Is there a reason most mountain ranges seem to run parallel to coastlines?

Question

Eyeballing a map of the world, it seems that most mountain ranges that don't occur along continental fault lines run parallel to coastlines. Is there a reason for this?

Answer 1

Yes there absolutely is! And the fact that you noticed it makes you quite the geologist already! This pattern was noticed by other scientists a long time ago and helped prove the theory of plate tectonics!

I assume you saw this clearly in the Andes- on the western coast of South America. This is the clearest and most active example of a subduction zone. A subduction zone is a type of plate boundary where oceanic crust (moving from the west towards the east) collides with continental crust (south America). The oceanic crust is denser, so when it hits the continental crust it begins to sink underneath it. When the oceanic crust begins to sink, it also begins to melt (as it gets deeper it gets hotter, but it melts mainly due to the release of water in the crust) and that melted crust is now magma, that ascends to the surface because it is not dense at all compared to the solid rock around it. That magma then forms volcanos (mountains!).

Also, there are some complicated structural geology going on that involves the subduction of buoyant crust that rises and causes 'buckling' of the crust above it, that raises the topography and makes mountains. But volcanos are the main way this happens!

There are very clear diagrams of this happening if you google 'subduction zone'.

But this main reason this happens near coasts is because it involves the interaction of oceanic and continental crust.