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Author Topic: Is it true that gravity is less in Hudson's Bay and, if so, why?  (Read 2240 times)

Offline Hiheels

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Offline P-Kasso2

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #1 on: 30 July, 2015, 03:08:46 PM »
Scientist first noticed Hudson Bay's gravity had gone missing back in the swinging 60s when the words scientist, spliff and hash cookie were frequently found in the same sentence.

Some websites still hold on to the idea that Hudson Bay's gravity is missing.

One such is the following popular but serious minded website http://science.howstuffworks.com/environmental/earth/geophysics/missing-gravity.htm

It says...

"One theory centers on a process known as convection occurring in the Earth's mantle. The mantle is a layer of molten rock called magma and exists between 60 and 124 miles (100 to 200 km) below the surface of the Earth . Magma is extremely hot and constantly whirling and shifting, rising and falling, to create convection currents. Convection drags the Earth's continental plates down, which decreases the mass in that area and decreases the gravity.

A new theory to account for the Hudson Bay area's missing gravity concerns the Laurentide Ice Sheet, which covered much of present-day Canada and the northern United States. This ice sheet was almost 2 miles (3.2 km) thick in most sections, and in two areas of Hudson Bay, it was 2.3 miles (3.7 km) thick. It was also very heavy and weighed down the Earth. Over a period of 10,000 years, the Laurentide Ice Sheet melted, finally disappearing 10,000 years ago. It left a deep indentation in the Earth.

To get a better idea of what happened, think about what happens when you lightly press your finger into the surface of a cake or a piece of really springy bread. Some of it moves to the sides and there's an indentation. But when you remove your finger, it bounces back to normal. A similar thing happened with the Laurentide Ice Sheet, the theory proposes -- except the Earth isn't so much "bouncing" back as it is rebounding very slowly (less than half an inch per year). In the meantime, the area around Hudson Bay has less mass because some of the Earth has been pushed to the sides by the ice sheet. Less mass means less gravity.

So which theory is correct? It turns out that both of them are. Convection and the ice sheet's rebound effect are both causing some of the decrease in gravity around Hudson Bay. First, we'll consider the ice sheet theory.

To calculate the impact of the Laurentide Ice Sheet, scientists at the Harvard-Smithsonian Center for Astrophysics used data gathered by the Gravity Recovery and Climate Experiment (GRACE) satellites between April 2002 and April 2006. The GRACE satellites are highly sophisticated machines, orbiting about 310 miles (500 km) above the Earth and 137 miles (220 km) apart. The satellites can measure distances down to a micron, so they can detect minor gravitational variations. When the lead satellite flies over the Hudson Bay area, the decrease in gravity causes the satellite to move slightly away from the Earth and from its sister satellite. This shift in distance is detected by the satellites and used to calculate the change in gravity. Any shifts detected can also be used to create maps of gravitational fields."


There is more on the website if you fancy reading on. Once you've read it, could you please explain it to me but in English and one teaspoonful at a time?
« Last Edit: 30 July, 2015, 03:14:51 PM by P-Kasso2 »
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Offline antonymous

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #2 on: 30 July, 2015, 03:35:56 PM »


There is more on the website if you fancy reading on. Once you've read it, could you please explain it to me but in English and one teaspoonful at a time?

Following the old epithet tha a picture paints a thousand words - attached two pictures derived fro the satellite gravity survey mentoned.
The greyscale picture arrows the Hudson Bay and 2other low gravity spots (the darkest ones on the map) the colour imahe is confusiing with so much colour detail present. Anyway I hope they help.
« Last Edit: 30 July, 2015, 03:42:46 PM by antonymous »
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Offline Hiheels

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #3 on: 30 July, 2015, 04:36:23 PM »
What I've gleaned is that basically there's a dimple there in the earth's surface meaning the mass has been pushed outwards making it less where the dimple is and, therefore, decreasing the gravity.
I bet someone better read than I is wetting themselves at my grasp of the situation, but ignorance is bliss.
Interesting, though - thanks all.

Offline P-Kasso2

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #4 on: 31 July, 2015, 01:57:21 PM »
How does Hudson's Bays missing gravity affect the local wildlife? I keep imagining armies of beavers and woodland caribou and lynxes and muskrats all enjoying playing at being Neil Armstrong and bouncing about in 90 ft high, gravity-free bounds leaving an audience of bemused Whistling Swans and Pintails and Ospreys scratching their heads in disbelief at flying mammals being so silly.
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Offline Hiheels

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #5 on: 31 July, 2015, 02:19:20 PM »
I've had a dig about and can't find anything that specifically mentions any effects at all, except for weighing less probably.
I think that, although it's measurable, it's not massive.
Matron.

Offline P-Kasso2

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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #6 on: 31 July, 2015, 03:07:30 PM »
Matron?  lmao    lmao    lmao    lmao   lmao   lmao   
« Last Edit: 31 July, 2015, 03:19:35 PM by P-Kasso2 »
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Re: Is it true that gravity is less in Hudson's Bay and, if so, why?
« Reply #7 on: 31 July, 2015, 03:31:56 PM »
 ;D