Geology and Natural History

Port Phillip Bay sits in an ancient rift basin shaped by deep faults and past volcanic activity.

The Selwyn and Tyabb faults helped lift the Mornington Peninsula above sea level and the rocky reefs to the shallows along the Mount Eliza coast. At various times in history, including the last 10,000 years, the bay was cut off from the ocean, becoming a landscape of low plains and winding river channels of the ancient Yarra River. This geological history is closely linked to the Bunurong people’s cultural and ecological connection to the region. Archaeological evidence shows near-uninterrupted human interaction with the coastal marine environment south of Rosebud for over 6,000 years. This marine interaction is only evidenced relatively recently in areas north of Rosebud, indicating re-filling of the Bay as we know it today occurred in the last 1,000 years.

Understanding Mount Eliza’s Underwater World The Mount Eliza rocky reef plays a vital role in the health of Port Phillip Bay:

• Ecological corridor: It connects important marine sanctuaries such as Point Nepean and Ricketts Point Marine Park, helping marine species move and thrive across the bay.

• Habitat support: The reef habitat can be considered analogous to known essential breeding and nursery grounds for diverse marine life (i.e. Ricketts Point Marine Park), supporting biodiversity and local fisheries.

• Unique geomorphology: Its steep cliffs, creeks, and seasonal streams create a distinctive coastal environment that helps the reef persist, even in areas impacted by dredging and commercial activity.