Chapter 25, Problem 8TE

Where does most magma originate?

To determine

The origin of magma.

Answer to Problem 8TE

Magma originates in the lower part of the Earth’s crust and in the upper portion of the mantle.

Explanation of Solution

Magma is mainly a very hot fluid, known as a ‘melt.’ Magma is made from the rocks and minerals which have melted and the quality or types can be classified on the basis of the presence of silica in it. All magma forms through the melting of pre-existing rock. Generally, this occurs in one of two ways:

1. By convection of rock upwards through the mantle until it melts.
2. By melting rock at a subduction zone.

When radioactive decay takes place deep within the Earth, the temperature of the rock rises that causes the expansion of the rock. Because of this expansion, the density of rock decreases, which causes mantle convection.

Conclusion:

Therefore, magma originates in the lower part of the Earth’s crust and in the upper portion of the mantle.