What would change if our earth lacks mountains?

Question

I just asked myself what is the role of the mountains on our planet earth? Well there's a well known role for the climate and weather.

But is there a kind of physical or geological role? What would happen if our earth lacks the mountains on it? Will we have more earth "Movements" (earthquakes, tectonics...) i suppose erosion will be much heavier then it is now. And therefore i suppose that human life in such a planet would be impossible.

In the Answers i would like to consider two scenarios:

1. Earth as we know but without mountains (mountains have never been formed or don't exist at all)
2. What will happen if the Mountains would just been taken away?

Well i would like to get some kind of scientific answer from a geological point of view!

Answer 1

Well, mountains are not a cause. Mountains are an effect. It's not that we have earthquakes because we have mountains. We have mountains because we have earthquakes.

Earth as we know but without mountains (mountains have never been formed or don't exist at all)

So by saying that mountains never existed at all, you are implying there are no tectonics. That would be a sad thing - one of the things that make Earth so alive and interesting is the fact that we have plate tectonics. Go and have a look on Mars, the Moon, etc. There are no active tectonics there are those are dead places.

What will happen if the Mountains would just been taken away?

They would just form again. First of all, there would be the effect of isostatic rebound. When you take away a certain mass from an elastic thing, that thing bounces back up. When you're sleeping on your bed, there is a dent in it. When you get up, it springs right up. This will happen also in the Earth. It is happening actually as we speak - certain places in the world (Scandinavia is one example) that are slowly rising because the huge ice sheets that existed during the last ice age melted. That said, India is still colliding into Asia and the Mediterranean is still closing so you would get more Himalayas and Alps. Plates are still subducting so you you will get volcanic arcs such as the Andes or Japan. It will take some time, but the mountains will come back.

Answer 2

There's a number of useful things mountains do and I'm not sure I'll get all of it, but one, mountains create slopes which directs rivers. Without any mountains and height variation at all, earth would be 1 big ocean. But if we ignore that and imagine that we have lighter granite plates (without mountains) and dense basalt below the oceans, then we could still have land masses (but no Hawaii), but rain, rivers and run-off would be significantly changed. Mountains also play an important role in snow storage, leading to melt runoff and providing water for rivers into the spring and summer so you could see a sizable reduction in rivers and more drought.

I also suspect, though I can't prove it, that mountains cool the air, they certainly pull water-vapor from the air and water-vapor is a powerful greenhouse gas though clouds can affect climate change both ways, the overall effect is likely a cooling one, so no mountains, Earth would probably be at least a degree or three warmer.

There's also, perhaps a change to wind strength and direction, but I'm not smart enough to predict that. I also agree with everything Michael said. without mountains, plate tectonics would slowly rebuild them and erosion would gradually re-create natural slopes in land.