This is a video of some sandstone near Balmoral beach in Sydney Harbour. I think these colours of brown, green and blue are very typical of Sydney harbour.
But yesterday I accidentally someone here eating his breakfast who actually knew about the geology of Sydney harbour.
According to him, the harbour is a "sunken valley". 7,000 years ago, the coastline was several kilometres East and the harbour was a valley. (note, this is not long ago. I have reached an age where I feel I know some people who were around then!!!). There would have been Aboriginal settlements in this valley.
Then over time the sea level rose and flooded the valley, creating Sydney Harbour. That is why the harbour is not like a normal river estuary, which might have a wide mouth surrounded by sand dunes. The mouth of Sydney harbour are cliffs only a couple of hundred metres apart. There are places in the upper reaches of the harbour which are deeper than the water at the mouth of the harbour.
Of course the sandstone of this river valley is a sedimentary rock, which was at one time at the bottom of a sea, but this happened millions, not thousands of years ago.
So the colours of the harbour are not only beautiful, they have an interesting history.
I suppose the seas rose at the end of the last Ice Age, creating rising sea levels and flooding the harbour.
ReplyDeleteSounds reasonable, so I consulted Wikipedia to learn more about ice ages. The theory now is that there were several down the millennia, the last starting 2.6 billion years ago. One opinion is that we are now at the last stages of this ice age, because of the existence of ice sheets in Greenland and the Arctic. However, the warming goes in fits and starts, with glacial (cold) and interglacial (warmer) periods. We are now in an interglacial period, the last glacial period being about 10,000 years ago. That would fit in with the idea that the seas started rising then.
DeleteIncidentally, the measurements indicate that the seas rose by 19 centimetres over the 20th century. Did anyone notice? I didn't and I lived through half of it.
Climate is complicated and is always changing. Another example is the very cold weather around 1816, which was called "the year without a summer". There is a theory that this was caused by a large amount of volcanic activity around that time. A byproduct of this cold weather was Mary Shelley's novel "Frankenstein". She was on holidays in Switzerland, but was cooped up at home all the time and thought of the plot for the novel. If you read Frankenstein, you can see all the descriptions of Frankenstein's monster walking though very cold, snowy weather.