[Award Winner] Using tectonic plates to draw a world map

[dhalsimrocks]

Digression - Basic Tectonic Plate Geology

The movement of Earth's tectonic plates has an enormous effect on its terrain. Most important to this are the boundaries of the plates, and there are two factors that come into play: the type of crust at the boundaries and the type of boundary.

There are two types of crust: oceanic and continental. Oceanic crust is exactly that: crust that forms ocean floors. Continental crust is that which creates landmasses, although not all continental crust is above water.

There are 3 types of plate boundaries:

Transform boundaries, where two plates slide past each other (rub the palms of your hands together for a visual aid). California's San Adreas Fault is an example of a transform boundary. Transform boundaries produce many earthquakes.

Divergent boundaries, where two plates are moving away from each other, creating oceanic ridges and continental rifts. The Atlantic Ocean was produced by divergent plate boundaries between the North American + South American plates and the Eurasian + African plates. They were once joined together in the Pangea supercontinent, but the plates movement spread them apart and the divergent boundary created an ocean. Africa's Great Rift Valley is also being caused by a divergent boundary.

Convergent boundaries, where two plates are colliding. This creates mountains and/or oceanic trenches or island chains, depending on the types of crust that are colliding. Convergent boundaries create a process known as "subduction", where the crust of one plate slides underneath the crust of the other. This creates volcanic activity along the line of subduction. This will be important later.

Transform boundaries have a lesser impact on terrain than divergent or convergent boundaries, although it is important to remember that they do cause earthquakes!

Divergent boundaries occur between two continental crusts or two oceanic When two oceanic crusts meet at a divergent boundary, it creates an oceanic ridge, not to mention new crust. These are basically crust formation points, and you should have one or two on your map. Example: The Mid-Atlantic Ridge.

When two continental crusts diverge, you get a rift valley, and over time, they separate into two landmasses. Example: Africa's Great Rift Valley.

Convergent boundaries between two oceanic crusts eventually create chains of islands (usually in an arc). The subduction causes volcanic activity that eventually builds up into islands. Examples: Aleutian islands, Phillipines.

Convergent boundaries between oceanic crust and continental crust creates volcanic mountain ranges on the edge of the continental crust, because of subduction. Examples: Andes Mountains in South America, Cascade and Sierra Nevada mountains in the USA.

Convergent boundaries between continental crusts creates dramatic mountain ranges as the landmasses smash into each other and buckle the landscape. One crust can subduct beneath the other. The classic example is The Himalayas. This was caused when the Indian Plate crashed into the Eurasian Plate at a high rate of speed (still very slow, however). The Indian Plate is slowly subducting beneath the Eurasian and is creating the tallest mountains in the world, as well as the Tibetan Plateau (the highest in the world).

For a visual of most of the scenarios:

http://en.wikipedia.org/wiki/Image:T...boundaries.png

Also, see the image of the Earth's plates.

So now that we know how the different boundaries and crusts effect the landscape, we can take the next step in producing our map.

[ravells]

This is a very interesting and educational read! Thank you very much for posting! (I'll delete this message after a few days so as not to interrupt the flow of your tutorial).

[jfrazierjr]

Thanks for the info AND the links. Though I will proabaly not delve this deep, it is nice to have an idea of what might be going on in the real world. I think for me, this will mainly help influence the idea behind why islands are where they are and how many of them there are.

I know some people over on the NBOS forums have had some debate about how most mapping programs that generate worlds don't take this into account and the general thing is that you would need hugh housepower or tons of time to even approximate getting this created right. Mainly, this is directed at Fractal World Explorer or Fractal Terrains autogeneration functions. For the most part, the people on that forum are fairly agnostic in how real geology affects world creation. Most people have the attitude (which I mostly have) that "its just a fantasy world, so as long as the rivers go down hill, thats probably good enough for me."

Joe

[dhalsimrocks]

Step 2 - Drawing the Continental Crust

It is now time to decide where the continents will be and give them their shapes.

When I did this, I made a few copies of the tectonic plate sketch on which to draw my continents and landmasses.

But where to start?

One good place would be to find your divergent boundaries. This is a possible location for an oceanic ridge/crust formation point. This is also a possible location for two continents that were one time joined together, but are now separated, like South America and Africa. So you might want these two continents to have coastlines that would mostly "fit together", but separated by a body of water.

Once you have those coastlines drawn, think about the rest of the continent. The shape can be entirely up to you and can have a lot of randomness.

Next, think about your Oceanic Plates. When looking at the Earth's plates, you will notice that only two major plates have no continental crust at all: the Pacific Plate and the Nazca Plate. One of your large plates could be entirely oceanic, and would therefore be a location for one of your oceans, if not the largest. It would also be a good location for a "Pacific Ring/Ring of Fire" type scenario, where most of the plate's boundaries have a lot of volcanic and seismic activity, not to mention some of the deepest trenches where there is the most subduction.

Then look at your convergent boundaries. They will be the locations of either Himalaya type mountain ranges, Andes or Cascade volcanic mountain ranges, or volcanic island arcs. Decide what you would like to have and where. This can help you decide where your oceanic and continental crusts will be.

Finally, think about whether or not you want any continental divergent boundaries, where there may be a large rift in the continent (and a new plate boundary forming).

Most of this step is up to you, but is also largely determined by how you drew your tectonic plates and what direction they are moving. Take some time with this step and make it your own.

Here is what my map looked like after adding the continents (it's not the finished product):



Continents A and B are separated by an ocean created by a divergent plate boundary. They were once together and as such, they would "fit" if placed side by side. Both would also fit with the southern continent, which I forgot to label, as that is also a divergent boundary.

A<->G, E<->B, F<->D and C<->D are all continental convergent boundaries and are creating large mountain ranges.

Notice the island arcs between all of the oceanic convergent boundaries.

All the way to the north is a continental rift caused by a continental divergent boundary. (x) will one day be its own landmass and tectonic plate.

The island between G and (x) has a ridge of mountains caused by a convergent boundary and subduction. B has one as well, but that's from a very old subduction that is not current.

Now, I'm sure a legitimate geologist would look at this and tell me a thousand little things I did wrong, but it has enough scientific base for me, and it has resulted in a realistic looking map. And what's more is that there was enough randomness involved that I didn't know exactly what it was going to look like in the end, so it was just a bit of a surprise.

I still have some more work and detailing to do before going on to editing this in the GIMP according to RobA's excellent guide.

Anyway, even if you don't use this whole method to create world maps, I do hope that there is information here that could be helpful in determining at least some of the terrain on your maps or help shape continents.

Thanks for reading!