Take our world and look at its surface geography: we have continents and oceans, mountains ridges and canyons, and so on. To my knowledge, most of it has been shaped by tectonic activity (feel free to correct me).
I'm looking into other things that would reshape a world on a large scale. It can be natural phenomena or artificial activities, it can occur over millions of years or in a matter of hours or days, and so on. Anything you can think of, which realistically would be able to change a worlds geography.
To be clear, I'm not looking for "small" regional changes (Mount St. Helen comes to mind), I'm looking for something that would at least reshape a big chunk of a continent, if not more. At the same time, I don't want it to be so extreme to completely destroy the world (eg. Earth's early days meteor shower, which pretty much melted its entire surface, or worse).
Hope it makes sense...
EDIT: I've read some interesting replies so far. I'd like to point out that the changes I'm referring to would be noticeable on a world map. For example, the creation of new landmasses (eg. volcanic islands), their disappearance, or their movement. Seas and oceans, mountain ridges, stuff like that. Is there something that could explain the sea level lowering permanently, leading to new lands emerging? Other than volcanoes (and tectonic activity), are there other ways for mountains to form? Is there something that would explain a huge (as in the sized of a large nation like the US or China) depression to appear? Stuff like that...
