Lava tubes are natural tunnels formed by flowing lava during a volcanic eruption. As the lava moves, the outer layer cools and solidifies, while the molten lava continues to flow beneath it. Once the eruption stops, the remaining lava drains away, leaving behind a hollow tube. These structures can vary in size and length, with some extending for miles. Lava tubes are often found in volcanic regions, such as those associated with Hawaiian volcanoes or Icelandic eruptions. They can provide unique ecosystems and are sometimes explored for scientific research or recreational activities.