h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Just been reading up on the great china three gorges dam project.
It seems there are quite a number of similar projects across africa in particular.
Sure they cause earthquakes locally, but is there any possibility that a combination of this kind of projects can cause disturbances in tectonic plate movement.
In particular over a considerable geographical distance?

yes, of course

surely that's common knowledge?

Hang on. These are sweeping statements that are not backed by research references and therefore unscientific.

This is science explained and therefore should be based on scientific evidence and rigor.

t.

this is bertie after all!!!

look what happend on the PFFT theread!!!

this is the opening gambit in pushing an agenda

thank you takk, i am honoured.

apolagies, Taff. (Late night)

I'm pretty sure that lakes are not heavy enough to cause earthquakes. Earthquakes happen down about 20km deep. 20km of rock weighs so much that adding the weight of 500m of water to it won't change things much.

I think there's some theory (reasonable robust) that melting ice affects .... can't remember if it's tectonics or volcanics.

Re the mega dams, the fact they're already destroying massive amounts of ecosystems and human lives would be more pertinent than theories about quakes

Sorry, that was a bit vague.

http://www.newscientist.com/article/dn13583-melting-ice-caps-may-trigger-more-volcanic-eruptions.html

The ice on Antarctica is so heavy that it presses the ground downwards and parts of the ground are below sea level. If the ice were to melt, these parts would rise, presumably causing somewhere else to go downwards.

I know that after the last ice age, Ireland and Great Britain rose when the weight of all that ice was taken off them.

But a lake wouldn't cause this to happen unless it were a few kilometres deep.

think you are right there,

at the end of the last ice age when all the ice melted some of the land masses rose because the weight of the ice had been holding them down

but these were enormous sheets of ice over vast areas and of a serious depth

>>
Vatnajökull is the largest ice cap in Iceland, and is disappearing at a rate of 5 cubic kilometres per year.

...

They say that, as the ice disappears, it relieves the pressure exerted on the rocks deep under the ice sheet, increasing the rate at which it melts into magma. An average of 1.4 cubic kilometres has been produced every century since 1890, a 10% increase on the background rate.

...

The situation in Iceland does not necessarily mean magma will be melting faster around the world. Vatnajökull sits atop a boundary between plates in the Earth's crust, and it is this configuration that is allowing the release in pressure to have such a great effect deep in the mantle.

But the thinning ice has another effect on volcanoes which will be more widespread.

As the amount of weight on the crust changes, geological stresses inside the crust will also change, increasing the likelihood of eruptions. "Under the ice's weight, the crust bends and as you melt the ice the crust will bounce up again," explains Bill McGuire of University College London in the UK, who was not involved in the study.
<<

##"Under the ice's weight, the crust bends and as you melt the ice the crust will bounce up again," ##

like taking a plaster off a zit???!!

Re Britain, that's still happening. Scotland is rising, and the South of England is dropping. It's not very much though.

http://www.computescotland.com/scotland-rising-for-a-century-of-land-change-2759.php

Point taken about a few hundred metres of water, but what about a few dozen major dams all emptying and filling at the same time - ive got a very funny feeling that they do.
Most of them around the centre part of the earth?

I know there is a mega dam which actually affected the Earth's rotation... can't remember which one though.

my point is that, is it possible that the recent earthquake in Japan was caused by these constructions.
If that is the case then we have a great many more earthquakes to look forward to. And worse.
wonder what it would take to set off the Caldera in yellowstone park, the St Andreas fault?
presumably if one went off then the other would too - doomesday scenario.

No, it is not possible that the recent earthquake in Japan was caused by anything man-made.

If we knew how to trigger earthquakes, we'd make lots of small ones to ease the pressure and reduce the chances of big ones.

chinas dam is on a different tectonic plate to where the sunami event happend

<bat

wow, brilliant answers, just what i needed to hear. many thanks.