I always love how landscapes can look like layers of tissue paper in the right light/haze. Nice treatment on this where the image transitions into nothingness. Cindy
Nothing to be surprized about. The original contrast range of the frame excluding the top and the bottom was probably less than one stop. You pushed this range two stops up in PS and voila, ISO 400 was transformed into ISO1600. ALWAYS shoot low contrast scenes at ISO100 if you plan to increase the contrast in PS and want to avoid noise. You may consider using NeatImage, it does a stellar work on such images