Transcript Where & Why Volcanoes Form

8.1 Notes
Where & Why
Volcanoes Form
 What
are volcanoes?
 Volcanoes - locations where hot magma
pushes up on Earth’s surface
– mountains with magma pushing up
 Where
are volcanoes located?
 Mostly on plate boundaries
 What
is the “Ring of Fire”?
 A chain of volcanoes border the Pacific
Ocean.
 What
is a volcanic eruption?
 when magma is pushing up through the
cracks of the crust
 What
causes a volcanic eruption?
 movement of the tectonic plates
 What
is magma?
 melted rock
 What
happens to the habitat (environment)
immediately after an eruption?
 It is destroyed. It dies. It is burnt.
 What
happens to the habitat 2-3 years
after an eruption?
 It regrows.
Mt. St. Helens, Washington
erupted in 1980
Mt. St. Helens, Washington
1982
How can volcanoes form at divergent
boundaries?
 The plates float on the asthenosphere, which
contains magma. So, when the plates pull
apart, at a divergent boundary, magma comes
up through the crust forming volcanoes. This is
what creates mid-ocean ridges.
 Most of the time this happens underwater (in
the ocean). However, there are a couple of
exceptions. Iceland is being pulled apart by a
mid-ocean ridge and is above sea-level.

How can volcanoes form at convergent
boundaries?
 When an oceanic crust collides with a
continental crust, the ocean crust sinks beneath
it because it is denser (heavier). The
continental crust goes up forming a mountain
because it is less dense than oceanic crust. As
the oceanic crust sinks, it is burned back into
magma because of the heat from the
asthenosphere (magma). Sometimes due to
the immense pressure the magma will rise up
under the mountain forming a volcano.

What is a hot spot?
 A volcanically active spot on a plate that is no
where near a plate boundary.

Why would there be a volcano no where near a
plate boundary?
 The plate may be weak or thin in that spot, so
the magma can break through easily.

How was Hawaii formed?
 Hawaii is over a hot spot.

How many Hawaiian islands are there today?
Were there less in the past? Will there be more
in the future?
8
 Yes
 Yes – the pacific plate is moving and the hot
spot does not, so more islands are growing
under water

Hawaii – A hot spot
Which island is the Hawaiian hot spot located
under right now?
 The big island – where the most active
volcanoes are
