Collapsed Lava Tube

It is difficult to understand what you are looking at in this picture. This is a collapsed lava tube near Sunset Crater in Sunset Crater/Wupatki National Monument in northern Arizona. These are dormant volcanoes. In some volcanic eruptions there are lava flows that come from a vent in the earth. The hot lava flows out over the ground and forms a lava field. Occasionally, some of the lava will harden before the vent stops pouring out lava, in that case the hot lava finds its way through the solidified rock, sometimes if the lava flow is constant enough, the lava will form channels, like streams, through the previously solidified rock. In some cases, the top of the stream of hot lava will also solidify and form a lava tube. The lava will continue to flow through the tube, slowly extending it out across the ground. When the lava stream stops, the still hot lava in the tube runs out, leaving the tube empty. This photo is one of those lava tubes where the rocks on top of the tube have fallen down into the space the lava left.

If the tube is big enough and strong enough not to collapse, sometimes you can get into the lava tubes and follow them. We have been in a few lava tubes, some of which go for more than a mile under the rock. They are similar to a cave and are sometimes called lava caves.