1. Cooling Rate:
* Underwater: When lava erupts underwater, it cools down much faster than lava that erupts on land. The water chills the lava rapidly, leading to a quicker crystallization process.
* On Land: Lava flows on land take longer to cool, allowing crystals to grow larger.
2. Nucleation and Growth:
* Underwater: The rapid cooling underwater encourages the formation of a large number of tiny crystals. This happens because the rapid cooling creates many nucleation sites, where crystal growth begins.
* On Land: Slower cooling allows fewer nucleation sites to form, but crystals have more time to grow larger.
3. Pressure and Dissolved Gases:
* Underwater: The pressure of the water also plays a role. Underwater eruptions are often explosive, and the pressure can suppress crystal growth. Dissolved gases in the lava can also influence the rate of crystallization.
* On Land: Lower pressure and fewer dissolved gases on land allow for more relaxed crystal growth.
In summary: The combination of rapid cooling, high pressure, and the influence of dissolved gases underwater makes it much more difficult for large crystals to form in basalt.
