VOLCANOES
A volcano is a vent or chimney which transfers molten rock known as magma from depth to the Earth's surface. Magma erupting from a volcano is called lava and is the material which builds up the cone surrounding the vent.
A volcano is active if it is erupting lava, releasing gas or generates seismic activity. A volcano is dormant if it has not erupted for a long time but could erupt again in the future. Once a volcano has been dormant for more than 10 000 years, it is termed extinct.
The explosiveness of a volcanic eruption depends on how easily magma can flow and the amount of gas trapped within the magma. Large amounts of water and carbon dioxide are dissolved in magma causing it to behave in a similar way to gas expanding in fizzy drinks, which forms bubbles and escapes after opening.
As magma rises quickly through the Earth's crust, gas bubbles form and expand up to 1000 times their original size.
As magma rises quickly through the Earth's crust, gas bubbles form and expand up to 1000 times their original size.
Volcanoes can be different in appearance with some featuring perfect cone shapes while others are deep depressions filled with water. The form of a volcano provides a clue to the type and size of its eruption which is controlled by the characteristics and composition of magma. The size, style and frequency of eruptions can differ greatly but all these elements correlated to the shape of a volcano. Three common volcanoes are:
TYPES OF VOLCANOES
Shield Volcano
When magma is very hot and runny, gases can escape and eruptions are gentle with considerable amounts of magma reaching the surface to form lava flows. Shield volcanoes have a broad, flattened dome-like shape created by layers of runny lava flowing over its surface and cooling. Because the lava flows easily, it can move down gradual slopes over great distances from the volcanic vents. The lava flows are sufficiently slow for humans to outrun or outwalk them. This type of magma has a temperature between 800°C and 1200°C and is called basaltic magma.
Composite Volcano (Strato)
Also known as strato-volcanoes, these volcanoes are characterised by an explosive eruption style. When magma is slightly cooler it is thick and sticky, or viscous, which makes it harder for gas bubbles to expand and escape. The resulting pressure causes the magma to foam and explode violently, blasting it into tiny pieces known as volcanic ash. These eruptions create steep sided cones. They can also create lava flows, hot ash clouds called pyroclastic flows and dangerous mudflows called lahars. This type of magma has a temperature between 800°C and 1000°C and is called andesitic magma.
CINDER CONE
Cinder cones are simple volcanoes which have a bowl-shaped crater at the summit and only grow to about a thousand feet, the size of a hill. They usually are created of eruptions from a single opening, unlike a strato-volcano or shield volcano which can erupt from many different openings.
They are usually made of piles of lava, not ash. During the eruption, blobs ("cinders") of lava, blown into the air, break into small fragments that fall around the opening to the volcano. The pile forms an oval-shaped small volcano, as shown in this picture.
Famous cinder cones include Paricutin in Mexico. Another well known cinder cone is in the middle of Crater Lake.
PARTS OF VOLCANOES
Magma - Molten rock beneath Earth's surface.
Parasitic Cone - A small cone-shaped volcano formed by an accumulation of
volcanic debris.
Sill - A flat piece of rock formed when magma hardens in a crack in a volcano.
Vent - An opening in Earth's surface through which volcanic materials escape.
Flank - The side of a volcano.
Lava - Molten rock that erupts from a volcano that solidifies as it cools.
Crater - Mouth of a volcano - surrounds a volcanic vent.
Conduit - An underground passage magma travels through.
Summit - Highest point; apex
Throat - Entrance of a volcano. The part of the conduit that ejects lava and volcanic ash.
Ash - Fragments of lava or rock smaller than 2 mm in size that are blasted into the air by volcanic explosions.
Ash Cloud - A cloud of ash formed by volcanic explosions.
ACTIVE VOLCANOES - is a volcano that has had at least one eruption during the past 10,000 years . An active volcano might be erupting or dormant.
ERUPTING VOLCANO - is an active volcano that is having an eruption
DORMANT VOLCANO - is an active volcano that is not erupting , but supposed to erupt again.
INACTIVE VOLCANOES - are those do not erupt as of today but have a potential to erupt again.
For Example : Mt.Pinatubo in Pampanga , was considered an inactive
volcano until 1991 , when it erupted. It's eruption is now recorded as the second largest eruption in the 20th century .
REFLECTIONS :
A.Which concept on the topic did you find easy to understand? What made them interesting?
- I easily understand of the definitions of part's of the volcanoe's and also the definition of the types of volcanoes . Its interesting because of the shape and the parts of the volcanoes .
B.What were your personal discoveries or learnings while studying the topic?
-About the types of a volcanoes . My learning is how does the volcanoes erupt and if it is a Inactive Or a Active Volcano.
C.Which area or concept do you like to expound more ?
-The Parts of the volcanoes and also about the erupting of a volcano.
-The Parts of the volcanoes and also about the erupting of a volcano.
THE END
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