The island is divided into three distinct areas. The fertile in-bye land lies to the east of the hill dyke and just beyond that to the west the island is bisected by a belt of glacial moraine about one and a half kilometres in length. Much of the rest of the area consists of a shallow stony soil probably derived from glacial till. There is also evidence to suggest that Shetland had its own ice cap.

The 21 miles of ruggedly beautiful coastline contain a wide range of volcanic, metamorphic and sedimentary rock formations. Papa Stour rocks originate from the Devonian age when Shetland was south of the equator and conditions were generally hot and dry with occasional very wet periods. The structure of the island is typically made up of ashes and lavas from the volcanic activity associated with this period.

The island is exposed to severe winter gales and is gradually being eroded. During one storm in 1953 the well-known headland, “The Horn of Papa” crashed into the sea and in 1981 one of the lochs above Kirsten’s Hole collapsed into the cave below. Wind, wave and tide combine with its unique geology to create the island’s distinctive and beautiful cliff scenery, with an abundance of geos, stacks, natural arches and caves. The latter having been described as some of the finest in the British Isles by the naturalist J.R.Tudor in his book “The Orkneys and Shetland” published in 1883. Of further geological interest is a Devonian fish bed at Lambar Banks, which due to its fragile state, is not to be disturbed by the removal of rock samples.