Can underground rivers exist? (re: dowsing)

[Patty_O_Furniture]

In the thread on dowsing, newcommer peter morris says

[Dowsers] claim to be able to find underground rivers, say 15 foot accross that runs for 15 miles.

Even more troubling is this, from even newercommer GMANCANADA:

The teacher then explained to us that we had “dowsed” and “detected” an underground stream that ran 30ft below the football field. He then pulled out a survey map of the neighborhood that clearly showed the stream.

Hmm… 30 feet below the surface of a football field. The surveyors knew about it and still built a football field and bleachers on top of it. :dubious:

The dowsing issue is being handily dealt with in the other thread, so just with respect to these mysterious underground rivers we’re always hearing about… could they even exist? Nature makes rivers by carving them out of the ground. Water runs down the side of a mountain, over level ground until gravity brings it to the sea or ocean. Along the way it carves out a channel in the earth. After a few million years, we get a river.

I can’t get my mind behind the mechanism that would have to be in place to create undreground rivers. Several problems come to mind.

1. Erosion would eventually cause the ground above the river to cave in, along with the bleachers, bandstands and football players. Suddenly there would be no more river (possible a lake would form).

2. For erosion to have a negligible affect on the surrounding earth, it would have to be very far below the surface, perhaps a mile or more. In this case where does the river empty, into the ocean floor? Not likely, in face the ocean would back-fill into any alleged subterrainean river and we’d end up with a “tunnel” full of standing water. The water would back up at the source and eventually we’d have a lake, until it overflows and starts cutting channels into the surface of the earth again, eventually creating a regular boring old surface river.

3. What is the source? Mountain ranges? Does melting snow leak “into” the mountain, punching holes through it rather than flowing over/around it? I can see how some water would wind up in pockets, thereby creating small pools or even lakes inside caverns.

The requisite Google searches:

Underground rivers, springs not the “pipes” they appear:

[O]ngoing studies by a University of Florida geologist offer new evidence that much of the water that feeds the springs in the region flows through tiny pores in the rocks, not large underwater conduits.

An amazing cave, carved out by underground rivers.:

They were carved out by an underground torrent during the Ice Age. They are still active and the erosion has not stopped, because there is occasional flooding in the caves. This form of erosion, which is very widespread in limestone regions, is called karstic erosion.

Links like this offer pictures of what appear to be more lakes than actual rivers. Cavernous lakes I can understand. But where are all the pictures of the rivers?

(searches for “karstic erosion”)

That wasn’t much help; more pictures of pools of water inside of caves. Color me unimpressed.

So how about it, resident geologists. Is it even possible?

[ultrafilter]

They do exist, and I’ve seen one, in a cave somewhere in southern Ohio.

[krisolov]

they most certainly do exist. They’re called aquifers and provide drinking water for a number of cities. I know an aquifer supplies the Upstate NY cities of Albany and Schenectady with a significant quantity of very good water.

[psychonaut]

Some rivers get to be underground rivers by human intervention. Toronto, for example, has at least one underground river because some people decided to build buildings on top of it. Part of it runs directly under the University of Toronto campus.

[NurseCarmen]

They are quite common around these parts.

[Chronos]

There’s the River Styx in Mammoth Caves, KY, but the tour skipped it when I was there, and I can’t find any good pictures to tell whether it’s the sort of thing you’re looking for.

Then, too, anything associated with Mammoth or Carlsbad is likely to be the exception, rather than the rule.

[Yossarian]

Basically, an “underground river” = “strongly anisotropic aquifer”. As mentioned, these occur mostly in karsted limestones where the secondary porosity (i.e., dissolution features, such as a cave) is structurally controlled and thus develops a preferred orientation.

[kniz]

from On-LinePravda
Russian scientists have discovered an underground river in the Sahara Desert**…**

At the Mauritanian Government’s request, the Russian geologists undertook a search for underground fresh water reserves. The drilling was carried out by Mauritanian military engineers**…**

a hugely powerful underground river was discovered at a depth of 250 metres below a thick layer of volcanic rock.…

the discovery of water beneath hard volcanic rock could be explained by an eruption of lava several thousand years ago, which followed the course of a powerful river, forcing it underground.

However an aquifer is something else:

from USGS (Ground Water)
It is difficult to visualize water underground. Some people believe that ground water collects in underground lakes or flows in underground rivers. In fact, ground water is simply the subsurface water that fully saturates pores or cracks in soils and rocks.

[JRDelirious]

The Camuy River, here in PR, runs underground for part of its course. Essentially what we have is a cavern system into which an upland stream falls, and the water then flows a few km thru the caverns to where it comes out the side of the hill and comes back out in the lowland. But yes, this is the exception. And yes, that terrain is very prone to sinkholes.

[MaryEFoo]

Virtually all underground free-flowing strems are in limestone regions, ie areas where the bedrock is limestone.

Water dissolves acid components (CO-2 from the air or decomposing plant material), which reacts on the limestone to dissolve it, opening up holes; it’s more effective than straight erosion. Cracks underground can develop into caves and sinkholes over time, this way.

The examples in prior posts were all in limestone country, ie Florida, Mammoth Caves, the area in Minnesota–with the exception of the lava flow in Mauritius, concerning which I would like to read the geologists’ report. Florida has a high water table, but areas like the Yucatan with plenty of rain and limestone base don’t have surface streams, as the water quickly finds a drain.

In non-limestone areas, a well is far more likely to tap into the ‘water table’, where surface water has sunk into porous material underground (soil or porous rock), and is available widely anywhere the well reaches the saturated porous material, ie the aquifer.

Aquifer means water-bearing; an aquifer may be a layer of porous rock that is beneath an impermeable layer, and the water may be entering the aquifer from rain a long way off; or even be ‘fossil’ water, water that has been there for geologic ages and is not being replenished.

An aquifer may be better thought of as a layer of saturated sand or shale, than as a river. The water does not flow free, but seeps.

[yabob]

Another example which isn’t in limestone is the Big and Little Lost Rivers in Idaho. That is also volcanic. The Lost River goes underground in the Snake River lava plains. It flows about 100 miles underground to emerge as a large number of springs in places like this:

Retired Site | PBS

But yes, flowing underground rivers are usually in limestone country.

[Peter_Morris]

I posted the question on a geology forum. This answer is based on what expert geologists told me. You can read the original answers here: http://tinyurl.com/bp5m

Here are a few choice comments.

<<Except for a few circumstances where streams and rivers can flow underground though limestone in karst country (where they have carved/dissolved cracks and caverns as channels thru the rock and flow thru these openings), underground water is NOT found flowing as “rivers”. It is found in the spaces between the particles that make up the soil or the rocks, filling in the space and flowing very slowly around the grains of rock. This is referred to as pore space, and porosity is the term used to tell what percentage of the material is open pore space. The porosity differs based on the size of the grains and the degree of sorting (i.e. - whether there is a mixture of large and small grains, or the grains are all roughly the same size).

There is more pore space, thus more water available, in sands and gravels than there is in silty fine-grained sediments. Since there is more open pore space to hold water, there is also less resistance to flow and the water will travel faster through these materials. You tend to find sands and gravels in old stream beds that have been buried, so you do find water flowing faster and in greater quantities through old buried rivers than through the surrounding materials, but it still doesn’t count as an “underground river”.>>

<<To which, I would add: Karst is about 15% of the earth’s surface, and in those areas which are karst, it is ubiquitous. Where these underground rivers emerge as springs, they can be quite “full-grown” discharging hundreds of millions of gallons a water daily. Notable US occurences of “underground rivers” are Florida and Missouri–any place people cave dive is liable to have this setup.>>

<<In addition to karst there are also other types of formations that could pass for “underground streams” although of an intermittant nature. In south Alabama where I live, we have formations that are composed of alternating clay and sand layers. During heavy rains it is not uncommon to find collapse features where the clay has collapsed revealing quite literally a window over an underground stream running just below the ground surface. The sand is quite fine and unconsolidated. It readily washes away leaving a conduit between clay layers that fill during heavy rains. I could see where people after seeing this phenomena could easily extrapolate further to “underground rivers” or “underground lakes” etc. The water flow can easily be hundreds of gallons per minute initially>>

So, to summarize, in 15-20% of the world underground rivers are very common, and in the rest of the world you get ancient buried riverbeds, which are very similar to undergrounbd rivers, but not quite the same. Water flows along the burried riverbeds at a rate vastly greater than in the surrounding rock.

[MC_Master_of_Ceremonies]

They are very common in the UK and the sport of pot-holing owes it’s existance to them.

[Flying_Monk]

I think someone could have asserted the fact that dowsing is complete nonsense by now…

[Patty_O_Furniture]

Check the (several) thread(s) in GD for that.

[RealityChuck]

*Originally posted by krisolov *
**they most certainly do exist. They’re called aquifers and provide drinking water for a number of cities. I know an aquifer supplies the Upstate NY cities of Albany and Schenectady with a significant quantity of very good water. **

As someone on the scene, let me point out that the Great Flats aquifer is not an “underground stream.” It’s an area of sandy soil where the water from the Mohawk River percolates through. The sand cleans the water (which needs it) and makes it drinkable, but there is nothing you could call a stream.

[Una_Persson]

Having seen underground rivers in caves as well, I really think they’re both cool and scary. Especially the ones where no one knows where they start, and no one knows where they end. You can almost imagine them somehow flowing for hundreds of miles, then plunging to a vast, sunless sea filled with Shoggoths…

[Patty_O_Furniture]

A cave is a hole in the side of a mountain. Do these rivers in caves really count as “underground” in the sense that they could be the type that the dowsers are claiming to be able to find? Back to the underground river I mentioned in the OP (30 feet below a soft, grassy football field) - could such a thing exist?

I can fully comprehend the seepage idea, where the ground gets saturated over the course of many years and great volumes of water slowly leech through gravel or porus rock. But… rivers? Great torrents of water gushing through channels just a few dozen feet below the soil we stand on, drive on and build houses on? This is what dowsers are talking about when they claim to find rivers, isn’t it?

[Johnny_L.A]

I was watching a documentary on the Discovery Channel. Some divers in Florida went into a spring or sink-hole. The water travelled underground for a very long way and eventually exited out of a submarine cave in the ocean.

[Patty_O_Furniture]

See, that just doesn’t make sense. Or maybe I’m not understanding you right. A channel that opens up below sea level would just become flooded and eventually top off at sea level. As more water continues to flow into this channel, it would eventually back up and we’d have a lake.