One explanation that I found was rainfall but it is not apparent that rainfall could contribute to such volume of water.
In: Geology
Is it ever the case that a spring on a hillside near a large lake is fed by water from the lake being pushed underground up the hill by the intense pressure of the lake?
Ever pop a zit? That’s like a tiny hill and the spring is inside it. Push down and toward the hill and something comes out the top. The earth is always moving like that and we can’t see it.
Some hills are not zits though. They are your nose. Dont pop your nose.
Has to be rainfall.
It’s all about gravity and the path of least resistance. The rainfall dribbles down through porous layers until it gets to a less porous layer. It then pools up on the less porous layers and follows the path of least resistance to where the layer emerges from underground and… voila! A spring.
If it truly is at the top of a hill then there HAS to be a higher hill that is feeding it, cuz…. gravity.
This information on artesian aquifers shows the concept nicely.
https://en.m.wikipedia.org/wiki/Artesian_aquifer
I have a very good spring in a cow lot. It is at least a mile to a mountain. I’m 76 and it was here before me.
Not springs, but many ponds on top of hills could be kettle ponds or kettle holes. These were formed by retreating glaciers. Big pieces of ice would be left behind and form a pothole, and then sometimes form a lake, pond and even other types of wetlands.
They’re connected to aquifers and when it rains the water is pushed up out of the cracks which bubble up to the surface of the planet to make room for more water from when it rains.
As rainwater falls and absorbs into the ground it is purified when it hits gravel in the ground down to microscopic size so by the time it gets into your well, you water is clean. Solid wastes are broken down by worms and other beneficial bacteria in the soil.
If part of the aquifer is near the surface of a creek bed, the water comes out to feed the streams. It’s a more shallow aquifer since it’s close to the surface. It feels like a low pressure jet of water that bubbles.
The springs are cold because under the soil it gets cold really fast about 300 feet down it can be 50 degrees year round but the water will never freeze usually due to this above freezing temp all year round.
So if you see a spring fed creek and it’s hot out, don’t jump in right away or youll be shivering really quick. The water is so cold it’s like a chilled soda almost. Trout and salmon love the deep parts of a stream where the water is clear fed from a spring. .
When it rains on top of your roof you get a substantial flow collected by your gutters and down through your water spout.
A hill is similar to roof roof except that the water flows over/through soil and rock instead of across your roof and discharges out springs instead of a water spout.
There is obviously more to it than just that, but that is an ELI5 version.
For those interested, water will also move more slowly through rock/soil which means your peak flows will be lower during rainfall relative to a roof, but they will continue for much longer. This is why springs can continue flowing days, months, or even years after the last major rainfall event. Some water will also be lost due to evapotransipiration or will migrate to depth.
Source: Hydrogeologist, water flowing underground is my thing.
In hydrology there’s two terms we’re interested in here. Water Table, and Potentiometric Surface.
The water table is simply the depth that the top of the water sits at (e.g. 10m below surface). Groundwater is under pressure, sorta like if you filled a baggie with water and then put a bunch of books on top. The weight of all the rock and stuff above it pressurizes the water. The Potentiometric Surface is the height that the water would rise *if that pressure was removed in an area*, like if you poked a pinhole in your baggie of water while the books are on top, it would spray upward.
An Artesian spring, which is what you’re describing, is simply a place where the Potentiometric Surface is **above** the ground surface. So when there’s a weak spot like a well, or cracks in the Earth, the water bubbles up out of the ground until gravity and other forces pull it back down.
Another thing that can happen is when water seems to flow out the side of a hill. What’s going on here is that under the water table beneath that hill there’s a layer of impenetrable material that water can’t pass through easily called a ‘confining layer’, or aquitard. The water can’t go down anymore, so it goes off to the side, going downhill. When it hits the side of the hill, it still can’t go down because of that aquitard, so it just dribbles out the side of the hill. You can see this if you look at a hillside and part way up there’s suddenly a bunch of greenery with nothing above it. The plants took root there because there’s lots of water percolating through the soil there.
Groundwater will follow the path of least resistance, like a river will on the surface. Underground, this means following cracks and other spaces that can lead well above the actual water table. Some of these springs may disappear and reappear depending on actual groundwater levels, or disappear entirely due to an opening some distance away that allows the release of pressure within the groundwater system.
There is so much water in the ground that it’s crazy. Springs are just where the land goes below the water table and it bubbles out.
The water comes from meteor strikes, volcanic eruptions, rainfall, glacial melt, etc. On top of all this geomorphological forces change the shape of the land and the water table over time, which moves where the rivers and streams are.
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