 About ninety percent of the archipelago's population lives on Fasta Åland.Its area is difficult to estimate due to its irregular shape and coastline, but estimates range from 740 square kilometres to 879 square kilometres to over 1,010 square kilometres, depending on what is included or excluded.On the east side of Fasta Åland is a large bay, Lumparn, which is now believed to be the impact crater from a meteorite impact about 100 million years ago.