* Lowering of Solidus Temperature: Water acts as a flux, meaning it lowers the temperature at which minerals in rocks begin to melt. This is the "solidus" temperature, marking the transition from solid to liquid.
* Partial Melting: Water facilitates the melting of specific minerals within the rock before others. This process, called partial melting, allows for the formation of magma even at temperatures below the complete melting point of the rock.
* Hydrostatic Pressure: Water pressure within the rock can also influence the melting point. Higher pressures generally increase the melting point, but water's presence often counteracts this effect.
Here's a breakdown of how water impacts melting:
1. Breaking Bonds: Water molecules can interact with the bonds within the rock's minerals, weakening them and lowering the temperature needed for melting.
2. Lowering Viscosity: The presence of water makes the magma less viscous, allowing for easier movement and melting.
3. Hydrous Minerals: Certain minerals, like hornblende, are more likely to melt in the presence of water. These "hydrous minerals" play a crucial role in magma generation.
Example:
* A dry, water-free rock may have a melting point of 1200°C.
* The same rock, with a 5% water content, might melt at around 900°C.
Significance:
* Volcanism: Water's influence on melting is a key factor in volcanic processes. Subduction zones, where water-rich oceanic plates descend beneath continental plates, are prime examples of this phenomenon. The added water significantly lowers the melting point of the surrounding rock, leading to the formation of magmas that fuel volcanoes.
* Geothermal Activity: Water's role in lowering melting points also plays a crucial role in geothermal energy production. Hot springs and geysers are often formed by the interaction of heated water with rocks.
In summary, water's presence in rocks is a significant factor in determining their melting point. It lowers the temperature at which rocks melt, leading to partial melting, magma generation, and various geological processes.
