Poon Saidak Cliffs

The Poon Saidak Cliffs on the northern coast of Christmas Island represent the most dramatic expression of the geological contrast that defines the island's character, where the volcanic plateau that forms the interior of the island ends abruptly at the coast and drops vertically for nearly three hundred metres into the Indian Ocean. From the cliff top the view is vast and windswept, with the full width of the eastern Indian Ocean visible on clear days, and the constant sound of the ocean swell crashing against the black basalt base far below creates a sensory environment unlike anything on the more temperate coasts of mainland Australia.

The cliffs at Poon Saidak are particularly impressive in their scale and their abruptness, the land simply ending at the cliff edge with no coastal plain or beach to soften the transition between terrestrial and marine environments. At the base of the cliffs the ocean swells that have travelled unobstructed across the full fetch of the Indian Ocean break against the volcanic rock with a force that sends spray high above the cliff top on the biggest swells, and the sound of the waves below is audible from the cliff top even when the wind is light, a constant low thunder that marks the boundary between the plateau forest above and the ocean below.

The cliff top is covered in the island's characteristic old-growth rainforest, but the canopy thins dramatically within a few metres of the cliff edge as the shallow soils give way to exposed rock and the wind exposure increases, creating a zone of transition between the sheltered forest interior and the fully exposed cliff face. This transition zone supports a distinctive set of plant species adapted to wind and salt spray, including the endemic Christmas Island jade vine and several species of pandanus that are found only in this narrow coastal fringe.

The seabird colonies nesting on the cliff face below are an important component of the cliffs' ecological significance, with red-footed boobies, white-tailed tropicbirds and great frigatebirds all nesting on the cliff ledges in significant numbers, their white droppings visible as a pale band across the dark basalt face from the cliff top above. The sight of frigatebirds soaring on the updrafts generated by the cliffs, their distinctive angular wings held motionless as they ride the rising air, is one of the most memorable avian spectacles available on the island and provides a direct visual demonstration of how the geological structure of the island has shaped its ecology.

The blowholes at the base of the Poon Saidak cliffs are the most spectacular coastal geofeature on the island, created when wave action forces air and spray through natural fissures in the basalt and limestone rock with enough pressure to create dramatic vertical eruptions of spray above the cliff top. The blowholes are most active when a significant swell is running from the southwest, and the associated sound of compressed air escaping through the rock creates a sound like a bellows or a slow exhalation that can be heard from the cliff top before the spray becomes visible.

They are the most dramatic expression of Christmas Island's geological character, where the volcanic plateau ends abruptly at the ocean in a three-hundred-metre vertical drop visible across the full width of the eastern Indian Ocean.

The seabird colonies nesting on the cliff ledges provide one of the most accessible and impressive seabird observation opportunities in the eastern Indian Ocean.

The blowholes at the base of the cliffs are a spectacular display of wave energy interacting with the island's volcanic rock formation.