The invention relates to a closure device for closing off, at least in part, a cavity (1) that is open at its top, said device comprising a set of panels (3) suitable for forming a closure cover and cover support means (13). In the invention, each panel has link means for linking to the neighboring panel(s) (3) so as to enable said set of panels (3) to go from a stacked configuration, in which they are superposed on one another in order to open up said opening in said cavity (1) at least in part, to a deployed configuration, in which the panels of at least some of said set of panels (3) extend in alignment with one another while bearing against said cover support means (3). Said device further comprises elastically deformable means (4) suitable for being compressed by said panels when said set of panels (3) are in the stacked configuration.