Cape Nelson

This information has been obtained from the report: Eruption Points of the Newer Volcanic Province of Victoria by Neville Rosengren. This report was published in 1994 and was prepared for the National Trust of Australia (Victoria) and the Geological Society of Australia (Victorian Division). The review of eruption points was based on an earlier unpublished manuscript Catalogue of the post-Miocene volcanoes of Victoria compiled by O P Singleton and E B Joyce (Geology Department, University of Melbourne 1970).

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 value. Reference should be made to the most recent reports. See the Earth Science Heritage (external link) section of the Geological Society of Australia website for details of geological heritage reports, and a bibliography.

Location:	38 26 00S 141 33 00E (external link); 7221-3-3 (Grant Bay) 480459, 10 km SW of Portland, Cape Nelson Road, Heywood
Land Tenure/Use:	Public land. Difficult and in places dangerous to access the significant exposures.
Type 9:	Composite eruption point. Cape Nelson and Cape Sir William Grant are peninsulas of volcanic rocks overlaid by sedimentary rocks, dominantly limestone and calcarenite dune limestone. In the high, steep coastal cliffs there are several basalt lava plugs marking eruption points, and associated lava flows and tuff beds. These volcanic structures suggest that the capes are the eroded remnants of a larger volcanic system, the southern parts of which have been faulted (caldera subsidence) and/or eroded to form the arcuate Nelson Bay and Grant Bay. On Cape Sir William Grant, three unusual eruption structures (“The Wells”) exposed along the shoreline are the tops of small adventive or parasitic cones built on the flank of the larger volcano. They are seen in cross-section as plugs of volcanic fragments filling a near-circular pipe in basalt. Along the northern shore of Nelson Bay between Cape Nelson and Cape Sir William Grant is a thick sequence of sediments (Lower and Upper Nelson Bay Formation and Bridgewater Formation) filling a synclinal depression in the volcanic surface. Different styles of unconformable contact between these formations and mild deformation (folding) is evident in coastal cliff sections. The coastal cliffs here are among the highest on the Victorian coast and are exposed to very strong wave action resulting in impressive displays of wave break and reflection. 90 m; 90 m.
National:	The coastline exposed a rich variety of volcanic structures including the unusual parasitic cones known as “The Wells”. Along with Cape Bridgewater, it forms part of a distinctive volcanic complex which has no counterpart on the Australian coast. It is an outstanding site to study the details of volcanic processes in the early (Pliocene) phase of the Newer Volcanics Province. It is one of only three sites in the Newer Volcanics Province where caldera formation has been interpreted. The northern coastline has an excellent display of different limestone sediments and is an important stratigraphic site for tracing Plio-Pleistocene stratigraphy in western Victoria.
Class 3:	The site needs detailed planning to allow visitor access to safely view the significant features. The eastern side would be threatened by expansion of the Portland aluminium smelter or other industrial works.
References:	Coulson, A. 1941. The volcanoes of the Portland District. Proceedings of the Royal Society of Victoria 65, pp 113-124. Boutakoff , N. 1963. The geology and geomorphology of the Portland area. Geological Survey of Victoria Memoir 22. Ollier, C.D. & Joyce, E.B. 1964. Volcanic physiography of the Western Plains of Victoria. Proceedings of the Royal Society of Victoria 77. Pp 357-376. Nicholls, I.A. & Sukhyar, J. 1984. Volcanic centres of Portland-Heywood district - age and geochemical characteristics. Volcanics Workshop 1984, Monash University, Melbourne (unpubl.)

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