Chapter 6 Volcanoes
Volcano- a mountain that flows when molten rock called magma is forced
to the Earth’s surface.
Magma- molten rock inside the earth
Lava- magma that flows onto the Earth’s surface
Two ways a volcano erupts: Non-explosive & Explosive
1. Nonexplosive Eruption
 Produces lava flows/or fountains
 Calm outpourings release huge amounts of lava
 Large mountains grew from repeated lava flows over hundred of
thousands of years
2. Explosive Eruption
 Clouds of hot debris & gases shoot out of volcano
 Molten rock blown into million of pieces & harden in air
 Blast millions of tons of solid rock
 Volcano may shrink after this eruption
Lava comes from nonexplosive eruptions
Four major lava types and descriptions:
1.Blocky lava- oozes from volcano, forms sharp- edged chunks.
2.Pahoehoe- flows slowly, forming glassy surface with wrinkles.
3.Aa- pours out quicker, forming brittle crust that is a jagged surface
4.Pillow lava –lava erupts underwater, forms rounded lumps in shape
and size of a pillow.
What is pyroclastic material? Fragments of rock created by explosive
volcanoes
Four major kinds of pyroclastic materials &descriptions:
1.Volcanic blocks- largest pieces, of solid rock
2.Volcanic bombs- largest blobs of magma harden in the air, shape
of bomb.
3.Lapilli- “little stone” little bits of magma become solid before hit
the ground
4.Volcanic ash- forms when magma expands rapidly and gas bubbles
explode into slivers.
Cross Section of Volcano
Vents- holes in earth’s crust that allows magma to rise to Earth’s surface
during eruptions.
An Explosive Impact Flows and Fallout:
Hot Volcanic Ash
 choking & searing every living thing in path
 mixes with water to creates cement like material
 buildings can collapse
 rivers dam up creating massive floods
 too much ash smothers crops (food shortage/livestock loss)
Climate Changes:
 ash and other gases reach upper atmosphere
 ash and gases spread around globe block sunlight enough to
cause surface temp. drops
Different Types of Volcanoes:
3 basic types
1- Shield Volcanoes
 built from layers of lava
 lava spreads out over a wide area
 gently sloping sides are formed
 Mauna Kea- largest mountain on Earth (measured from base on
sea floor)
2- Cinder Cone Volcanoes
 small cones made entirely of pyroclastic material
 steeper slopes with a narrow base
 erupt for a short time and often in clusters
 Commonly found on side of composite and shield volcano
3- Composite Volcanoes
 Stratavolcanoes
 formed by both eruptions (explosive & nonexplosive)
 alternating layers of pyroclastic & lava material
 broad base and sides, steep at the summit