Magma is molten rock. It is so hot that the rock has melted to become a thick and sticky liquid. Magma is lighter than the harder rock around it and it tends to rise up towards the crust. Sometimes it collects in large pools called magma chambers. If the Earth's crust is weak above a magma chamber, the magma can burst through the surface and then flow out as lava.
The classic picture of a volcano erupting shows a mountain spewing out fire and ash from its top. This is what happens in a lot of eruptions. Magma builds up in the chimney of the volcano and mixes with gas that comes out of the melted rock. The gas in the mixture makes it light and it rises to the top of the chimney. It then explodes from the cone of the volcano because of the build up of pressure.
Magma is liquid rock that has gases and minerals mixed in with it and it is found several kilometers below the earth’s crust. Although the earth feels like solid rock to those of us living on it’s surface, there is a softer rock a few kilometers below the surface and then magma below that.
Magma is a molten rock that is extremely high in temperature. Most known materials will melt by a temperature of about 593.33 C (1100 F) but most of the magna under the earth’s crust maintains a temperature between 700 – 300 C (1292 – 2372 F). Molten rock that has reached the earth’s surface, usually due to a volcanic eruption, will quickly lose heat energy although it will still easily burn anything in it’s path and can quickly start a forest fire.
Lava is defined as molten rock that is on or above the earth’s surface. This is also referred to as extrusive. Apart from lava flows, molten rock can be found above the earth’s surface in the form of igneous rocks. All igneous rock is formed from magma and rocks will sometimes resemble the previously fluid flow of magma. Obsidian is a naturally occurring glass that is shiny and brittle and is formed when magma fails to crystallize as it cools. This gives it a smooth texture and obsidian can resemble the flow of certain types of magma.
A relatively well-known igneous rock is pumice. It is a unique rock in that it is so light that it will float in water and most other fluids. It’s appearance is almost the opposite of obsidian as it is extremely porous with regular pockmarks that make it resemble a sponge. This texture is created when gases create bubbles in the rock that doesn’t reform before it cools. This results in pumice’s very low density and bubbly appearance.
Temperature and pressure increase as you go deeper into the earth’s layers. The hottest part of the earth is in the centre of the interior and this is what creates magma. Under the correct conditions when heat is extreme, part of the rock forming beneath the earth’s crust will begin to melt. When heated rock rises, it will naturally cool which is how the igneous rock portions of the earth’s crust were formed. If magma comes to the surface, slowly cooled rock will be pushed upwards creating volcanic mountains which are a potential source for the extrusion of lava.
Mars is another planet that has magma. Scientists have compared Hawaiian volcanoes with Martian volcanoes and have posited that some previously thought to be extinct may actually only be dormant.
Inside the earth it is very hot. This great heat melts some rock material that is there and makes it liquid rock. Liquid rock lies in huge underground pockets. This liquid underground rock is called 'Magma'.
Magma is lighter in weight than the colder hard rocks around it. So it is slowly pushed upward by the pressure of the rock around it. In many places the magma never does reach the surface but slowly cools down and hardens underground.
It takes many thousands of years for magma to harden and convert into a rock. In other places the cold, hard rocks near the surface can not withstand the pressure of the magma beneath them. They crack a little bit and the magma rises up along the cracks.
Magma usually starts cooling while it is still being pushed upward. As the magma slowly rises, certain minerals in it grow into big crystals sooner than any other minerals do. The crystals float in the magma. When this magma reaches to the surface of the earth, the liquid rock turns into solid in a short time.
