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Volcanoes
What is a volcano and how are volcanoes
formed?
A volcano is a mountain that opens downward to a pool
of molten rock below the surface of the earth. When
pressure builds up, eruptions occur. Volcanoes are
formed when magma from within the Earth's upper
mantle works its way to the surface. At the surface, it
erupts to form lava flows and ash deposits. Over time
as the volcano continues to erupt, it will get bigger
and bigger.
What are the different stages of volcanoes?
Mount Saint Helens near Portland in Washington state,
USA.
Scientists have categorized volcanoes into three main
categories: active, dormant, and extinct. An active volcano is one which has recently erupted and
there is a possibility that it may erupt soon. A dormant volcano is one which has not erupted in a
long time but there is a possibility it can erupt in the future. An extinct volcano is one which has
erupted thousands of years ago and there’s no possibility of eruption.
Why do volcanoes erupt?
The Earth's crust is made up of
huge slabs called plates, which fit
together like a jigsaw puzzle.
These plates sometimes move and
collide. When that happens, one
plate can slide under the other
causing the mantle underneath to
melt from extreme friction and
make magma. The magma pushes
upward, melting more rock. The hot
magma collects under the surface of the Earth. If the pressure is high enough or a crack opens
in the crust, the magma spews out. The theory that explains this process is called plate tectonics.
How many volcanoes are there and where are they found?
There are more than 1500 active volcanoes on the Earth. We currently know of 80 or more which
are under the oceans. Volcanoes are found all over the world, however, the Pacific Ring of Fire is
an area of frequent earthquakes and volcanic eruptions encircling the basin of the Pacific Ocean.
The Ring of Fire has 452 volcanoes and is home to over 50% of the world's active and dormant
volcanoes. Ninety percent of the world's earthquakes and 81% of the world's largest earthquakes
occur along the Ring of Fire. Volcanoes in Canada are in remote rugged areas and the level of
volcanic activity is less frequent than with other
volcanoes around the Pacific Ocean. Canada is
commonly thought to be in a gap in the Pacific
Ring of Fire between the volcanoes of western
United States to the south and the Aleutian
Voclanoes of Alaska to the north. There are more
than 100 volcanoes in Western and Northern
Canada, but only 21 are still active. Volcanic
activity has been responsible for many of Canada's
geological features including the formation of the
Canadian Shield.
What are the different types of volcanoes?
Volcanoes are grouped into four types: cinder cones, composite volcanoes, shield volcanoes and
lava volcanoes.
Cinder Cones
Cinder cones are circular or oval cones made up of small fragments of lava from a single vent
that have been blown into the air, cooled and fallen around the vent.
Composite Volcanoes
Composite volcanoes are steep-sided volcanoes composed of many layers of volcanic rocks, usually
made from high-viscosity lava, ash and rock debris. Mt. Rainier and Mount St. Helens are examples
of this type of volcano.
Shield Volcanoes
Shield volcanoes are volcanoes shaped like a bowl or shield in the middle with long gentle slopes
made by basaltic lava flows. Basalt lava flows from these volcanoes are called flood basalts. The
volcanoes that formed the basalt of the Columbia Plateau were shield volcanoes.
Lava Domes
Lava domes are formed when erupting lava is too thick to flow and makes a steep-sided mound as
the lava piles up near the volcanic vent. The eruption of Mount St. Helens in 1980 was caused in
part by a lava dome shifting to allow explosive gas and steam to escape from inside the mountain.
What is the difference between lava and magma?
Magma is liquid rock inside a volcano. Lava is liquid rock (magma) that flows out of a volcano.
Fresh lava glows red hot to white hot as it flows.
Effects of Volcanic Eruptions
Volcanoes can change the weather. They can cause
rain, thunder and lightning, and can trigger tsunamis,
flash floods, earthquakes, mudflows and rockfalls.
Volcanoes can also have long-term effects on the
climate, making the world cooler. Fast-moving lava
can kill people and falling ash can make it hard for
them to breathe. They can also die from famine, fires
and earthquakes which can be related to volcanoes.
People can lose their possessions as volcanoes can
destroy houses, roads and fields. Lava can kill plants and animals too. The Mount St Helens volcano
in 1980 killed an estimated 24,000 animals including 11,000 hares, 6,000 deer, 300 bobcats, 200
black bears and 15 mountain lions.
People tend to think of volcanoes as destructive but they can have some benefit. Volcanic ash is
very good for soil, so plants can grow quickly and strong after a volcano. Volcanic slopes left after
an eruption are very steep, so if rare and delicate plants and animals set up home there they are
naturally protected.