Straight Dope Message Board > Main Melting an Iceberg
 Register FAQ Calendar Mark Forums Read

#1
12-14-2004, 11:43 PM
 Tuckerfan Guest Join Date: Jan 2001
Melting an Iceberg

Okay, let's say I wanted to melt an iceberg at one of the poles, roughly the size of Delaware for some fiendish evil overlord plot of mine. Could I do it with a giant fresnel magnifying lens (no doubt at least the size of a football field) in a period of a few days? Assume that I'm attempting to do this during the summer region at that particular pole. Or would I need some kind of exotic superweapon to do it?
__________________
***Don't ask me, I don't post here any more, and I'm probably not even reading this now.***
#2
12-15-2004, 12:19 AM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
Quote:
 Originally Posted by Tuckerfan Okay, let's say I wanted to melt an iceberg at one of the poles, roughly the size of Delaware for some fiendish evil overlord plot of mine. Could I do it with a giant fresnel magnifying lens (no doubt at least the size of a football field) in a period of a few days? Assume that I'm attempting to do this during the summer region at that particular pole. Or would I need some kind of exotic superweapon to do it?
To find out you have to start with the size of the iceberg in grams. It takes 80 calories to convert one gram of ice at 0 C to one gram of water at 0 C. One calorie is 4.186 Joules of energy so it takes 334.9 Joules to melt a gram of ice. If you want to do that in 3 days that's 2.6*105 seconds. Since it is summer I'm assuming the sun is up all of the time. So to melt that gram you need to supply heat at the rate of 334.9/2.6*105 Watts = 1.29 milliwatts.

Look up what the sun's rate of energy delivery to the surface is in Watts per square meter. The sun's input at the surface will vary during the day as the sun angle above the horizon changes but I'll ignore that because I'm lazy and it's too much trouble to take account of. Multiply the heat input/gm of iceberg times the weight of the iceberg in grams to get the total heat required to melt it in 3 days. Divide that number by the sun's surface energy delivery and that gives you the number of square meters required for the lens.

Sure it's possible if you can figure out how to build the lens and keep it stable in the correct position above the berg. Lotta luck.
#3
12-15-2004, 12:29 AM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
One little, but crucial detail that I didn't add. You have to find out how much of the light from the lens is reflected by the surface of the berg. Since the light hits the berg at various angles because of the rough surface this is going to be a bit of a task. In any case, for example say 80% is reflected. In that case you have to divide the lens size you get from the above method by 0.2. And you also have to figure in the heat transfer between the berg and its environment.

If you want to put it in a sci-fi story of some kind you've got some sticky problems if you want to be accurate. If it's a story for kids I wouldn't use a lens. I'd use a transmogrifier.
#4
12-15-2004, 12:32 AM
 Shagnasty Charter Member Join Date: May 2000 Posts: 21,310
I think you have some serious problems with the size of your mirror. There state of Delaware is about 55 billion square feet. A football field sized mirror is only 48,000 square feet. That means that your mirror is over 1.1 million times smaller than the iceberg. Somehow I just can't see the 3 day mark working or even if it ever would.
#5
12-15-2004, 12:37 AM
 oh&s Guest Join Date: Dec 2004
Quote:
 Originally Posted by Tuckerfan Okay, let's say I wanted to melt an iceberg at one of the poles, roughly the size of Delaware for some fiendish evil overlord plot of mine. Could I do it with a giant fresnel magnifying lens (no doubt at least the size of a football field) in a period of a few days? Assume that I'm attempting to do this during the summer region at that particular pole. Or would I need some kind of exotic superweapon to do it?
How's a geo-stationary satellite with a ionised microwave cannon sound. should be cheaper than that magnifying glass. Or you could build a giant trebuchet on the moon and throw boulders at the earth. Then there's the build a nuclear power plant on the pole and send it into melt-down.
#6
12-15-2004, 01:05 AM
 Squink Guest Join Date: Oct 2000
Candidate Bergs

Quote:
 Originally Posted by Tuckerfan Okay, let's say I wanted to melt an iceberg at one of the poles, roughly the size of Delaware...
B-15
Quote:
 B-15 was a tabular berg that broke off the ice shelf in March. It measured 180 miles long and 25 miles wide - more than twice the size of Delaware and was probably the largest iceberg ever seen. The only other contender was spied in 1956, but its size could not be confirmed. ... B-15 stayed close to home and eventually broke into several pieces, now called B-15A, B-15B, etc. ... •Before it broke apart, B-15 was about the size of Jamaica and weighed an estimated 4 trillion tons. ... •Most icebergs that calve off the Ross Ice Shelf are thought to be a thousand feet thick or more, only 10 percent of which floats above the surface.
B-15A or B-15B look to comprise about half the original berg, so they're about the size of Delaware, and weigh about 2 trillion tons each. Two trillion tons is 1.8 x 10^15 grams.
#7
12-15-2004, 01:51 AM
 Berkut Guest Join Date: May 2001
Quote:
 Originally Posted by oh&s How's a geo-stationary satellite with a ionised microwave cannon sound
Like this: "wooooooOOOOOOOOO-BEEEEEEEEEEEEEEEEEEEEEEEE"
#8
12-15-2004, 02:23 AM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
using Squink's figure for the mass of the berg, assuming a reflectivity of .8, a solar constant of 600 W/m2 and ignoring heat transfere to and from the environment, I get a lens with a diameter of 136 kilometers. In the words of Ralph Kramden, a mere bag a shells.
#9
12-15-2004, 04:50 AM
 Mangetout Charter Member Join Date: May 2001 Location: Kingdom of Butter Posts: 49,004
Paint it black

Spray the surface of the iceberg with soot or something (and be prepared to repeat the process periodically as it sloughs off); this will increase the rate of energy absorption.
#10
12-15-2004, 06:32 AM
 InvidiousCourgette Guest Join Date: May 2004
Quote:
 Originally Posted by David Simmons using Squink's figure for the mass of the berg, assuming a reflectivity of .8, a solar constant of 600 W/m2 and ignoring heat transfere to and from the environment, I get a lens with a diameter of 136 kilometers. In the words of Ralph Kramden, a mere bag a shells.
A 136 km lens is concentrating the light from 156 billion square feet onto an area of 55 billion square feet. So the energy impacting the iceberg will be three times the value that would be there without the lens' presence. I can't see this melting the iceberg in three days. It might be within an order of magnitude or two of the lens size required though.
#11
12-15-2004, 09:42 AM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
Quote:
 Originally Posted by InvidiousCourgette A 136 km lens is concentrating the light from 156 billion square feet onto an area of 55 billion square feet. So the energy impacting the iceberg will be three times the value that would be there without the lens' presence. I can't see this melting the iceberg in three days. It might be within an order of magnitude or two of the lens size required though.
I also questioned this size and I suspect my WAG of 0.8 for the reflectivity is too low. Those with better numbers can have at it.
#12
12-15-2004, 09:54 AM
There's a nice article about B15 today in the times. You could always test the mirror first and help these little guys.... right before you cause mass extinction of course..

The Times (just search on B15)
#13
12-15-2004, 04:54 PM
 Tuckerfan Guest Join Date: Jan 2001
Quote:
 Originally Posted by Squink B-15 B-15A or B-15B look to comprise about half the original berg, so they're about the size of Delaware, and weigh about 2 trillion tons each. Two trillion tons is 1.8 x 10^15 grams.
Yeah, that's a good one, since it's a penguin killer!
#14
12-15-2004, 05:06 PM
 Tranquilis Guest Join Date: Dec 2000
Sorry, Tuckerfan!

Looks like you'll have to do it the hard way - can't do it on the cheap.

OTOH, if you wanted, you could build a satellite program, and send a series of big honkin' mirror arrays into orbit. Then you can put a beam of sunlight on it nearly 24x7. Of course, it'll still cost. Savin' penguins ain't cheap.
#15
12-15-2004, 05:16 PM
 Tranquilis Guest Join Date: Dec 2000
B-15a, by rough calculation, contains ~ 180 cubic miles of ice. Give or take a few tens of cubic miles...

~90 miles X ~20 miles X ~.1 mile thick

(thickness ranging from 100 meters to 270 meters, depending on which edge you're on)
#16
12-15-2004, 05:21 PM
 Tuckerfan Guest Join Date: Jan 2001
Quote:
 Originally Posted by Tranquilis Sorry, Tuckerfan! Looks like you'll have to do it the hard way - can't do it on the cheap. OTOH, if you wanted, you could build a satellite program, and send a series of big honkin' mirror arrays into orbit. Then you can put a beam of sunlight on it nearly 24x7. Of course, it'll still cost. Savin' penguins ain't cheap.
Yeah, but look at the benefits of doing something. And we'd be saving baby penguins in the process! Won't someone please think of the baby penguins?
#17
12-15-2004, 09:39 PM
 moriah Member Join Date: Jun 1999 Location: NJ, USA ♂ Posts: 4,122
Well, if it were in the antarctic, it would get sunlight 24/7 during the winter months, albeit at an oblique angle. You'd want to set up hundreds of thousands of mirrors all over the ice shelf to catch the sunlight on a more direct angle and reflect it downward on the ice.

You'd be able to regain the expense of the project by selling tanning bed spaces on your Antenordic Tanning Shelf Spa!
#18
12-15-2004, 10:33 PM
 kanicbird Guest Join Date: May 1999
Could we use nukes, I think the N. Korians are willing to sell a few?
#19
12-15-2004, 11:03 PM
 Squink Guest Join Date: Oct 2000
Quote:
 Originally Posted by kanicbird Could we use nukes, I think the N. Koreans are willing to sell a few?
Nukes would work. Using Simmon's 334.9 Joules to melt a gram of ice, and a mass of 1.8 x 10^15 grams, it'd take 6.03 x 10^17 Joules to melt the berg.
A megaton of TNT puts out about 4.18 x 10^15 Joules, so we'd need the total heat from a 144 megaton burst.
Because the berg is so thin relative to its length and width, you'd probably have disperse the nukes in 144 one megaton packages, each buried under 300 feet of ice.
#20
12-15-2004, 11:24 PM
 EmeraldGrue Guest Join Date: Nov 2004
You'd need a 1920's-style death ray.

:ducks & runs:
#21
12-16-2004, 06:59 AM
 kanicbird Guest Join Date: May 1999
Quote:
 Because the berg is so thin relative to its length and width, you'd probably have disperse the nukes in 144 one megaton packages, each buried under 300 feet of ice.
Wow, I would think more would be needed, but then again many ice blocks will be blown away and not melted, others will be vaporized and remove much of the heat, so I still think we would need more then 144 MT's.
#22
12-16-2004, 07:13 AM
 oh&s Guest Join Date: Dec 2004
Quote:
 Originally Posted by EmeraldGrue You'd need a 1920's-style death ray. :ducks & runs:
Oi Cobber.
What do you think a ionised microwave cannon is?
#23
12-16-2004, 11:19 AM
 Squink Guest Join Date: Oct 2000
Quote:
 Originally Posted by kanicbird I still think we would need more then 144 MT's.
Yeah, that was a calculation of the absolute minimum needed. It showed that a nuclear solution is feasible, but in real life, heat loss through the rising fireball and vaporized water would push the megatonage required up by a good big coefficient.
#24
12-16-2004, 01:41 PM
 Tuckerfan Guest Join Date: Jan 2001
Quote:
 Originally Posted by Squink Yeah, that was a calculation of the absolute minimum needed. It showed that a nuclear solution is feasible, but in real life, heat loss through the rising fireball and vaporized water would push the megatonage required up by a good big coefficient.
Nah, I mean after all, if NASA can send a bunch of guys up there to drill that far into an asteroid the size of Texas, drop a nuke down the hole, and then have it split the thing cleanly in two when it goes off, 144 warheads should be more than enough on something like an iceberg.
#25
12-16-2004, 10:46 PM
 David Simmons Charter Member Join Date: Nov 2001 Posts: 12,684
Quote:
 Originally Posted by Tuckerfan Nah, I mean after all, if NASA can send a bunch of guys up there to drill that far into an asteroid the size of Texas, drop a nuke down the hole, and then have it split the thing cleanly in two when it goes off, 144 warheads should be more than enough on something like an iceberg.
The problem is explosions, as was pointed out earlier, is that they blow things apart and don't couple the available energy into the berg in such a way as to melt it. That's a problem with the reactive material of the explosive itself. The explosive charge, or the reactive mass in the case of nuclear, has to be contained long enough for the chemical or nuclear reaction to reach all or the greatest possible fraction, of the active elements.

My computation of 136 km diameter ignored the interchange of energy between the berg and the environment. I don't think that was a very good thing to ignore. It really doesn't matter because no one is actually going to do the experiment asked about in the OP. If someone were to try it, the melting of an iceberg floating in the ocean is a lot more complicated than just putting the proper amount of energy into it and then standing back.
#26
12-17-2004, 02:42 AM
 Sam Stone Charter Member Join Date: Jun 1999 Posts: 25,047
What would happen if something the size of B-15 rolled over? Would it create a Tsunami or something?
#27
12-17-2004, 03:06 AM
 danceswithcats Guest Join Date: Dec 2002 Location: Voting anti-obamanation Posts: 10,300
Thanks Mangetout. Now I've got the blasted Rolling Stones stuck in my head.
__________________
Crows. Keeping our highways clear of roadkill for over 80 years
#28
12-17-2004, 08:15 AM
 The Cat Guest Join Date: Dec 2004
Just for the record building a nuclear powerplant and "melting it down" would definetly not melt an iceberg the size of delaware althought it might melt a hole in it. Hitting the ice berg with a nuclear warhead would probably not melt an ice berg the size of the deleware. If you could somehow put the iceberg in direct contact with the great nuclear reactor in the sky we call the sun it would melt.

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is Off HTML code is Off
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Main     About This Message Board     Comments on Cecil's Columns/Staff Reports     Straight Dope Chicago     General Questions     Great Debates     Elections     Cafe Society     The Game Room     In My Humble Opinion (IMHO)     Mundane Pointless Stuff I Must Share (MPSIMS)     Marketplace     The BBQ Pit Side Conversations     The Barn House

All times are GMT -5. The time now is 05:05 PM.