Why do lakes not just seep into the earth?

291 views

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

Lakes are usually fed by rivers, streams, springs, or regular rainfall.

They do lose water to seepage and evaporation, and that water is replaced by new water coming in. If no water comes in, the lake eventually dries up.

Nothing, really. All lakes lose water to evaporation, and all lakes exchange water with the surrounding groundwater. Lakes persist where the rate of rainfall and runoff into the lake is greater than the rate of evapration and seepage out of it.

Under the bottom of the lake is a layer of impermeable rock. Otherwise it does leak into the ground, forming an aquifer, and leaving a dry lake bed in it’s wake.

The rate of recharge is also pretty close to the rate of evaporation in many cases; when it’s greater than evaporation rates, it overflows causing flooding, when it is less than evaporation rates, the water levels in the lake start to drop.

The hydrologic cycle is a good place to start looking to satisfy your curiosity

Both of these things are happening constantly, but the rate at which they happen (overall) is not fast enough to make the lake be empty =)

For water to seep into the dirt it has to have somewhere to go. The dirt at the bottom of the lake is already saturated, so it can’t absorb more water. Usually you have to go pretty far away to find soil that can hold a lot more water for the exact reason you asked about.

Likewise, water is constantly evaporating from the lake. But a lake only has so much surface area so it can only evaporate so fast.

In contrast, lakes are typically areas where lots of rivers/streams/runoff feeds into a single location (the lake), so they are constantly refilling.

They do. They just get refilled by all the water sources that made it a lake in the first place.

It’s important to remember, dirt isn’t a normal. It’s organic, created by living things that broke down rock. So if you go down far enough you get rock. Water eroding away at certain rocks creates things like clay, which you can think of as dust that clings to water. Clay doesn’t really flow and so isn’t likely to sink much lower, it’s taken on as much water as it can and so the water above doesn’t move into the ground as quickly as it would through porous rock or soil. It sets up a situation where you’re likely to have as much if not more water coming in as it leaving.

As for evaporation not just drying up any given lake, they are usually at a low point in the surrounding area, meaning it doesn’t have rain directly on the lake to regain the water it loses to evaporation. Of course lakes do evaporate sometimes, but as lake gets deeper it’s going to have less surface area to lose water from compared to the total volume of water.

Geologist here. There are at a few basic reasons the water won’t seep into the ground beneath lakes (from what I can remember off the top of my head).

1. Some lakes are a ‘window’ into an aquifer, where subsurface water has collected and sat for thousands of years. This water can be depleted but as long as the incoming water is greater than or equal to the outgoing water it will remain.

2. Soils (or bedrock) that make up most lakes have a low hydraulic conductivity (the rate at which water permeates through). Soils such as clay or glacial till are excellent soils if you wanted to create a lake. (Fun fact: many landfills are lined with specific types of clay for this exact reason so no pollutants will go into the surrounding earth). If you have terrain where water will pool and sufficient rain or streams, it will create a pond or lake.

3. A surface depression with incoming water may create a lake or pond as long as that water flow is enough to keep the water there. Over time dying plants and the deposition of silt and clay can create a hydraulically restrictive later, ie, peat and organic silts and clays.

There’s a simple equation to express how lakes exist. It is Inflow – Outflow = Storage.Lakes can be fed directly by rivers and groundwater, and indirectly by rainfall or other forms of runoff (snowmelt is one i’m thinking of)

The reason why they don’t seep into the earth is because soil can have different permeabilities. In areas with high groundwater tables and low permeability you don’t need much inflow to cause standing water (e.g. wetlands, swamps). In other area standing water is very temporary (e.g. sandy areas)

The ground is like a sponge, it can soak up water but once the sponge is soaked it can’t soak up any more.

Put the sponge in a tub the water can’t escape through the sides and the excess water pools on top.

The ground under lakes is at saturation point so can’t drain any more (or at least at a rate faster than water is being added by rivers).

If you’ve ever had a lot of rain in your garden you see this in miniature. The ground becomes really wet (to the point you can squish water out by walking on it) then if it keeps raining you can get puddles in the middle of your lawn.

I think the misunderstanding you have is that you believe water just seeps into the ground and disappears forever. That’s not correct.

When water lands on your lawn, for example, it may seep into the soil, but it’s not going very far. Most of that water will be making it’s way underground to the nearest ditch, steam, river. The water doesn’t (much) go into the bedrock. And anywhere that it does, it will reach an aquifer which is already full of water from the millions of years of this happening.

Also after a very short amount of rain, the soil is full, and will absorb no more water. After that, the water is going to start ‘flooding’ by an inch or so and flowing overland to the nearest stream.

As for evaporatolion, it does evaporate, but slowly, and lakes are fed by streams and rivers. They in turn feed bigger rivers. A huge amount of the rain that lands in the USA east of the rockies eventually winds up in the Mississippi River this way, via various streams and lakes along the way.

Lately, in any place where a lake’s evaporation or draining is faster than it’s inputs, there isn’t a lake anymore. They dry up. So if you see a lake, that means that it’s currently in or very close to it’s equilibrium, where inputs = outputs.

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.

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’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.

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.

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.

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/)