Download Ch 7 S 4 Volcanic Landforms

Chapter 7: Volcanoes
Section 4: Volcanic Landforms
1. Volcanic eruptions create landforms made of lava, ash, and other materials.
a. Include shield volcanoes, cinder cone volcanoes, composite volcanoes,
and lava plateaus
b. Shield Volcanoes
i. A wide, gently sloping mountain
ii. Formed with thin layers of lava pour out of a vent and harden on top
of previous layers
iii.Created the Hawaiian islands
c. Cinder Cone Volcanoes
i. Ash, cinders, and bombs build up around the vent in a steep, coneshaped hill or mountain
ii. Paricutin in Mexico built up a cinder cone about 400 meters high
d. Composite Volcanoes
i. Tall, cone-shaped mountains in which layers of lava alternate with
layers of ash
ii. Formed when lava flows alternate with eruptions of ash, cinder, and
bombs
iii.Mount Fuji in Japan and Mount St. Helens in Washington
e. Lava Plateaus
i. Some eruptions of lava form high, level areas
ii. Lava flows out of several long cracks in an area, the thin lava flows a
long way before cooling and solidifying, and the layers flow on top of
each other forming a high plateau
iii.Columbia Plateau in Washington, Oregon, and Idaho
f. Calderas
i. A huge hole left by the collapse of a volcanic mountain
ii. The hole is filled with pieces of the volcano that have fallen inward
iii.Form when an enormous eruption empties the main vent and the
magma chamber beneath a volcano causing the mountain to
become hollow
1. The top of the mountain collapses inward
iv. Ex: Crater Lake in Oregon
1. The caldera that formed eventually filled with rain and snow
g. Soils from Lava and Ash
i. People live near active volcanoes to take advantage of the fertile
volcanic soil
ii. When the hard lava, ash, and cinders break down to form soil, it
releases potassium, phosphorus, and other substances needed by
plants
iii. Some volcanic soils are among the richest in the world
2. Landforms from Magma
a. Magma sometimes tries to force its way through cracks in the crust, but
fails to reach the surface
i. The magma hardens and forces of erosion eventually strip away the
layers above the magma and expose it
ii. Features formed include volcanic necks, dikes, and sills, as well as
batholiths and dome mountains
b. Volcanic Necks
i. Forms when magma hardens in a volcano’s pipe
ii. The softer rock wears away leaving the hard rock of the volcanic
neck
iii.Ex: Ship Rock in New Mexico
c. Dikes and Sills
i. A dike is formed when magma that forces itself across rock layers
ii. A sill is formed when magma squeezes between horizontal layers of
rock
1. Ex: Palisades in New York and New Jersey
d. Batholiths
i. A mass of rock formed when a large body of magma cools inside the
crust
ii. Form the core of many mountain ranges
e. Dome Mountains
i. Forms when uplift pushes a batholith or smaller body of hardened
magma toward the surface
ii. Ex: Black Hills in South Dakota
3. Geothermal Activity
a. Geo means “Earth”
b. Therme means “heat”
c. Magma a few kilometers beneath Earth’s surface heats underground
water
d. Geothermal activity includes hot springs and geysers
i. Hot Springs
1. Forms when groundwater is heated by a nearby body of magma
or by hot rock deep underground
2. The hot water rises to the surface and collects in a pool
ii. Geysers
1. A fountain of water and steam that erupts from the ground
a. Rising hot water and steam become trapped underground
in a narrow crack
b.Pressure builds until it eventually sprays above the surface
iii. Geothermal Energy
1. Energy source produced when water is heated by magma
2. In Iceland, people pipe this hot water into their homes for
warmth
3. Can also be used as electricity
4. Steam from underground can be used to spin wheels in turbines
which will generate the energy of motion into electrical energy
5. Produces some of the energy in California and New Zealand