Magma is created through the melting of rocks found within the Earth's lithosphere and asthenosphere. This melt, which is primarily a very hot liquid, originates from these two distinct geological zones.
Where Magma Forms
- Lithosphere: This is the Earth's rigid outer layer, comprising the crust and the uppermost part of the mantle. Rocks within this layer can melt under certain conditions.
- Asthenosphere: Located beneath the lithosphere, the asthenosphere is a semi-molten layer. This region can also contribute to magma formation.
The Melting Process
The specific processes leading to rock melting and magma formation typically involve:
- Increased Temperature: Elevated temperatures within the Earth's interior can cause rocks to reach their melting point. This can be due to various factors, including radioactive decay or the Earth's residual heat.
- Decreased Pressure: Rocks under high pressure have higher melting points. A reduction in pressure can facilitate melting even if the temperature isn't extremely high. This commonly occurs at divergent plate boundaries or within mantle plumes.
- Addition of Volatiles: The presence of substances like water or carbon dioxide can lower the melting point of rocks. These volatiles often originate from subducted tectonic plates, contributing to magma formation at convergent boundaries.
Summary
| Formation Component | Description |
|---|---|
| Primary Substance | Molten rock, referred to as a 'melt'. |
| Location | Earth's lithosphere (crust and upper mantle) and the asthenosphere (below the lithosphere). |
| Melting Factors | Increased temperature, decreased pressure, and the addition of volatiles like water or carbon dioxide. |
Magma, once formed, is less dense than the surrounding solid rock and tends to ascend towards the Earth's surface, potentially leading to volcanic activity.
