Rottnest Island Geology

One of the biggest impacts to change the natural environment of Rottnest Island is a change in sea level. Through the Island’s geological features, a story of sea-level change can be told that spans over 140,000 years.

Rottnest wildlife

Rottnest Island is the largest island in a chain of limestone islands and reefs on the continental shelf opposite Perth. The island is characterised by alternating limestone headlands and bays with white sandy beaches. The coast is fringed by shoreline platforms and offshore ‘reefs’ formed by marine planation (levelling out of land surfaces).

Sea levels have fluctuated which have continually shaped the formation of Rottnest Island. When sea levels were much lower than present levels, Rottnest Island wasn’t an island; it was actually connected to the mainland. It remained in connection with the mainland along this belt of dunes until final separation occurred about 6,500 years ago.

One location that provides evidence of Rottnest being submerged are the salt lakes. Initially sheltered marine environments, the salt lakes were formed by the collapse of cave systems, which filled with sea water as a result of rising sea levels. Once cut off from the sea, they became highly saline lakes. Evidence of this can be seen along the shore where tubeworm cases and seashells exist. 

Major changes in the flora and fauna follows this separation with only a few of the original plants and animals surviving. The sole marsupial to remain on the land was the quokka.

Areas of geological significance include, but are not limited to the Salt Lakes, West End, Parker Point and The Basin.