CTV News featured the flood the night of April 24, telling the stories of local residents and cabin owners who are beginning to lose the fight against the rising flood waters.
I don't want to detract from those owners' grief or hardship; I can't begin to imagine how difficult and agonizing the situation must be for them.
But the CTV reporter made what I think is an obvious error. Standing in rubber boots in a flooded yard, with the lake behind her, she said that the waters will rise more once the lake's surface ice, visible in the shot, melts over the coming weeks. The story is repeated on CTV's website, here, and here's the quote:
As the lake's ice cover melts, water levels are expected to rise further, with the peak not expected for three more weeks.
This is a glaring error that more and more people make these days, especially when some environut worries about melting icebergs. When ice floating in water melts, the water level will drop. This is because, as any fourth grade student will tell you, ice has more volume than water. As it melts and changes back into liquid, the overall volume it requires decreases.
You've all filled an ice cube tray and seen it come out with ice cubes that take up more space than the water you put in the tray. That's because ice is about 9% less dense than ice (neatly explained by the good folks at Elmhurst College), and when the same amount of matter becomes less dense it requires more volume.
Now there may be a scenario in which the ice dams and causes a rise in water behind it, but the visual and the scenario the reporter explained don't refer to that. Just how does a network reporter get away with such a obvious mistake?
I suppose I should feel obliged to point out that likely more than 9% of the ice's volume will float above the water (we're talking about surface ice with greater surface area, not iceburgs), which will consequently add to the water level as it melts, despite its decreased density.
ReplyDeleteAdditionally, as the surface ice melts, so will the surrounding snow that drains into the lake. Granted, that wasn't the cause directly mentioned in the story...
It seems that bad science abounds. When ice in a volume of water melts, the level of the water neither rises nor falls, it stays constant. We can thank the Archimedes principal for this:
ReplyDeleteThe weight of fluid that a submerged object displaces is equal to the buoyancy force applied to the submerged object.
Ice floats on the surface of water in equilibrium – neither rising nor sinking so the weight of the ice is the same as the weight of the water that it displaces. Ice is water in a different phase, so once the ice melts the water from the ice perfectly fills in the volume of the water that the ice displaced (since the masses are the same).
Surface area has nothing to do with it.
I'm just waiting to hear from the GW people that the Red River floods of the past centuries are also the consequence of GW.
ReplyDeleteUmmm.....
ReplyDelete"...That's because ice is about 9% less dense than ice..."
In any case the story is crap .... the regions affected are in a flood plain that has existed for thousands of years and the spring flooding is all too common.
Ditto for the Red River Valley!
I'm amazed that a CTV "reporter" actually went to Fishing Lake.
Based on the numerous camera shots they took, there was no surface snow left around. Also, roughly 9% of any given body of floating ice will be above the surface, no matter what physical shape it is.
ReplyDeleteHomer nods: Given that, I can see fen's point; the amount of water displaced is going to be equal to the amount of ice below the surface. Thus it is indeed a zero-sum equation. When the whole ice sheet melts there will be no difference in the water levels.
I'm just a humble blogger in his basement who Googled a few facts. CTV however, has a vast army of fact-checkers - you'd think somebody would have caught this one.
The only way the ice melting can causing water levels to rise is if the ice wasn't IN inthe water ot start.
ReplyDeleteHence if the greenland ice cap melts , yeah, the water level might rise. Ditto Antarctica.
The northPole is essentially inthe water, aside from those islands which are irrelevant.
Now.
Thought experiment.
Take the volume of ice on top of Greenland + Antarica and above sea level. How many cubic Km's?
Spread across the area of the worlds major oceans. (This is a VERY big number.)
How high is that in the WORST case scenario?