Recent landslide events on the Mornington Peninsula have brought renewed attention to ground stability and the risks associated with building on or near slopes. While the January 2025 McCrae landslide is one of the most widely publicised examples, it is important to understand that landslide risk is not isolated to one location.
Landslides are rarely caused by a single factor. In most cases, they result from a combination of conditions such as rainfall, groundwater, drainage issues, vegetation removal and slope modification. Groundwater plays a critical role, with increased moisture reducing soil strength and stability.
The region contains a mix of granitic formations (e.g. Dromana Granite), sandy and clay soils, residual soils derived from rock weathering, weathered rock profiles (ranging from highly weathered to fresh rock), as well as alluvial soils (deposited by water) and aeolian soils (wind-blown sands).
In geotechnical terms, as outlined in AS 1726 Geotechnical Site Investigations, material behaviour is strongly influenced by the degree of weathering. Fresh rock typically exhibits high strength and stability, whereas weathered rock and soils often display reduced strength characteristics. Alluvial soils are commonly loose and compressible, while aeolian sands are typically cohesionless and can only maintain stability at limited slope angles.
Soft, loose, saturated or highly weathered soils are typically more susceptible to landslip, particularly where groundwater pressures increase or where additional moisture reduces friction between particles effectively acting like a lubricant and weakening the ground.
Landslides have been recorded across multiple locations within the Mornington Peninsula Shire under a wide range of conditions, including both coastal and inland environments.
Historical records, council data and regional studies indicate that slope instability has occurred periodically throughout the Peninsula, often associated with rainfall events, groundwater conditions, and localised ground characteristics.
While some events have been well publicised, many smaller or less visible landslips also occur and are documented through geotechnical investigations and council records. This highlights that landslide risk is not limited to isolated incidents, but rather forms part of a broader regional pattern.
Mornington Peninsula Shire applies the Erosion Management Overlay (EMO) to identify areas of potential instability. These overlays act as an initial screening tool and may be conservative in some cases.
Detailed geotechnical investigation is required to determine site-specific risk and support development approvals.
A landslide or EMO investigation typically includes a site inspection, subsurface investigation and detailed reporting. These assessments consider slope stability, groundwater behaviour, erosion potential and interaction with structures.
SITE Geotechnical provides locally informed investigations tailored to Mornington Peninsula conditions and council requirements.
⦁ Landslide risk assessments aligned with AGS guidelines
⦁ EMO investigations for planning permit applications
⦁ Geotechnical reports for building and subdivision
⦁ Slope stability and groundwater assessment
⦁ Foundation and retaining wall design input
Landslide risk across the Mornington Peninsula is influenced by multiple interacting factors. A site-specific geotechnical assessment is essential to properly understand and manage this risk.
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