What is a volcano?
A volcano is an opening in the Earth’s
crust from which materials such as magma
and gases are ejected.
Volcanoes may be described as:
An active volcano is one which erupts and
has a high level of vulcanicity.
These volcanoes are ones that are currently
erupting or noticeably building pressure in
preparation of an eruption.
Eg Lassen Peak (California) and Mt St
Dormant Volcanoes are volcanoes which has
been inactive for a long period of time eg. 100
One that has been known to have erupted in
modern history but is now inactive or "sleeping"
Eg. Mount Rainier (Washington State), Mount
Hood (Oregon) and Mount Shasta (California)
An extinct volcano is one that scientist
believe will not erupt again because it
shows no volcanic activity.
However, we cannot be absolutely certain.
Eg. Mt St Helens (Extinct Active)
Types of volcanoes
Broadly, volcanoes can be classified into 3
Basic lava volcano (shield)
Acid lava volcano
Basic Lava Volcano
This type of volcano is formed from lava which
flows quite rapidly spreading over a large area
before it solidifies.
This category of volcano is made from quiet,
rapid lava flows spread over a large area. After
several eruptions, a gentle dome mountain is
formed (e.g.. Mauna Loa in Hawaii)
Eruption in this case is gentle.
Acid Lava Volcano
The acid lava which forms this volcano is
thick or viscous.
It is slow flowing and solidifies quickly
near the vent
This produces a cone with steep slope.
Eruptions in this case is usually violent.
Eg. Mt Stromboli in italy
A composite volcano consists of alternate
layers of viscous lava, ash and cinder.
Slopes of the volcano are usually steep near
the summit and gentler near the base
Lava often escapes through the sides of the
cone and builds up to form secondary
Eg Mt Mayon in the philippines
Distribution of volcanoes
3 major zones
1. Ring of Fire: This goes all around the
edge of the Pacific Ocean
2. Mediterranean Zone: the extends across
Asia and into India including Italy, Greece
3. Mid-Atlantic Ridge: Passes through
Iceland and down the middle of the Atlantic