On the JET tokamak the divertor outer target plate made by carbon-fibre composite is monitored by an InfraRed (IR) camera, of which both time and spatial resolutions allow for an accurate study of the deposited heat flux patterns. This paper reports on a survey carried out over 7686 JET discharges, the majority being high powered H-Mode plasmas with NBI injected power of 10 to 23MW. The appearance and the temporal development of features, which are attributed to changes of the surface heat conduction due to plasma surface interaction, i.e. deposition of carbon layers on the target plate, are shown and their effect is characterized. The link connection between these modifications of the surface thermal properties and the position of the Outer Strike Point (OSP) on the target is also established.