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This question focuses on the initial creation of landmasses.

  • What are the processes that causes land-masses to form, and continents and islands to rise up from the sea and sink back into it?

  • How can those processes be easily drawn upon to create realistic looking maps?


Note:

This is part of a series of questions that tries to break down the process of creating a world from initial creation of the landmass through to erosion, weather patterns, biomes and every other related topics. Please restrict answers to this specific topic rather than branching on into other areas as other subjects will be covered by other questions.

These questions all assume an earth-like spherical world in orbit in the habitable band.


See the other questions in this series here : Creating a realistic world Series

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    $\begingroup$ Unfortunately, it is not easy to simulate plate tectonics, unless you have a ferrous sphere and some thin flexible magnetic sheeting, or the right software... $\endgroup$ – Monty Wild Sep 29 '14 at 15:09
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    $\begingroup$ Are we working within the realms of plate tectonics to answer this question, or do we have some leeway in type of formations? Earth is a bit unique with our plate setup...A planet like venus lacks the plates, and this gives it very distinctive volcanoes that release the pent up energy instead...with turns into some pretty massive volcanoes that dominate the scene, as opposed to mountain ranges. $\endgroup$ – Twelfth Oct 3 '14 at 19:19
  • $\begingroup$ @Twelfth That's a good question, and I'm actually really interested to see the answer. So long as it's a geological process that can create a habitable planet at the end then it would fit the question although plate tectonics will provide a more "familiar" result which gives them some advantage. $\endgroup$ – Tim B Oct 3 '14 at 19:26
  • $\begingroup$ Tried to give a tectonic vs hard-shell answer for you...the other questions you ask will have interesting answers (like erosion and valley formation...the grandcanyon is a combination of ice flattening out and crushing the rocks into fine sediment, followed by years of rivers cutting into that left behind sediment) $\endgroup$ – Twelfth Oct 3 '14 at 21:06
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While bowlturner's answer provides a list of processes to work with, I think that, since this is about worldbuilding, there should be some technique in applying all of these possibilities in a practical way.

Practical means, since we're not talking about software explicitly here, possible to do with pen & paper and fit it all in your head.

Keep in mind, the following technique is intended to give a realistic result, but it doesn't necessarily depend on absolute realism or application of mainstream theory in every step

Elevation

Starting out with a barren rocky planet, we can apply some elevation to reduce how smooth it is, which can help later. This can be done randomly - a nice noise algorithm can help of course, but since we're on paper here, we can just divide the world into a few large sections and roll dice for the elevation at each intersection.

To do this properly, we need a range of elevations that make sense. We need a mean elevation and a higher bound. We can't define the lowest elevation as sea-level since we have no sea yet. Since Mars is considered to be close enough to a young Earth, we can use its elevations at this point since there's less corrosion there (which gives us room to apply our own corrosion later).

The highest and lowest points on Mars are 30km apart, the highest mountain is 22km and the mean elevation (datum surface) is at around 8km. Apply any elevation at the intersections within these bounds and adjust until you have a proper mean elevation. Then subdivide the grid and perform the process again at all new intersections. This will give a very artificial look to it, so just merge and divide peaks and valleys until it looks more reasonable.

Now is the time to place craters and stuff if you have to - make sure they're big impact craters since smaller ones will erode away anyway.Decide whether to apply the surface features due to elevation over or under the craters (did the impact happen after a mountain was formed?) Craters should be large and cover a 2 digit percentage of the surface. They should also not be too deep, at most a tenth of the elevation range (in this case 3km, but less is better).

If you don't want oceans in the world, you can pretty much stop here. If you want earth-like, it's time to break it up. This will give you continents.

Seas & Continents

Create fault lines around the caps and across the entire surface, more if you want lots of continents, less if you want less of them. Then, recede the surface from the fault lines - the further away land is from the faults, the larger the oceans and the deeper they will be. Feel free to reduce dry land to 30% of the surface or less. All of this doesn't need to be done with detail, just roughly.

After you're done getting continents, create more fault lines all over the place. Don't recede them - these are your tectonic plates. If you're unsure about how they should look, here's a pic. From the picture it's obvious the plates neither coincide exactly with continents nor are they completely random.

Volcanoes

Now randomly place volcanoes - all over the place. The previous grid approach can work. The number of volcanoes throughout history is probably too high to work with, but it seems that today there are about 1500 potentially active ones. About 15 volcanoes should be enough because, as you can see here, they're pretty well clustered along the tectonic plate fault lines. After randomly placing them, bias them heavily towards those lines. Those that are very close should be multiplied to cover large lines along the faults. There should still be a few left far from those lines however. If they are placed on dry land, they create volcanic mountains, if they're close to land but not on it, you get an island - if they're far from land, in the ocean, you get an underwater volcano.

After noting the spots, their scale needs to be decided. There's the VEI scale for that. The scale goes from zero to 8, where zero is relatively inert and 8 is apocalyptic.

We need to make sure we've got the volcano's surroundings covered as well. The tephra would be ejected into the atmosphere and would eventually be deposited on the ground. There's also lava covering the surroundings. How far would these go? We can divide the total volume of tephra (find it out by the scale of each volcano, from the VEI) by a thickness and get an area of settled tephra for that thickness. Apply it to the surrounding area. Wind and weather would of course affect things, but we can be freeform about this since simulating weather for each eruption etc. will quickly get too tiresome for this. The magma bubbling out based on index can be seen here. You can assume that all those cubic meters turn into a large mountain. But how tall and wide does it get? We can use the right circular cone formula and solve for either height or radius to get a result - fortunately, google has us covered - search for "cone volume" and it should give you a calculator to work with, along with the formula if you need it.

Obviously this is hard to do for 1.5k volcanoes, so just do some quick calculations for those that are solitary and then pick some points along the volcano lines, calculate something for those and interpolate the rest of the volcanos (so that they are larger when closer to large ones and they get smaller as they get near the small ones). If you need a thickness for the line, use the average volcano radius for that - you can also just assume the tephra is distributed in a circle and take that radius for the tephra circle line. Fuzzy it up a bit for "realism".

An alternative would be to distribute the sizes based on frequencies, that you can derive from a chart like this.

Canyons, Mountain Ranges, Island Series

This is where our plates start to matter the most. Canyons and mountain ranges are easy. Look at an example - here's a rough map of mountain ranges. It's obvious there is a fault-line relationship. Since both canyons and mountain ranges are results of plate interactions, we need to shake them to get some of these made. An easy way is to place random vectors on each tectonic plate - for each plate, make an arrow of a length and direction. They should start roughly from the center of each plate. To get the horizontal and vertical components and make our life easier, use a calculator or more easily, just draw a rectangle aligned to the grid for which the vector is its diagonal - the left and right sides are your vertical component and the up and down sides are your horizontal.

Now look at where all the new arrows are pointing. If two plates are pointing to each other, make it a mountain range if they meet on land or a series of islands (can be underwater islands) if they meet at sea. If they're pointing away from each other, that's a canyon.

We need to know how tall these ranges are going to be and how deep the canyones are going to be. There's two quick approaches to this - use the same range of elevations from above, from Mars (since we're going to erode mountains to 2/3rds to 1/2 later, don't use Earth ranges - highest point should be ~20km and lowest trench underwater should be ~5 km below sea level - canyons should go at most 1.5km below sea level) or move around the plates multiple times (like 3-5 times) and count collisions and retractions for each edge within the total number of movements; divide the total elevation with the number of iterations to know how much difference each ones makes and then do a simple addition to make out their depths and heights.

All of these collisions are earthquakes - like volcanoes, if you want a rough estimate of how powerful they can be and how often they can happen (for more detail) take a look at this.

What about erosion?

Seems to be planned for later, so I'm stopping here.

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Plate tectonics are the main forces that create and shape land masses. The lithosphere (earth's crust) is floating on a magma core. As the different plates move grind and bump into each other they cause different effects on the surface. Just like ice on a lake or other large body of water. When two plates collide you get pressure ridges, (mountains) separate and you get trenches (Mariana Trench) often one plate will slide under another. This will raise one up and the other will sink into the mantel. Some plates grind edge to edge like the San Andreas Fault. All the plate edges are very earthquake prone locations.

On a planet with plenty of water it will fill the low spots creating oceans. Many islands are caused by volcanic action along the fault lines under the ocean. Others are the tops of mountain ranges such as the mid-atlantic ridge including the Azores.

What powers the drifting? The magma, the planet spin, the moon orbiting, and the sun pulling, all put stresses on the earth to keep things moving, though it is still in dispute how much each one contributes to the whole.

Now, how to apply this knowledge to actually making a map. First the important thing to realize is that many of more impressive features are along the plate edges. Knowing the two ways mountains are made (upthrust vs volcanic) would help decide what kind of mountain(s) you put where. A 'Lonely Mountain" really should be volcanic in origin. This works similar for islands in the oceans and seas. Mountain ranges will tend to follow long arcs.

Pay attention to elevation, water goes downhill and fills up holes until it finds an outlet. Places like death valley are uncommon, at least without them being filled with water. India ran into Asia and created the Himalaya's, so that is 2 separate plates with large above ocean areas.

Barring other factors continents will tend to be lifted up at one end or the other (or both or in the middle etc...) So really large inland seas will tend to be rare, since the continents tend to 'dump' them off.

So after having some idea what your continents look like, (expecting lots of arc in their creation), decide where the plates might reside to help explain the features, mountains, lowlands, oceans etc.

Apparently I am not nearly so good at describing the uses of the tectonic knowledge for creating maps.

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    $\begingroup$ This is a good answer to the first part of the question but how can this information be drawn on to create realistic looking maps? $\endgroup$ – Tim B Sep 29 '14 at 13:28
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    $\begingroup$ Ah, yes, got so caught up in the first part forgot the second. I will be adding more to the answer later to rectify that deficiency. $\endgroup$ – bowlturner Sep 29 '14 at 13:34
  • $\begingroup$ Another major terrain modifier is Glacial action. The Great lakes in the US and the many lakes of Wisconsin, michigan, Minnesota, and Canada are the result of the Ice Ages. $\endgroup$ – Chad Sep 29 '14 at 19:19
  • $\begingroup$ @Chad That's true if you are referring to Continental Glaciers (like what made the Great Lakes). $\endgroup$ – bowlturner Sep 29 '14 at 20:00
  • $\begingroup$ @Chad yes, Glacial action is a big modifier but I'm trying to keep the scope reasonable for each one so I'll ask that as a follow on question. $\endgroup$ – Tim B Sep 29 '14 at 21:54
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I've made a bachelor's thesis out of this topic. It contains a throughout explanation on how plate tectonics form the land masses and a simple model that actually does the job. The thesis is available at Theseus.fi and the source codes along with few screenshots are at sourceforge.net/projects/platec/ . I like the results of my work, e.g. Computer generated terrain with plate tectonic simulation has a very nice topography that's impossible to attain with equally simple fractal methods.

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    $\begingroup$ Hi Laurimann. Welcome to WB.SE. Could you summarise the methods you used for that thesis? Links may be broken at some point, and that would limite to usability of your answer. $\endgroup$ – clem steredenn Jul 28 '15 at 9:20
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In answer to the second part of your question, there are a number of different algorithms that have been designed for use in procedural game content generation that make use of simplified plate tectonics to generate world maps. An example is platec, but there are many others.

These can easily be used to generate realistic looking maps, including in more feature rich simulations, mountain ranges and general heightmaps. However, I am unclear on whether any exist that work with a sphere. - the only examples I've seen are based off of a flat surface.

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    $\begingroup$ PlaTec is quite interesting. Could you provide links or names of other plate tectonics procedural world generators? (The Tectonics.js one that Colin links below is one that uses a sphere, but I haven't seen it produce particularly realistic-looking worlds, though I imagine it could be tweaked and run at higher resolution for better results.) $\endgroup$ – Dronz Oct 6 '14 at 16:29
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When your planet first cools you'll have a choice to make...tectonic plates vs one hard shell. There are examples within our solar system (actually, Earth is pretty unique)...in my personal opinion, I beleive that there needs to be a big impact early in a planets formation to start plate tectonics (The Earths moon being created from the earth is the impact that started earth along it's way)...not sure if I can defend this position with links, but it's a potential conclusion. The main impact on the geology of a planet at this phase is how it's going to release it's energy.

-Tectonics. Not much to add here that other answers haven't covered... Moving the plates around on the planet is an incredibly efficient way of releasing the pent up energy in a planet. This motion is going to form mountains along the plates borders (giving rise to mountain ranges). An interesting effect of this is what was once an ocean can be lifted and turned into high mountain ranges. India used to be detached from the continent of Asia and there was a sea between the two bodies. This sea had an abundance of life, including a 20-30 foot long eel like creature that was an offshoot of the Whale (it became a dead end in an evolution sense as they died off, but it shares a common ancestor with whales). As the plate of India crashed into Asia, this sea was pushed high up in the mountain ranges...many many years later, humans find the remains of an eel like mammal deep in the Himalaya mountain range. The Rocky Mountains in north america contain some of the earliest sea life (trilobytes) at some of the higher elevations on this planet. Plate tectonics = ever changing.

Early in the galaxies formation (we're talking 4-5 billion years ago), space was a messy place with a crap ton of debris floating around waiting for somewhere to impact (we can see this in the moon where lack of plate tectonics and erosion have left these billion year old impacts place for us to see). The constant change of plate tectonics do much to hide this history and it's only in recent years that we've gained the technological know how to look for ancient impacts on Earth.

-Hard shell Planets like Mars and Venus are in this setup where they are pretty much covered by one giant plate and not a series of moving plates...from a world creation standpoint this is actually several times easier to process...one large landmass dotted with Volcanoes to release energy. Volcanoes in this sense become immense stand alone giants that rise out of the ground and tower above anything else. Olympus Mons on Mars is approximately 3 times the height of mount Everest (we actually theorized this mountain existed from looking at mars, long before satellites confirmed it's existence) and over 600 miles wide (about the size of France). It can be seen for a silly distance and will actually stick out past the curvature of the planet.

Lacking plate tectonics to change the elevation of the ground leaves meteorite impact much more noticeable on planets that formed like this and it's likely lakes/sea's are left behind impact craters (leaving them a very round shape).

Gigantic single mountains and round impact crater lakes...plains nearly anywhere else. Much more straight forward than plate tectonics at any rate as the 'constant change' isn't a worry on a system like this.

Incidentally, I've seen the theory that volcanic activity isn't enough of a release of energy for a planet like Venus and it continually builds up the energy and warming the surface 'crust'...in a once every 250 million years in an event that takes over 1 million years to complete, the surface of Venus 'melts', completely reforming itself. I'm really not sure how feasible this is, but it's an interesting theory nonetheless.

I guess the rest of the comments here are aimed at your other question threads...Erosion (particularly ice) is probably next, no? You'll need to decide on 'other planetary bodies' to determine gravitational forces on erosion such as tide and the sort.

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Kind of peripheral to the original question, but I have found a "good"(with some quibbles) tectonics simulator here: http://davidson16807.github.io/tectonics.js/

It should work with most modern browsers, and is usually good at producing credible maps. Because of the way the spherical surface is partitioned into cells the edges are a bit sketchy, and it's intrinsically slow, especially if your browser doesn't have a good js implementation, but it's pretty cool.

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The best way to start designing a realistic world I found here. In my answer, I will use some of the thoughts from that article.

I think of the world as a pitted soccer ball, where elevation rises and falls. The low parts are swallowed by the ocean, average height is your flat lands, and your high points are mountains or islands if they are isolated from other high points. Now each section of the soccer ball is a separate tectonic plate. You can change the number of plates, how each one is shaped, but in the end your plates will join together to form a sphere. Where each plate meets, the elevation gets higher as they push together and rise. Mountains form where the plates crash together. Where the plates enter the ocean, you will typically find a few islands nearby as the land is pushed just high enough to rise over the ocean.

When designing your map you can start with a concept, the overall shape and feel of the continent and a few important mountain ranges. Then you can draw the plates on top of that sketch along the mountain ranges to flesh the map out and guide the placement of more mountains and islands. Or you can start with the plates, just whip up a few shapes that run into one another, draw mountains at the intersection then gradually give way to ocean as you retreat further from the mountains. It is really up to you.

You can also figure out how your landmass came to be. Did your world just slowly rise out of the see? Your seacoast is likely smooth and gradually falls off into the water. Do you want a Pangaea that split, caused upheaval and potential for conflict like the merging of India and Asia? That could give you more ocean cliffs from where the land split.

The final factor is water. Where are your rivers, lakes, and floods? Has there been time in your world to cut the Grand Canyon out? You can draw rivers from the mountains you create in the previous step to the ocean. The path it takes is the lowest elevation at each point, and the constant flow of water just makes it lower over time.

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  • $\begingroup$ The giantitp articles are fantastic for world building, I have used them in part. $\endgroup$ – James Jul 27 '15 at 19:16

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