Pyroclastic materials
Steeper, form in clusters
(on sides of
shield/composite)
Most common
Are both explosive
and nonexplosive
Shield Volcano
Nonexplosive
Runny lava= sloping sides
Crater
• Central vent in a volcano
• Funnel shaped
Caldera
• Larger than craters
• Magma chamber empties, roof
collapses (ground sinks)
Fissures
Long cracks in the Earth
Runny lava oozes out
Makes lava plateaus
Forming Magma
• Solid in the earth= pressure keeps the atoms
of mantle rock packed tight, keeping it solid
• Magma forms=
• Temperature increases
• Pressure decreases
• Becomes less dense, floats to surface
Hot Spots
• Places directly above columns of
rising magma (mantle plumes)
• As the plate moves, new
volcanoes form in a chain
How to Predict Eruptions
• Measure earthquakes
• Measure the slope
(bulges)
• Measure volcanic
gases
• Measure temperature
from orbit