4-9 Tumuli on Harman Valley lava flow at Wallacedale

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:	7222-757004. Four kilometres south-west of Wallacedale.
Access:	Wallacedale-Byaduk Road.
Geology/Geomorphology:	The Harman Valley lava low is a young valley flow originating in the last stage of volcanic activity at Mount Napier. Approximately 12 prominent tumuli are found on the southern side of the flow at Wallacedale. These are dome-shaped mounds of basalt 5 to 7 metres high with a diameter of 30 metres, and are strongly fractured or jointed.
Significance:	National. The mode of elevation of these features is not entirely clear - early investigators described them as lava blisters formed by stream pressure from swamp waters covered by the hot lava. More recently, they have been considered as upwellings of the lava surface due to localised pressure variations in the flow, as it seems apparent that the tumuli are solid throughout whereas true lava blisters are hollow.
Management:	The features must be preserved in their entirety and any removal of lava material should be absolutely prohibited.
Reference:	Ollier, C.D. and Joyce, E.B. (1964). 'Volcanic physiography of the Western Plains of Victoria', Proc. Roy. Soc. Vic. 77 (2) : 357-386.

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