Water seeps from between layers of rock on the wall of a cliff, crater, or other type of depression.
The alcove forms above the site of seepage as water comes out of the ground and undermines the material from which it is seeping. The erosion of material at the site of seepage causes rock and debris on the slope above this area to collapse and slide downhill, creating the alcove. The channel forms from water and debris running down the slope from the seepage area.