A tube or cave is left when, after the eruption stops, the roof remains intact as the molten rock drains away. These tubes or caves can be large like subway tunnels or small like storm drains. Lava tubes are usually near the surface with openings through the thin roof. Sea caves form by ocean waves pounding at the base of seashore cliffs. The combined action of the waves, tides, and heavy rains erode the weaker rocks near the base of the cliffs, slowly hollowing out a cave.
Sea caves can be homes for starfish, crabs, seals, and sea lions.
Sandstone caves are shallow caves that form at the base of cliffs, carved out by water and wind. The water loosens the natural cement holding the sand particles together, then the moving water and wind carry away the grains of sand. Native Americans used these sandstone caves for shelter, or built their homes inside caves with the appropriate orientation for protection from the weather.