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We study projective Type II degenerations of K3 surfaces polarised by acertain rank 18 lattice, where the central fibre consists of a pair of rationalsurfaces glued along a smooth elliptic curve. Given such a degeneration, onemay construct other degenerations of the same kind by flopping curves on thecentral fibre, but the degenerations obtained from this process are not usuallyprojective. We construct a series of examples which are all projective andwhich are all related by flopping single curves from one component of thecentral fibre to the other. The components of the central fibres obtainedinclude weak del Pezzo surfaces of all possible degrees. This shows thatprojectivity need not impose any meaningful constraints on the surfaces thatcan arise as components in Type II degenerations.

Normal Forms and Tyurin Degenerations of K3 Surfaces Polarised by a Rank 18 Lattice