Finland was long emerged under a sheet of ice. When the ice sheet began to retreat at the end of the Ice Age, at around 11,000 years ago, Finland began to emerge. This process is ongoing because the ice is still retreating. Finland rises between 8 and 31 inches per one hundred years.
For further information, please consult Jason Lavery's book History of Finland, published by Greenwood Presss. He explains the surface area expansion process on page 19.