A coastal landscape shaped by ice, tides, and tectonic shifts

Science · Published 20 October 2026 Swipe more like this →

In short: The Mornington Peninsula is more than a scenic getaway; it is a geological crossroads. From ancient glacial flooding to active fault lines capable of 7.5 magnitude earthquakes, the region's physical makeup reveals a violent and dynamic history of land formation.

The peninsula's current form was largely dictated by the end of a glacial period approximately 10,000 BCE, which led to the flooding of Port Phillip Bay. However, the coastline has been in flux for millennia; evidence suggests the peninsula may have extended into the bay during a period between 800 BCE and 1000 CE when the bay may have dried out. The landmass currently stretches roughly 40 kilometres from the mainland. Its eastern edges meet mudflats and mangroves in Western Port. The peninsula also serves as a physical barrier between Port Phillip and Western Port.

Geologically, the region is defined by complex structures including monoclines, synclines, and anticlines. It is crossed by several seismically active fault lines. The most significant is the 100-kilometre-long Selwyn Fault, which has the potential to produce earthquakes of around 7.5 magnitude. While the peninsula experiences many minor earthquakes annually, most are too small to be felt by residents. The topography transitions from flat northern plains to hilly southern landscapes. The highest point, Arthurs Seat, reaches 305 metres above sea level. This peak is situated remarkably close to the shoreline.

A 5.0 magnitude tremor hit the southern Tyabb Fault's end near Flinders on 7 July 1971, marking the most recent major seismic activity. This tectonic activity, combined with the peninsula's role in separating the waters of Port Phillip from Bass Strait, creates a unique maritime and geological environment that continues to shape the coastline today. The coastline spans approximately 190 kilometres in total. The western shore features sheltered bays and headlands. In contrast, the southern coast becomes very rocky between West Head and Cape Schanck.

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