where do rivers start? Can we trace rivers to a spot where it starts to pour out like a tap?
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I thought this was a dumb question, not fitting this sub, but reading the replies, I see it might not be.
Water that will become rivers (or streams, brooks, creeks, there’s no official definition of river, it’s all just colloquial names) usually comes from either a spring or a glacial lake.
A spring is a point where underground water from an aquifer emerges to the surface. There is often literally a human constructed tap you can drink out of.
Aquifer is water underground, but it’s not like a lake of water in a cave, the water is in the ground itself, similar to when you pour water on the ground and it disappears. At some places, there is are ground layers that will let water through followed by a ground layer that will not let water through anymore (bedrock) and that’s where aquifers form. This is also how wells work, btw.
Glacial lakes are usually formed in a basin in a mountain, and they aren’t fed by another river, but rather by rain and snow melting and flowing into the lake. Rivers can flow out of them.
Most rivers will eventually flow into another body of water (and I mean really almost all of them). Often it’s another river, and then the smaller rivers are called the bigger river’s tributaries. Some rivers “originate” at a spot where two or more tributaries meet, but that just means they are named a new name at that spot. Most rivers are tracked through a single stem to some source I described above. This is called a main stem. But there’s usually not really a “real” way to differentiate between which river is the tributary and which is the main river. It’s usually just done based on which river is bigger or based on the angle.
Many comments here seem to misunderstand what “drainage basin” means. Drainage Basin is an area from which all flowing water eventually converges to a single spot. It can be defined for any body of water, and drainage basins will include other drainage basins. It is not related to rain and snow flowing into some basin and forming rivers.
For example, let’s say river A flows into river B, rivers C and D flow into river E, which then flows into river B, which the flows into some sea. The drainage basin of river E containes the are around rivers C and D. The drainage basin of river B containes the area around river A and the entire drainage area of river E. The drainage area of that sea containes the drainage area of river B (plus sny other rivers that flow into it).
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