 Lihou is the furthest west of the Channel Islands and at low tide it is linked to the nearby L <unk> headland , on Guernsey , by a 400 m ( 1 @,@ 300 ft ) stone causeway . Apart from shingle beaches , the island has a 20 m ( 66 ft ) high ridge running approximately north @-@ south . Lihou is mainly composed of weathered rock below which are found granite and gneiss bedrock . The island has a mild oceanic climate like other Channel Islands , due to being buffered by the nearby English and French coastlines . Lihou shares the weather features of Guernsey , with winter temperatures falling to 4 @.@ 4 ° C ( 39 @.@ 9 ° F ) in February and summers with a high of 19 @.@ 5 ° C ( 67 @.@ 1 ° F ) in August . 
