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