A photo essay on the limestone at the mouth of the Margaret River.
The Margaret River empties into a sandy bay sheltered from the north by a limestone Cape. It is a complex liminal space, where fresh and salt water, land and sea meet. The delicate sculptures along the shoreline are easy to overlook. Margaret River has a spectacular coastline, and it’s easy to miss the small-scale beauty in the landscape in favour of those famous grand ocean vistas.
The present Rivermouth was not always the shore. The sea has been at its current level for around 8000 years, creating an illusion of stability. The sea has encroached and receded from the land multiple times within human experience. At the height of the last ice age around 17 000 years ago the sea was 30 to 40 kilometres further west of its current position. There have been many Rivermouths over time, all of them drowned by the waves.
The physical process is still occurring on a smaller scale. It can be seen in action at Cape Mentelle, the limestone headland that runs north from Rivermouth beach. The heavy waves rolling in off the Indian Ocean concentrate their weathering in the intertidal zone, undercutting the limestone and causing sections to collapse. The reefs surrounding the Cape are wave-cut platforms, remnants of the western side of the headland already devoured by the sea.
Now there is a new force impacting on the stability of the limestone. Since Europeans arrived in the 19th century, human pressure on the fragile coast has risen astronomically.
In the 1860s cattle were introduced to the dune system, and the sand began shifting. In the 1920s marram grass was imported and planted to stop the dunes encroaching on the river. A new dune grew, anchored by the marram grass, and changed the course of the river.
The cattle have long gone, but there are new impacts on the fragile ecosystem. In the early days of private vehicles, locals drove all over the coastline, causing huge sand ‘blowouts.’ During the 1980s and 1990s, many of these were repaired, and public education about staying off the dunes had some effect. More recently, with so many people unfamiliar with the ways of the coastline, this early restoration work is being reversed.
Since the 1980s the population of the Augusta-Margaret River Shire has tripled. Add to this thousands of visitors drawn to the area every week (pre Covid 19), and the visible impact on the coast has increased dramatically. Vegetation is trampled and dunes eroded by people who have no conception of the long term impact they are having.
The limestone cliffs at Cape Mentelle are particularly fragile. Weathering has sculpted beautiful shapes, but it only takes one footfall for them to crumble away. People are fascinated by the sheltered coves, and scramble down the sculpted cliffs to access the shore, as there are no paths down the steep inclines.
The Tamala limestone of Western Australia is ‘aeolian’, or made in the air, rather than under water. It is soft, fragile and crumbling. The limestone is unstable and can be dangerous. The edges at Cape Mentelle are undercut, and many people seem unaware of this and walk right to the edge. Some ledges near the Cape to Cape Track, where it heads south to the Rivermouth, have cracks in them. It is only a matter of time before they collapse and tumble 50 metres down to the sea.
There have been coastal tragedies before. In 1996 a cave collapsed on a group of people on the beach at Gracetown. Finding ways for people to safely enjoy the landscape while protecting its fragility is not easy. Putting up signs and barriers would impact on the wild aesthetic of the place, but may be necessary for safety and to maintain the long-term integrity of the fragile National Park.
Tread lightly, look closely, and enjoy the view!
Traditional custodians have been leading some of the restoration works along the coast. They can be contacted through the Undalup Association.
Nature Conservation Margaret River co-ordinates some of the coastcare around the Margaret River
The Friends of the Cape to Cape Track co-ordinate some coastal monitoring and coastcare activities
The Augusta Margaret River Shire oversees ongoing geological risk assessment and management along some areas of the coast