How does magma reach the earth’s surface?
Through volcanoes and rift valley’s.
Magma is a liquid mixture of molten and semi molten rock in the mantle beneath the earth’s crust.
Magma also contains dissolved gases ( this is key ) and crystallized minerals. It’s present in pockets known as magma chambers.
Magma is terrifically hot – 700 to 1300 degrees Celsius hot! (water boils at 100 degrees Celsius)
Contrary to popular belief, it comes from the mantle, not from the core.
Movement of the tectonic plates on top of the mantle causes temperature and pressure changes that melts the rocks.
With that out of the way, let’s get down to business.
The magma contains dissolved gases just like a bottle of Coke contains dissolved Carbon Dioxide.
When you open a Coke bottle, a fizzing sound produced by escaping Carbon Dioxide gas bubbles. These bubbles, as you can see with your own eyes, keep rising from the Coke after you pour it into a transparent glass.
What happens when you open the bottle immediately after shaking it vigorously? A lot of Carbon Dioxide bubbles rise up quickly and they bring a lot of Coke with it.
In exactly the same way, the gas in the magma forms a lot of small bubbles.
Now, the pressure on the magma of the surrounding rocks decreases( decompression ) due to movement of tectonic plates.
This causes the gas bubbles to expand and rise to the surface of the magma(gas rises because it has lower density then the surrounding semi liquid magma).
As the many bubbles escape quickly , they bring a lot of magma with it, the pressure of which breaks the thin crust and out comes a spewing eruption from a volcano. The magma erupting from a volcano is now called lava.
Just like the gas and Coke escape as the bottle cap is opened and pressure on the Coke decreases.
Volcanoes are formed at boundaries where two tectonic plates collide as those are the regions where magma chambers are formed.
There’s a great animation of this route of magma to the surface here:http://news.bbc.co.uk/2/hi/sci/tech/7533964.stm
Cooled and solidified lava is called igneous rock . A volcano(of the conical mountain shape) is formed after many magma eruptions, which lead to accumulation of .
There also another less dramatic way magma reaches the surface.
At some places, the tectonic plates move away from each other, thus creating fissures in the earth’s crust. This almost always happens at the ocean floor. This region is called a rift vally.
Because of the fissure, pressure on top of the magma decreases. It flows out of the magma chamber to fill the gap in the crust. Then cools and hardens to form new crust .
See for yourself:
