Every time I think about it, I feel compelled to think again: geologic changes are NOT supposed to happen in the blink of an eye, on a timescale of a mere 10,000 years. Yet at the very place where I live, Ottawa, a little over 10,000 years ago whales were swimming. How is that possible?
The answer is isostatic rebound. Up until about 13,000 years ago, this region was covered by the remnants of the last ice age, a layer of ice up to three kilometers thick. When this ice receded, the region was flooded by the sea, whales and all. This subsea was called the Champlain Sea, and may have been as much as 150 meters deep right here where I presently sit.
However, once the huge weight of the thick ice layer was gone, the Earth’s crust underneath rose up. This process is known as isostatic rebound. In a mere 3,000 years, the Champlain Sea was gone.
I suppose the same ice layer was also responsible for leveling the Ontario landscape such that this huge province, perhaps as large as France and Germany put together, has no point higher than 693 meters above sea level. Even tiny Hungary beats Ontario by more than a thousand feet!
I can see why people find geology fascinating.