How to do realistic mountain ranges

Transcription

1 How to do realistic mountain ranges When starting an ambitious realistic global map on planetary or continental scales, 4 features are fundamental for a successful and readable result. The coastlines. There are no specific rules beyond having fractal curves on appropriate places. The rivers. Rivers are result of erosion and precipitation. Some softwares like Wilbur or Fractal Terrain do that in a highly realistic and pleasant way. But even without software, rivers are not difficult to do if one observes a handful of simple rules. After all a river is just a line. The biomes. Putting appropriate biomes on a right place needs knowledge of physics, astronomy and biology. However when such knowledge is not available, also here a set of empirical rules about typical temperature and precipitation distributions is enough to achieve a realistic result. The mountain ranges. For many reasons this appears to be often the biggest hurdle and it is in this compartment that maps often lack realismus. So as there is no tutorial about this topic yet, I decided to create one. Thinking about this project I decided that I wouldn't give advice about shading and other graphical methods and tricks. This would yield just another tutorial "How to draw a mountain" what could be useful for an art class but not for a realistic cartography purpose because there is not one method to draw mountains on a map but an infinity and everybody should use the style where he feels most confortable. So my ambition is to rather describe how Mother Nature creates mountain ranges. For it is by understanding her methods that everybody can emulate her and, with his personnal style, obtain a realistic (e.g natural) result.

2 The above 2 pictures illustrate my note about the style. Both pictures are recognised as mountains. Neither is more "mountainous" than the other. Merely there could be a slight doubt whether the first one means a very abstract mountain or a very realistic pyramid, doubt that will be fast removed by the context. With the second one there is no room for doubt because I just added details to my pyramid to allow immediate recognition as a mountain. However regardless of the style chosen, this would not answer our quest for a mountain range. A mountain range is not just a random collection of shapes like above. It is a being in itself, it has a specific structure and it is an example that 1+1 is not always 2 but sometimes 3. So we will start by creating a mountain range by hand with our carpet. How? Like that : Well this is exactly how Mother Nature creates mountain ranges. The only difference is that instead of hands she uses the gigantic power of plate tectonics. This power is sufficient that millions of cubic metres of rock are forced to behave like a carpet. The following picture shows the working. 2 continental plates moving in opposite directions collide frontally and displace rock to heights of many kilometers.

3 You can observe how the 2 continental plates ported by the mantle are forced by the convective movement of the cells below so that they collide frontally with each other. Also note that in both pictures the central region of the collision has a higher altitude than the folds following behind. So now that we understood the mechanism how mountain ranges are born, we will look more in detail how this knowledge can be used in cartography. For this purpose I will use the simplest and therefore highest abstraction. Don't worry - our goal is to achieve realistic results, so as we'll follow Mother Nature's workings, we'll get more and more realistic. After all she needs millions of years to get her result and we want to get there in an hour ;) As it is rare that a continental scale map is created with a strictly vertical point of view because this perspective destroys most of the interesting details, I choose the more usual isometric view. Of course the purists might object that there is nothing such as an isometric perspective for a sphere but we'll indulge this minor violation of geometrical laws. For the sake of simplicty the following picture represents only a part of a mountain range. You will note that the central fold is higher and wider than the 2 on either side. I did them symmetrical even if in the real world such a symmetry is only approximative. This is our starting point. Our mountain range is just born and awaits our pleasure.

4 The tectonics is not alone at shaping mountains. There is another much slower process that works against it and tries to undo what the tectonics have done - the erosion. The principal agent is water but ice, wind and temperatures also contribute. There is water flowing through the valleys and there is also water carving the mountain sides joining valley rivers on the bottom. It is not because this process is slow and weak that it doesn't significantly change the mountain ranges. For instance the Rockies when they were born, were about 2 times higher than what they are today. It was just the erosion that removed about half of their original mass and water caried the remains in the plains around.

5 It is now time to take in account the results of the erosion. Again for the sake of simplicity I show only the effect on the central fold. Of course it is rigourously identical for the peripheral smaller ones but their exact shapes will be different because there is no reason that the water flows are exactly identical on every fold. In red on the upper side we see how the footprint of the central fold looks like. We already see a crest line appearing but most importantly we see the spurs jutting out in the valley. These spurs are characteristic of any realistic mountain range and are due to the fact that there are smaller streams going down the mountain flank and these streams carve their own small valleys orthogonal to the big one created by tectonics at origin. Now it's time to remove all the material that has been carried away by erosion.

6 Here we have added a guide for the ridge line and schematically showed the relief. I have arbitrarily decided that the erosion would be strong so that the red characteristic triangle showing the cross-section of the basic mountain shape is rather small compared to the original size of the central fold. You are free to make the erosion as big or as small as you like. Yes it looks ugly but first, drawing with a mouse is not the best way to obtain beautiful lines and second we remind that we don't care for esthetics... yet. The one before last step is to add a broken crestline and we are almost there. This sketch contains already everything that is necessary for a realistic mountain range. Valleys, crestlines, the characteristic jutting spurs. Of course you follow the same process on the smaller folds right and left of the main chain to create similar shapes. Also I choose an old mountain range with small mountains and large valleys. You are free to make it much younger in which case the mountains will be high and rugged and the valleys narrow. The last step is a formality. You decide where the light source is and add shading and details according to your abilities and your heart's desire. Et voilà! It is nowhere polished, just a fast sketch to show how the previous process where we were imitating Mother Nature transforms in a consistent and realistic mountain range.

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