Lava tubes are created as a direct result of volcanic activity, specifically during basaltic lava flows. They form through two primary mechanisms: surface crusting and inflation.
1. Surface Crusting
- Formation Process: When lava flows, the surface exposed to the air cools and hardens faster than the lava beneath. This creates a crust. As more lava flows beneath this solidified crust, it can create a roofed-over channel, which eventually becomes a lava tube.
- Analogy: Imagine pouring honey. The surface of the honey will skin over relatively quickly, but the honey underneath remains liquid. If you continuously pour honey, the liquid honey can flow beneath the skin.
2. Inflation
- Formation Process: Another way lava tubes form is through inflation. This occurs when lava is supplied to an area covered by a previously solidified flow. The new lava then flows beneath the old surface, uplifting it and creating space. This space can then become a lava tube.
- Sequential Flows: Over time, multiple flows can occur on top of each other, with the latest flows going under the older cooled ones, forming extensive tube systems.
Key Factors Influencing Lava Tube Formation
Several factors influence the formation and size of lava tubes:
- Lava Viscosity: Low-viscosity basaltic lava (meaning it flows easily) is essential for lava tube formation. Highly viscous lava tends to cool and solidify too quickly, preventing the formation of long, continuous tubes.
- Lava Supply Rate: A consistent and sufficient supply of lava is crucial to maintain flow and prevent premature cooling. A high flow rate allows the lava to travel longer distances and form larger tubes.
- Ground Slope: Gentle slopes allow lava to flow more evenly, promoting the development of stable lava tubes. Steeper slopes can lead to turbulent flow and collapse.
- Insulation: The solidified crust of the lava flow acts as insulation, preventing the underlying lava from cooling too rapidly. This allows the lava to travel further and form longer lava tubes.
Summary
In essence, lava tubes are natural conduits formed within lava flows. They result from the complex interplay of cooling, flow dynamics, and lava properties, creating underground pathways that were once rivers of molten rock.
