How come bodies of water (lakes, rivers, wetlands, oceans even…) exist above ground instead of the water simply being absorbed by the earth?
In: 855
Impermeable rock is deep underground. The soil and rock above it DO have water inundated in them much of the time. When the water is fully saturated it has nowhere else to go but the surface.
Ever though the water might be in a lake etc that is in clay or a non permeable rock?
How can the water make its way through a waterproof clay layer?
So dirt/mud, which is clay, silt, and sand. Is permeable. Water will sink into it. (And soil is just dirt with organic matter mixed in) so you pour water on it, water will sink into it. So how do ponds and lakes form? Well two ways. The first and most important. Is bedrock. Rock is typically not permeable. Limestone and sandstone are, but the rate at which water permeates is so slow it’s negligible. Igneous rocks, and metamorphic rocks are not permeable. So when the bedrock is made of one of those, water can drain down through the dirt until it hits rock and then it starts to pool, when the pooling gets above the dirt you get a lake or pond. This is also why water tables are at different heights and aren’t all just universally sea level.
The other way is saturation. The dirt can only hold so much water. And it can only diffuse it to neighboring dirt so quickly. So if you’re adding water to dirt faster than the dirt can absorb or pass it through then you’ll again end up with standing water. This happens a lot with rainstorms. But also some creeks and rivers work this way, at least partially or in some sections. Especially during floods.
Oils, mostly clays, formed after millennia of breaking down dead dinos, plants, and bacteria. It settles to the bottom due to gravity, and formed a water-tight seal preventing the water from falling any further.
The closer dirt is to the center of the earth the more dense it becomes, this happens rapidly due to gravitational force. The more intense gravitational pull at the center of the earth causes dirt and sediment to become denser and subsequently hotter, eventually impenetrable. Water and it’s relation to how far underground it can sink is a similar principle to oxygen and how high into our atmosphere it can exist, except in reverse. Eventually the dirt and sediment becomes denser and heavier than the water and so it cannot sink below that level, oxygen and the other elements which make up our atmosphere like methane alternative are too dense to reach out into space, thus creating our atmosphere.
The open space available within soil and rock is not infinite and is not constant from place to place or as you go deeper into the earth. Surface water bodies are basically locations where the open space below is completely filled. In effect, in reality, the water table intersects with the surface (the “lake” of groundwater is filled to overflowing).
In some situations, river flow can be faster than infiltration (rate of sinking of water into the ground) and the river or its destination lake or pond can be “perched” (getting water across the surface faster than the ground fills up), sitting above the groundwater level, but usually the situation is the opposite, where the ground is saturated, all open space is filled with water right up until the surface.
If you have ever been to the beach, a lake or the ocean, does not much matter, and dug a hole in the beach itself, you must have noticed that the underground is filled with water to about the very same level as the nearby lake or ocean. The water levels are linked, and essentially the same in close proximity to the surface water body. The only real question is whether water is flowing TOWARD the water body (acting like an underground river in a way, and dumping water into the hole that is the surface of the ground) or doing the opposite, and seeing water from the lake or river or whatever adding to the nearby groundwater and raising its level locally.
Reality is a bit more complicated than this story, because the ground interferes with water movement, so sometimes the flow is so slow through the ground that it is effectively impermeable and you get perched water bodies above the local groundwater level (kind of like a puddle on the surface of a solid rock outcrop, with no way to flow into the ground, but on a bigger scale).
The earth, though, is pretty much water-saturated from a short distance below ground surface to as far down as there is open space where water can get. Basically, there is so much water on this planet that the inside of the earth cannot come even remotely close to holding it all.
Although depths to groundwater table surface (where saturation is complete) can vary a lot from place to place, it is generally only a few meters or so down to that level, to the top of the water table, although many tens of meters is the situation some places. Mostly, though, at least in any reasonably wet region, it will only be a few meters down until you hit groundwater. This is why houses have French Drains and sump pumps. The basement bottoms are very close to the water table, and water table will rise and fall a bit (a few feet or a meter or two, perhaps, depending on climate) over the course of the year, so perhaps in spring you would get a flooded basement if you did not have the sump and drains.
How deep does the water table go? That was a point of argument in geology for a very long time, with the favored view being that groundwater that can migrate being absent after a couple kilometers or so, meaning that the inside of the earth was “impermeable” (lacking open space that water could flow through). Deep drilling has proven this to be false. Fractures exist even at many km down below. The water down that far tends to be quite hot, though.
Think about it in a different way…
Sand sinks. Rocks sink. Clay sinks. Lava (usually) sinks.
The same applies when you have a few quadrillion tonnes of them.
If you would like some ELI5 videos on this subject I recommend practical engineering.
He does a really good job of explains what’s going on with models he builds to show you.
https://youtube.com/c/PracticalEngineeringChannel
The US state of Georgia, where I am, has NO natural lakes – every one is behind a man made dam.
With bodies of water being like 3/4 of Earth’s total surface
I would argue that You have it backwards,
As All land exists on Top of a body of water
Latest Answers