1-19 Glenaulin landslips and Lake Crawford

This information has been developed from the publications:

An assessment of the Geological/Geomorphological Significance of Private Land in the Shire of Portland (1981) by N. Rosengren, J Mallen, T Shepherd.

Geological heritage sites, including sites of geomorphological interest and volcanic heritage sites, are under regular revision by the Geological Society of Australia, especially in the assessment of significance and values. Reference should be made to the most recent reports. See the Earth Science Heritage section of the Geological Society of Australia website (external link) for details of geological heritage reports, and a bibliography.

1. Western Landslips

Locality:	7122-359024. Six kilometres north-east of Greenwald.
Access:	Koonalunda property. Big Hill Road.
Geology/Geomorphology:	A massive rotational slide has exposed sediments of the Heytesbury Group in a headwall 10 metres high. The exposures are of highly fossiliferous light grey marly limestone of the Glenaulin Clay Member and orange brown polyzoal limestone of the Wataepoolan Limestone Member.

2. Eastern and Southern Landslips

Locality:	7122-366026. Six kilometres north-east of Greenwald.
Access:	Koonalunda property.
Geology/Geomorphology:	Extensive, active landslips on the eastern side of the Crawford River expose sediments of the Heytesbury Group. The beds are recognised as being the type sections of the Glenaulin Clay Member, the Koonalunda Lens and the Wataepoolan Limestone Member of the Gellibrand Marl. The landslips are massive, complex features and are amongst the largest rotational slide or slump forms in Victoria. Below the headwall scarp are large, fractured slump blocks showing backward tilt. Small areas of swamp are impounded behind these tilt blocks. an earthflow at the base of the slide displays parallel compression ridges and furrows. These landslides have blocked the Crawford River and the river waters have backed up for approximately three kilometres to form the partly swamp filled Lake Crawford. The lake has overflowed the rock and earth dam created by the landslide and the river valley is now strewn with large boulders of yellow-grey fossiliferous limestone of the Wataepoolan Limestone member, over a distance of 300 metres.
Significance:	State. This is one of the largest active landslips in Victoria and is a classic example of a rotational slide and earthflow. It is one only three known instances in the state where lakes have been formed by landslides damming a river valley. The exposures in the headwall are used as type sections.
Management:	Because of the particular interest of the landslide dam across the Crawford, it is recommended that the lower sections of the landslip be left undisturbed. Artificial slope restoration or quarrying and removal of the limestone boulders in the river should be prohibited

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