How do we know 9/10ths of an iceberg is under water- Has anyone ever really measured?

Factual Questions
1

I often see this fact about icebergs quoted. How do we know this ratio is a fact?

2

Because you can observe a similar ratio by floating an ice cube in a glass of water?

3

To be accurate, you should observe an ice cube floating in a glass of salt water.

4

As implied by MLS, if you know the density of ice, and you know the density of water…

5

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,

6

Uh, ignore the last two lines the above post…

7

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?)
8

Damnit! IN the above post.

9

The density of sea water is closer to 1.03. That gives us pretty much exactly 90%

10

It’s a total lie, but still a cool piccie: iceberg (for illustrative purposes only).

11

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.

12

Sure is. How density is affected by temperature and pressure is called the equation of state. All known substances have one.

13

Not necessarily; glaciers often calve into lakes.