How do bodies of water exist above ground?


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

Imagine you have a cup without any holes in it. Now, imagine that cup made out of layers of dense rock.

There’s a limit to how much water the ground can absorb. When the ground is full of water, the extra water sits on top.

If you’re near a body of water, and you dig a hole, you’ll find the underground water pretty quick.

1) They *do* sink into the ground. Eventually it’ll hit an *impermeable* layer of dense bedrock that the water can’t go through. The ground will become saturated and no more water can drain down.

2) The ground slows the water down: imagine a cup with small holes in it. The water will drain out, but as long as water goes *in* faster than it drains, the water level will stay elevated.

3) Some kinds of soil are less permeable to water, like clay. Rock, obviously, doesn’t allow water to sink through very easily.

4) Water that drains through the soil will eventually either sink into an aquifer or get forced back up from pressure and form a spring.

One big misconception about lakes is they’re like a cup of water. They get filled and stay that way. Nothing is further from the truth. All lakes are constantly being fed by springs or other flowing waters. At the same time, all lakes have an outflow down a river, stream or into a swampy area which acts like a broad slow moving river. If the rate of drainage in a low lying area is less than it’s rate of fill then you get water building up. If the rate equals out then you simply have a river or stream. And rivers and streams do lose some water through seepage into the ground but the water is moving too fast for any significant loss of water per volume flowing over an area.

Now a couple geological conditions help lakes reatin their water. Chiefly, the bottoms of a lake is either made up of tight nonporous soil like clays or is part of the bedrock itself. If the bottom of an area with a large inflow of water is not like that, that’s when it becomes a swamp because the soil becomes oversaturated.