Formation of mountains
A mountain is a landform that rises high above the surrounding terrain in a limited area (Resources.woodlands-junior.kent.sch.uk, 2014). They are made from rocks and earth and those that are very tall may be covered in show or ice.
Generally, mountains are higher than 600 metres; those less than 600 metres are called hills (Resources.woodlands-junior.kent.sch.uk, 2014).
Mountains are found all over the world, even under the ocean. Mountains usually have steep sloping sides and sharp or rounded edges. A mountain range is a series or chain of mountains that are close together (National Geographic, 2014).
Mountains cover one fifth of the earth's surface (Taylor, 2006), and many are part of ranges. Ranges can stretch for hundreds of miles, as shown in the diagram below.
Generally, mountains are higher than 600 metres; those less than 600 metres are called hills (Resources.woodlands-junior.kent.sch.uk, 2014).
Mountains are found all over the world, even under the ocean. Mountains usually have steep sloping sides and sharp or rounded edges. A mountain range is a series or chain of mountains that are close together (National Geographic, 2014).
Mountains cover one fifth of the earth's surface (Taylor, 2006), and many are part of ranges. Ranges can stretch for hundreds of miles, as shown in the diagram below.
The Himalayas in Asia form one massive wreck that started about 55 million years ago (National Geographic, 2014). There are thirty of the world's higest mountains found here. The top of Mount Everest is 8 850 metres tall, and the highest point on earth. However, the tallest mountain is Mauna Kea, an inactive volcano on the island of Hawaii that stands 10, 203 meters tall. But, it only rises 4 205 meters above the sea (National Geographic, 2014), which is where the height of mountains are measured.
Most mountains form where the earth's plates move towards one another and are subjected to huge forces (Bbc.co.uk, 2014). A very good example of this is when the Indian plate and the Eurasian plate collided; as the plates pushed together, the rocky seabed was forced upwards, creating fold mountains, as shows in the below diagram.
Another way that mountains form is through magma. Sometimes magma can be pushed up but not actually break the surface of earth (Cain, 2009). The bludge of magma eventually hardens into rock, such as granite. The old softer rock erodes away, and the remaining structure is a dome–shaped mountain (Cain, 2009).
Most mountains form where the earth's plates move towards one another and are subjected to huge forces (Bbc.co.uk, 2014). A very good example of this is when the Indian plate and the Eurasian plate collided; as the plates pushed together, the rocky seabed was forced upwards, creating fold mountains, as shows in the below diagram.
Another way that mountains form is through magma. Sometimes magma can be pushed up but not actually break the surface of earth (Cain, 2009). The bludge of magma eventually hardens into rock, such as granite. The old softer rock erodes away, and the remaining structure is a dome–shaped mountain (Cain, 2009).
Volcanoes - mountains of fire
Being creators and destroyers, volcanoes prove that the earth is a constantly changing planet, and is very much alive.
A volcano is a vent or chimney which transfers molten rock known as magma from depth to the Earth's surface (Ga.gov.au, 2014). Magma erupting from a volcano is classified as lava and is the material which builds up the cone below the opening.
A volcano is classified as active if it is emitting lava, releasing gas, or generating seismic activity large enough to affect a population (Ga.gov.au, 2014). A volcano is classified as dormant if it has not erupted for quite a while, but has the potential to in the future. An extinct is a volcano that has not erupted for more than 10, 000 years (Ga.gov.au, 2014).
There are a number of different things that affect the explosiveness of a volcano; one of these is how easily magma can flow out, and the amount of gas trapped inside the magma. As magma rises to the crust, gas bubbles can expand up to 1000 times their original size (Ga.gov.au, 2014).
Formation of a volcano
The earth's crust is made up of tectonic plates. Volcanoes are formed when magma from the earth's mantle pours out through the cracks in the crust (Taylor, 2006). Once magma reaches the earth's surface, it is called lava. Once the lava from the eruption cools, it forms a new crust, just like at the bottom of the ocean where seafloor spreading occurs. Over time, after a number of eruptions, the rock builds up, and a volcano forms. Volcanoes can still get bigger and bigger as they continue to erupt and new crust is added each time.
A volcano is a vent or chimney which transfers molten rock known as magma from depth to the Earth's surface (Ga.gov.au, 2014). Magma erupting from a volcano is classified as lava and is the material which builds up the cone below the opening.
A volcano is classified as active if it is emitting lava, releasing gas, or generating seismic activity large enough to affect a population (Ga.gov.au, 2014). A volcano is classified as dormant if it has not erupted for quite a while, but has the potential to in the future. An extinct is a volcano that has not erupted for more than 10, 000 years (Ga.gov.au, 2014).
There are a number of different things that affect the explosiveness of a volcano; one of these is how easily magma can flow out, and the amount of gas trapped inside the magma. As magma rises to the crust, gas bubbles can expand up to 1000 times their original size (Ga.gov.au, 2014).
Formation of a volcano
The earth's crust is made up of tectonic plates. Volcanoes are formed when magma from the earth's mantle pours out through the cracks in the crust (Taylor, 2006). Once magma reaches the earth's surface, it is called lava. Once the lava from the eruption cools, it forms a new crust, just like at the bottom of the ocean where seafloor spreading occurs. Over time, after a number of eruptions, the rock builds up, and a volcano forms. Volcanoes can still get bigger and bigger as they continue to erupt and new crust is added each time.
Volcanoes do not only just occur on earth; the biggest volcano in the solar system is on planet Mars. It is named Olympus Mons (Mount Olympus) and is more than double the height of Mount Everest (Lofts and Evergreen, 2011)!
Volcanoes can vary in size, appearance and composition. There are three common types:-
Shield volcano
Shield volcanoes are large volcanoes that are built almost entirely of fluid lava flows (K12.hi.us, 2014). Shield volcanoes have a broad, flattened dome shape created by layers of runny lava flowing over its surface, and then cooling (Ga.gov.au, 2014). As the lava flows easily, it can spread for great distances from the vent. Because the lava flows at a sufficient rate, it can be slow enough for humans to outrun or even outwalk them. The magma has temperatures between 800 and 1200 degrees Celcius, and is known as basaltic magma (Ga.gov.au, 2014). Shield volcanoes are produced by the action of gas with heat from the core; this, in turn, melts rock and turns it into magma. The pressure from the heat of the gas forces the magma upwards until it eventually explodes (K12.hi.us, 2014).
Shield volcanoes are large volcanoes that are built almost entirely of fluid lava flows (K12.hi.us, 2014). Shield volcanoes have a broad, flattened dome shape created by layers of runny lava flowing over its surface, and then cooling (Ga.gov.au, 2014). As the lava flows easily, it can spread for great distances from the vent. Because the lava flows at a sufficient rate, it can be slow enough for humans to outrun or even outwalk them. The magma has temperatures between 800 and 1200 degrees Celcius, and is known as basaltic magma (Ga.gov.au, 2014). Shield volcanoes are produced by the action of gas with heat from the core; this, in turn, melts rock and turns it into magma. The pressure from the heat of the gas forces the magma upwards until it eventually explodes (K12.hi.us, 2014).
Composite volcano
Composite volcanoes, or stratovolcanoes, are much more explosive than shield volcanoes (Bbc.co.uk, 2014). These large and generally cone-shaped mountains that are typically steeply-sided (K12.hi.us, 2014). Composite volcanoes form along plate boundaries. Composite volcanoes contain magma that is more viscous than that of shield volcanoes (Bbc.co.uk, 2014). Because of this, the 'stickiness' plugs up the volcano, which in turn creates pressure. The result once the pressure is released is an explosive, dangerous eruption. Composite volcanoes erupt in different ways at different times. These volcanoes form in layers by multiple eruptions, which may occur over hundreds of thousands of years. Most types of composite volcanoes have a crater at the summit which contains a central vent of a cluster group of vents. In some instances, composite volcanoes can grow to such heights that their slops are classified as unstable, and may crumble due to the force of gravity (K12.hi.us, 2014). The type of magma that erupts from this volcano usually has a temperature between 800 and 1000 degrees celcius (Ga.gov.au, 2014).
Composite volcanoes, or stratovolcanoes, are much more explosive than shield volcanoes (Bbc.co.uk, 2014). These large and generally cone-shaped mountains that are typically steeply-sided (K12.hi.us, 2014). Composite volcanoes form along plate boundaries. Composite volcanoes contain magma that is more viscous than that of shield volcanoes (Bbc.co.uk, 2014). Because of this, the 'stickiness' plugs up the volcano, which in turn creates pressure. The result once the pressure is released is an explosive, dangerous eruption. Composite volcanoes erupt in different ways at different times. These volcanoes form in layers by multiple eruptions, which may occur over hundreds of thousands of years. Most types of composite volcanoes have a crater at the summit which contains a central vent of a cluster group of vents. In some instances, composite volcanoes can grow to such heights that their slops are classified as unstable, and may crumble due to the force of gravity (K12.hi.us, 2014). The type of magma that erupts from this volcano usually has a temperature between 800 and 1000 degrees celcius (Ga.gov.au, 2014).
Caldera volcano
Caldera volcanoes are ones where the diameter (distance across) of the crater exceeds a distance of 1 mile (approx. 1.6 km). They erupt so violently that little material builds up near the opening (Ga.gov.au, 2014). As the volcano erupts, the below-ground magma chamber is partly or wholly emptied, which in turn, causes the unsupported vent to collapse under its own weight (Ga.gov.au, 2014). The remaining basin-shaped area is usually several km more in diameter. The lava that erupts from a caldera volcano ranges from 650 to 800 degrees, and is known as rhyolitic magma. Being rare, these types of volcanoes are the most dangerous; a number of hazards arise from this type of volcano, such as ash fall and tsunamis triggered by the seismic activity. Only recently have scientists been able to get an understanding of this type of volcano. Since this type of eruption has not occurred during recorded history, there hasn't been any human witnesses to describe the eruption (Extremescience.com, 2014).
Caldera volcanoes are ones where the diameter (distance across) of the crater exceeds a distance of 1 mile (approx. 1.6 km). They erupt so violently that little material builds up near the opening (Ga.gov.au, 2014). As the volcano erupts, the below-ground magma chamber is partly or wholly emptied, which in turn, causes the unsupported vent to collapse under its own weight (Ga.gov.au, 2014). The remaining basin-shaped area is usually several km more in diameter. The lava that erupts from a caldera volcano ranges from 650 to 800 degrees, and is known as rhyolitic magma. Being rare, these types of volcanoes are the most dangerous; a number of hazards arise from this type of volcano, such as ash fall and tsunamis triggered by the seismic activity. Only recently have scientists been able to get an understanding of this type of volcano. Since this type of eruption has not occurred during recorded history, there hasn't been any human witnesses to describe the eruption (Extremescience.com, 2014).
Structure of a volcano
There are four main parts of a volcano:
There are four main parts of a volcano:
- Magma chamber: this is where magma from the inside of the earth collects.
- Main vent: this is the main outlet in which the magma escapes.
- Secondary vent(s): just like the main events, magma escapes from here. However, they are smaller outlets and may have many running through the volcano.
- Crater: this is created after an eruption blows the top of the volcano off.
Cause of volcanic eruptions:-
Most volcanic activity occurs at plate boundaries of plates.
Spreading plates:
Where plates move apart, volcanic eruptions are gentle extrusions of basaltic lava (Ga.gov.au, 2014). Most of these occur underwater where magma rises from great depth to fill in the split space created by tectonic plates diverging. Spreading occurs at the rate of about 10cm/year.
Colliding plates:
At colliding plate boundaries one plate is pushed under another. In addition to the old plate being forced down and melted into magma, wet sediment and sea water is also forced down (Ga.gov.au, 2014). In turn, this creates andesitic lava, and more violent eruptions containing ash. These types of volcanoes form cone shapes.
Most volcanic activity occurs at plate boundaries of plates.
Spreading plates:
Where plates move apart, volcanic eruptions are gentle extrusions of basaltic lava (Ga.gov.au, 2014). Most of these occur underwater where magma rises from great depth to fill in the split space created by tectonic plates diverging. Spreading occurs at the rate of about 10cm/year.
Colliding plates:
At colliding plate boundaries one plate is pushed under another. In addition to the old plate being forced down and melted into magma, wet sediment and sea water is also forced down (Ga.gov.au, 2014). In turn, this creates andesitic lava, and more violent eruptions containing ash. These types of volcanoes form cone shapes.
The Ring of Fire
The Ring of Fire is a ring of volcanoes around the Pacific Ocean that result from subduction of oceanic plates beneath lighter continental plates (Volcano.oregonstate.edu, 2014). Most of the volcanoes on earth are located around the Ring of Fire, as this is where most of the earth's subduction zones occur.
As a matter of fact, the Ring of Fire isn't actually circular at all; instead, it is more like a horse shoe, and is about 40, 000km (Society and Society, 2014). A strong of 452 volcanoes stretches from the tip of South America, up along North America, across the Bering Straight, down through Japan and finally into New Zealand (Society and Society, 2014).
It is no coincidence that the Ring of Fire lies where it does. The edges of several tectonic plates meet along the Ring of Fire, which in turn, results in a divergent, convergent or transform boundary.
A convergent boundary is when plates crash into each other. Most are often subduction zones, and the heavier slips under the lighter (Society and Society, 2014). Volcanoes are usually at subduction sites, and the heavier plate melts back into the earth's mantle.
At divergent boundaries, tectonic plates are pulling apart. As this happens, magma wells up in the rift as the old crust pulls itself in opposite directions (Society and Society, 2014). Once the magma comes into contact with the cold sea water, new crust is created.
A transform boundary is when plates are sliding past each other. In the Ring of Fire, transform boundaries are often the site of earthquakes.
The Ring is Fire is, nevertheless, home to most the active volcanoes on earth, with most located on the eastern edge.
As a matter of fact, the Ring of Fire isn't actually circular at all; instead, it is more like a horse shoe, and is about 40, 000km (Society and Society, 2014). A strong of 452 volcanoes stretches from the tip of South America, up along North America, across the Bering Straight, down through Japan and finally into New Zealand (Society and Society, 2014).
It is no coincidence that the Ring of Fire lies where it does. The edges of several tectonic plates meet along the Ring of Fire, which in turn, results in a divergent, convergent or transform boundary.
A convergent boundary is when plates crash into each other. Most are often subduction zones, and the heavier slips under the lighter (Society and Society, 2014). Volcanoes are usually at subduction sites, and the heavier plate melts back into the earth's mantle.
At divergent boundaries, tectonic plates are pulling apart. As this happens, magma wells up in the rift as the old crust pulls itself in opposite directions (Society and Society, 2014). Once the magma comes into contact with the cold sea water, new crust is created.
A transform boundary is when plates are sliding past each other. In the Ring of Fire, transform boundaries are often the site of earthquakes.
The Ring is Fire is, nevertheless, home to most the active volcanoes on earth, with most located on the eastern edge.
Pompeii
It is certain that when the eruption of Mount Vesuvius started on the morning of 24 August, AD 79, it caught the local city population utterly surprised. Although at the same time, as we now know in retrospect, all the signs were there to warn them (Bbc.co.uk, 2014). One eye-witness, by a young man named Pliny, was able to write preserved letters and help modern geologists and historians understand what happened. He also describes the reactions that people had as the volcano erupted.
Because of this major eruption, volcanologists today still measure any changes in the seismic activity from the observatory on Vesuvius. However, with today's modern equipment, scientists can predict an eruption months in advance (Bbc.co,uk, 2014).
The eruption
The earthquake that occured before the eruption on AD 63 caused damage to both Pompeii and Herculaneum. Some areas were worse affected than others. More impressive is the signs of resilience that the population did. Houses were being repaired at the time of eruption. So, instead of preparing for the eruption, the city was extensively repairing all the buildings from the previous quake.
Taken by surprise of the eruption, the towns could only respond in panic (Wikipedia, 2013). The eruption of the volcano lasted for more than 24 hours from the start. It was clear that many thought their best chance was to take shelter and weather the storm (Bbc.co.uk, 2014). It was not until around midnight when the first surges of lava flowed. The power of the volcano was a hundred thousand times the thermal energy of the Hiroshima bombing.
Several days before the eruption reports of the ground groaning and 'giants' were roaming the earth. And, to top it off, an eruption had not occured for over 100 years. No one foresaw the disaster that would strike (Dl.ket.org, 2004).
To get a recreation of the volcano erupting, see this link from the Museum of Victoria: Recreation of Vesuvius Erupting
Because of this major eruption, volcanologists today still measure any changes in the seismic activity from the observatory on Vesuvius. However, with today's modern equipment, scientists can predict an eruption months in advance (Bbc.co,uk, 2014).
The eruption
The earthquake that occured before the eruption on AD 63 caused damage to both Pompeii and Herculaneum. Some areas were worse affected than others. More impressive is the signs of resilience that the population did. Houses were being repaired at the time of eruption. So, instead of preparing for the eruption, the city was extensively repairing all the buildings from the previous quake.
Taken by surprise of the eruption, the towns could only respond in panic (Wikipedia, 2013). The eruption of the volcano lasted for more than 24 hours from the start. It was clear that many thought their best chance was to take shelter and weather the storm (Bbc.co.uk, 2014). It was not until around midnight when the first surges of lava flowed. The power of the volcano was a hundred thousand times the thermal energy of the Hiroshima bombing.
Several days before the eruption reports of the ground groaning and 'giants' were roaming the earth. And, to top it off, an eruption had not occured for over 100 years. No one foresaw the disaster that would strike (Dl.ket.org, 2004).
To get a recreation of the volcano erupting, see this link from the Museum of Victoria: Recreation of Vesuvius Erupting