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Author Topic: Impact of a melting ice berg on sea levels? A little brain teaser for you all...  (Read 4121 times)

Craig Dickson

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If you know the answer to the question please let me know. Please also offer some explanation. Your answers may help settle a little debate Iíve been having with some friends!

Question:
When a drifting  iceberg eventually melts, what impact does it have on the sea level? Or similarly when a floating ice cube in a glass eventually melts what happens to the water level in the glass?


Cheers
Craig
 ;)
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jimmy2310

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Craig,
wouldn't the level stay the same, as the ice cube is put in the drink it raises the level within the glass and the level will stay the same even as the cube melts,
unless someone cant wait and drinks it all.

Jimmy
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rmaddock

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Let me think.......

To float, the ice must displace its own weight in water. But it also expands when frozen. So, does the volume above water equal the amount of expansion? The "space" taken up by the below water level ice must weigh the same (if it was full of liquid water that is) as ALL the ice so they're the same amount. Does the ice's melting have no effect on the water level at all?

That made very little sense.

Robert
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DavieTait

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Water level drops , frozen ice expands taking up more volume than the liquid so an iceberg that melts lowers sea level ( although by an absolutely tiny amount ) , if a glacier melts though sea level does rise since the ice is on land not in the sea
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Davie Tait,
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CF-FZG

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It doesn't matter if it expands when frozen, (although strictly speaking it expands when it thaws) - the MASS stays the same, which is the displacement :-))
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pettyofficernick

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The mean sea level would stay the same. The amount of water on the planet is fixed, little or no new water is produced (except for man made, from industrial processes, jet and rocket exhausts etc). The existing water is constantly circulating through evaporation and rainfall. when an iceberg melts the volume of water contained within will be replacing water evaporated by wind and solar radiation, this then condenses to form clouds and ultimately rainfall, which will fall as snow in polar regions, replacing ice that has broken off glaciers and floated off into the ocean. The water, as you can see ( I Hope) from my explanation is constantly recirculating.

I did an OU course in natural sciences, and the above is a much condensed extract from one of my assignments. :-)) :-))
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dougal99

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(although strictly speaking it expands when it thaws)

Sorry not true, Ice expands when it freezes, quite a bit, which is why pipes burst in cold conditions. The leak may only become noticeable when the thaw comes. The curve for volume against temperature is almost vertically up at freezing point. However, it does slowly contact as it gets colder. It's known as the anomalous expansion of water.
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Craig Dickson

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Water level drops , frozen ice expands taking up more volume than the liquid so an iceberg that melts lowers sea level ( although by an absolutely tiny amount ) , if a glacier melts though sea level does rise since the ice is on land not in the sea

Hi Folks

Fascinating answers from you, thank you. I think that only Davie so far has  suggested that the water level wouldl actually drop.

I will let this thread run for a little time and then reveal my own opinion which did change. I guess there are only three possible answers, the water level drops, increases or stays the same.

In the meantime thank you again for your responses.
Craig :-))
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dodgy geezer

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Do you think that icebergs being made of fresh water rather than salt might have an effect...
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Craig Dickson

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Do you think that icebergs being made of fresh water rather than salt might have an effect...

Do you think it would make any difference to the answer to the question originally put?

Craig
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justboatonic

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If you know the answer to the question please let me know. Please also offer some explanation. Your answers may help settle a little debate Iíve been having with some friends!

Question:
When a drifting  iceberg eventually melts, what impact does it have on the sea level? Or similarly when a floating ice cube in a glass eventually melts what happens to the water level in the glass?


Cheers
Craig
 ;)

Water is a strange substance. When it freezes, it expands unlike a lot of other things that expand when hot.

So, when your freezing ice cube melts, the level of water in the glass will actually be lower.  Ice bergs in the sea is slightly different as they are made of freshwater while the seas are saline.
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pettyofficernick

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As far as the ice cube in the glass is concerned, the water level in the glass will rise because extra water is put in the glass in the form of ice, so if a glass contains 100ml of water, and an ice cube of 25 ml is added, there will be a total of 125ml of water in the glass. As the glass has a fixed volume, the water level has to rise in the glass. Things are a bit different with the iceberg in the ocean scenario, as this is part of the water cycle, the iceberg replenishing what has been evaporated elsewhere. :-)) :-))
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Shipmate60

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Archimedes Principle states that the buoyant force on a submerged object is equal to the weight of the fluid that is displaced by the object.
So there will be no difference at all in the level.
In the Global Warming Scenario the ice that is melting is not in the sea but on land mass so will increase the water level.

Bob
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snowwolflair

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All the ice in the poles melting on land or off will not significantly increase the depth of the oceans. 

However as the oceans heat up their volume is so great they will expand big time and we will all need to head for high ground.
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kinmel

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Shipmate60 is correct, the volume of ice that is submerged equals the volume of all the water that created the iceberg, including that visible above the water.

However as the oceans heat up their volume is so great they will expand big time and we will all need to head for high ground.

Given that the Specific heat of water ( 4.187 kJ/kgK ) is large and water's Thermal expansion from 4 oC to 100 oC ( 4.2x10-2 ) is extremely small, there is no way that such a huge body of water will absorb enough heat to expand sufficiently to alter sea levels by a measurable amount.

If ice the ice fields on land do melt then that will have an effect on sea levels.
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snowwolflair

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Shipmate60 is correct, the volume of ice that is submerged equals the volume of all the water that created the iceberg, including that visible above the water.

Given that the Specific heat of water ( 4.187 kJ/kgK ) is large and water's Thermal expansion from 4 oC to 100 oC ( 4.2x10-2 ) is extremely small, there is no way that such a huge body of water will absorb enough heat to expand sufficiently to alter sea levels by a measurable amount.

If ice the ice fields on land do melt then that will have an effect on sea levels.

Im referring to published works on anticipated ocean rise with global warming.  But experts have been known to be wrong.

Thermal Expansion for salt water is different, as is the thermal expansion for water under pressure, and you have to remember that 98% of the volume of the oceans water is at a presurised depth of 100 feet or deeper and greater.



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kinmel

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It's good to know that the experts have accurately measured the exact volume of water in the oceans and measured the salinity in each place, allowing for the seasonal variations caused by the great rivers and then added in all the variables on temperature and pressure before moving on to calculate the sea area now against the changing sea area as it  rises and discovered it will go up 110mm.

Such enormous accuracy, or just another guesstimate from experts whose living depends on a doomsday scenario ?

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Craig Dickson

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Hi folks
Firstly thank you very much for so many interesting replies. Getting back to the original question and keeping it simple (excluding salt water), my own answer is based upon the simple scenario of a big ice cube floating in a bucket of water:
I believe that after the ice cube has melted, the water level in the bucket will remain unchanged.
Here is my reasoning:
Letís assume that the ice cube weighs 1kg. The water displaced by the floating cube will be 1kg. Now let us imagine that we pluck out the ice cube and the hole left remains a temporary hole. We instantly melt the ice cube and are left with exactly 1kg of fresh water. Put that 1kg of water back into the hole (which was 1kg of displaced water) and the resulting level is the same.
The density of the cube of ice will make no difference as the reasoning still applies. Does this make sense?
Cheers
Craig
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rmaddock

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Does this make sense?

It's about what I said so, YES, it makes sense.  {-)
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malcolmfrary

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Of course it makes sense.  Archimedes wasn't daft.
Just done some back of the fag packet calculations after getting some numbers from wiki and wondering what would happen if the ice covering Antarctica melted.
Assume that the numbers are about right - Antarctica is about 5.4million square miles, and is covered with ice, mostly over land.  To go into metric, about 14 million square kilomtres.
Assume that the average ice depth is 100 metres (purely for the simplicity of doing sums)
The diameter of the Earth is about 12.8 thousand Kilometers, giving a surface area of a bit over 500million square kilometers using the formula A=4Πr2
If 4/5 of this is water, thats 400million square kilometers of wet area.
If all that land based ice melts, the sea level surface has to move up by 3 metres.
How many of us live less than 3 metres above sea level, or, more importantly, depend on services that are within 3 metres of sea level?  Thinking in terms of power stations getting washed out by unexpected water, docks becoming underwater oddities, coastal roads vanishing etc.
Of course, if the average depth that gets melted off is greater, so is the sea level rise.
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nick_75au

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It is because of the expansion the ice floats, it becomes less dense for the same quantity ;) Nobody has pointed that out as far a I could see?

Quote
All the ice in the poles melting on land
will increase the volume of water as this is not displacing an equal amount of water in the ocean.

Nick
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