Floating Rock Raft: New Zealand Questions Answered

[pnmeadowcroft]

Can anyone answer a couple of questions about the new floating rock raft off New Zealand ?

How much mass does it contain ?

Where is it headed ? ( or will it disperse ? )

 

[Evo]

Can anyone answer a couple of questions about the new floating rock raft off New Zealand ?

How much mass does it contain ?

Where is it headed ? ( or will it disperse ? )

Please post a link, do not make members hunt for the source.

 

[Bobbywhy]

It has just been discovered around 09 August and there have been not published estimates of its total mass, as far as I know.

http://www.bbc.co.uk/news/science-environment-19207810
http://news.yahoo.com/bizarre-rock-ice-shelf-found-pacific-104349304.html

.

 

[pnmeadowcroft]

Here is a link to one of the better articles I have found, but information is scetchy on google for sure.

http://news.nationalpost.com/2012/08/10/volcanic-rock-mass-off-new-zealand/

I guess it it right to give some context to the question too. I know what happens when a oil slick hits a coastline. What about 26,000 square kilometers of rock ?

 

[davenn]

Can anyone answer a couple of questions about the new floating rock raft off New Zealand ?

How much mass does it contain ?

Where is it headed ? ( or will it disperse ? )

well time for you to try some maths ;)
you have some of the info, and wiki will provide the rest

its 26,000 sqr km x ~ 600mm (0.6metre thick)

wiki gives an example of ~ 0.25 g / cubic cm for pumice

work out the volume from the first 2 measurements then multiply it by the density

watch your values I would suggest get everything into cubic metres rather than trying to work with km, cm etc


Dave

 

[pnmeadowcroft]

Yeah, 3.9 billion tonnes, but I don't really like that answer much. The picture on this page:

http://en.mercopress.com/2012/08/10/volcanic-pumice-mass-size-of-belgium-floating-off-the-coast-of-new-zealand

shows that the depth is far from uniform.

Suppose 0.3 billion tonnes is closer to the mark, you can compare this to a vary large oil spill (100,000 tonnes) and we have a ecological event that is 3,000 times larger.

 

[davenn]

Yeah, 3.9 billion tonnes, but I don't really like that answer much. The picture on this page:

http://en.mercopress.com/2012/08/10/volcanic-pumice-mass-size-of-belgium-floating-off-the-coast-of-new-zealand

shows that the depth is far from uniform.

yup some bad maths there I think ;)

26,000 sqr km = 26,000,000 sqr metres ( 26 million) x 0.6 metres = 15,600,000 (15.6 million) cubic metres

0.25g / 1ccm => 2.5g / 10 ccm => 25g / 100ccm (ccm = cubic cm) 100ccm = 1 cubic metre

25g = 0.025kg

15,600,000 cubic metres x 0.025kg = 390,000 kg = 390 tonnes ( 1 Tonne = 1000kg)

some one check my maths please :)

Dave

 

[billiards]

yup some bad maths there I think ;)

26,000 sqr km = 26,000,000 sqr metres ( 26 million) x 0.6 metres = 15,600,000 (15.6 million) cubic metres

0.25g / 1ccm => 2.5g / 10 ccm => 25g / 100ccm (ccm = cubic cm) 100ccm = 1 cubic metre

25g = 0.025kg

15,600,000 cubic metres x 0.025kg = 390,000 kg = 390 tonnes ( 1 Tonne = 1000kg)

some one check my maths please :)

Dave

Those numbers aren't right. I reckon:

26,000 sqr km = 26,000,000,000 sqr metres

0.25g / 1ccm = 250 kg/m³

EDIT: Imagine a cubic metre of rock. Now how much does that weigh? 25 grams? No way!

 

[davenn]

Those numbers aren't right. I reckon:

26,000 sqr km = 26,000,000,000 sqr metres

0.25g / 1ccm = 250 kg/m³

EDIT: Imagine a cubic metre of rock. Now how much does that weigh? 25 grams? No way!

crap, I really screwed up my calcs.. doh... I'll bow to your better maths, no wonder I failed school cert maths twice haha

after using some online convertors I agree with your m²
I will work on the rest as well

Dave

 

[davenn]

using online calculators

gosh am getting such huge numbers its freaky haha
I need to work through this for my own understanding/sanity please correct me if I go wrong

so 10,000 cm² = 1 metre²

therefore 10,000 x 10,000 x 10,000 cm = 1 m³

now here's something that has always caught me out...
thats 1 with 12 0's is that the same as 1 x 10¹² or 1 x 10¹¹ ... I was thinking 11

Dave

 

[billiards]

using online calculators

gosh am getting such huge numbers its freaky haha
I need to work through this for my own understanding/sanity please correct me if I go wrong

so 10,000 cm² = 1 metre²

therefore 10,000 x 10,000 x 10,000 cm = 1 m³

now here's something that has always caught me out...
thats 1 with 12 0's is that the same as 1 x 10¹² or 1 x 10¹¹ ... I was thinking 11

Dave

Hi Dave

1 m = 100 cm
1 m² = m * m = 100 cm * 100 cm = 10,000 cm²

You got that bit right.


Next:

1 m³ = m * m * m = 100 cm * 100 cm * 100 cm = 1,000,000 cm³

You slipped up with that bit.

Incidentally: 1 with 12 0's is the same as 10¹².

This stuff is not really maths. It's just working with units. Try to picture a square metre, then imagine how many square cm would fit inside it, then try to imagine a cubic metre and image how many cubic cm would fit inside it. The maths just drops out of the mental picture.

Cheers

 

[davenn]

OK thanks

This stuff is not really maths. It's just working with units.

yeah something that will trip me up easily haha
i will continue working through this in this thread because I eventually want to confirm for myself the cubic volume and mass of the pumice ... besides there may be others that learn something too haha

OK so we have 26,000,000,000 metres² and for an avg let's just pick 0.5 m thick = 13,000,000,000 m³

now the fun of converting 0.25g / cm³ to kg / m³

0.25 x 1,000,000³ (1m³) = 250,000g / 1m³ = 250kg / 1m³
which is what you said earlier, billiards :)

so 13,000,000,000 m³ x 250kg / 1m³ = 3,250,000,000,000 kg = 3,250,000,000 metric Tonnes

OK how did I go that time ? :)

Dave

 

[pnmeadowcroft]

OK how did I go that time ? :)

Dave

good that time :) - I use a depth 0.6 to get the 3.9 billion verse 0.5 to get 3.2

 

[billiards]

Good but the thickness assumption is probably whacky.


One article says the pumice fragments are golf ball sized.

Now golf balls have a diameter of about 5 cm. So I would scale down your answer by a factor of 10 (dave).

Then there is the issue that this thickness is not uniform over the areal extent. You could make another assumption -- e.g. close hexagonal packing -- to account for the gaps in between the pumice fragments: multiply your answer again by 0.74.

 

[davenn]

Good but the thickness assumption is probably whacky.


One article says the pumice fragments are golf ball sized.

Now golf balls have a diameter of about 5 cm. So I would scale down your answer by a factor of 10 (dave).

Then there is the issue that this thickness is not uniform over the areal extent. You could make another assumption -- e.g. close hexagonal packing -- to account for the gaps in between the pumice fragments: multiply your answer again by 0.74.

yes agreed, the calcs were for a uniform thickness/density, but at least I finally got my units and maths sorted out haha

D

 

[billiards]

yes agreed, the calcs were for a uniform thickness/density, but at least I finally got my units and maths sorted out haha

D

Awesome. Glad to be able to help out