# Floating A Boulder In Ice

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### #1 Turtle

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Posted 19 April 2020 - 02:26 PM

In geology we have artifacts known as ice floated erratics which are boulders that were trapped in glacial ice and then transported and deposited on the land surface by flooding. Missoula floods and all that.

So if i have a 40 ton andesitic basalt boulder, what volume of ice is necessary to float it at the surface?
Approximate Volume of boulder 485ft^3
Estimated Density 180lb/ft^3
Let the stone be a sphere and the ice a cube. (If that helps?)

I appreciate the aid; mind is rather foggy at this juncture with no immediate signs of clearing. šµ
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### #2 exchemist

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Posted 19 April 2020 - 03:10 PM

In geology we have artifacts known as ice floated erratics which are boulders that were trapped in glacial ice and then transported and deposited on the land surface by flooding. Missoula floods and all that.

So if i have a 40 ton andesitic basalt boulder, what volume of ice is necessary to float it at the surface?
Approximate Volume of boulder 485ft^3
Estimated Density 180lb/ft^3
Let the stone be a sphere and the ice a cube. (If that helps?)

I appreciate the aid; mind is rather foggy at this juncture with no immediate signs of clearing.

Let me have a go. Please check my logic and arithmetic.

The density of ice is about 0.9.

So 1mĀ³ has a mass of 900kg and can take an extra mass of 100kg before it starts to sink.

So you need 10mĀ³ of ice per tonne of mass you want it to support.

So a 40tonne boulder will need a volume of 400mĀ³.

Does that look right?

### #3 Turtle

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Posted 19 April 2020 - 04:42 PM

Let me have a go. Please check my logic and arithmetic.

The density of ice is about 0.9.

So 1mĀ³ has a mass of 900kg and can take an extra mass of 100kg before it starts to sink.

So you need 10mĀ³ of ice per tonne of mass you want it to support.

So a 40tonne boulder will need a volume of 400mĀ³.

Does that look right?

Thank youš looks right to me. So then I get a 3 meter sphere in a cube just over 7 meters on a side. Does that sound right?
If so, that's a much smaller block of ice than I expected.š¤

### #4 exchemist

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Posted 20 April 2020 - 03:58 AM

Thank you looks right to me. So then I get a 3 meter sphere in a cube just over 7 meters on a side. Does that sound right?
If so, that's a much smaller block of ice than I expected.

Let's try that.

Density of basalt ~3, so 40mt would occupy 40/3mĀ³

So we have 4/3 Ļ rĀ³ = 40/3mĀ³, => rĀ³ = 10/Ļ => r = Ā³ā 3.183 ~1.5m.

So by my estimation a 40mt boulder has a radius of 1.5m, so yes a sphere 3m in diameter.

And it would need a volume of ice of 400mĀ³, i.e a cube of side  Ā³ā400 ~ 7.4m.

So yes that indeed checks out.