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Paraclete
08-16-2010, 07:20 PM
Hey, all.

With my current project, I'm aiming for geographical/-logical realism, and reading some of the brilliant posts on these forums made me realize that I need to have an idea of planet-wide geography/geology before I can begin to map on a smaller scale. Even the smallest topographical features are the product of a long, interdependent chain of events that begins all the way back at tectonic plates and their movement.

So, I have a rough draft of the continents, major islands, and some mountains, and I need a second, third, fourth, etc pair of eyes to tell me how it looks. My primary goal is realism, though perhaps not diehard, ruthless realism - that is to say, I want the landscape to follow physical and geological laws, but I'm not obsessed with crazy, obsessive details. My project is for fantasy rather than sci-fi, after all (albeit very low-magic fantasy, so "the gods did it" or "magic did it" cannot excuse an uphill-flowing river or a mountain springing up from nowhere).

I've attached two pictures: one is the tectonics and their movement, and the other is the major landmasses overlaid onto the first, with ugly gray blobs where I think the mountains are supposed to go based on the plates' locations. The scale is the same as Earth. I have a few specific questions in mind, but would also welcome other input and direction.

1. Are the plate boundaries alright? (They're roughly modeled on Earth's plates, but are otherwise just random freehand.)

2. Do the plate movements (red arrows) look ok? Again, mostly random, but with cues taken from the real-world model.

3. Are the general shapes and scales of the landmasses plausible? Do they line up where they should with the tectonics?

4. Granted that all of the above is correct or correctable: where, then, would mountains occur? Where would there be volcanic activity? Where would smaller island chains occur?

5. Am I able to place further mountain chains at my leisure (though sparingly)? Where might they go? Specifically, I'd like some kind of inner-continent ranges so as to separate countries/cultures, but I'd rather not just magically plop them there without any (pseudo-)scientific basis.

Thanks for reading, everyone. Looking forward to any tips.

waldronate
08-16-2010, 08:32 PM
What's the map projection?

Where are your hot spots (mantle plumes)?

Paraclete
08-16-2010, 10:24 PM
What's the map projection?Good question. I didn't put any thought into the projection, since I don't have much use for this planet-scale map - I just want to know what's going on in general so that I can then zoom in and map a particular continent on a much smaller scale, at which point I imagine the projection won't matter nearly as much. But to answer the question: I've been using http://en.wikipedia.org/wiki/File:Plates_tect2_en.svg as the bottom layer of my GIMP file, so that I can refer to it whenever I need a general idea of the scale of various real-world landforms that can then inspire the shape and scale of my imaginary landforms. So whatever projection it uses is the projection my map uses.


Where are your hot spots (mantle plumes)?I'll sheepishly admit that I don't even know what hot spots/mantle plumes are in a geological context.

Thanks for the reply. I wish I could provide some better-informed answers.

cfds
08-17-2010, 11:53 AM
Roughly spoken: hot spots are the source of vulcanism on a tectonic plate, in contrast to vulcanic activities ad the edges of plates. Hawaii is the prime example.

Paraclete
08-17-2010, 01:38 PM
Roughly spoken: hot spots are the source of vulcanism on a tectonic plate, in contrast to vulcanic activities ad the edges of plates. Hawaii is the prime example.That's one of my questions, actually: I don't know where such spots would occur, given my plates' locations and movement.

waldronate
08-17-2010, 05:35 PM
I'm not known for being too good at pleasantries, so please try not to be too offended. I'm also well known for inchorent rambling, but I will try to stay focused.

Whenever you have a liquid that's being heated from below and cooling above (a pot of water on a hot plate that's open to the air or a planet with a liquid mantle that's being driven by core crystallization from below and cooling to space above) then the liquid will form that's called convection cells. Cooler liquid will sink along linear features as whole sheets of the surface cool and get more dense, while thin streams of warmer liquid will rise to the surface. What's important to drive the whole thing is that warmer liquid is less dense and cooler liquid is more dense. What does this mean in the context of plate tectonics? The rising plumes of warm liquid form what are called hot spots, while the sinking sheets of liquid form what are called subduction zones. Because there is a very thin layer of crunchy material floating on top of the liquid, that material gets carried along to some extent.

Hot spots are, as said above, rising plumes of warmer material from deep in the liquid part of the earth (the mantle). These plumes are hot enough to burn their way through the overlying crunchy bits (the crust). When the warmer liquid hits the surface it starts to cool, turning into mountains. Probably the best-known example of a hot spot is the Hawaiian island chain. I say chain, not island, because the whole plate that the hot spot is burning through keeps moving, preventing the islands from getting too large. The motion of the plate can be tracked by a whole chain of islands and seamounts stretching most of the way across the Pacific.

Why does the Pacific plate move? Because it's riding on a layer of rock that's sinking in what's called a subduction zone. In this case, the lengthy trench system off the coast of Japan and the Phillipines marks the place where the crust is being pulled down by the cooling mantle liquid. Another famous one is the Andean subduction zone by the western coast of South America.

Both of these areas show important features of subduction zones: Things get crumpled and melted and try to float. When the plates collide at a subduction zone there is an area along the joint that gets rumpled up and thrust skyward, making mountains. At the same time, the colder things start to dive down into the hotter mantle. Eventually they start to warm a bit, making them a little more buoyant, which causes the less-movign side of the zone to rise even more. Finally, the water that's carried along with sediments makes the rock melt at much lower temperatures than they would otherwise, resulting in nice fluid lavas and lots of volcanoes along the rising part of the zone.

A note on sinking crust: it has to come from somewhere. New crust is typically born at that are called spreading centers. The longest mountain range on the planet is a spreading center. It's in the middle of the oceans, the mid-ocean ridge system. 40,000 km long. On land, spreading areas manifest as rift valleys such as the East African rift valley that's currently splitting Africa into two pieces.

Anyhow... I recommend a little research on the term "physical geography" if you're interested in this sort of thing.

How does this play into what you're trying to accomplish? Plate size is roughly a function of the heating/cooling balance on the planet. Lots of heating will form smaller plates and lots more volcanoes, while less heating will form larger plates. Water seems to be important to lube all this. We know it works at 70% water cover (Earth) and doesn't work at 0% water cover (Venus).

TO answer your initial questions:

1. the boundaries are reasaonble. They seem a little bit vertically-elongated, but that seems to be largely a function of your map projection. Plate triple-junctions tend to be more at 120-degree angles ( Y ) than at 90 degree angles ( T ).

2. Movement seems acceptable. The importance of plate movement is that relative plate movement is what causes mountains. The more that plates are moving toward each other, the more likely that you'll have mountains. Plates that are sliding toward each other will usually raise spectacular mountains on one side of the junction (Andes and Himalayas). Plates that have a less-dramatic impact angle will tend to have less-dramatic mountains. Plates that are pulling apart may also have impressive mountains (Kilimanjaro in Africa, for example, is along a rift valley).

3. The continent shapes are plausible. What's important for tectonics is more the edges of the continental shelves (the sharp drop-off at the edges of the actual continental mass that's usually covered by sea). You didn't include the continental shelf boundaries so I will assume that they are plausible.

4. Volcanic activity will tend to be near active plate boundaries and over hot spots. Hot spots can occur in the center of plates (e.g. the Yellowstone hot spot in North America), but they will either be burning their way through the overlying crust or causing rifting, depending on the balance of forces. Smaller island chains will tend to occur near oceanic subduction zones (e.g. Japan) or over hot spots (e.g. Hawaii).

5. You have a pretty good handle on where mountains should go. There are some areas on the map that have a few more mountains than I might expect and some areas with less. These expectations are based on the relative motion of the plates. Inner-continent mountain ranges such as the Ural mountains are worn-down stumps of long-dead plate collisions. Plates go scooting around the surface of the world and hit, stick, then break apart into new pieces (look up Rodinia and Pangaea if you're not familiar with them). The mountain zones from the impact tend to be stronger than the surrounding crust so the new breaks will be in a different place than where two plates fused.

Map projection is pretty important when doing these sorts of maps because converting the spherical world into a flat map will distort areas and/or angles. Distorted areas will mean that things that look the same size on paper won't be when put back on a globe. Distorted angles mean that things won't be going in the right direction. For example, a plate moving across the north pole may have a direction of "up" on the left-hand side of your map, but that same direction on a real globe will be "down" on the right-hand side of the projected flat map. There seems to a bit of that going on with your map as well.


Anyhow, I'll stop rambling now.

Paraclete
08-18-2010, 09:43 PM
I'm not known for being too good at pleasantries, so please try not to be too offended. I'm also well known for inchorent rambling, but I will try to stay focused.No pleasantries needed...considering the effort you put into the post, and the info you provided, you've earned the right to insult my mother, for all I care. (But please don't.) Thanks a ton...I'll take your tips into consideration.