how deep does fresh water go?

whitelackington

New member
We know that in phreatic loops, moving fresh water can reach down 100 metres or so below sea level
but how deep can fresh water actually go?
 

Reeve

Member
Non salt water (although not necessarily that fresh) can well up in hot sulphur pools like those in Iceland or the Rockies at temperatures in excess of 50deg, so that woyld reduire a very deep loop to well up at that temperature. Some of them have quite a sizeable flow of water.

Not sure exactly how deep they go though.
 

langcliffe

Well-known member
whitelackington said:
We know that in phreatic loops, moving fresh water can reach down 100 metres or so below sea level
but how deep can fresh water actually go?

The water emerging from the Bath hot springs are thought to originate from the Mendips, and rise up about 4km.
 

Pitlamp

Well-known member
Some of the inland blue holes in the Bahamas are extremely deep, with fresh water in them.

Water can even flow "uphill" from its inflow point, as in that wierd spring on Argostoli.

Aren't there supposed to be some springs where the water is of non meteoric origin (i.e. with water emerging which was produced by chemical reactions in volcanic rocks all the way down in hell?)
 

graham

New member
Pitlamp said:
Some of the inland blue holes in the Bahamas are extremely deep, with fresh water in them.

But isn't the fresh stuff higher up & separated from the saline by a halocline?

Pitlamp said:
Water can even flow "uphill" from its inflow point, as in that wierd spring on Argostoli.

Can't remember the detail but isn't this powered by differential density of saline & fresh water?

Pitlamp said:
Aren't there supposed to be some springs where the water is of non meteoric origin (i.e. with water emerging which was produced by chemical reactions in volcanic rocks all the way down in hell?)

Aye, except possibly for the reference to the infernal realm, I thought that was somewhere round the back of Penwyllt.
 

bograt

Active member
whitelackington said:
We know that in phreatic loops, moving fresh water can reach down 100 metres or so below sea level
but how deep can fresh water actually go?
Depends where its coming from and where its going, heads of pressure, relative densitives, Tempretures, etc. etc.
 

bograt

Active member
Pitlamp said:
water emerging which was produced by chemical reactions in volcanic rocks all the way down in hell
Give me a reference, I'll work on the speliogenesis.
 

mrodoc

Well-known member
The answer has to be miles or if you are metric kilometres. Think of very deep mines etc etc.
 

Pitlamp

Well-known member
bograt said:
Pitlamp said:
water emerging which was produced by chemical reactions in volcanic rocks all the way down in hell
Give me a reference, I'll work on the speliogenesis.

Bit short of time as I type so, without checking, I think there's various mentions of this is "Limestone & Caves of the Peak District" (by TDF).

Penwyllt - infernal realm - tee hee.

(Graham - I'm pretty sure that some of the blue holes have fresh water very deep - again a bit busy at the mo to go looking things up - but wasn't there a Cave Science / Cave & Karst Science themed edition on the blue holes? You might find some info there.)
 

graham

New member
Pitlamp said:
(Graham - I'm pretty sure that some of the blue holes have fresh water very deep - again a bit busy at the mo to go looking things up - but wasn't there a Cave Science / Cave & Karst Science themed edition on the blue holes? You might find some info there.)

My memory tells me that where a Blue Hole had both, then a lens of fresh water sat above the saline stuff. What I would need to look up is at what sort of level the halocline separating them was generally found. I would guess that this would vary depending on the volume of fresh water being put in to the system.

I do not deny that fresh water can be found at great depth, langcliffe's example of the Bath Hot Springs is the one that I, too, would use. I might also mention the Great Spring in the railway tunnel under the Severn Estuary which is, clearly, below sea level. See this paper.
 

Ouan

Member
A fresh water vauclusian resurgence near Krabi in southern Thailand, located 5 km from the coast, has been dived to -240m.
The resurgence is about 10 m above sea level i.e. fresh water is found 230 m below sea level.
 

Pitlamp

Well-known member
That Bahamas blue hole themed issue is Cave & Karst Science 25 (2) (Aug 1998) in case anyone wants to browse through it. It may be less useful that the post from Ouan above though, as it was published almost 14 years ago and cave diving techniques have evolved a lot in the years since - so direct exploration of extremely deep underwater caves has since become possible.
 

Ouan

Member
Ouan said:
A fresh water vauclusian resurgence near Krabi in southern Thailand, located 5 km from the coast, has been dived to -240m.
The resurgence is about 10 m above sea level i.e. fresh water is found 230 m below sea level.

Forgot to mention that this resurgence is the subject of a Cave & Karst Science paper:-
SMART, DEAN (2003) "Sub-sea Level Speleothems From The Andaman Coast of Southern Thailand and Sea Level Change in Southeast Asia" Cave & Karst Science Vol. 30 No. 1 pp39-42

This paper was written before the really deep dives which were carried out in 2007.
 

robjones

New member
bograt said:
Perhaps we should be looking at how far salt water reaches?

Quite so - surely salt water is - generally speaking - a near-surface contaminant in the context of the crust as a whole, with non-meteroic sources, which can originate at great depth, being non-marine and hence not 'salty' - unless associated with water having acquired salt through having derived it from evaporites?
 

graham

New member
I would doubt that nascent water accounts for more than a very small % of the total and would lay a bet that it was also heavily laden with dissolved minerals, just not in the same proportion as is found in the seas.
 

garethjdavies

New member
An oil exploration well just west of Nashville, Tennessee, (USA obviously) hit fresh water > 1,500 m deep, in a dolostone (carbonate rock with dolomite) - the Knox Group.  In the same rocks I have been told that there is fresh water > 4,000 m deep in Oklahoma in the Arbuckle/Ardmore complex.  The reason for this was after formation of these carbonate rocks, about 380 million years ago, they were infiltrated by water driven deep by uplift of the ancestral Appalachians and Ouachita Mountains.  I attach link to a paper here - look at the figure near the end, it show a flow path several kilometers deep that is >1,000 km long.  http://www.jsg.utexas.edu/banner/files/Isotopic-and-trace-element-constraints-Geochimica-1989.pdf

The Knox Group is, in part, a paleoaquifer that was on the surface in the geological past and in many locations is again. Even though the brine migration initiated the original flow, it remained open and has now been invaded by fresh water.  This suggests that (some) caves form deep and the karst on the surface may have originated as paleokarst as suggested by Dave Lowe (see recent articles in BCRA)

Gareth J. Davies (formerly SWCC)
 

Scoff

New member
And then there's the obvious one - Fontaine de Vaucluse. I seem to recall reading that a remote video device recorded an elbow to the sump at 330m depth. This is 'the' classic resurgence bringing water from the plateau around the Aven Jean Nouveau I believe. The water flows from the resurgence as the River Sorgue and eventually to the sea.

With regard to the Bahamas and similar places, where limestone is connected to the sea directly, there can be an ingress of salt water. As this water is more dense than the fresh/ rain-sourced water, the latter 'floats' on top of it.

In the case of Mitiaro in the Cook Islands, because of a volcanic origin 'plug' in the niddle of the island, the surrounding 'ring' of very young limestone contained a 'doughnut' of fresh water sitting on the sea water below with those 'weird' haloclines in between. If you're interested try digging out an expedition report by Steve Swabey (ex-Wessex) of Oxford University who conducted studies of this feature and the effects of winds and tides on the shape of the freshwater lens. Google will have a record of it somewhere....

Scoff
 
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