5-11 Tyrendarra lava flow (South)

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.

Locality:	7221-675710 to 680663. Tyrendarra lava flow for a distance of five kilometres near Tyrendarra.
Access:	Princes Highway and Private roads.
Ownership:	Mainly Private. Public land in the south and adjacent to creeks.
Geology/Geomorphology:	The Tyrendarra flow as constricted through a narrow passage in the valley of the Fitzroy River at the point now crossed by the Princes Highway. South of here the flow broadened until a further constriction near Quamby Park (Frontispiece). In the northern part of this site the Fitzroy River and Darlot Creek are well-defined as twin lateral streams. This is particularly evident at the Princes Highway crossing. Of special interest here are twin parallel, sinuous ridges that extend for several kilometres on the flow surface. These are clearly defined south of the highway where they lie on the western side of the flow. The exact mode of evolution of these features is not clear. They may represent pressure ridges, side curtains, or a collapsed lava tube.
Significance:	National, or possibly International. It is possible that the significance of these features has been overlooked in previous investigations. Parallel ridges on a lava surface resulting from pressure developed at bottlenecks or constrictions along the flow are common, but the Tyrendarra ridges are unusually long, pass through the bottleneck relatively unaltered, and then extend a further four kilometres towards the coast. The site has been given a high significance rating although the classification and origin of the ridges is not clear. Their length, continuity, and configuration allows for comparison to be made with lava surface features from some of the classic volcanic localities in others parts of the world. Further detailed studies of the geometry and composition of the ridges is required to more accurately determine their mode of origin and hence their scientific importance on a national or international basis.
Management:	It is clear that any activity which disturbed the form of the ridges would be incompatible with their maintenance as a major site of scientific interest. Therefore any quarrying of the ridge material or alienation of land for large-scale construction purposes must be prohibited.

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