INSIDE EARTH: CHAPTER 3VOLCANOES
Section 1: Volcanoes and Plate Tectonics
WHAT IS A VOLCANO?
Volcano - weak spot in the crust where molten
material, or magma, comes to the surface
 Magma - molten mixture of rock, gasses, and
water from the mantle
 Lava- magma that reaches the surface

LOCATION OF VOLCANOES
There are about 600 active volcanoes on land.
Many more lie below the sea.
 Ring of Fire:a major volcanic belt formed by
many volcanoes at the rim of the Pacific Ocean
 Most volcanoes occur along diverging plate
boundaries, such as the mid-ocean ridge or in
subduction zones around the edges of oceans

VOLCANOES AT DIVERGING PLATE
BOUNDARIES

Volcanoes form along the mid-ocean ridge,
which marks a diverging plate boundary. Most of
this is located underwater, except for places such
as Iceland and the Azores Islands in the
Atlantic Ocean.
VOLCANOES AT CONVERGING
BOUNDARIES
Many volcanoes form near the plate boundaries
where the oceanic crust returns to the mantle
(subduction)
 Subduction causes ocean crust to sink into the
mantle forming a trench.
 The crust melts and forms magma, which then
rises back towards the surface.

 Many
volcanoes occur on islands, near
boundaries where two plate collide. The
resulting volcanoes create a string of islands
called an island arc.
HOT SPOT VOLCANOES
 Some
volcanoes
result from “hot
spots” in Earth’s
mantle. A hot spot is
a weak spot where
magma from deep in
the mantle melts
through the crust
like a blow torch.
 Hot spots often lie in
the middle of
continental or
oceanic plates far
away from plate
boundaries.
•
Can gradually
form a series of
volcanic
islands, for
example the
Hawaiian
Islands, which
formed one by
one over
millions of
years as the
Pacific plate
drifted over a
hot spot.

They can also form under the continents. An example of
this is Yellowstone National Park in Wyoming, which
marks a major hot spot under the North American
plate.