Gradualism emphasizes slow changes on Earth over long periods of time, while catastrophism emphasizes change through natural disasters.
I would like to refer you to this website, it has everything you are asking about--
http://thediplomat.com/2015/01/china-the-influence-of-history/
Hope this helps!
Because hot air is less heavy cold air is more heavy causing them to shift if cold air is placed on top.
I would think the erosion and wethering im just guesting since i dont know if theres any answer choices