The Shark Bay World Heritage Area is defined by striking contrasts between land and sea. Red sand dunes on Peron Peninsula roll into white beaches and clear waters, while to the west pale dunes and rocky headlands culminate in towering sea cliffs. These landscapes are shaped by two dominant geological materials: red Peron sandstone and white Tamala limestone.
Although visually timeless, Shark Bay’s geology is dynamic. Areas that were once dry land during the last ice age are now submerged, and vast seagrass meadows trap sediments that alter salinity, tidal flow and ecosystems. These ongoing processes underpin Shark Bay’s global geological significance.
Geological History
Over the past two million years, sediments eroded from inland ranges were transported by wind and water and deposited around what is now Shark Bay. Quartz sands accumulated against ancient ridges and formed rolling dune systems. These wind-blown red sands became Peron sandstone, which underlies much of Shark Bay and is exposed on Peron Peninsula and nearby islands.
Later, white Tamala limestone formed from broken shells and coral blown inland during periods of lower sea level. These deposits now make up Edel Land Peninsula and offshore islands. Together, Peron sandstone and Tamala limestone record cycles of aridity, wind and changing sea levels.
Zuytdorp Cliffs
Forming the western boundary of Shark Bay, the Zuytdorp Cliffs rise up to 200 metres and stretch more than 200 kilometres. They are the longest fault scarp in Australia and are constantly shaped by powerful Indian Ocean waves, creating dramatic features such as blowholes, wave-cut platforms and spouts.
Composed of Tamala limestone, the cliffs formed around 5,000–10,000 years ago following movement along a fault line. Their scale, geology and exposure make them one of Shark Bay’s most spectacular World Heritage features.
Changing Coastline
Shark Bay’s peninsulas, islands and bays are the result of fluctuating sea levels, winds, waves and earthquakes over the last two million years. During glacial periods, sea levels were far lower and the coastline lay up to 100 kilometres further west than today.
As the most recent ice age ended about 10,000 years ago, rising seas flooded low-lying areas, isolating Dirk Hartog, Bernier and Dorre Islands and shaping the bay’s modern form. These changes created the complex coastline that characterises Shark Bay today.
Birridas
Birridas are shallow, salty depressions formed from ancient landlocked lakes that dried as sea levels fell. They range from small circular hollows to elongated basins several kilometres long and are a distinctive visual feature of Shark Bay, contributing to its World Heritage listing.
After rain or during high winter tides, birridas can temporarily fill with water, triggering blooms of small invertebrates that attract migratory shorebirds. Many occur within Francois Peron National Park, where some are connected to the sea, forming shallow lagoons that act as important fish nurseries.
Salinity
Shark Bay is one of the few marine environments in the world with hypersaline waters. High evaporation, low freshwater input, restricted ocean circulation and shallow seagrass banks combine to concentrate salt in the southern parts of the bay.
Areas such as Hamelin Pool are almost twice as salty as the open ocean, creating conditions that support unusual ecosystems. These hypersaline environments, shaped by geology and climate, are central to Shark Bay’s outstanding universal value.
