Lava tube is a type of geological formation resulted from volcanic activities.
When the molten rock was formed, the top, sides and bottom of the
flow cooled and solidified first, but lava continued to flow inside
of the tube and eventually the tube was emptied out.
Lava River Cave in Coconino National Forest is very close to
Flagstaff, Arizona. This 0.77-mile-long cave was formed about
700,000 years ago by molten rocks that erupted from a volcanic vent
(probably that is Kendrick Peak. I hiked there on the same way).
Because it is underground, you cannot see the tunnel even if you are
standing above it. It is not exposed until the ceiling of a part of
the tube collapses. This created the cave entrance that was discovered in 1915.
The cave maintains a constant temperature (about 40 degree
Fahrenheit) throughout the whole year. As shown in the photos, the
rocks are very icy. I forgot to bring my jacket while going there.
Fortunately, a good Samaritan loaned me a sweat shirt.
