I know some wells yield salt water but why not all of them? With the bulk of the water on the planet being salty ocean water, why isn’t the ground water full of salt too?
It gets filtered by rocks through percolation, you can find well water with significant saturated minerals in West Texas for example
The oceans are salty primarily because of the salts dissolved by rivers running into the oceans. A well is dug down for pooled rain water, and in the main, does not have dissolved salts. If you live near an ocean, a deep enough well will hit salty water, but a shallower well will not.
When saltwater evaporates, the water vapor goes into the air and leaves the salt behind, and when water vapor condenses into liquid it falls as rain. So, even if you start off with nothing but salty ocean water, you’ll soon get weather and rain and ponds and lakes and groundwater that is not salty.
San Antonio’s water utility just recently tapped into a “brackish” aquifer south and west of town (http://www.saws.org/our_water/waterresources/projects/desal.shtml) The project will include a desalination plant to make the water usable. San Antonio currently gets its water from a different, non-brackish aquifer. The new project is meant to reducing the dependency on the main aquifer into the future.
Which rivers are those? All the rivers I know are fresh except where they meet and mix with the ocean.
The rivers are fresh, but the is some level of salt. The oceans are salty because the water evaporates, leaving the salt. The evaporated water then rains back down, some of it picks up some more salt and carries it to the ocean, etc., etc…
That’s wrong in that it sounds as if the water in the oceans doesn’t do any dissolving itself - which it does. Some of the salts in the seas come from inland; some comes from the bottom of the seas themselves.
Have you ever seen water spots on glasses? Those white spots are the minute amount of salt (calcium carbonate, sodium chloride) left behind when the “fresh” water evaporates.
A lot of the ground water of inland Australia is brackish. Bore water is of very variable quality and commonly bores are dug only to yield water too salty for livestock. Of course most of the working bores are potable, because the saline ones are capped.
In times of low flow this can even extend to the major rivers. When discovered in 1829 by Charles Sturt, the Darling River (the country’s second longest river) was too salty to drink.
In northern Victoria there is the Barr Creek which drains (though oozes might be more descriptive) into the Murray. Admittedly it is hardly one of the worlds significant waterways, but often has EC measurements of above 20. Rain water has an EC around 0.02, fresh water under 1.5, sea water about 55.
It’s worth mentioning that the oceans are not becoming more salty. The oceans are very old and will have reached an equilibrium level a long long time ago, between the amount of salt added by the means you describe and the amount removed from the oceans by various mechanisms (e.g. waves resulting in salt spray being blown inland).
Seas are salty but don’t get any saltier
Q: Why is the sea water salty ?
A: As the rains fall and water flows over the land, the water dissolves salt out of the rocks, washes the salt into streams, then rivers, and finally carries the salt to the sea. The salt stays in the sea because no water flows out of the sea-just as no water flows out of the Great Salt Lake in Utah. When seawater evaporates to form clouds, almost all of the salt stays behind. The left-behind salt slowly accumulates until, over the eons, the seas became salty-now about three percent.
That’s the simple picture, which is true but incomplete.
Seawater also picks up salt from the oceanic crust. The ocean floor has places, called hydrothermal vents, where seawater seeps into the rocks of the oceanic crust, gets hot, dissolves salts from the crust, flows back into the ocean with its salt load, and increases the ocean’s saltiness.
Volcanos erupting under the sea is yet another way the sea gets salty. Seawater, once again, dissolves salts from the molten rock.
Will the seas keep on getting salty? No. The oceans have stayed at about three percent for hundreds of million years because they lose salt in several ways.
Pick up a clamshell and heft it in your hand: heavy. All creatures need sodium to live and most need calcium to build skeletons and shells. The clam, like all sea creatures, gets its sodium and calcium from seawater salt. When the creatures die, their salt gets locked up in sediment. Some of the sediment gets pushed deep within Earth-more about that in a moment.
Round here at least, those water spots are mostly chalk. Calcium carbonate is a salt in the chemical sense, but it certainly doesn’t taste salty.
Which is why we have this. (It’s the salt of choice in our home.)
Thanks, lot’s of good answers here. I get the mountain streams being relatively salt free because they are from rain and snow which was recently “distilled” as precipitation.
How about the Great Lakes in the midwestern US? There must be lots of “old” water in those massive lakes that has had plenty of time to accumulate salt from evaporation. Is it because of the geologic formations around and under the lakes that keep them from becoming brackish?
If there’s no salt to begin with, evaporation isn’t going to produce more. The minerals around the Great Lakes do not include salt.
Also, the Great Lakes are very young–20,000 years ago they were under a mile thick sheet of ice.
Rivers flowing into the Great Lakes carry a small amount of dissolved salt. However, the Great Lakes also drain into the ocean, carrying salt out of the lakes, hence no build up.
The Great Salt Lake in Utah has no outlet, so the most of the salt stays put. Lake levels fluctuate, leaving a salty beach, some of which is carried away by winds.
The fancy word for this is an endorheic lake. Other notable examples are the Caspian Sea , the former Aral Sea, and Australia’s Lake Eyre.
And the Dead Sea.