Both his mother and grandmother were born and bred in Narooma so between conversations with them and family photos of the town, Mr King has considerable knowledge of how the town has changed over the last 100 years.

He is concerned that where Australia Rock joins the cliff face is steadily eroding.

Dr Chris Fergusson is a retired geologist and honorary fellow of the University of Wollongong who knows "quite a bit" about the geology of the area.

He said the coast has at least one major storm a year with waves six to seven metres high and pointed to many examples of coastal erosion transforming rock formations and the coastline.

These included Cathedral Rocks at Bombo, north of Kiama, and Berrewarra Point where the lighthouse is at Tomakin.

At Wollongong there are concrete blocks to protect the harbour from coastal erosion.

"They have to replace a certain number of those each year," Dr Fergusson said.

The rocks around Narooma are made from a very hard rock called chert.

However it has lots of fault lines, bedding planes and quartz veins.

Chert is made from the relatively hard and common mineral quartz.

Beach sand and shells are also made from quartz.

"Chert is a quartz cement," Dr Fergusson said.

"It is very small but sticks together to make big rocks.

"It has lots of bedding planes that make the rock face easier to erode than if it was solid quartz."

Dr Fergusson said climate change will make coastal erosion an increasing problem.

"As the sea levels rise, the oceans get warmer and the greater intensity of storms it is going to be a harder world to live in.

"I guess we are already seeing that," he said.

Mr King fears that when the join between Australia Rock and the cliff face erodes, Australia Rock will be lost forever.

"What would they do if one of the Three Sisters at the Blue Mountains was falling?"

A spokesperson for the NSW Department of Planning and Environment said "given the location of the formation in the coastal zone, it would not be technically or financially feasible to prevent physical coastal processes from affecting it and continuing to alter its shape over time".

A geotech survey was conducted by SLR Consulting Australia Pty Ltd in June 2022.

"The weathering process will more than likely lead to the collapse of the Australia Rock feature and regression of the cliff face as the chert geology unravels along natural foliations and defects," the report said.

"The timeframe for such events to occur is near impossible to state as the process is of geological time scales and directly dependent on environmental conditions."