Slowing of Earth's rotation??

So I was watching NGC and they happened to mention that since humans have re-routed so much water for their use that this is has caused the Earth's rotation to significantly slow down.....that the day is longer than it use to be because all the damns, irrigation systems, man made rivers....all the relocation of Earth's water has done this.

How?...Seems interesting how moving water made the Earth slow down. I am betting it wasn't a direct effect but was most likely caused by chain reaction of events.

 

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Weird, does water affect the rotation of the earth?!

Or maybe theyre just paranoid that the days in the summer seems so long.

Bah, if it is true, someday we'll have a thirteen on our clock.

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I don't know how diverting rivers and erecting damns can seriously effect the rotation of the planet. Rivers, damns, and irrigation systems represent a very small fraction of the total water coverage of the planet ... and as far as I can see, only the oceans can create the required force to alter the movement of the planet in any significant manner ... if needed.

 

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perhaps you could provide a link to that story.

My two cent guess is the law of maintaining angular momentum, like the ice skater.

As water for irrigation is brought to a higher elevation it's distance to the spin axis increases and like the ice skater, the spinning speed must decrease to preserve the angular momentum. To me this seems indefinitely small looking at the mass differences. Alternately, melting glaciers will speed up the Earth spinning.

There is a whole lot more to say about Earths angular momentum. Anybody interested?

 

Earth's rotation has slowed down more in the past before humans arrived. Natural instances such as waves in the ocean and tidal forces from the sun and moon make human activities insignificant in comparison.

 

In tidal forces, I mean, tidal friction.

 

Yes it does

However I think that the tidal friction is not the main reason for Earth to slow down.

 

How so, Andre?

I think tidal friction is the main reason, because it is what supposedly caused Mercury and the Moon to slow down to a near 1:1 ratio of orbit period to day length.

The earth has liquid water. That makes it even more intense, given that the waves would want to wrap around the continents.

 

Yes absolutely but we tend only to think of what we can see. What we don't see is that Earth is made of a couple of giant gyroscopes (fluid and solid core, mantle) wobbling around (Milankovitch cycles). The interaction between those causes friction, causing the Earth slow down.

Friction is heat. So at least part of the heat of the Earth core can be friction heat.

 

To Andre:

Based on several of your posts, I have come to think you usually know what you are talking about, but in this one I have some doubts. Certainly there are circulations in the interior of the earth and some frictional torques that transfer angular momentum to the crust. (We judge the Earth's rotational period only by the crust's rotational period. Thus I agree such transfer could change the length of the day.) BUT, I find it hard to believe that the difference between internal and crust rotation rates could be even 0.0001 % of the rate the tidal bulges race around the earth. Thus I tend to think your effect is very insignificant. Correct me if my intuition is wrong, by giving some data or reference. Thanks in advance.

 

How about para 3.2., halfway down.

There is no numerical value filled in but the total energy of the Earth magnetic field may be about equal to the dissipation of spinning energy due to core mantle friction. I think we are still on the brink of a poorly understood phenomena.

 

Interesting. It must be a combination of both tidal forces on ocean and mantle.

 

Don't forget the influence of volcanos may possibly have producing enormous amounts of lava flows in the past. This may help earth to spin a little off balance, perhaps helping to slow it's rotation just a bit. Example being approx. 65 million ago when what is now India was mostly covered in huge sheets of lava hundreds of meters thick........Check it out!

Atta Boy

 

Ah, yes, the Deccan traps... that may have slowed it down at a much faster rate, but only for a small period of time.

Weren't there also the Siberian fissure eruptions in the Permian? I reckon this would have had a larger impact, since it was located up north.

 

Yes........The Siberian fissure eruptions in the Permian period must have had a big influence too.........Probably a much bigger influence than we can imagine! Also, the asteroid 'tap' the earth recieved 65,000 million years ago might have caused the earth to slow just a bit too!

Atta Boy

 

The Siberian traps were indeed the largest vulcanic activity on record. Makes Yellowstone shrink to a cigaret lighter.

Anyway a possible inbalance of mass or actually angular inertia changes the direction of the Inertia tensor of the Earth. It is assumed that this inertia tensor realigns with the spinning of the earth. This is a proposed mechanism for the so called True Polar Wander.

 

would it be something to do with the pull of the moon on large bodies of water?

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Who knows....

 

Getting back to SargentLard's original question: human activity will definitely affect the Earth's rotation, by an infinitesimal but very real amount. In fact, every sizeable nudge the ground receives (from bombs, demolitions, plane crashes, landslides, earthquakes or whatever) will affect the whole Earth to some extent, however immeasurably. On the whole, however, all of these tiny influences will tend to counteract one another - and could never add up to anything noticeable, even in a billion years...

By damming up or diverting major rivers, humans have probably reduced the volume of water flowing across the continents at at any given time - certainbly, the amount of drag those rivers can exert on the lithosphere. Thus, it seems to me that any slowing effect on the Earth's rotation will have been diminshed by our engineering, not increased. And, as Singularity said, it's all negligable compared to the daily ocean tides anyway.

I don't think that shifting of rock masses due to volcanic activity will do more than generate localised gravitational anomalies measurable by satellites. If a huge new mass of rock is extruded onto the surface somewhere - as with the Deccan Traps - that magma is only rising a relatively short distance further from the Earth's centre than it was before. And slightly more weight on one part of the globe will be balanced by a reduction somewhere else.

 

But in that scenario we might have some problems with the law conservation of angular momentum.

 

I've heard it said (or read it written?) that the Sun's red giant phase will come long before the Moon slows the Earth's rotation to synchrony. Assuming that our planet survives in some form beyond that point, eventually it will keep one face permanently towards the Moon. After that, the gravity of the degenerate white dwarf Sun will continue to slow Earth's rotation - making a day longer than a month, so that the whole Earth-Moon system will lose angular momentum into the Earth's widening solar orbit, and the Moon will move closer to Earth again.

Ultimately - tens of billions of years hence, when the Sun has cooled into a black dwarf - the Moon will be close eough to the Earth to be torn apart by tidal forces, forming a Saturn-like ring system around our planet. By then, of course, there will be no-one to appreciate the beauty of the rings; or any bright luminary to illuminate them...

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