A volcano is a extrusive geological landform (usually a mountain) where magma (rock of the earth's interior made molten or liquid by high pressure and temperature) erupts through the surface of the planet. This phenomenon tends to occur near the boundaries of the continental plates. However, important exceptions exist in hotspot volcanoes.
WHAT ARE ITS FEATURES
It is generally a conical or dome shaped structure which is formed when magma escapes to the earth's surface as lava through an opening called a vent. At the top of most volcanoes is a deperssion which is called a crate. this is where gases, pyroclasts and lave are thrown out. An enlatged crater is called a caldera. The crater of a dormant or extinct volcano may contain a lake. The crater is joined by a central passageway, called a pipe to the ven. The magma that escapes through the vent comes from a magma chamber deep below. Some volcanoes have parasitic or secondary cones on its flanks.
HOW IS IT FORMED
Volcanoes are formed by rising magma from below the earth's crust. The magma which contains dissolved gases, such as carbon dioxide and sulphur dioxide are subject to great pressure under the earth. When there are breaks or fractures in the rocks, the magma moves into them. As it moves upwards, the pressure on it is greatly reduced. This allows the dissolved gases to expand and eject hot volcanic material through the vent to the earth's surface. The volcanic eruption piles up on the ground around the vent. The accumulation of the material, resuting from repeated eruptions, eventually builds up a volcano.
WHAT ARE THE TYPES OF VOLCANIC MATERIAL
When volcanoes erupt, the eject lava, gases and solid material.
LAVA: there are two types of lava - acid and basic lava.
Acid lava is produced when there is subduction at destructive plate boundaries. The subducting oveanic crust partly melts because of friction and hear and the magma produced, being less dense than the mantle, rises to the surface through lines of weakness.
-This acid lava is rich in silica.
-It is not as hot as basic lava
-It cools and solidifies quickly so it does no move very far
-It is viscous, so it moves very slowly
-It produces steep sided volcanoes (e.g. Mount pelee in the Caribbean island of Martinique)
-When viscous lava solidifies in the central pipe, it blocks the passageway. The build up of pressure by rising magma causes loud and violent explosions
Basic lava is produced at constructive plate boundaries beneath the oceans by the upward movement of magma from the mantle and above hot spots. This lava is rich in iron and magnesium. It has a lower silica content than acid lava.
-It is hot
-It is a fluid
-It flows for quite a distance before solidifying
-It forms gently sloping volcanoes that genetrally erupt quietly (e.g. Mauna Loa in Hawaii)
GASES:
Hot gases which are emitted during an eruption include steam, carbon dioxide and sulphur dioxide. The steam comes from heated underground water and surface water of crater lakes and the sea. It condenses to form clouds that bring rain.
SOLID MATERIALS:
The solid materials include ash, dust, cinders and volcanic bombs. They are collectively called pyroclasts.
photo of a volcano erupting lava as well as lava flowing down its flanks
MAKE YOUR OWN VOLCANO!
First, you need to make the model. You can make it out of clay, paper mache'; or plasticine. The items needed are:
Mix together:
1 small bottle
enough plasticine in a volcanic color: e.g. brown, red, pink etc.
2 table spoons of baking soda
enough vinegar
red food coloring
eno salts
water
Shape the plasticine around a small plastic bottle to make a mountain. The bottle acts as the chimney of the volcano.
You can add red food coloring to the vinergar to get a red eruption. With a funnel add 2 tablespoons of baking soda into the bottle. Then slowly add red vinegar to the bottle. The liquid will foam and flow down the sides of the mountain.
When you mix vinegar and baking soda together, it creates carbon dioxide. Carbon dioxide is the same gas that causes the lava to bubble and is produced during a volcanic eruption.
You can also repeat this with Eno and water. Add red food coloring to the water for the same desired lava color. Take some Eno salts and add it into the bottle. Pour the red water in.
This will give you a thicker flow than the baking soda and vinegar one.
You can then use it to compare between the different types of lava. Baking sode and vinegar as basic lava. And the more viscous Eno one as acid lava.
ENJOY! courtesy of HANNAH! : D
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