 Fissure
eruptions
 Shield volcanoes
 Cinder cone volcanoes
 Composite volcanoes ( andesite volcanoes)
A
simple crack in the lithosphere
from which molten volcanic rock may spew on
the ocean floor
Found at mid-ocean ridge or east coast of
South America and west coast of Africa
 When
basaltic lava flows from a fissure area
creating a plateau. When the lava cools it
tends to fracture into cylindrical columns
called columnar jointing.
 Occur
predominantly on ocean floors,
 They have gentle slopes and may be
kilometers in diameter
 Basaltic lava- like wet concrete
 Hawaiian
Islands forming over a hotspot are
all shield volcanoes. Mauna Loa, largest peak
rises about 10km. From seafloor
 Predominantly
found on continents
 Have steep sides and consist of layers of
cinders and ash.
 Violent explosive eruptions are associated
with cinder cone volcanoes as the less fluid
andesitic lavas associated with cinder cone
volcanoes.
 Violent erupted material is collectively
referred to as pyroclastics
 Volcanoes,
andesitic ones especially, erupt
different materials at different times
 Built layer cake fashion out of lava and ash
 Most of the volcanoes formed over the
subduction zones are composite volcanoes.
 They have a symmetrical shape and are snow
and iced capped.
 Mt
St Helens erupted in May 1980 much of
the damage was caused by Lahars- Mudflows
 Super
heated plumes in the upper region of
the mantle or asthenosphere
 Pressure from the lithosphere above keeps
this area from melting
 If a crack occurs in the lithosphere, the
pressure from above is reduced and the
magma then takes a liquid state and flows
freely up onto the earth’s surface
 Hawaiian Islands- plate has been moving NW
over the hotspot
 Dike
Sill
 Laccolith
 Volcanic Neck
 Batholith

 Define
these and tell me about them
 Draw Figure 9.8 Pg 22

Lava- igneous rock that has reached the
surface of the earth. Continental volcanic
eruptions often do not involve a lot of lava
 Pyroclastics:
refers to any material blasted
out of a volcano- Dust and ash caused more
problems locally than globally
A
huge volcanic crater that is formed in one
of two ways---A) as a volcanic eruption
begins the magma chamber below the
mountain begins to feed molten rock to the
surface---If a lot of lava flows out of the
volcano the magma chamber below may
begin to empty faster than it can be refilled:
the mountain loses it support and collapses
in on itself creating a huge crater
 B) if the eruption is particularly violent the
entire top for the mountain may be blown off
to form a cladera.
 Lahars:
Volcanic mudflow
 Nuees ardentes- pryroclasic flows of super
heated denser than air gas exceeding 1000
degrees Celsius in temperature and 160 km
per hours in speed

Eruptions that occur on the ocean floor can create new
land as is the case in Hawaii and Iceland- many island
chains are volcanic in origin

Volcanic dust is loaded with nutrients and with each
eruption more nutrients are deposited on the surrounding
landscape. Farmers in Indonesia, for example, have
farmed the slopes of volcanoes for hundreds of years,
reaping the benefits of the rich soil.

Hot magma close to surface in volcanic regions can be a
source of environmentally clean geothermal energy.
Throughout the Pacific Ring of Fire the potential exists for
geothermal energy. In Iceland more than 85% of the homes
are heated geothermally; in north-western California
nearly 60% of the electricity is produced by geothermal
power plants.
 Volcanoes
are major tourist attractions.
Millions of people each year visit Mount. St
Helens National Volcanic Monument in
Washington State. Other
 Volcanoes around the world are also popular
tourist destinations.
 Hot springs and geysers, a result of volcanic
activity, also attracts many visitors each
year.