Phillip Island Excursion Site 3: Kennon Head

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Kitty Miller Bay, Phillip Island
Kitty Miller Bay, Phillip Island

At the southern end of Kitty Miller Road there is parking at Kitty Miller Bay from where you can visit three points of interest. The first is the rocky headland to the west called Kennon Head. Go down the steps and around the beach and headland. Be careful on the rocks. This is about 2 kilometres return—approximately 1 ½ hours return.

Notice from your geological map that Kennon Head is a basalt outcrop that forms part of the Older Volcanics. This outcrop was once an island (as was The Nobbies) but it is now joined to the rest of Phillip Island by a huge sand dune deposit. The structure that joins a rocky island to the mainland is called a tombolo. In this case the area is called the Summerland Tombolo Complex. You can see the location of the dunes on the geological map.

Of geological significance at Kennon Head are two dykes that intrude the basalt platform to the south and west of the Head. A dyke is formed when lava flows through a wide crack in the earth and so it looks like a wide band of different rock that cuts across the basalt surface. Dykes are usually the conduit through which the molten magma flows to the surface.

Zeolite mineral deposit in small cavities in basalt cobble.
Zeolite mineral deposit in small cavities in basalt cobble.
Also significant is a large zeolite chamber over 1.5 metres long and 25 cm wide that has been broken open so you can see inside. See if you can find the dykes and the chamber but don’t take risks. Make sure you remain alert to danger from the sea, especially unpredictable waves.

As you walk along Kitty Miller Beach toward Kennon Head, you will notice an impressive layer of columnar jointed basalt in the distance sitting on the top of the higher wave platform. Extending from this platform to the base of the bluff is a stranded boulder rampart 1–1.5 metres above high water mark and now covered with vegetation. The boulders are similar in size to those of the modern beaches (up to 20 cm long) and appear to have been put there by storm waves when the ocean level was slightly higher than it is now.

Recall that the black basalt outcrops formed from a flow of volcanic lava. Imagine what it was like when it was still red hot and flowing. Note the appearance of the basalt rock. Check the colour and jointing. How tall are the columns? Check for holes (vesicles) in the basalt. Are there any minerals in the holes? Are there any mineral deposits in the joints?


These deposits illustrate the extent of the volcanic eruptions with one lava flow indicated by the height of the columns. The holes (vesicles) in the basalt point to the release of gases during the eruptions. The flat surfaces between the lava flows indicate that there was not a lot of time between flows. The cliffs and rock platforms were eroded as the water receded from the land late in the Flood, and in the 4,500 years afterwards.

Guide available as a booklet
This entry is taken from the geological excursion guide for Phillip Island. The complete guide is available as a booklet on Aussie store.