WHAT IS A VOLCANO?
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.
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.
main parts of a volcano
1. Crater Cone
- Is the most striking part of the volcano. It is usually composed of mixtures of lava and pyroclastic. Volcano cones vary in size and shape depending on the type of magma that is ejected by a particular volcano.
2. Vent
- Is the opening through which an eruption takes place. This main part of a volcano supplies the magma from the underlying source to the top of the volcano.
3. Lava
- Is the rock or magma expelled from a volcano during eruption. Its temperature upon ejection can reach up to 700°C hence it flows until it cools and hardens.
4. Magma Chamber
- Is the large underground pool of liquid rock found beneath the earth's crust.
5. Ash and gas cloud
- Is expelled in the atmosphere; volcanic ash or ash cloud is composed of pulverized rock and glass created during eruption.
1. Crater Cone
- Is the most striking part of the volcano. It is usually composed of mixtures of lava and pyroclastic. Volcano cones vary in size and shape depending on the type of magma that is ejected by a particular volcano.
2. Vent
- Is the opening through which an eruption takes place. This main part of a volcano supplies the magma from the underlying source to the top of the volcano.
3. Lava
- Is the rock or magma expelled from a volcano during eruption. Its temperature upon ejection can reach up to 700°C hence it flows until it cools and hardens.
4. Magma Chamber
- Is the large underground pool of liquid rock found beneath the earth's crust.
5. Ash and gas cloud
- Is expelled in the atmosphere; volcanic ash or ash cloud is composed of pulverized rock and glass created during eruption.
TYPES OF VOLCANOES
Cinder Cones
A cinder cone, also called a scoria cone, is a volcano composed of volcanic cinders (scoria), or small, rough particles of hardened lava. When lava that is highly charged with gas bubbles erupts from a vent under pressure, it tends to shoot straight up into the air. This effect is called a fire fountain, and it can sometimes be hundreds of meters high.
Blobs of the frothy lava break apart, cool quickly, and fall relatively close to the vent. Over time, a cone-shaped hill builds up around a circular crater.
A cinder cone, also called a scoria cone, is a volcano composed of volcanic cinders (scoria), or small, rough particles of hardened lava. When lava that is highly charged with gas bubbles erupts from a vent under pressure, it tends to shoot straight up into the air. This effect is called a fire fountain, and it can sometimes be hundreds of meters high.
Blobs of the frothy lava break apart, cool quickly, and fall relatively close to the vent. Over time, a cone-shaped hill builds up around a circular crater.
Composite Volcanoes
A composite volcano, also known as a stratovolcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic explosive eruptions and effusive eruptions, although some have collapsed craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far due to high viscosity.
Shield Volcanoes
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.
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.
Volcanic Domes
A volcanic dome, also called lava dome, is rounded, steep-sided mound that is formed by small, bulging masses of lava primarily composed of either dacite or rhyolite. Lava coming from a dome is too viscuos to flow from the vent, lava piles over and around the vent until it cool down and solidifies. A dome grows mainly by expansion from within.
A volcanic dome, also called lava dome, is rounded, steep-sided mound that is formed by small, bulging masses of lava primarily composed of either dacite or rhyolite. Lava coming from a dome is too viscuos to flow from the vent, lava piles over and around the vent until it cool down and solidifies. A dome grows mainly by expansion from within.
Supervolcanoes
A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta mass greater than 1015 kg.Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for the Yellowstone Caldera). They can also form at convergent plate boundaries (for example, Toba). Large igneous provinces can cover huge areas with lava andvolcanic ash, causing long-lasting climate change (such as the triggering of a small ice age or global warming), which can threaten species with extinction.
A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta mass greater than 1015 kg.Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for the Yellowstone Caldera). They can also form at convergent plate boundaries (for example, Toba). Large igneous provinces can cover huge areas with lava andvolcanic ash, causing long-lasting climate change (such as the triggering of a small ice age or global warming), which can threaten species with extinction.
Submarine Volcanoes
This type of volcano is created when magma erupts in the underwater fissures of the earth. Majority of these volcanoes are found near ocean ridges while some can exist in shallow water. Submarine volcanoes in shallow water can eject basaltic magma and the lava formed is known pillow lava.
This type of volcano is created when magma erupts in the underwater fissures of the earth. Majority of these volcanoes are found near ocean ridges while some can exist in shallow water. Submarine volcanoes in shallow water can eject basaltic magma and the lava formed is known pillow lava.
Subglacial Volcano
A subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava. Today they are most common in Iceland and Antarctica; olderformations of this type are found also in British Columbia and Yukon Territory, Canada.
A subglacial volcano, also known as a glaciovolcano, is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava. Today they are most common in Iceland and Antarctica; olderformations of this type are found also in British Columbia and Yukon Territory, Canada.
classification of volcanic activity
Active Volcanoes
- A volcano that is erupting or has repeatedly erupted in a short period of time.Is one that has erupted since the last ice age (i.e., in the past ~10,000 years).
Dormant Volcanoes
-A volcano would then be one that hasn’t erupted in the past 10,000 years, but which is expected to erupt again.
Extinct Volcanoes
- volcano would be one that nobody expects to ever erupt again. When a volcano becomes extinct, no further material is added to the cone.
- A volcano that is erupting or has repeatedly erupted in a short period of time.Is one that has erupted since the last ice age (i.e., in the past ~10,000 years).
Dormant Volcanoes
-A volcano would then be one that hasn’t erupted in the past 10,000 years, but which is expected to erupt again.
Extinct Volcanoes
- volcano would be one that nobody expects to ever erupt again. When a volcano becomes extinct, no further material is added to the cone.