BBC Kids: The Big Question: Why do volcanoes erupt?
Volcanoes erupt when molten rock called magma rises to the surface. Magma is formed when the earth's mantle melts.
Melting may happen where tectonic plates are pulling apart or where one plate is pushed down under another.
Magma is lighter than rock so rises towards the Earth's surface. As the magma rises, bubbles of gas form inside it.
Runny magma erupts through openings or vents in the earth's crust before flowing onto its surface as lava.
If magma is thick, gas bubbles cannot easily escape and pressure builds up as the magma rises.
When the pressure is too much an explosive eruption can happen, which can be dangerous and destructive.
Another way an eruption happens is when water underneath the surface interacts with hot magma and creates steam, this can build up enough pressure to cause an explosion.
Volcanoes erupt when molten rock called magma rises to the surface. Magma is formed when the earth's mantle melts.
Melting may happen where tectonic plates are pulling apart or where one plate is pushed down under another.
Magma is lighter than rock so rises towards the Earth's surface. As the magma rises, bubbles of gas form inside it.
Runny magma erupts through openings or vents in the earth's crust before flowing onto its surface as lava.
If magma is thick, gas bubbles cannot easily escape and pressure builds up as the magma rises.
When the pressure is too much an explosive eruption can happen, which can be dangerous and destructive.
Another way an eruption happens is when water underneath the surface interacts with hot magma and creates steam, this can build up enough pressure to cause an explosion.
Curious Kids: Why do volcanoes erupt?
The rock inside the planet we live on can melt to form molten rock called magma. This magma is lighter than the rocks around it and so it rises upwards. Where the magma eventually reaches the surface we get an eruption and volcanoes form.
The top part of the Earth is made up of a number of hard pieces called tectonic plates. Magma and volcanoes often form where the plates are pulled apart or pushed together but we also find some volcanoes in the middle of tectonic plates.
Volcanoes have many different shapes and sizes, some look like steep mountains (stratovolcanoes), others look like bumps (shield volcanoes) and some are flat with a hole (a crater or caldera) in the centre that is often filled with water.
The shape of the volcano and how explosively it erupts depend largely on how “sticky” and how “fizzy” (how much gas) the magma is that is erupted.
For example, if you try to blow bubbles in cooking oil though a straw, the bubbles can escape quite easily because the cooking oil is runny. If you try to blow bubbles in jam or peanut butter you would find it very difficult because the jam and peanut butter are very sticky, they wouldn’t move much at all if you tried to pour them out of the jar. It is the same with volcanoes. When magma rises towards the surface gas bubbles start to form. Whether or not they can escape as the magma is rising affects how explosive the eruption will be. Where the magma is runny like cooking oil and doesn’t have much bubbly gas mixed in it, such as places like Hawaii, then we see lots of slow-moving lava flows and shield volcanoes. Lava is what we call magma when it reaches the surface.
However, where the magma is very sticky, like jam or peanut butter, and if it contains a lot of bubbly gas then the gas can get stuck and eruptions can be very powerful and explosive, like the recent eruptions at Fuego volcano in Guatemala.
Damage caused by eruptions:
In explosive eruptions the frothy, bubbly magma can be ripped apart into tiny bits called volcanic ash. This is not ash like you get after a barbecue or fire, it does not crumble away in your fingers. It is very sharp and is dangerous to breathe in.
Some explosive volcanoes can send ash high up into the sky and it can travel around the world over different countries. If aeroplanes travel through an ash cloud from a volcano it can cause a lot of damage to the engine.
Other explosive eruptions create fast-moving, hot clouds of volcanic ash, gas and rocks that travel down the sides of the volcanoes and destroy pretty much everything in their path.
The benefits of volcanoes:
Despite the great damage they can cause, volcanoes also help us to live. Volcanic ash provides food for the soil around volcanoes which helps us grow plants to eat. The heat from some volcanoes is used to make energy to power lights, fridges, televisions and computers in people’s houses.
The rock inside the planet we live on can melt to form molten rock called magma. This magma is lighter than the rocks around it and so it rises upwards. Where the magma eventually reaches the surface we get an eruption and volcanoes form.
The top part of the Earth is made up of a number of hard pieces called tectonic plates. Magma and volcanoes often form where the plates are pulled apart or pushed together but we also find some volcanoes in the middle of tectonic plates.
Volcanoes have many different shapes and sizes, some look like steep mountains (stratovolcanoes), others look like bumps (shield volcanoes) and some are flat with a hole (a crater or caldera) in the centre that is often filled with water.
The shape of the volcano and how explosively it erupts depend largely on how “sticky” and how “fizzy” (how much gas) the magma is that is erupted.
For example, if you try to blow bubbles in cooking oil though a straw, the bubbles can escape quite easily because the cooking oil is runny. If you try to blow bubbles in jam or peanut butter you would find it very difficult because the jam and peanut butter are very sticky, they wouldn’t move much at all if you tried to pour them out of the jar. It is the same with volcanoes. When magma rises towards the surface gas bubbles start to form. Whether or not they can escape as the magma is rising affects how explosive the eruption will be. Where the magma is runny like cooking oil and doesn’t have much bubbly gas mixed in it, such as places like Hawaii, then we see lots of slow-moving lava flows and shield volcanoes. Lava is what we call magma when it reaches the surface.
However, where the magma is very sticky, like jam or peanut butter, and if it contains a lot of bubbly gas then the gas can get stuck and eruptions can be very powerful and explosive, like the recent eruptions at Fuego volcano in Guatemala.
Damage caused by eruptions:
In explosive eruptions the frothy, bubbly magma can be ripped apart into tiny bits called volcanic ash. This is not ash like you get after a barbecue or fire, it does not crumble away in your fingers. It is very sharp and is dangerous to breathe in.
Some explosive volcanoes can send ash high up into the sky and it can travel around the world over different countries. If aeroplanes travel through an ash cloud from a volcano it can cause a lot of damage to the engine.
Other explosive eruptions create fast-moving, hot clouds of volcanic ash, gas and rocks that travel down the sides of the volcanoes and destroy pretty much everything in their path.
The benefits of volcanoes:
Despite the great damage they can cause, volcanoes also help us to live. Volcanic ash provides food for the soil around volcanoes which helps us grow plants to eat. The heat from some volcanoes is used to make energy to power lights, fridges, televisions and computers in people’s houses.
GNS Science: Types of Volcanoes & Eruptions
Volcanic Fields
Volcanic fields, such as Auckland and Northland, are where small eruptions occur over a wide geographic area, and are spaced over long periods of time (thousands of years). Each eruption builds a new single new volcano, which does not erupt again. Mount Eden and Rangitoto Island are examples in Auckland.
Cone Volcanoes
Cone volcanoes (also called composite cone or stratovolcanoes) such as Ruapehu, Taranaki / Egmont and Ngauruhoe, are characterised by a succession of small-moderate eruptions from one location. The products from the successive eruptions over thousands of years build the cones.
Caldera Volcanoes
Caldera volcanoes, such as Taupo and Okataina (which includes Mt Tarawera), have a history of infrequent but moderate-large eruptions. The caldera forming eruptions create super craters 10-25 km in diameter and deposit cubic kilometres of ash and pumice.
Types of eruptions:Multiple types of eruptions can occur at each of New Zealand’s volcanoes - the eruption type can vary minute to minute. The style of eruption depends on a number of factors, including the magma chemistry and content, temperature, viscosity (how runny the magma is), volume and how much water and gas is in it, the presence of groundwater, and the plumbing of the volcano.
Hydrothermal eruption
An eruption driven by the heat in a hydrothermal systems. Hydrothermal eruptions pulverise surrounding rocks and can produce ash, but do not include magma. These are typically very small eruptions
Phreatic eruption
An eruption driven by the heat from magma interacting with water. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea. Phreatic eruptions pulverise surrounding rocks and can produce ash, but do not include new magma.
Phreatomagmatic eruption
An eruption resulting from the interaction of new magma or lava with water and can be very explosive. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea.
Lava
Lava is molten rock erupted at the ground surface. When molten rock is beneath the ground, it is called magma.
These are the least violent types of explosive eruptions. Hawaiian eruptions have fire fountains and lava flows, whereas Strombolian eruptions have explosions causing a shower of lava fragments.
Vulcanian eruptions
Vulcanian eruptions are small to moderate explosive eruptions, lasting seconds to minutes. Ash columns can be up to 20 km in height, and lava blocks and bombs may be ejected from the vent.
Subplinian and Plinian eruptions
Eruptions with a high rate of magma discharge, sustained for minutes to hours. They form a tall, convective eruption column of a mixture of gas and rock particles, and can cause wide dispersion of ash. Subplinian eruption columns are up to 20 km high, and are relatively unsteady, whereas Plinian eruptions have 20 to 35 km tall columns which may collapse to form pyroclastic density currents (PDC’s). Very rare Ultraplinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions.
Volcanic Fields
Volcanic fields, such as Auckland and Northland, are where small eruptions occur over a wide geographic area, and are spaced over long periods of time (thousands of years). Each eruption builds a new single new volcano, which does not erupt again. Mount Eden and Rangitoto Island are examples in Auckland.
Cone Volcanoes
Cone volcanoes (also called composite cone or stratovolcanoes) such as Ruapehu, Taranaki / Egmont and Ngauruhoe, are characterised by a succession of small-moderate eruptions from one location. The products from the successive eruptions over thousands of years build the cones.
Caldera Volcanoes
Caldera volcanoes, such as Taupo and Okataina (which includes Mt Tarawera), have a history of infrequent but moderate-large eruptions. The caldera forming eruptions create super craters 10-25 km in diameter and deposit cubic kilometres of ash and pumice.
Types of eruptions:Multiple types of eruptions can occur at each of New Zealand’s volcanoes - the eruption type can vary minute to minute. The style of eruption depends on a number of factors, including the magma chemistry and content, temperature, viscosity (how runny the magma is), volume and how much water and gas is in it, the presence of groundwater, and the plumbing of the volcano.
Hydrothermal eruption
An eruption driven by the heat in a hydrothermal systems. Hydrothermal eruptions pulverise surrounding rocks and can produce ash, but do not include magma. These are typically very small eruptions
Phreatic eruption
An eruption driven by the heat from magma interacting with water. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea. Phreatic eruptions pulverise surrounding rocks and can produce ash, but do not include new magma.
Phreatomagmatic eruption
An eruption resulting from the interaction of new magma or lava with water and can be very explosive. The water can be from groundwater, hydrothermal systems, surface runoff, a lake or the sea.
Lava
Lava is molten rock erupted at the ground surface. When molten rock is beneath the ground, it is called magma.
- Lava flows are the effusive (non-explosive) outpourings of lava, and usually flow slower than walking pace. Lava flow types include a’a, blocky and pahoehoe.
- Lava fountains are a fountain of runny lava fragments from a vent or line of vents (a fissure). They can form spatter piles, and if the fragments accumulate fast enough, they can form lava flows.
- Lava domes are mounds that form when viscous lava is erupted slowly and piles up over the vent, rather than moving away as a lava flow. They are generally caused by viscous, thick, sticky lava that has lost most of its gas. They can range in volume from a few cubic metres to cubic kilometres.
These are the least violent types of explosive eruptions. Hawaiian eruptions have fire fountains and lava flows, whereas Strombolian eruptions have explosions causing a shower of lava fragments.
Vulcanian eruptions
Vulcanian eruptions are small to moderate explosive eruptions, lasting seconds to minutes. Ash columns can be up to 20 km in height, and lava blocks and bombs may be ejected from the vent.
Subplinian and Plinian eruptions
Eruptions with a high rate of magma discharge, sustained for minutes to hours. They form a tall, convective eruption column of a mixture of gas and rock particles, and can cause wide dispersion of ash. Subplinian eruption columns are up to 20 km high, and are relatively unsteady, whereas Plinian eruptions have 20 to 35 km tall columns which may collapse to form pyroclastic density currents (PDC’s). Very rare Ultraplinian eruptions are even larger and have a higher magma discharge rate than Plinian eruptions.
OneGeology:
The name volcano comes from Vulcan, the Roman god of fire!
A volcano is formed when hot molten rock, ash and gases escape from an opening in the Earth’s surface. The molten rock and ash solidify as they cool, forming the distinctive volcano shape shown here.
As a volcano erupts, it spills lava that flows downslope. Hot ash and gases are thrown into the air.
Some volcanoes are covered with snow and ice. If they erupt, melted snow and ice mixes with mud and volcanic ash and flows down mountain. Volcanic flows are called lahars.
Volcanoes are made of unique rocks called extrusive igneous rocks . They are shown on geological maps with bright colours.
Volcanoes are classed as active, dormant or extinct. Active volcanoes could erupt at any time; dormant volcanoes have been known to erupt but have not erupted recently and extinct volcanoes are unlikely to erupt again.
Volcanoes can produce different types of lava. Some is runny and flows down slope; it has a smooth, ropey, wrinkled texture. This is called Pahoehoe lava.
Some volcanoes can be more explosive and produce hot gasses and much thicker rough textured lava that is sticky. This is called Aa lava.
Lava that erupts under water is called Pillow Lava because it forms shapes like pillows. They wouldn’t be very comfy to sleep on though!
The Earth’s surface is made up of several tectonic plates which are constantly moving, although very very slowly. Where tectonic plates are being pushed together, some of the Earth’s crust is pushed deeper into the Earth’s mantle where it melts and rises to the surface again to form volcanoes. A large area where this occurs on earth is called the Pacific Ring of Fire and is shown on these globes.
Where tectonic plates are being pushed apart, openings in the Earth’s crust allows molten rock to escape, forming volcanoes. An area where this occurs on earth is called the Mid-Atlantic Ridge and is shown on this globe.
Volcanoes can also form in areas where there is a hotspot in the mantle. This is an extra hot plume of molten rock which causes the earth’s crust too thin allowing molten rock to escape onto the surface. The movement of the earth’s tectonic plates means that volcanoes form a trail along the earth’s surface. An example of this is Hawaii.
The name volcano comes from Vulcan, the Roman god of fire!
A volcano is formed when hot molten rock, ash and gases escape from an opening in the Earth’s surface. The molten rock and ash solidify as they cool, forming the distinctive volcano shape shown here.
As a volcano erupts, it spills lava that flows downslope. Hot ash and gases are thrown into the air.
Some volcanoes are covered with snow and ice. If they erupt, melted snow and ice mixes with mud and volcanic ash and flows down mountain. Volcanic flows are called lahars.
Volcanoes are made of unique rocks called extrusive igneous rocks . They are shown on geological maps with bright colours.
Volcanoes are classed as active, dormant or extinct. Active volcanoes could erupt at any time; dormant volcanoes have been known to erupt but have not erupted recently and extinct volcanoes are unlikely to erupt again.
Volcanoes can produce different types of lava. Some is runny and flows down slope; it has a smooth, ropey, wrinkled texture. This is called Pahoehoe lava.
Some volcanoes can be more explosive and produce hot gasses and much thicker rough textured lava that is sticky. This is called Aa lava.
Lava that erupts under water is called Pillow Lava because it forms shapes like pillows. They wouldn’t be very comfy to sleep on though!
The Earth’s surface is made up of several tectonic plates which are constantly moving, although very very slowly. Where tectonic plates are being pushed together, some of the Earth’s crust is pushed deeper into the Earth’s mantle where it melts and rises to the surface again to form volcanoes. A large area where this occurs on earth is called the Pacific Ring of Fire and is shown on these globes.
Where tectonic plates are being pushed apart, openings in the Earth’s crust allows molten rock to escape, forming volcanoes. An area where this occurs on earth is called the Mid-Atlantic Ridge and is shown on this globe.
Volcanoes can also form in areas where there is a hotspot in the mantle. This is an extra hot plume of molten rock which causes the earth’s crust too thin allowing molten rock to escape onto the surface. The movement of the earth’s tectonic plates means that volcanoes form a trail along the earth’s surface. An example of this is Hawaii.