Earth Science
Chapter 6
Section 3
A. Volcanic Landforms:
1. Landforms from Lava and Ash:
a. Shield Volcanoes – a place on the Earth’s crust where
lava pours out of a vent (hotspot) onto the surface and
harden on top of previously hardened layers. The result is
a gently sloping mountain with a broad base. Example:
Mauna Loa in Hawaii.
b. Cinder-Coned Volcano – A steep, cone-shaped hill or
mountain formed from ash, cinders and bombs. Example:
Paricutin in Mexico. A 400 meter high volcano that
formed in a farmer’s cornfield in 1943.
c. Composite Volcanoes – A tall, cone-shaped mountain in
which layers of lava alternate with ash. Examples: Mount
Fuji in Japan and Mount St. Helens in Washington state.
Other landforms:
d. Lava Plateaus – A high level area formed from lava
pouring from long cracks in an area. The runny lava
travels long distances before solidifying. After millions of
years these layers form a high level plateau. Example:
Columbia Plateau, covers parts of Washington, Oregon
and Idaho.
e. Calderas – The collapsed cone of a volcano. Example:
Crater Lake in Oregon.
2. Soils From Lava and Ash:
- Volcanic soils are very fertile.
- Volcanic ash breaks down and releases potassium,
phosphorus, and other materials that plants need to grow.
3. Landforms From Magma:
a. Volcanic Neck – forms when magma hardens in the
volcano’s pipe.
b. Dikes – an intrusive igneous rock formation that forms
when magma is forced into cracks across rock layers and
hardens.
c. Sills – an intrusive igneous rock formation that forms
when magma is forced between rock layers and hardens.
d. Batholiths – a mass of rock formed when a large body of
magma cools inside the crust. These formations are the
core to many mountains. Example: Sierra Nevada
Mountains in California.
e. Dome Mountains– forms when rising magma is blocked
by horizontal layers of rock. The magma forces the layers
of rock to bend upward into a dome shape. The rock
layers wear away and expose the granite. Example: Black
Hills of South Dakota.