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tech / alt.astronomy / Re: There is a ‘gravity hole’ in the Indian Ocean, and scientists now think they know why

OK. I'll admit, I'm confused by this.
They say it's a " “gravity hole” in the Indian Ocean — a spot
where Earth’s gravitational pull is weaker, its mass is lower
than normal, and the sea level dips".
If the pull is weaker, why does not the water bulge out?

from
https://www.cnn.com/2023/07/24/world/gravity-hole-geoid-low-indian-ocean-scn/index.html

There is a ‘gravity hole’ in the Indian Ocean, and scientists now think
they know why
Jacopo Prisco
By Jacopo Prisco, CNN
Updated 10:33 AM EDT, Mon July 24, 2023

In 2011, GOCE delivered a model of the 'geoid' pictured here. At the
time, it was the most accurate ever produced. The colours in the image
represent deviations in height (--100 m to +100 m) from an ideal geoid.
The blue shades represent low values and the reds/yellows represent high
values.
The sea level dips by over 328 feet (100 meters) in a "gravity hole"
first discovered in 1948. Today, scientists hypothesize that the hole in
the Indian Ocean was shaped by plumes of magma coming from deep inside
the planet, according to a new study.
ESA/HPF/DLR
Editor’s Note: Sign up for CNN’s Wonder Theory science newsletter.
Explore the universe with news on fascinating discoveries, scientific
advancements and more.

CNN
—
There is a “gravity hole” in the Indian Ocean — a spot where Earth’s
gravitational pull is weaker, its mass is lower than normal, and the sea
level dips by over 328 feet (100 meters).

This anomaly has puzzled geologists for a long time, but now researchers
from the Indian Institute of Science in Bengaluru, India, have found
what they believe is a credible explanation for its formation: plumes of
magma coming from deep inside the planet, much like those that lead to
the creation of volcanoes.

To come to this hypothesis, the team used supercomputers to simulate how
the area could have formed, going as far back as 140 million years. The
findings, detailed in a study published recently in the journal
Geophysical Research Letters, center around an ancient ocean that no
longer exists.

A disappearing ocean
Humans are used to thinking about Earth as a perfect sphere, but that’s
far from the truth.

“The Earth is basically a lumpy potato,” said study coauthor Attreyee
Ghosh, a geophysicist and associate professor at the Centre for Earth
Sciences of the Indian Institute of Science. “So technically it’s not a
sphere, but what we call an ellipsoid, because as the planet rotates the
middle part bulges outward.”

Our planet is not homogeneous in its density and its properties, with
some areas being more dense than others — that affects Earth’s surface
and its gravity, Ghosh added. “If you pour water on the surface of the
Earth, the level that the water takes is called a geoid — and that is
controlled by these density differences in the material inside the
planet, because they attract the surface in very different ways
depending on how much mass there is underneath,” she said.

The “gravity hole” in the Indian Ocean — officially called the Indian
Ocean geoid low — is the lowest point in that geoid and its biggest
gravitational anomaly, forming a circular depression that starts just
off India’s southern tip and covers about 1.2 million square miles (3
million square kilometers). The anomaly was discovered by Dutch
geophysicist Felix Andries Vening Meinesz in 1948, during a gravity
survey from a ship, and has remained a mystery.

Earth core structure. Elements of this image furnished by NASA
Hidden molten rock layer found beneath Earth's tectonic plates
“It is by far the biggest low in the geoid, and it hasn’t been explained
properly,” Ghosh said.

To find a potential answer, Ghosh and her colleagues used computer
models to set the clock back 140 million years in order to see the big
picture, geologically. “We have some information and some confidence
about what the Earth looked like back then,” she said. “The continents
and the oceans were in very different places, and the density structure
was also very different.”

From that starting point, the team ran 19 simulations up to the present
day, recreating the shifting of tectonic plates and the behavior of
magma, or molten rock, inside the mantle — the thick layer of Earth’s
interior that lies between the core and the crust. In six of the
scenarios, a geoid low similar to the one in the Indian Ocean formed.

The distinguishing factor in all six of these models was the presence of
plumes of magma around the geoid low, which along with mantle structure
in the vicinity are believed to be responsible for the formation of the
“gravity hole,” Ghosh explained. The simulations were run with different
parameters of density for the magma, and in those in which the plumes
were not present, the low did not form.

The plumes themselves originated from the disappearance of an ancient
ocean as India’s landmass drifted and eventually collided with Asia tens
of millions of years ago, Ghosh said.

“India was in a very different place 140 million years ago, and there
was an ocean between the Indian plate and Asia. India started moving
north and as it did, the ocean disappeared and the gap with Asia
closed,” she explained. As the oceanic plate went down inside the
mantle, it could have spurred the formation of the plumes, bringing
low-density material closer to Earth’s surface.

More humans have visited the moon than the bottom of the ocean
01:31 - Source: CNN
The future of the geoid low
The geoid low formed around 20 million years ago, according to the
team’s calculation. It’s hard to say whether it will ever disappear or
shift away.

“That all depends on how these mass anomalies in the Earth move around,”
Ghosh said. “It could be that it persists for a very long time. But it
could also be that the plate movements will act in such a way to make it
disappear — a few hundreds of millions of years in the future.”

Aerial view of Downtown Chicago River.
‘Underground climate change’ is deforming the ground beneath buildings,
study finds
Huw Davies, a professor in the School of Earth and Environmental
Sciences at Cardiff University in the UK, said the research is
“certainly interesting, and describes interesting hypotheses, which
should encourage further work on this topic.” Davies was not involved
with the study.

Dr. Alessandro Forte, a professor of geology at the University of
Florida in Gainesville who was also not involved with the study,
believes there is good reason to carry out computer simulations to
determine the origin of the Indian Ocean geoid low, and that this study
is an improvement over earlier ones. Past research only simulated the
descent of cold material across the mantle, rather than including hot
rising mantle plumes as well.

However, Forte said he found a couple flaws in the study’s execution.

“The most outstanding problem with the modeling strategy adopted by the
authors is that it completely fails to reproduce the powerful mantle
dynamic plume that erupted 65 million years ago under the present-day
location of Réunion Island,” he said. “The eruption of lava flows that
covered half of the Indian subcontinent at this time — producing the
celebrated Deccan Traps, one of the largest volcanic features on Earth —
have long been attributed to a powerful mantle plume that is completely
absent from the model simulation.”

Another issue, Forte added, is the difference between the geoid, or
surface shape, predicted by the computer simulation and the actual one:
“These differences are especially noticeable in the Pacific Ocean,
Africa and Eurasia. The authors mention that there is a moderate
correlation, around 80%, between the predicted and observed geoids, but
they don’t provide a more precise measure of how well they match
numerically (in the study). This mismatch suggests that there may be
some deficiencies in the computer simulation.”

Terra Bella, CA - October 14: Matt Davis's company drills a 1300 feet
deep well in an orchard at Setton Farms on Thursday, Oct. 14, 2021 in
Terra Bella, CA. (Irfan Khan / Los Angeles Times via Getty Images)
Humans pump so much groundwater that Earth’s axis has shifted, study finds
Ghosh said that not every possible factor can be accounted for in the
simulations.

“That’s because we do not know with absolute precision what the Earth
looked like in the past. The farther back in time you go, the less
confidence there is in the models. We cannot take into account each and
every possible scenario and we also have to accept the fact that there
may be some discrepancies on how the plates moved over time,” she said.
“But we believe the overall reason for this low is quite clear.”

On Thursday, July 27, 2023 at 4:30:28 AM UTC+10, a425couple wrote:
> OK. I'll admit, I'm confused by this.
> They say it's a " “gravity hole” in the Indian Ocean — a spot
> where Earth’s gravitational pull is weaker, its mass is lower
> than normal, and the sea level dips".
> If the pull is weaker, why does not the water bulge out?
....

The mental model is "mass concentration".
A masscon would attract more water to the region.
But the hole is the opposite so it attracts less.

Gravity surveys of the whole planet starts in 2002 with the GRACE sat train..
An animation of results to date
show holes and mascons can vary over time. Some of the holes may correspond with
interesting things the Pen[REDACTED]

<kym.massbus.org/graceanim.gif>.

Kym Horsell wrote on 27/7/23 5:27 pm:
> On Thursday, July 27, 2023 at 4:30:28 AM UTC+10, a425couple wrote:
>> OK. I'll admit, I'm confused by this. They say it's a " “gravity
>> hole” in the Indian Ocean — a spot where Earth’s gravitational pull
>> is weaker, its mass is lower than normal, and the sea level dips".
>> If the pull is weaker, why does not the water bulge out?
> ...
>
> The mental model is "mass concentration". A masscon would attract
> more water to the region. But the hole is the opposite so it attracts
> less.

If there is 'a “gravity hole” in the Indian Ocean', shouldn't that mean
matter (i.e. the water) is held more loosely so it should tend to bludge
outwards??

> Gravity surveys of the whole planet starts in 2002 with the GRACE sat
> train. An animation of results to date show holes and mascons can
> vary over time. Some of the holes may correspond with interesting
> things the Pen[REDACTED]
>
> <kym.massbus.org/graceanim.gif>.
> --
Daniel

On Thursday, July 27, 2023 at 8:56:51 PM UTC+10, Daniel65 wrote:
> Kym Horsell wrote on 27/7/23 5:27 pm:
> > On Thursday, July 27, 2023 at 4:30:28 AM UTC+10, a425couple wrote:
> >> OK. I'll admit, I'm confused by this. They say it's a " “gravity
> >> hole” in the Indian Ocean — a spot where Earth’s gravitational pull
> >> is weaker, its mass is lower than normal, and the sea level dips".
> >> If the pull is weaker, why does not the water bulge out?
> > ...
> >
> > The mental model is "mass concentration". A masscon would attract
> > more water to the region. But the hole is the opposite so it attracts
> > less.
> If there is 'a “gravity hole” in the Indian Ocean', shouldn't that mean
....

If it's held more loosly then it moves to
where it's held more tightly -- i.e. everywhere else nearby.
I.e. a dip in the ocean.

Problems are often of the "who shaves the barber" type.

A man arrives in a small town with 2 barbershops.
One shop is a mess with ahir on the floor.
The barber there looks like he was dragged through
a fence backward. Badly shaven, hair a mess.
Plus all the chairs are taken and you have to wait 1/2 and hour to get a haircut.

The other shop is clean. The barber of that shop has a close shave and great hair.
The foor is clean and there's no waiting.

Which one should the new guy go to?

(Also works with websites).

--
Date delnept massanomindocn
2012.71 29.1195 1.36337
2014.79 29.3741 0.387552
2014.88 29.8299 -0.697913
2013.96 30.3744 -0.686367
2016.21 30.834 -1.81756
2015.12 30.9908 -1.20513
2016.88 29.632 0.0654497
2016.38 30.156 -1.66697
2016.54 29.2506 0.592272
2016.04 30.5873 -1.83637
2010.88 29.9953 -0.249577
2009.79 29.4984 1.36543
2008.29 30.4843 -0.343731
2009.04 30.8968 -1.0724
2016.62 29.0044 -0.838145
2015.04 30.7031 0.318831

DelNept == dist between E and Neptune in AU
massanomindocean == GRACE mass anom in
central Indian Ocean in equiv liquid water cms (i.e. +1cm == 10kt per km2).

Kym Horsell wrote on 28/7/23 11:28 pm:
> On Thursday, July 27, 2023 at 8:56:51 PM UTC+10, Daniel65 wrote:
>> Kym Horsell wrote on 27/7/23 5:27 pm:
>>> On Thursday, July 27, 2023 at 4:30:28 AM UTC+10, a425couple
>>> wrote:
>>>> OK. I'll admit, I'm confused by this. They say it's a "
>>>> “gravity hole” in the Indian Ocean — a spot where Earth’s
>>>> gravitational pull is weaker, its mass is lower than normal,
>>>> and the sea level dips". If the pull is weaker, why does not
>>>> the water bulge out?
>>> ...
>>>
>>> The mental model is "mass concentration". A masscon would
>>> attract more water to the region. But the hole is the opposite so
>>> it attracts less.
>> If there is 'a “gravity hole” in the Indian Ocean', shouldn't that
>> mean ...
>
> If it's held more loosly then it moves to where it's held more
> tightly -- i.e. everywhere else nearby. I.e. a dip in the ocean.

Sorry!! What?? If something is held LESS tightly, it would tend to float
off elsewhere ..... sort of like air in a balloon ... if there is some
sort of opening, the air spills out that opening .... until the air
pressure with-in the balloon equals the air pressure outside the balloon.

> Problems are often of the "who shaves the barber" type.
>
> A man arrives in a small town with 2 barbershops. One shop is a mess
> with ahir on the floor. The barber there looks like he was dragged
> through a fence backward. Badly shaven, hair a mess. Plus all the
> chairs are taken and you have to wait 1/2 and hour to get a haircut.
>
> The other shop is clean. The barber of that shop has a close shave
> and great hair. The foor is clean and there's no waiting.
>
> Which one should the new guy go to?

One barber doesn't have time to even cut his own hair whilst the other
barber is looking for something, anything, to do!!

Am I in a hurry to get my hair cut or not??
>
> (Also works with websites).
>
--
Daniel

Subject	Author
There_is_a_‘gravity_hole’_in_the_Indian_O	a425couple
_There_is_a_‘gravity_hole’_in_the_Indian_Ocea	Kym Horsell
_There_is_a_‘gravity_hole’_in_the_Indi	Daniel65
_There_is_a_‘gravity_hole’_in_the_Indian_Ocea	Kym Horsell
_There_is_a_‘gravity_hole’_in_the_Indi	Daniel65
There is a ‘gravity hole’	Bob Campbell
_There_is_a_‘gravity_hole’_in_the_Indi	Daniel65