Santa Cruz, Friday 11th December, 2009: Lava Tunnel
Lava tunnels are formed when liquid lava flows rapidly downhill, but then the surface
cools and solidifies, while the underneath continues to flow. Eventually, as the
eruption slows, the lava flows out of the tunnel, leaving it empty, like this one.
You get them on Hawaii as well, only there the eruptions are still going on, and you
sometimes see movie footage of them on TV. I was surprised at how big this one was.