Site 36 Mt Fraser - Eruption Point

This information has been developed from one or more of these publications:

Sites of Geological and Geomorphological Significance in the Westernport Bay Catchment (1984) by Neville Rosengren.
Sites of Geological and Geomorphological Significance in the Western Region of Melbourne (1986) by Neville Rosengren
Sites of Geological and Geomorphological Significance on the Coast of Port Phillip Bay (1988) by Neville Rosengren.
Sites of Environmental Significance in the Flood Plain of the Upper Yarra Valley Region (1983) by Neville Rosengren, Douglas Frood and Kim Lowe (as part of a study of Sites of Environmental Significance by the University of Melbourne for the then Upper Yarra Valley and Dandenong Ranges Authority).

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 for details of geological heritage reports, and a bibliography.

Location:	CLONBINANE 5000/04.01 E21400 N51900
	5 km south of W Wallan.
Access:	Donovans Road.
Ownership & Municipality:	Private Land, Shire of Kilmore.
Site Description:	Mount Fraser (435 m) is a large scoria cone complex with two craters. The diameter of the base average 1 200 m and the highest point on the rim rises 125 m above the basalt lava plain immediately east of the Hume Freeway. It is a relatively simple volcanic structure with no tuff ring or parasitic cones. There is a wide, shallow crater open towards the south-west and a smaller closed inner crater. The cone is the youngest element of a volcanic system that includes a large are of lava flows. The system first erupted large volumes of fluid basalt and was the source of much of the lava that flowed along creek valleys tributary to the Yarra River. Potassium-argon dates between 1.06 and 0.82 million years for the lava flows five a maximum age for Mt Fraser as the scoria cone was the final phase of the eruption process. The cone has step, straight sides and a high, intact northern rim but the southern rim has an uneven margin. This may be due to there being several closely spaced vents, to uneven fire-fountaining of scoria during eruption, or collapse or breaching by explosion or outflow of lava. The only natural exposures of rock on the cone are in the lava flows around the base. A large scoria quarry operating at the 350 m level on the southern slope is a major supplier of scoria for Melbourne. The quarry exposes bedded coarse scoria with occasional volcanic bombs. Studies of the ejecta have shown it to be from a primary mantle-derived magma. The scoria is a relatively minor component of the total volcanic ejectamenta but forms the most conspicuous topography of the area.
Significance Rating:	State
	This is the largest scoria cone near to Melbourne and ranks as one of the larger on a comparative scale with other cones in the Newer Volcanic Province. Its location on a low elevation lava plain with little relief makes it a conspicuous element of the terrain of the plains north of Melbourne. It provides a clear illustration of the typical form of a simple scoria cone with straight sides and a well-defined base contour. It occurs to the western limit of Newer Volcanic activity and is one of the younger volcanic features of the Melbourne district. It is one of a very small number of scoria cones in the eastern (Melbourne) sector of the Newer Volcanic Province. Peridotite inclusions in basalt ejecta from Mt Fraser have been used in developing models of petrogenesis of Newer Volcanic basalts. Mt Fraser is also significant as a source of lava flows that filled the valleys and some of the northern tributaries of the Yarra River. It is possible that this volcano provided the lava that filled the ancestral Merri and Darebin Creeks and continued along the Yarra valley.
Site Sensitivity:	Class 2.
	A large part of the western and southern scoria rim has been removed by quarrying. The area available for quarrying needs to be defined in relation to its impact on significant volcanic features.
References:	Edwards, A. B. 1938 The Tertiary volcanic rocks of central Victoria. Q. J. geol. Soc. Lond. 94: 243-320. Hanks, W. 1955. Newer Volcanic vents and lava fields between Wallan and Yuroke, Victoria. Proc. Roy. Soc. Vict. 57L 1-16. Vandenberg, A. H. M. 1973 Geology of the Melbourne district, in McAndrew, J. and Marsden, M. A. H. Regional Guide to Victoria Geology: Unit of Melb. 1973. Vandenberg, A. H. M. 1991 Report on the Kilmore 1:50 000 Geological Map. Geol Surv. Vic. Rept. No. 91.

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