 It is possible that in AD 709 a storm washed away the strip of land that connected Jethou to Herm.About off the northern coast of Jethou is the islet of Crevichon, which measures about by , with an area of less than three hectares.To the west, between Herm and Guernsey, lies the channel Little Roussel (Petit Ruau); between Herm and Sark, to the east, lies the Big Roussel (Grand Ruau).