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Creating Realistic Terrain
Creating realistic terrain involves more than simply sculpting out a feature
and plonking it on the landscape. To truly create a believable landscape, the
process of natural mountain formation has to be understood else Mountain ranges
may be formed in places that simply make no sense, or worse, disrupt the sense
of locations around them.
Mountains are best looked at as huge ripple lines or wrinkle lines in a world's
surface. They exist where the land bunches up and raises, in long lines called
ranges. Several mountain ranges next to each other are called chains.
The height of a mountain is typically measured in metres above the level the
sea normally reaches - not to be confused with tides. As the mountain rises,
the atmosphere around it becomes less and less dense, able to hold less and
less water, and becoming colder and colder. The net effect of this is mountains
usually have lots of snow and ice on them, on the side facing into the prevailing
wind. The side sheltered from the wind also has some snow and ice, but not much
as most fell as it was pushed out of the colder, thinner air. The side away
from the wind is usually dry, and a long rain shadow stretches out.
Making Mountains out of Molehills
It is an interesting quirk with mountains that the taller the mountain, usually
the younger it is. Over hundreds of millennia, tall mountains are worn down
by wind and rain, carved by ice, and mud. Therefore, really tall mountains are
far more likely to be over an active fault in the crust than short, stubby ones.
Mountains are made on planets where like the Earth; the crust of the planet
floats on a heavily pressured molten core. If your intended world does not have
a hot, molten core, it is unlikely mountain ranges would have formed.
A planetary crust is not one solid mass, and is broken up into several large
plates, which move about as the currents in the liquid beneath them ebb and
flow. Sometimes the plates grind together, sometimes they are pulled apart.
These changes happen slowly, over millions of years, and it's when they grind
together that mountains can form.
When two plates collide, one of the plates slides under the other. The one
that is pushed up, wrinkles and folds, contorting as it twists and bends,
pushing up high, thick mountains full of warped layers of rock. This often
exposes layers that had previously been buried miles under ground, and in
this way, often exposing fossils millions of years old, by forcing them up
to the surface in jagged, uneven lines.
Sometimes when cracks or faults appear in the crust, the plates are not forced
together. Instead, one side or another may actually sink downwards, creating
a 'mountain' which in reality has not pushed upwards at all, simply the cliff
line of where the land used to be. Even so, these blocks can be several kilometres
high on Earth.
Alternatively, a block of land can be pushed up, sliding against fault lines
either side, to create a tableau mountain, rising as a single pillar - until
the wind and rain get at it and carve it, of course.
Weather, Water and Wind
All mountain ranges start out as blocks of rock, misshapen or otherwise. Cracks
and chasms appear as the rock splits and breaks forming the basic outlines of
future mountains, but they lack so many of the features the nooks, crannies,
caves, and slopes of the mountains you might expect. This is because mountain
landscapes are carved, worn away by the heat of the sun, and the power of wind
The process known as weathering, erodes the rock, claiming the loose stones
and softer rocks first, leaving the harder rock peaks less affected. Over tens
of millions of years, even the highest mountains will be worn down by weathering
to the same height as the land around them.
Heat from sunlight warms exposed rocks during daylight hours - this process
will be much quicker with multiple suns. The heat makes the rocks expand. When
the sun(s) set, the night air rapidly cools the rock and it shrinks. Over time,
the stress this puts on the rock, can make them crack apart. Water then seeps
into the cracks, and, if this freezes, the ice that forms will push the rock
apart. At the same time, the wind is whipping up stones, and loose pebbles and
bashing them at exposed rock faces with a sanding motion. Over time the cliffs
collapse as the wind wears them away, and contribute more loose material for
the next face.
Most rivers start in mountains as the excessive snow, and sometimes glacier
output is an excellent source of water. Failing that, a river can start from
a spring - a place where a higher, porous rock meets a lower laying non-porous
rock strata, and the groundwater flowing from higher ground, bursts forth
and flows above ground. This is how rivers start in hilly terrain, and they
always start partway down a mountain slope, never at the top, but always where
two differing rock strata meet.
The steep river is not one single river, but many tributaries, each flowing
a separate path until they slowly join up, one after another, the river getting
wider each time. Each tributary flows fast enough to pick up loose stones,
and dirt. Over time, the effect of the rocks banging on the river floor, and
the water lifting particles out, carves a channel out of the rock.
These channels are always V shaped, because the water always flows fastest
in the middle. Over time it wears down into the rock, until the sides collapse
in, and the river carries away the loose material - a V shaped depression
forms with the river in the middle.
Waterfalls often occur in mountains, and are spectacular forces of erosion.
As with the springs, waterfalls happen where two different rock strata meet.
Waterfalls are usually found where the fast river flows over a layer of hard
rock, then a layer of soft rock. The soft rock is worn away far faster than
the hard rock, until a straight drop is achieved, where the original terrain
would only call for a slope. Over time the harder rock too is worn away, but
the softer rock is worn away faster, and deeper, creating a greater and greater
drop, with an overhanging hard rocky crust, with littered pieces of the harder
rock buried in the floor of the waterfall, where the old cleft has fallen.
Just the same as with waterfalls, rapids require a mixture of hard and soft
rocks. The softer rock wears away first, leaving outcroppings of hard rock
forming almost a mini-delta, high up in the mountains or hills, forcing the
water to flow in sub-channels round them, creating conflicting currents, each
of which wears the rock away at different angles, slowly expanding the rapids
Rivers of Ice
Glaciers are rivers of ice. They start high up in the mountains, and flow
down the mountainsides extremely slowly, but with far more power than liquid
water. A glacier is made as snow builds up and up on a mountainside. Every
time new snow falls, its weight compacts the snow under it. Eventually, the
old snow hardens into something halfway between snow and ice - slush called
névé or hard snow forms. The great weight of névé
forms a hollow in the side of the mountain. As new snow continues to fall,
the névé pulls away from the upper edge of the hollow, or cirque,
and begins to erode the lower edge, to form a crevasse. As it moves, the névé,
free of the weight of the snow on top of it, hardens into ice, and begins
to flow steadily downhill. Moving anything from a few centimetres to a few
metres each day, the sluggish glacier is an unstoppable juggernaut, and rips
out rocks in its path, carrying the larger lumps with it, smoothing out everything
else into a U shaped valley.
As with other rivers, many tributaries often join together to form one large
glacier, maybe as much as a mile across, carving out and smoothing down a
U shape valley. The only jagged rocks left will be above the glacier level.
Rocks carried by the glacier are worked out to the sides until they are deposited
at the edge of the valley in long lines called moraines. Occasional rocks
which manage to stay in the flow, are carried to the glacier's final melting
point lower down, called the snout. There, great piles of heaped, smoothed
rocks, called a terminal moraine, mark the end of the glacier. Even if the
glacier eventually stops flowing, these piles will remain as monuments, as
will the great, U-shaped valleys.