Or is like the darkness in a deep sea. It is covered by waves, above which are waves, above which are clouds. Darkness, one above another. Scientists have only recently discovered that there are internal waves which occur on density interfaces between layers of different densities. The internal waves cover the deep waters of seas and oceans because the deep waters have a higher density than the waters above them.
Internal waves act like surface waves.
They can also break just like surface waves. Internal waves cannot be seen by the human eye, but they can be detected by studying temperature or salinity changes at a given location.