I have enjoyed a few days in Anglesea on Victoria’s coast. The sea imposes a moderating influence on the weather. It was a cool and pleasant interlude while at home it was hot. Adding to my personal sense of moderation was the pleasant company and generous hospitality of the very good friends I was staying with.
Anglesea is towards the eastern end of the Great Ocean Road. If you’re traveling east to west it’s where the journey starts to be interesting. The road is Victoria’s premier tourist attraction and although I have mixed feelings about it there is no doubt that it is both visually splendid and worth a fortune to the state’s economy.
It’s been in the news a bit lately because, woe be upon us, erosion. The media have been discussing the impending crisis in terms of climate change and sea level rise. Thousands of tourists travel thousands of miles to see the effects of thousands of years of erosion. Sea stacks, arches, steep cliffs are all the result of erosion. And we’ve just started making a fuss about … erosion.
Coasts can be classified in several ways one way is to divide them into coasts of submergence and coasts of emergence. There are nice examples of both in the map above. To the right is Port Phillip Bay. At the height of the last glaciation the Yarra River ran across a plain and discharged into the ocean at the heads. As the sea rose the plain was inundated providing Melbourne with a large bay to sail around looking at a coast of submergence. For most of its length the Great Ocean Road skirts a coast of emergence.
Emergent coasts are a result of local tectonic uplift of the land surface or a fall in the elevation of sea level because of a reduction in the water volume of ocean basins. Quite often, emergent coasts have rocky coastlines with cliffs and nearly flat platforms that extend inland where older coastal plains have been tectonically raised and are now elevated above the modern land and water interface.
Another way of classifying coasts is as erosional or depositional.
In places where there is an abundance of wave energy or ocean currents and/or a lack of sediment available for deposition, erosion of the coast will be the dominant mechanism of change. Quite often, erosional coasts are narrow and characterized by resilient rocky shorelines that are exposed to high energy waves and supply relatively little sediment to the adjacent shore.
Where deposition dominates the land is advancing, where erosion dominates the land is in retreat.
One of the features people go to see is the Twelve Apostles.
There were never twelve but there’s one fewer today.
These stacks are formed of limestone that was laid down under the sea about 23 million years ago. The region was subsequently uplifted. The seaward edge of the uplifted land has been undergoing erosion ever since. At the height of the last glaciation, 21,000 years ago, sea level was about 125m lower than at present. (And has been as much as 2m higher in the intervening period.) The cliffs and stacks we see today have been carved out by the Southern Ocean since then.
The sea may have a moderating influence on the temperature but it can have a savage impact on the land. That bulge in Victoria’s coast and the Southern Ocean are not in equilibrium. The sea will continue to eat that coast regardless of further sea level rise.