are formed at tectonic plate boundaries.
At these boundaries, magma (molten rock) heats up the under layers of
the earth over time, pressure builds up, and sometimes eruptions occur.
(For more detailed information from the USGS, click
volcanoes tend to grow at divergent boundaries in the ocean.
volcanoes grow at convergent boundaries at the subduction zone because
the thinner but denser oceanic crust slides under the thicker, but
less dense continental crust. Once the oceanic crust slides under,
the molten magma heats up the crust and pushes upwards.
volcanoes grow in the middle of a tectonic plate at a weak spot. We
say that these volcanoes grow at hot spots.
Two examples of hot spots in the United States are the entire volcanic
chain of Hawai'i, and Yellowstone National Park.
here to see a Quicktime video clip about where volcanoes form.
to the top
the earth, hot magma and gasses look for weak spots to push through.
Magma and gasses will push up through not only the main conduit, but
also through any cracks (vents) it can find. Once magma (molten rock)
leaves the inner earth and finds its way to land, then we call it lava.
are cross-sections of each of the different kinds of volcanoes.
cinder cone volcano
to the top