Rock layers at Point Ritchie-Moyjil show the influence of very different climate conditions over the past 300,000 years. Sea level has risen and fallen – at its highest reaching present levels about 125,000 and 220, 000 years ago. During these times of higher sea level and milder climate (called Interglacial Periods) dunes formed on ancient coasts just as they do today (we are living in an Interglacial Period). Over time the sand grains were cemented together and the loose sand became a rock called calcarenite. The large hill to your right is a sand dune formed 125,000 years ago. The rock stack at the sea’s edge opposite the lookout behind you is the remains of an older dune – formed over 200,000 years ago. Remains of a beach from 125,000 years ago are also preserved at Pt Ritchie. Sea level then was about 3-5m higher than now.
Between these Interglacial Periods the Earth was colder and sea level fell. The fall in sea level is caused by ice build-up on the continents – leaving less water in the oceans. These cold times are called Glacial Periods or Ice Ages. Dune building ceased here at these times and terra rosa (“red earth”) soils developed on the now stable dune surface. Natural cement layers, called calcrete formed at the base of the soils because of the dry conditions. One rock layer at Pt Ritchie consists of a one metre thick dust storm deposit (loess) reflecting these arid times.
Also preserved here is evidence of ancient earthquakes and a volcanic ash mantle, a legacy of the Tower Hill eruption 35,000 years ago. Tower Hill is one of the largest maars in the world and was formed when groundwater came into contact with hot rising basaltic magma. Tower Hill is included in the Kanawinka Geopark, a region of south-west Victoria and south-west South Australia that encompasses the the Newer Volcanic Province of Southeastern Australia.
It is hard for us to imagine the violent events that have shaken this headland in the past. Moyjil has evidence that it was occupied by Aboriginal people during these dramatic natural events.
