Well Greece is pretty tectonically active, so perhaps particular parts of it are sinking. Combine this with sea level rise (google 'sea level change greece') and it will be disappearing more. Then I guess you have tectonically triggered landslides, so lots of sediment will slide into the sea. And lots of Greece is low lying so it is particularly susceptible to sea level rise. And Greece is particularly coastal, so coastal erosion is probably significant.
Oh – and for heaven's sake, DO NOT REFERENCE WIKIPEDIA. By all means use it to give you pointers, but you should read some actual journal papers. Pictures are good, and not too many words – but enough to tell a story. E.g. The aim of the poster is to explain why greece is disappearing, suggest some physical processes (sea level change, tectonics, coastal erosion) and some evidence (measured rates, model predictions) and then show why greece is particularly susceptible (cos it is low lying and coastal). Job done. Big picture in the middle showing a part of greece and then another image showing same part of greece with projected sea level rise plotted over it (I am sure some modelling papers will have something like that). And it never hurts to have some actual data on there – e.g. graph of predicted sea level change according to IPCC.
Oh, I'm an earth scientist in case you were wondering… and now you are going to tell me that you are not studying any form of earth science at all and that I've just wasted my time…
