In H-mode plasmas, Edge Localised Modes (ELMs) are responsible for large energy losses and have been observed on all major tokamaks. They have been described in machines where fast density measurements are available as a fast collapse of the top of the pedestal and a rise of the Scrape-Off Layer (SOL) density occurring in less than 200ms. During the same time interval, filament structures are observed. The SOL density has been reported to decay in a few ms and occurs in parallel with the slower recovery of the pedestal top. This paper presents new measurements, made on the JET tokamak, of the evolution of the density profile during type-I ELM crashes. The reflectometer used for this study is first described. The typical ELM crash dynamics are then presented. Finally an unexpected highdensity event observed during some ELM crashes is described.