# How do we know 9/10ths of an iceberg is under water- Has anyone ever really measured? **URL:** \ **Category:** Factual Questions\ **Created:** [November 26, 2006, 9:20pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869 "2006-11-26T21:20:56Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [November 26, 2006, 9:20pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/1 "2006-11-26T21:20:56Z")
I often see this fact about icebergs quoted. How do we know this ratio is a fact? ---
**Author:** ![MLS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MLS](https://boards.straightdope.com/u/MLS)\ **Post date:** [November 26, 2006, 9:25pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/2 "2006-11-26T21:25:55Z")
Because you can observe a similar ratio by floating an ice cube in a glass of water? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [November 26, 2006, 9:36pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/3 "2006-11-26T21:36:10Z")
[QUOTE=MLS] Because you can observe a similar ratio by floating an ice cube in a glass of water? [/QUOTE] To be accurate, you should observe an ice cube floating in a glass of salt water. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [November 26, 2006, 9:38pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/4 "2006-11-26T21:38:28Z")
As implied by **MLS** , if you know the density of ice, and you know the density of water… ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [November 26, 2006, 9:40pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/5 "2006-11-26T21:40:19Z")
[QUOTE=astro] I often see this fact about icebergs quoted. How do we know this ratio is a fact? [/QUOTE] It doesn’t have to be measured - it can be calculated from the density of water and ice. Things float by displacing an amount of water equal to their own mass (that’s why you hear some ship’s weights described in terms of ‘displacement’ - it’s the same thing). This is equivalent to saying: an object floats when it’s submerged volume is equal to the volume of water with the same mass as the object. One gram of ice occupies 1.08 cm^3. One gram of water occupies 1 cm^3. Thus, one gram of ice will float when it has displaced one gram of water, meaning 1 cm^3 of it is submerged, and .08 cm^3 of it is floating above the surface. Thus, about 92% (=1/1.08) of floating icecube will be submerged. Icebergs are just big icecubes (they’re probably a little less dense, but I doubt the difference is that significant). We know the density of ice and the density of water, thus we can calculate how much water a piece of ice must displace in order for it to float. Water’s density is 1 g / cm^3. Ice’s density is .92 g / cm^3. Thus, ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [November 26, 2006, 9:41pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/6 "2006-11-26T21:41:46Z")
Uh, ignore the last two lines the above post… ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [November 26, 2006, 9:41pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/7 "2006-11-26T21:41:54Z")
Of course, there are 2nd order effects that will affect the accuracy of the calculation, like: - density gradients in water and ice - temperature gradients in water and ice - composition and impurities in water and ice - temperature dependence on density of water - temperature dependence on density of ice (is there one?) ---
**Author:** ![Absolute](https://avatars.discourse-cdn.com/v4/letter/a/b2d939/32.png) [@Absolute](https://boards.straightdope.com/u/Absolute)\ **Post date:** [November 26, 2006, 9:42pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/8 "2006-11-26T21:42:55Z")
Damnit! IN the above post. ---
**Author:** ![mr.jp](https://avatars.discourse-cdn.com/v4/letter/m/48db29/32.png) [@mr.jp](https://boards.straightdope.com/u/mr.jp)\ **Post date:** [November 26, 2006, 9:47pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/9 "2006-11-26T21:47:49Z")
The density of sea water is closer to 1.03. That gives us pretty much exactly 90% ---
**Author:** ![jjimm](https://avatars.discourse-cdn.com/v4/letter/j/ba8739/32.png) [@jjimm](https://boards.straightdope.com/u/jjimm)\ **Post date:** [November 26, 2006, 9:47pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/10 "2006-11-26T21:47:54Z")
It’s a total lie, but still a cool piccie: [iceberg](http://www.snopes.com/photos/natural/iceberg.asp) (for illustrative purposes only). ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [November 26, 2006, 10:22pm UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/11 "2006-11-26T22:22:37Z")
It’s actually far more impressive and unusual (and likely critical for the development of life as we know it) that one tenth is _above_ the surface. ---
**Author:** ![JustAnotherGeek](https://avatars.discourse-cdn.com/v4/letter/j/58f4c7/32.png) [@JustAnotherGeek](https://boards.straightdope.com/u/JustAnotherGeek)\ **Post date:** [November 27, 2006, 2:32am UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/12 "2006-11-27T02:32:52Z")
[QUOTE=Crafter\_Man] - temperature dependence on density of ice (is there one?) [/QUOTE] Sure is. How density is affected by temperature and pressure is called the equation of state. All known substances have one. ---
**Author:** ![Chefguy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chefguy/32/138_2.png) [@Chefguy](https://boards.straightdope.com/u/Chefguy)\ **Post date:** [November 27, 2006, 4:14am UTC](https://boards.straightdope.com/t/how-do-we-know-9-10ths-of-an-iceberg-is-under-water-has-anyone-ever-really-measured/381869/13 "2006-11-27T04:14:49Z")
[QUOTE=friedo] To be accurate, you should observe an ice cube floating in a glass of salt water. [/QUOTE] Not necessarily; glaciers often calve into lakes.