Last updated on September 17, 2021
So far in the worldbuilding series we have mapped a fictional world from plate tectonics to climate. Now we look at landforms, which fills in more detail in the geography of the map. This topic covers a wide range of areas, including erosion, drowned river valleys, barrier islands, coral reefs, and salt deposits.
We want to deal with these things after climate and not after creating the basic continent map because most of these things are dependent on climate. Climate affects landforms. We need to know where it is cold or warm. We also need to see what areas have high precipitation.
Erosion
We touched on erosion briefly in the plate tectonics article, merely to say high mountains erode down to low hills. Water is the main driving force behind erosion, though wind also plays its part. Rain, rivers, and storms all move particles from place to place as water moves. Normally, water starts high and travels down. This is the main method of erosion. Rain and storms in high areas bring rock, sand, and silt to low areas.
In high areas, streams cut into rock and soil, wearing it down. The high mountains created by the clash of continents will erode away eventually. The forces created by continents colliding generate high heat and temperature deep in the earth, precipitating minerals such as copper, gold, silver, tin, and iron out of the rock.
The intense heat and pressure of mountain building affects layers of sediment. Metamorphism will turn shale into slate, schist, or gneiss. Slate one of the basic resources used by cultures in areas where it is abundant. Metamorphism also creates many types of gemstones by crystallizing sedimentary rocks.
Erosion will expose these minerals or bring them closer to the surface. For this reason, areas that were once high mountains between continents become areas rich in mineral resources. This will become important later on when we discuss societies and economics. The mountains of Wales, northern England and Scotland are this older mountain type.
Also, stream erosion takes these minerals away from their source and deposits them with gravel and sand in placer deposits. The gold fields of California are an example of this.
When worldbuilding your fantasy setting, you could put miners in these areas. The dwarven city of Moria and its mines are probably the most famous community of miners in fantasy literature. Also, gold has been a major motivator in literature and real life throughout history. How many Macguffins are some type of gold object, idol, or gleaming treasure?
Rivers and Streams
River and stream environments offer the sort of bucolic setting that we often see at the beginning of fantasy stories. They don’t have to be, though. They also offer the potential for danger in the fast moving rapids or waterfalls. Also, you can find dangerous creatures hidden in marshes at the edges of slow moving rivers.
As mentioned, rivers bring sediment from the high areas and deposit them in low areas. As rivers and streams move from highlands to lowlands, they become slower. Water turbulence determines the size of the particle deposited. As the stream slows, it deposits larger particles first, leaving behind gravel in mountains and hilly areas.
Meandering Rivers
Where the stream slows, it will deposit sand along its edges and at its mouth. In flat lowlands, this process will build up the floodplain in a process called aggradation. The river eventually moves across a nearly flat plain, resulting in a meandering river with oxbow lakes. We don’t need to get too deep into the mechanics of this, we just need to know where a river will tend to create a meandering course.
One aspect of a meandering river is that, if tectonics lifts the entire area, the river will cut down into the surrounding landscape, creating some of the most interesting landforms, like Goosenecks State Park in Utah.
Deltas
The final step of the river’s course is at the mouth where it hits a larger body of still water such as a lake or sea. The water in these large bodies are still, so the larger particles will deposit here, often extending the floodplain out into a delta. The most famous is the Nile delta. The smallest particles will settle to the bottom of the lake or sea, creating muddy bottoms.
Sedimentary Rocks
All the sediments washed down from the hills and mountains form layers of sand and mud in the lowlands. Under the weight of sediment above, they form layers of rock. Sand becomes sandstone and mud becomes shale. We will see how other types of rock such as coal and limestone get sandwiched between these basic rock types.
When tectonics lift large areas of the continent, the layers get lifted as well. Erosion cuts through them, exposing the layers. This is why we see so many mountains with layers of rocks piled on top of each other. Piled sedimentary rocks form most of the Alps and Himalayas , though much of it has undergone metamorphosis.
The layers also tilt up 90° or more as the land lifts. This creates long rows of mountains as the softer layers erode into valleys. They usually form at the edges of the central mountain core. The western Appalachian Mountains are of this type.
Drowned River Valleys
Another feature of river systems is that they cut valleys into hills. If these valleys are near coastlines and sea levels rise, seas flood the valleys and create estuaries. Some might be open to the ocean, others might be blocked by barrier islands.
Bar-blocked estuaries tend to have brackish water. In dry areas, evaporation will cause the water to become highly saline, perhaps depositing salts in dry lagoons. In wet areas, such estuaries are marshy, depositing layers of carbon-rich plant material. Again, here is an opportunity in worldbuilding your fantasy setting to find dangerous swamp creatures.
Salt Deposits
Salt also precipitates in arid areas in places that a lake would otherwise form. Seasonal precipitation will bring water to a desert depression where it evaporates, leaving behind salt deposits. These deposits can be hundreds of meters thick.
We see this sort of evaporating inland sea in places on earth such as the Great Salt Lake in the United States or the Aral Sea and Caspian Sea in Asia.
Layers of sandstone and shale might sandwich layers of carbon or salt as sea levels rise and fall with climate change or due to tectonic forces. In such cases, the carbon might turn to coal. The salt deposits might become a layer of salt, gypsum, or other evaporate mineral.
When other sediments bury thick salt deposits, the salt can be mined. There are some huge salt mines throughout the world. I visited the Wieliczka salt mine in Poland some years ago. It is large enough to have an entire church underground. Such a location can provide many ideas for worldbuilding your fantasy setting.
Barrier Islands
Earlier, I mentioned barrier islands in relation to drowned river valleys, but they also form offshore along coastlines.
There is some debate as to how these islands form. The offshore bar theory posits that waves moving into shallow water churned up sand. As bars developed vertically, they gradually rise above sea level, forming barrier islands. The longshore drift and spit accretion theories posit that sediment moving in the breaker zone constructs spits extending from headlands parallel to the coast. In tropical areas, the sands might include limestones from coral reefs.
However they form, these barrier islands also create bodies of water behind them with brackish water, mangrove swamps, and marshes. Real world examples of this are along the eastern seaboard and gulf coast of the United States from Texas to Long Island, NY.
Like marshy estuaries, these lagoons might have deposits of carbon-rich plant material. As sea levels rise, the sands will accumulate in layers as the barrier islands move inland. The seams of rich carbon deposits might turn to coal under the pressure of the overlying rock.
The barrier islands are often sandy and have their own ecosystems. Moving inland, you would find first a beach, then grassy dunes. One might find woods and thickets landward of the dunes and marshy bays farthest inland. When worldbuilding your fantasy setting, marshy bays provide opportunity for dangerous creatures hidden below the surface. Think the Dead Marshes of Tolkien or even the more mundane alligators of Florida.
Coral Reefs
I briefly mentioned limestone earlier as a type of rock sandwiched between layers of sandstone and shale without explaining where the limestone came from. Coral reefs create limestone along continental edges in warm, shallow water about 60-90 feet deep.
The ideal environment for reef building is in the tropics between 20°N and 20°S where the water is between 20-29° Celsius. This means that, if plate tectonics didn’t bring your continent across those latitudes, it is unlikely to have limestone deposits. It might have carbonate rich mud dredged up from ocean bottoms, but is less likely to have pure white or grey limestone.
Coral reefs form offshore obstacles like the barrier islands, but under water. The Great Barrier Reef of Australia or the Florida Keys are the most famous reef systems, but most of the islands in the South Pacific or the Bahamas are atolls made of coral reefs.
I stretched the range of coral reefs far enough north on my map to surround the jungle-covered volcanic island in the middle of the sea. The sea is fairly shallow and has no cold currents, so reefs might grow farther north than normal.
I am intrigued by this island. It would make a great King Kong setting, but it might just be something like Hawaii. Worldbuilding is about creating settings. What happens in those settings is up to the creativity of the author.
Coral Reefs Become Limestone
As ocean levels rise and fall, sediments cover these coral reefs, creating layers of limestone. When tectonics lift these layers up into mountains or hills, the limestone will erode away due to underground water seepage, creating extensive cave systems. These caves might have their own unique ecosystems. Perhaps a species of glow-worm illuminates it or a shriveled creature resides in the depths, eating blind fish and obsessing over a precious magical trinket.
The pressure of plate tectonics will metamorphose limestone into marble. Such marble deposits lie in areas of tropical continental margin that have been pushed up into mountains. Italy and Greece are two such areas on earth. Needless to say, such marble deposits might be a common building material for cultures in areas where it is found. Later, when this worldbuilding series has an article about culture, art, and architecture, we will see how this becomes important.
Glaciers and Ice Caps
The last topic we’ll cover in this article is how ice affects landforms, from glacier carved lakes, isostatic rebound, and fjords. We’ve discussed the unique landforms of warm and wet climates. Now, let’s move to the frigid north.
As the temperature of a planet cools, ice accumulates at the poles and at high elevations. During ice ages, these accumulations can cover hundreds of thousands of square miles in ice sheets. We had such an ice age in human prehistory. It ended about 200,000 years ago, just in time for the arrival of modern Homo Sapiens to Europe.
Your fantasy story could be set in a region such as this where glaciers are retreating and humans are moving in. There is an entire sub-genre of this type of story. The worldbuilding for this type of setting is almost completely ready to start writing. It just requires the author to do some basic research.
These giant sheets of ice scrape the top layers of rock, carrying sediments hundreds of miles from their source. They also carve out valleys in mountains. Where these valleys meet the sea, they form fjords. Mapping out fjords on a fictional world can be an exercise in baroque art. The character Slartibartfast was proud to have designed all the fjords when constructing Earth in Hitchhiker’s Guide to the Galaxy. Slartibartfast was the ultimate worldbuilder.
Glacial Lakes
Ice sheets are responsible for many of the lakes in northern latitudes. Retreating glaciers carved extensive lake system of Finland and the Great Lakes of North America.
Retreating ice sheets can also leave behind large lakes and seas. The weight of huge ice sheets depress continents due to isostatic adjustment. Water fills these depressions, either from runoff or from the invading sea, creating large lakes or bays. Hudson’s Bay in Canada and the Baltic Sea in Europe are examples of this.
Over time, these areas rebound, rising up and shrinking the size of the depression. The Baltic Sea first formed as runoff and seawater filled the depression of the retreating Weichsel glaciation. As the land rebounded, the bay became a Ancylus Lake. The lake only became an arm of the sea about 7500 years ago when the north sea broke through the straits between Sweden and Denmark.
Final Map
There we have it. Now we have a map of continents created by plate tectonics and influenced by climate. The map has more detail, with mineral resources, unique landforms such as coral reefs, glacial lakes, fjords, drowned river valleys, and barrier islands with marshy wetlands.
Can’t I Just Make It All Up?
All the steps we have taken to this point have been to create a world that is familiar to your readers. But this is fantasy, you say. Why not just make it all up? You are certainly welcome to do so, but any story needs internal consistency and this is how we make sure we have it.
You are free to change aspects of the world to make it more fantastical. We will be doing just that in future articles. At this point, if you have something that doesn’t fit this framework, it should have a fantastical explanation. Magic is the most common. A wizard piled rocks high enough to create mountains. A dragon dragged himself across the land, creating a giant valley. These were the kinds of stories ancient societies told because they didn’t fully understand the natural processes that created landforms.
In our next article we will detail out the basic flora and fauna of ecosystems in different areas. With fully fleshed out ecosystems, we will be able to identify sentient creatures, whether they be humans, humanoid, or evolved along a different path. When we start getting into creatures and civilizations, we have a lot of leeway to create more fantastic elements for our stories.
