Volcanoes
Volcanoes can be created on the earth's surface or deep below the crust. examine this statement with reference to examples you have studied.Volcanoes can be created on the earth's surface or deep below the crust. Surface volcanic landforms are called "extrusive" landforms.
Volcanic landforms below the surface are called "intrusive" landforms. Extrusive Landforms *The earth is made of 3 layers. The core, mantle and the crust. The crust is divided into plates. *The innermost part of the earth is called the core and is the hottest. It causes the magma in the mantle to heat up. As it rises, it cools and sinks back down in a circular motion. These are called convection currents. *The convection currents drag the plates above causing them to separate (diverge) Crust can be created at these boundaries. New crust is cooled volcanic material. Basalt is formed this way. *The rising magma forces its way to the surface through cracks in the crust. It cools rapidly and overtime a volcano is formed. This is why basalt has small crystals. Several underwater volcanoes may occur together and form an underwater mountain range. *This is known as a Mid-Ocean ridge and occurs along a divergent plate boundary under the sea. Eg the North American and Eurasian Plate Boundary are separating and this forms the Mid-Atlantic Ridge. *Ireland was once at the edge of this boundary. Lava spilled up through a large fissure creating the Antrim-Derry Plateau. The regular hexagon Basalt shapes at the Giant Causeway occurred when lava flowed into a valley and cooled in a unusual pattern. |
Intrusive Landforms
*As magma forces its way up through the crust it takes the easiest route possible. It forces its way through existing cracks and joints in the bedrock. *Sedimentary rock such as Limestone is laid down in layers or strata. Between each layer is a bedding plain, the magma forces its way through here. *The magma may cool slowly and solidify in these areas creating plutons. Rock such as granite is created this way. The slow cooling process causes large crystals. *Batholiths are the largest of the plutons. They can be 70km deep and 100s of km wide. *The Wicklow Mountains also known as the Leinster Batholith was formed this way. Over millions of years the overlying rock has been eroded and the granite is now exposed. *Horizontal plutons are called sills. They are called laccoliths when the arch upwards and lopoliths when they bulge downwards. Vertical plutons are called dykes. |
Fissure Eruptions
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5 Types of Volcanoes By David Olmstead
In planet’s surface or earth crust there are openings or ruptures that allows volcanic ashes, different gases and hot magma to escape are generally known as Volcanoes. Generally when the tectonic plates converges or diverge these volcanic eruptions takes place. different types of volcanoes of volcanoes that can be found in nature are such as composite volcanoes, shield volcanoes, cinder cones, spatter cones and complex volcanoes. Volcanoes can also be classified according to the types of volcanic eruptions.
Composite or Strato-volcanoes: A composite volcano is also known as strato-volcano because composite strata or layered structure is formed due to the eruptive material. These volcano formations take place due to number of eruptions for several thousand years. These volcanoes are tall and conical in shape and is formed when hot lava escapes through the ruptures or fissures and flows long way. Andesite magma generally forms the composite cones. The main characteristics of the composite volcanoes are periodic and quiet explosion.
Where are composite volcanoes located? Composite volcanoes are generally found in chains along the Pacific Rim and are also called the rim of fire.
Shield volcanoes: Shield volcanoes are entirely formed of the fluid lava. These are large structures and are circular fan shaped in nature and thus look like a shield. Shield volcano formation takes place when pressure formed due to heat of the gas raises the magma upward. The molten lava through the central vent comes out and flows rather than explode upward. Examples of shield volcanoes Examples of shield volcanoes Examples of shield volcanoes are the Hawaiian Islands. Here the shield volcanoes are 1600 to 2300 feet high and have a diameter of four to five miles long.
Cinder cones: Cinder cone volcano are generally steep sided cones of basalt fragments. Liquid lava blobs are carried by streaming gases in the atmosphere and comes down to earth surface. Ashes, bombs and cinders piles up and the forms the conical vent. Cinders are small pebble sized melted volcanic stones where as bombs are large pieces of rock. Cinder cones are not more the 350 to 500 meter high. The Paricutin in Mexico and the Surter I and Surter II of Iceland are the best example of cinder cone.
Spatter cones: Spatter cones are steep sided and low mounds formed of lava fragments that form a linear fissure. As the eruption takes place the molten magma does not cool down completely and forms spatter on the ground. The shapes thus forms are very irregular in nature.
Spatter cones generally consist of highly fluid magma. The Hawaiian island consists of few spatter cones.
Complex volcanoes: Complex volcanoes or compound volcanoes are formed when there is a change in the eruptive nature of the volcano or the main vent area. Strato-volcanoes can also sometimes forms the complex volcanoes since they gets overlapped after repeated eruptions of the volcano, proclastic flows and lava flows and forms multiple vents or summits. Examples of complex volcanoes: Precambrian rocks of Mexico and the long valley of California are well known complex volcanoes. Other Volcanoes Apart from these there are few other types of volcanoes such as super volcanoes, cryptodomes, lava domes, submarine volcanoes. The volcanic emission injects sulphur dioxide, carbon dioxide, water vapor and sulfuric acid in the atmosphere that contributes a lot to acid rain. This is a major effect of volcanic eruption. You can also find types of volcanoes according to activity.
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Quiz
- Name 3 places where you would find a volcano. (3)
- What does dormant mean? Give an example (2)
- What landform develops at a fissure eruption? Give an example (2)
- What is meant by term geo-thermal energy?
- What % of Iceland's energy is generated this way?
- Describe acidic lava. (3)
- Describe basic lava. (3)
- When did Mt St Helen's erupt? What caused the eruption (3)
- What damage occurred? (3)
- What is a composite volcano?
- Whats the difference between a shield and dome volcano? (2)
- What is a caldera?
- Name an Irish volcano.
- Name 2 Italian volcanoes. (2)
- List 3 plutons. (3)
- Which is the biggest?
- Which is vertical?
- What is the difference between a laccolith and a lopolith?
- What is a lahar? Give an example (2)
- What does pyroclastic mean?
- Name 2 instruments used to measure volcanic activity. (2)
- What is a parasitic cone?
- What type of volcanic landform are A. The Wicklow Mountains and B. The Giant's Causeway? (2)
- List 3 positive effects of volcanoes- give examples for each (6)
- List 3 negative effects of volcanoes- give examples for each (6) TOTAL 54