Some internet users were quick to dismiss UFO claims made by others below you YouTube video posted by a local radio station.
“This video should be called ‘Fly seen at Nevado del Ruiz,'” was the top recommended comment on YouTube from Josue A.
Another top comment listed objects that the dark spot could be, including “an insect, ash, a leaf, a bag, a boomerang, a ball, etc.”
Source
Animación de imágenes del volcán Nevado del Ruiz, 14 de Marzo (Servicio Geologico Colombiano)