While in the Rauer Island group on Filla Island, Tom and Ali witnessed a Fata Morgana, a mirage sometimes seen at high latitudes.
A Fata Morgana is an unusual form of superior mirage that is seen as a narrow band(s) above the horizon. It distorts the object or objects on which it is based, often making them unrecognisable and often changes rapidly. This type of mirage can comprise many stacked layers and alternating compressed and stretched zones.
The mirage occurs as rays of light pass through air layers of different temperatures in a steep thermal inversion where an atmospheric duct has formed (this is where a layer of warm air rests on colder dense air forming a refracting lens).