Volcanos and Plate
Tectonics
Chapter 7.1
Introduction
1.Introduction
a.While scientists cannot directly
measure earth’s interior
temperatures, they can estimate
them using seismic wave analysis,
heat flow near the surface of the
earth, and computer modeling.
Introduction
b. Most of the rocks in the lower part
of the mantel are kept below their
melting point due to the
temperature and pressure in that
zone.
i.Due to this high pressure, most of the
rock in the asthenosphere is also kept
solid.
Introduction
ii. However, sometimes this rock
will melt and form magma.
1.Magma is liquid rock produced
inside of the earth, and is formed
when mantle material flows to areas
of lower pressure faster than it can
lower its temperature by heat flow,
or when liquids such as water are
added to the mantle material.
Volcanism
2.Volcanism
a.Volcanism is any activity that
results in the movement of
magma toward or onto the
earth’s surface.
Volcanism
b. When rock melts in the earth,
pockets of magma are formed and
continue to melt rock around it. As
this rock melts, it also expands and
becomes less dense which causes it
to move through the more dense
crustal rock toward the surface of
the earth.
Volcanism
c. Most magma forms at plate
boundaries, usually oceanic –
continental.
i.When the mantle material
subducts, it allows water to come
in contact with the asthenosphere
which causes the rock to melt.
Volcanism
d. Lava is magma that breaks through
to the earth’s surface.
i.A vent is the opening through which
the molten rock flows.
ii.A volcano is the structure formed by
the vent and the volcanic material that
builds up on the earth’s surface around
the vent.
Major Volcanic Zones
1.Major Volcanic Zones
a.Most active volcanos and
earthquakes occur in zones near both
convergent and divergent boundaries
of the lithospheric plates.
b.One of the three major earthquake
zones is the Pacific Ring of Fire.
Major Volcanic Zones
i.This zone includes areas in North
America, South America, Asia, and
the islands of the western Pacific
Ocean.
ii.This increased volcanic and
earthquake activity is caused by
subducting plates encircling the
Pacific Ocean.
Major Volcanic Zones
iii. Many island arcs are also
formed in this area.
1.Island arcs are formed by magma
breaking through the earth’s surface
and cooling to form solid rock. As
this is occurring, the plate continues
to move and create a new volcanic
island and island arcs.
Major Volcanic Zones
4. A mid-ocean ridge is a place
where a large amount of
magma surfaces due to plate
moving apart from each other.
The surfacing magma hardens
and forms new lithosphere and
underwater volcanos.
Major Volcanic Zones
a.Iceland is an example of the Mid-Atlantic
Ridge that is above sea-level.
i. One half of Iceland is on the North American
plate and is moving westward while the other
half is on the Eurasian plate and is moving
Eastward.
ii.The middle of Iceland is cut by large
fissures.
1.Fissures are cracks through which lava flows.
Major Volcanic Zones
1.Hot spots are areas of volcanism within
the lithospheric plate
a.Hot spots occur where magma makes its
way to the earth’s surface within the
interiors of lithospheric plates.
b.At a hot spot, the lithospheric plate
continues to move while the hot spot stays
in place. Hot spots create volcanic chains
of islands such as the Hawaiian Islands.