How Do Rivers and Lakes Form and What Determines Their Type?

[caters]

I have heard that rivers form from meltwater and rainwater flowing down mountains. But I know that not all rivers start near mountains. As an example the Mississippi river doesn't start near any mountains. Rather it starts at Lake Itasca which is surrounded by taiga(coniferous forest). This lake itself has water coming into it from Nicollet Creek and the Elk Lake outlet stream. Nobody knows if Nicollet Creek starts near mountains or not.

But even if people did know that, it still wouldn't mean that the Mississippi River originated in mountains.

So no, not all rivers form from mountains. Excessive rainfall in the long term in any area of land can form rivers.

As an example:

Suppose Person A survives in the wild for years and more south winds than usual brings more rain to the area where Person A is. Over years, this becomes the norm and soil starts to erode but during the winter there is ice in the depressions in the soil. Once it warms up more soil erodes to a point that after several decades a body of water has formed. This eventually becomes a river.

So why do people often say that rivers form from mountains when that isn't always the case?

And what determines whether the body of water that forms is a lake, river, or other body of water? Water speed? Amount of water over time?

 

[HallsofIvy]

I can't answer your question because I have never met a person who said that! Can you give a specific quote of a person saying that?

 

[caters]

People in fantasy cartography often say that rivers form from mountains. Lots of river formation diagrams also have mountains or steep hills like this one:

So this leads to a lot of people thinking "There have to be mountains in order for a river to form." when a river can form on land without mountains from erosion of soil causing water to flow which causes there to be more erosion until it becomes a river.

 

[SteamKing]

And what determines whether the body of water that forms is a lake, river, or other body of water? Water speed? Amount of water over time?

A lake is a large inland body of standing water.

A river is a large, natural stream of water flowing in a channel into the sea, a lake, or another such stream.

The key difference between a river and a lake is high-lighted above.

 

[256bits]

People in fantasy cartography often say that rivers form from mountains. Lots of river formation diagrams also have mountains or steep hills like this one:

So this leads to a lot of people thinking "There have to be mountains in order for a river to form." when a river can form on land without mountains from erosion of soil causing water to flow which causes there to be more erosion until it becomes a river.

Fantasy cartography??
If it is story telling then part of the plot to induce the mystery of the origin of the river adds to the suspense and imagination if the river forms in the far off mystical mountain wilderness area.

Seriously though.
Rivers are nothing more than drainage systems of the land of water.
At time melt from glaciers or snow topped mountains can be the source of a river, in which case the flow make become intense as more and more water is added, and also due to the gradient of the land.
At other times a river drains a relatively flat area.

Such an area would along be the Mississippi.

Another area is the Red River basin.
https://en.wikipedia.org/wiki/Assiniboine_River
There are not any mountains there either. The rivers there are what you see when the water table breaks the surface of the land in lower lying regions.

So, back to your premise. Anyone living in those areas would be not guessing that a river source is only from mountains. In fact, in spring the snow melt from the flat land is responsible for the surge in river volume, bank overflow and flooding. The Red River flowing north towards Winnipeg with a quick spring can be a problem as it cannot drain the land fast enough. Farther east, the Qu'Appelle river may become just a mud bottom in certain places in a hot dry summer, with little replenishment to keep the flow going. A good rainfall and the river is back in business.

 

[HallsofIvy]

People in fantasy cartography often say that rivers form from mountains. Lots of river formation diagrams also have mountains or steep hills like this one:

I have no idea what "fantasy cartography" is!

So this leads to a lot of people thinking "There have to be mountains in order for a river to form." when a river can form on land without mountains from erosion of soil causing water to flow which causes there to be more erosion until it becomes a river.

Apparently it leads to you thinking that but I see no evidence that "a lot of people" do. Water flows from higher levels to lower levels that does not necessarily mean "mountains".

 

[caters]

Fantasy cartography is making maps of fantasy worlds whether they are game worlds or worlds in books.

Lots of people make maps of fantasy worlds. Lots more people look at river formation diagrams with mountains.

Because of this lots of people think rivers form from mountains. I don't think that is always the case. I even think that flat land can have water flow on it and thus rivers can form.

 

[SteamKing]

Because of this lots of people think rivers form from mountains. I don't think that is always the case. I even think that flat land can have water flow on it and thus rivers can form.

You may think the land is flat where the river is, but there must be a gradient of some sort in order for the stream to flow. If the water isn't flowing, you just have a long, skinny lake.

Take the Mississippi River, for example.

https://en.wikipedia.org/wiki/Mississippi_River

Its source is Lake Itasca in Minnesota, which has an elevation of 1475 feet (450 m) above sea level. The River runs for some 2320 miles (3734 km) before emptying into the Gulf of Mexico. The average gradient is thus 0.64 feet per mile, or about 0.012%.

 

[Vedward]

The Chicago river starts as drainage from a trailor court that flows into a marshy area. Many of the feeder streams and rivers for Mississippi start in ponds or drainage ditches in the flat areas of the Mid-West, Of course the main feeders are the Missouri & Ohio rivers which do start in mountains.

 

[jim hardy]

It's as simple as water runs downhill.

If you've ever hiked, you know mountainsides are a lot more "downhill"(or uphill) than prairies.
That steepness not only makes water flow more visibly
it encourages precipitation as air moves up to get over the mountain

so sure, many mountains have streams running off them
and artists have long known that

 

[Monali Khandagle]

Streams and Rivers form by eroding soil due to the flow of water. It can happen anywhere on relatively flat ground too. As the soil erodes the water channel carves out valleys, and canyons too. The force of gravity aids the flow of water, so a steep slope leads to faster erosion than a low slope.

 

[DaveC426913]

Replace the word mountains with highlands. (Note that your fantasy cartographic diagram does not say anything about 'mountains'.)

The source of any river (and any tributaries leading into it) will always be at a higher altitude than its mouth.

The Mississippi may have Nicollet Creek and the Elk Lake as two of its sources, but it is fed by countless tributaries, all at higher ground.

Note how many tributaries that contribute to the Mississippi watershed start at the Rockies in the west and the Appalachians in the east (All the others start in highlands):

 

[DaveC426913]

Oh, and apropos of nothing except a love of beauty and maps, here is a beautiful framed-poster-worthy map of Mississippi meandering:

 

[Hornbein]

You may think the land is flat where the river is, but there must be a gradient of some sort in order for the stream to flow. If the water isn't flowing, you just have a long, skinny lake.

Take the Mississippi River, for example.

https://en.wikipedia.org/wiki/Mississippi_River

Its source is Lake Itasca in Minnesota, which has an elevation of 1475 feet (450 m) above sea level. The River runs for some 2320 miles (3734 km) before emptying into the Gulf of Mexico. The average gradient is thus 0.64 feet per mile, or about 0.012%.

I once went down the Porcupine River in Alaska. I recall that it dropped 20 feet in 200 miles for 0.1 feet per mile. It flowed a good four knots or so and didn't meander much most of the time.