To explain further, what stops lakes from simply seeping into the dirt, and thus vanishing? As a follow up question, what stops water from getting evaporated, and then the clouds move somewhere else and rain, thus depriving the lake of the water it lost?
In: Earth Science
On a side note:
Clay particles are like playing cards on a much smaller level. When they are first deposited, they can stack up like a house of cards; however, when enough weight is placed on top, they will flatten out. This arrangement of the clay particles will keep water from flowing through these layers.
On the other hand, sand particles act like little balls. The rounder the balls, the more void space between each sand grain. Imagine a swimming pool full of bowling balls. If you pulled the drain, there would be nothing preventing the water from draining out.
There are some great answers here. I’m going to try to break it down a bit for you.
It’s pretty obvious that water flows downhill. It might not be as easy to see but water flows downhill where you can’t see it too.
Imagine you are at the beach. A common fun game is building a sand castle. Every castle needs a moat, right? So you dig down, and boom… you strike water! You found the water table, or water level.
The water table at the beach is *very* nearly the same as ocean level (or lake level if you are at a beach on the lake… **spoilers**). If you go further and further from the beach the land elevation generally increases. But the water table generally increases too! At least near stream, rivers, and lakes. So if you are in an imaginary house, digging an imaginary well, *near* a stream, then the well will be pretty shallow. If your imaginary house is *far* from an imaginary stream, the imaginary well will be deep. Don’t be fooled by soil, clay, or rock. They all hold bunches of water in different ways.
Here’s the thing if your imaginary well was a few feet/meters closer to the stream, at the same height, your well would be correspondingly deeper. The water, underground, is flowing downhill!
A lake (sea or ocean) is temporary place where the surface ground is lower than the water level. Most of the time a lake is like a hidden waterfall moving water over the “edge” in slow motion and hidden from view.
There can be exceptions due to spring fed lakes. They can be *higher* than local water table because the spring that feeds them is from an artificially higher water table. Central Florida USA is famous for them. Water from “high up” in Georgia gets trapped beneath impermeable ground and is kind of under pressure. It’s positively asking to get out and up. As it flows “downhill” to flat old Florida it finally pops out, making lakes and rivers galore.
Lastly all lakes (seas or oceans) are geologically temporary things. Lakes silt up into marshes really “quickly”. Seas too. Oceans open and close all the dang time (geologically speaking). In current news there is a volcano in Iceland going bonkers. That volcano is on the Mid-Atlantic-Rift. A place where the ocean floor is **spreading** and making the ocean bigger. Other times it gets smaller, even till it has disappeared altogether.
A lot of areas have clay soils which form a seal, and do not let water penetrate once a wet seal has formed. These clays are often used for sealing dams and other man-made structures. In areas where the clay isn’t necessarily under the lake naturally, it washes down from other areas and accumulates in a low area, forming the lake bed, sealing it from water seeping away.
If you have ever come across mud where, once you dig into it a few inches, the soil under the mud is dry, you likely came across this kind of clay. I believe these clays are known as smectite clays. Correct me if I’m mistaken, any geologists out there.
This is just one type of water-holding geology. I’m sure there are others. If you make a man-made pond, and don’t want to line it with plastic (which works, but which can get ruptured), lining it with a substantial layer of sealing clay before filling it with water is the old fashioned way of making a pond.
There’s also water inside the earth, the lake is just a low point. Think of the Earth like a sponge that is constantly getting saturated with water (from rain). It keeps absorbing until it can’t hold any more, then the excess water will start to flow right out of the sides of hills etc as small springs which eventually coalesce into creeks and rivers and then flow into lakes. If you looked at a sponge very close-up and see water collected in one of the indentations, that is a lot like a lake.
Just stopped by to suggest reading this article on a lake that did exactly that: it dried up. Now it’s coming back.
[Giles County’s mysterious Mountain Lake rising once again (wsls.com)](https://www.wsls.com/news/local/2020/07/14/giles-countys-mysterious-mountain-lake-rising-once-again/)
Most soils have something called the *water table,* which is a way of referring to soils that are completely saturated with water. Most streams, rivers, and lakes exist as visible parts of the top of the water table. The lake doesn’t seep into the dirt because the dirt below it is already saturated with water, and can’t hold any more.
There are exceptions. Most deserts don’t have a water table or if they do, it’s so deep there are no surface manifestations of it.
For your follow up question, this does in fact happen in some cases. Lake Tahoe (CA, NV USA) is a very deep, rainwater-fed lake entirely contained by rock; it’s outlet is the Truckee River, which flows through Reno, NV and then north to Pyramid Lake, where 100% of the water is lost to evaporation.
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