Underwater lava flows behave differently than those on land, primarily because of the interaction with water. Although underwater lava flows don't float, the upward buoyancy forces partly counteract the downslope pull by gravitational forces, causing them to flow more slowly.
Factors Influencing Underwater Lava Flow
Several factors contribute to the unique way lava flows underwater:
- Buoyancy: While lava is denser than seawater and therefore doesn't float, the surrounding water exerts an upward buoyant force. This force counteracts gravity, slowing the lava's descent and forward movement.
- Cooling and Solidification: The rapid cooling caused by the water leads to the quick formation of a solid crust on the lava flow's surface. This crust can insulate the molten lava underneath, allowing it to continue flowing for a time.
- Pillow Lavas: A common feature of underwater lava flows is the formation of "pillow lavas." These are bulbous, pillow-shaped structures that form when lava erupts or flows into water and quickly cools. The outer skin solidifies instantly, forming a pillow shape, while molten lava continues to flow into and inflate the pillow until it buds off or the internal pressure breaks the skin, forming another pillow.
- Hydrothermal Vent Formation: Underwater lava flows can create hydrothermal vents when seawater seeps into cracks in the newly formed volcanic rock, is heated by the magma, and then rises back to the surface, carrying dissolved minerals.
- Viscosity: The viscosity (resistance to flow) of the lava itself plays a crucial role. More viscous lavas will form thicker, more resistant flows, while less viscous lavas will spread more easily, even underwater. The high pressure at great depths can also influence the viscosity.
Comparison to Lava Flows on Land
| Feature | Lava Flow on Land | Lava Flow Underwater |
|---|---|---|
| Cooling Rate | Relatively slow | Very rapid |
| Flow Rate | Generally faster | Generally slower |
| Morphology | Sheets, channels, lava tubes | Pillow lavas, sheet flows |
| Interaction | Interaction with air and land | Interaction with water |
| Buoyancy Effects | Minimal | Significant; reduces the effect of gravitational pull |
In essence, underwater lava flows are a complex interplay of gravity, buoyancy, cooling rates, and the lava's inherent properties, resulting in unique geological formations.
