Phillip Island Excursion Site 4: Kitty Miller Beach and Watt Point

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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 Kennon Head described at Site 3. The second is Kitty Miller Beach itself and the rocky outcrops to the east. Go down the steps to the beach and east over the beach to the first few rocky outcrops towards the headland called Watt Point (about 1 kilometre return). Be careful on the rocks.

Sand clast shape and arrangment
Sand clast shape and arrangment
Note the sand on the beach. Check the grains, size, roundness, composition. Note that the sediment is loose. What would need to happen for the sediment to become hardened sandstone?

Note the black basalt outcrops on rocky headlands to the east (and west) of the beach. This basalt hardened from a flow of volcanic lava. Imagine what it was like when it was still glowing red hot and flowing over the land. Note the appearance of the basalt rock. Check the colour and jointing. Can you see any layers that represent one lava flow? How thick are the layers? Check for holes (vesicles) in the basalt. Are there any minerals in the holes? Are there any mineral deposits in the joints? Note from your geological map that these rocks are called the Older Volcanics.

Sediment size classification
Sediment size classification
Note the beach to the east and near the sandy bluff is strewn with rounded cobble sized rocks. Check the composition of the cobbles. Where do you think they have come from? Agates and zeolites are often found in the cavities, or vesicles, of the cobbles, gravels, and rock outcrops here. Good specimens are popular with mineral collectors. See if you can find some.

Note the contact between the sandy/cobbly beach and the black basalt headland. Which was deposited first, the sand or the basalt? How do you know?

Basalt rock platform at Kitty Miller Bay
Basalt rock platform at Kitty Miller Bay. Black basalt in foreground, red agglomerate in background and Kennon Head in distance to right.
Note the steep beach embankments around the rocky headland. Note that the basalt in these embankments has been weathered and is crumbly. Note that the soft material in the embankments still show signs of vertical columns in places—the remnant of an original columnar basalt deposit. Note that there is a second sort of rock in the headland—one that is red to orange, indicating it is iron-rich. Does it lie under or over the black basalt flow? If you can get a good look without putting yourself in danger, note that the layer is up to 1 metre thick and composed of rounded cobbles in a fine matrix. It looks like a sedimentary rock and is interpreted as a volcanoclastic deposit, i.e. a deposit where the volcanic material has been ripped up and reworked by water. Specifically it is described as agglomerate which is a coarse accumulation of large blocks of volcanic material that contain at least 75% rounded volcanic bombs—ejected lava that assumes a round shape. But it’s often subjective to say that these rounded rocks were bombs and not just water-rounded stones. This red layer forms part of the Older Volcanics (see geological map).


These deposits show that the basalt lava was erupting over the landscape while there was much flowing water and sedimentation—a situation that is consistent with the Flood. You can also see something of the way the basalt was altered after it was deposited, producing soft bleached soil in the bluffs.

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.