AIN'T NO MOUNTAIN HIGH ENOUGH,
AIN'T NO RIVER WIDE ENOUGH:
Siting Mountains, Rivers, Valleys,
and All That
These are so closely related they cannot be
untangled. If your story demands that a mountain be exactly here
then there are things local rivers will do, and if your river
must flow this direction, you are going to have to place
high country to allow this.
Mountains, especially chains, are formed mostly
by continental collision. Spread a towel on the table. Put your
palms flat on the towel a couple of spans apart. Slowly slide
your hands together. See? Mountain building! It's a lot like
that when tectonic plates come together. "Tectonic plates"
are vast rafts of solid rock that float on the molten magma,
moving infinitesimal amounts each year into new configurations.
Some plates carry above-water continental masses; some are sea-floor
plates. They are the basis of the continental drift theory of
tectonic development, also known as plate tectonics, which has
worked out better than any of its predecessor theories.
Mountains that are remnants of ancient collision
zones will be lower, rounded and worn away by erosion, like the
Appalachian Mountains. Present collision zones will have relatively
sharp and rugged chains, like the Rocky Mountains and Andes cordilleras
(cordillera = chain of chains), where the American plates are
hitting the Pacific plates. The speed with which the continents
are colliding may be just enough to keep up with erosion, a little
less, or may even build mountains faster than they can be worn
down. The Himalayas are like this: Mount Everest is a trifle
taller every year.
The second way mountains form is by volcanic
activity. This is actually a minor note. Vulcanism occurs only
in a relatively few places. Most common is where a sea-floor
plate is sliding under a continental plate. The leading edge
of the sea-floor plate not only is melted back into magma as
it goes deep enough, but provides a path for magma, molten rock,
to reach higher into the lithosphere, the rocky crust that we
call "solid earth." Only under these circumstances
can the magma find its way to cracks in the pressure shattered,
thinner leading edge of the continental plate, and rise to the
surface. Our prime example here is the Ring of Fire around the
Pacific, an ocean which is slowly shrinking. Its floor plates
are being subducted under all the surrounding continents. However,
if you check, there are other "lines of fire" all around
the Old World. These coincide with the earthquake zones.
The second volcanic zone is where two plates
are moving away from each other. In this case, the tiny gap between
plates allows the magma to rise. The most dramatic example of
this is the Mid-Atlantic Ridge and other submarine expansion
ridges. However, these can be found in continents if two plates
are moving apart. Such areas are marked by "rift valleys,"
valleys created by a giant split in the earth, moving faster
than wind and water-borne sediment can fill them up. The Great
Rift Valley of Africa is a classic, though there are smaller.
The Gulf of Baja and the Central Valley of California are one
rift valley, the lower end of which has subsided enough to be
under water. You will find vulcanism in Africa follows a neat
line along the Great Rift. However, if you pay close attention,
you will find there is much, much less volcanism along a continental
rift than along a subduction zone, and vastly less than along
an oceanic ridge.
This is less humbug to work out for an imaginary
world than you may be thinking. Simply, you say, "I need
big mountains here, so I declare these areas plates in collision.
I need a mid-continental volcano here, so I'll put a rift valley
nearby." You're the demiurge: the plates are wherever you
like. The point to look out for here is that you can't have a
perfect volcanic cone in Appalachian-round mountains, or amid
otherwise non-volcanic features. Also, volcanism runs in strings
and lines; it is not isolated, one mountain here, another two
thousand miles away. There may be gaps in a string of hundreds
of miles, but not thousands.
There is a third type of volcanic mountain,
but it forms only over thin spots in an oceanic plate, and is
pretty rare. If this "hot-spot volcano" rises high
enough, it becomes an island. The Pacific is scattered with them.
Again, they occur in strings, like the Hawai'ian Islands.
Once you know where the really high peaks
are, you can figure that next to them are the foothills, then
the highlands. Continents tend to be higher in the middle and
lower at the edges -- going down to sea level, you know. So the
seaward side of a mountain chain may slope more quickly than
the inland side, where the highlands may form a massif or plateau
hundreds of miles across. The lowest spots in any continent will
be a water feature, or a former water feature. Many desert low
spots are dried beds of prehistoric lakes, like the Salt Flats
In earthquake zones you can have the occasional
irregular hill or hole in the terrain. The high level of faulting
leaves the ground fractured in a relatively small patchwork.
Blocks created by faulting are under great sideways pressure.
Depending on their shape, this can result in emerging fault blocks
and subsiding fault blocks. A classic emerging fault block hill
is Palos Verdes Hill (which would be called a mountain in some
parts of the world) on the Los Angeles Harbor, or the nearby
Signal Hill across the harbor in Long Beach. These rise out of
the the flat plain inside a ring of "real" mountains
in a high earthquake zone. Subsiding fault blocks normally result
in lakes or sudden coves or harbors. Not far from Palos Verdes
is Bixby Slough (now Harbor Lake).
If an area used to be an earthquake
zone, some of these emerging fault block hills may be left as
worn down stubs in otherwise flat plains.
Undersea volcanoes that build their cones
high enough emerge from the water as small islands. This goes
on in the Mediterranean and Caribbean, but especially in the
North Atlantic Ridge up by Greenland.
The Wet Way
The number one point to remember -- the oft-forgotten
"Duh!" -- is that water moves by gravity, which means
it flows downhill at all times. Water can never flow over a hill
or up a rise. To do that artificially requires the use of locks
(look up any encyclopedia article on canals, especially the Panama
Canal, for how locks work). A river cannot pass over mountains:
it must flow through them in a deep gorge. Remember that when
you look at a real world map of a river in mountainous country:
it is always following the path of least resistance, always from
one spot to the next lowest.
In nature, the water will flow around the
hill, or if it is a whole ridge, the water will puddle up until
the body of water formed is deep enough to start spilling over
the lowest part of the ridge. Eventually, the moving water will
start eroding a channel in that low part, cutting it ever lower,
unless it is very tough rock. The water may only be able to cut
down to a tough layer, and the escape stream will still pour
from a lake.
On the other hand, the bed of the lake will
cease to erode when it is formed. While it was a stream bed,
cut by moving water, it might have eroded, but once the force
of the stream is slowed in the holding waters, it ceases to cut.
A lake with a very fast current may carry all the debris and
dirt deposited in it along the outlet stream, but in most cases
the load of sediment carried by in-coming streams is dropped,
so that the lake slowly becomes more shallow, and therefore broader.
Eventually, the rising lake bed and the down-cut channel may
meet, and the lake ceases to exist, becoming just a wide spot
in the river. At this point, the soft sediment bottom is easy
for the river to cut in a deep, narrow channel. Geology is a
constant state of evolution from one form to another.
Many, many features in the landscape are cut
by moving water. For example, the earnest layman may think that
the shapes of desert rocks are cut by sand blown by the wind.
Never. Every one of them is water-cut, including the natural
arches. If you compare, you will find the only other place rocks
are cut in arches like this is along sea coasts or the courses
Water doesn't fall often in a desert and may
only run occasionally in some stream beds, but all those landforms
like Monument Valley were either cut when the area was wetter
(in some cases along giant ice-age lakes) or are being slowly
bitten out by the annual gully-washer. The Grand Canyon of the
Colorado is entirely water-cut, in the midst of a thorough-going
desert. This applies on other planets, too: the Grand Canyon
of Mars shows all the dendritic form of a water-cut river valley.
At some time up there, it ran really wet, even if ten million
So in desert areas you will have dry lakes
and dry stream beds. They may have been dry since ancient times,
or they may be only presently intermittent. A storm in the mountains
can send a ten-foot deep flash-flood down a dry stream bed, or
a near-empty watercourse gully, neatly wiping out any party camped
Excepting rift valleys and folds between mountains,
all other valleys are river valleys -- that is, cut by moving
streams, even if the "valley" is only a ten-foot wide
gully. On soft ground, streams merge in what is called a dendritic
or tree-like pattern. On hard rock, they may be forced into angular
patterns, following the fractures of the stone beds where it
is easier for the water to chip off a path.
So now you have mountains uplifting, with
slopes down to the sea and gentler ones between chains or between
the arms of chains. Then, from the crags down to the sea, you
have rivers and lakes.
Uh, not always. The idea that if you follow
any stream down you will eventually reach the sea has killed
a certain number of explorers, hikers, and lost people in general.
Water is not bright. It is not forward-looking.
It doesn't check the map and say, "I can reach the ocean
by turning left here." All water knows is the next inch
of travel. It will always follow, not only the slope, but the
steepest slope it touches. Sometimes those slopes lead
to inland basins, not the sea. Nothing feeds out of them.
Very large blind basins are the likes of the
Caspian Sea, Lake Baikal, the Great Salt Lake of Utah, and the
Dead Sea. The last is much saltier than sea water; centuries
of incoming water bearing mineral salts, followed by evaporation
of the diluting water off the surface of the Sea, have resulted
in extreme salinization. The Caspian is also becoming more brackish
at the present time.
The Great Salt Lake is only the remnant of
a far vaster prehistoric lake, one of many that dotted the Southwest.
When the pluvial rains and glaciers that fed them ceased, and
the climate warmed as well, they slowly evaporated, like any
lake that loses all its feeders. Only the likes of the Great
Salt Lake and Lake Mono remain. If you see the Salt Flats in
Utah, you are looking at the dried-out bed of a giant lake that
became as salty as the Dead Sea, then saltier, then left only
its bones of salt behind.
Your world may have blind-basin lakes in any
of these stages. The size seems to depend less on local rainfall
than on the overall climatic stage, swinging from ice-age to
As well, streams may peter out in nowhere,
and never even reach a lake. They may feed a bog, or disappear
through the soil into completely non-spectacular underground
Where Fresh Water Comes From
It all starts as rain. This falls and runs
down hill, always seeking the path of least resistance. Most
obviously, this creates freshets and rivulets that combine into
streams that combine into rivers that go down to the ocean or
blind basins. That's surface water.
Sometimes that path involves soaking into
the soil or porous stone. This creates a local "water table"
-- a level of underground water. When you drill a well to get
water, you are drilling down to the water table. Water table
height can vary seasonally, so that well level drops in the dry
season, even with no increase of use. Since the dry season is
when you need your well water most, lots of wells tapping the
water table can reduce its height drastically, more so than it
would drop naturally. As an area overbuilds, wells have to be
In some cases, the ground dips below the level
of the water table. At this point a seep pond or slough (pronounced
like slew; rhymes with through, not rough or bough) forms as
the water comes out of the soil. A slough may have no entry or
exit streams, only perhaps seasonal run-off from the banks around
it, but still remain full all year.
Where do oases and other water in the desert
come from? In some cases wells are dug hundreds of feet deep
to a distant water table. In others, especially natural outbreaks
of water, you are dealing with "aquifers" -- a porous
layer of stone sandwiched between impervious layers of some different
stone, the aquacludes. Somewhere far away, perhaps in the mountains,
one end of the aquifer is exposed to ground water or surface
water, and sucks it down its length. It dips and rises, since
most rock layers are curved by pressures of mountain-building.
Where it rises, it may break surface, and this lower exposed
end emits the water acquired in the mountains. Next time you're
using the hose outside, turn the water pressure low and hold
the nozzle pointing up, but below the level of the faucet. Out
the water bubbles by force of gravity and the slight pressure
of water behind. That's how aquifers work.
Of course, aquifers emerge wherever the ground
has broken or worn down to them. This doesn't have to be in deserts.
Plenty of well-watered places have natural springs, as these
outbreaks of groundwater are called. There's a lovely one bubbling
up in a vest-pocket park in Kalihi.
If the blocking layer over the aquifer is
only cracked, not worn away, water may shoot up under pressure,
like a pinhole in your hose, causing it to surface unnaturally.
This creates natural artesian fountains. If enough soil
blocks the emerging water, you can still dig down to it, or even
through the hard layer to the aquifer, to get an artesian well
that stays full higher than the local water table.
Of course, after a certain primitive level
of technology, people can dig or drill down to aquifers and create
their own artificial springs and wells. Say, Bronze Age, certainly
early Iron Age. It does not require big steam drills, just picks,
shovels, and long ropes.
As this 1851 encyclopedia engraving shows,
artesian fountains will not shoot up any higher than their source
at the open end of the rock bed. This is important if you are
relying on artesian pressure to feed water up a pipe into the
upper stories of a building, or a raised garden terrace. They
also only fountain when broken through from the upper end to
the lowest point. The farther side of the curve will only provide
artesian wells (d). Next to that, (e) shows a slough fed by the
Water can also emerge from rocks when a stream
comes out of hidden caverns. Most cave systems are cut by water
(caves are a whole world to themselves).
This is tricky for public health reasons. A true spring has pure
waters, filtered by miles of passing through stone. A cave spring
can be full of germs of decay from a hole into the cave system
being used as a garbage dump by the locals. In France, identifying
true springs and cave springs is a matter of some concern for
water supply. Most "cave systems" are not something
you can crawl around in: they are just channels cut underground
by moving water, like natural drain pipes. Tracing a stream that
dives underground and emerges later may require dyes, not a hard-hat
For world-building, this means you really
can site waterholes wherever you like in basins surrounded by
mountains. Just declare the presence of an aquifer. Because most
aquifers are layers of stone, this means springs will break out
in a line along this exposed edge, kind of parallel to the mountains,
letting you have a string of oases, like that which supported
the Classical Saharan Garamantes horse-chariot culture. You can
have "poisonous" wells or springs anywhere, not just
in volcanic zones, because the water comes through a deposit
of arsenic or cadmium on its way to the surface, or just because
there's a regular supply of dead animals in a cave on the other
side of the ridge where this cave spring first goes underground.
You can always cause thirst or save from it, by order of world-building