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Just before 9.30am on Sunday 11 November, a series of unusual seismic pulses rippled around the world almost undetected.
The waves rang for over 20 minutes, emanating about 15 miles off the shores of Mayotte - a tiny island in the Indian Ocean between Madagascar and Africa.
From here, they reverberated across Africa, setting off geological sensors in Zambia, Kenya, and Ethiopia.
They crossed the Atlantic, and were picked up in Chile, New Zealand, Canada, and even Hawaii nearly 11,000 miles away, the National Geographic reports.
Despite their huge range, the waves were apparently not felt by anybody. However, one person monitoring the US Geological Survey's live stream of seismogram displays did notice the unusual waveform and posted it to Twitter, sparking the interest of other geologists and earthquake enthusiasts.
[...] The bizarre waveform is what scientists call "monochromatic". Earthquakes normally produce waves of so many different frequencies, the wave readings appear more jumbled.
But the mystery waveform from Mayotte was a crisp zigzag, which repeated after steady 17-second intervals.
"They're too nice. They're too perfect to be nature," joked the University of Glasgow's Helen Robinson, who is study[ing] for a PhD in applied volcanology.
(Score: 1) by IndigoFreak on Wednesday December 05 2018, @03:59AM (8 children)
I'm honestly confused. How are sea levels dropping when all we have been hearing is that they are rising.
Ignore my other post, I replied to the wrong comment!
(Score: 2) by c0lo on Wednesday December 05 2018, @04:48AM (5 children)
How do you define the "zero level" in an absolute way that's also easy to measure?
For the non-scientific population, only the "easy way to measure" is addressed - in the form of what area of land are above and below the surface.
Thus, Canadians will see the sea level dropping, even if the sea level raises in absolute value, eh? Because Canada is raising faster.
While the NewYorkers and the politicians in Wa DC will be sinking faster than the sea level rainsing, because the crust underneath them go further down.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by IndigoFreak on Wednesday December 05 2018, @04:48PM (2 children)
I'm disagreeing with these terms. Sea level to me, implies depth. When a land mass sinks, that isn't the ocean rising, that's the ocean staying the same level, and the land mass sinking. If you want to pretend that the ocean level can rise and fall in different areas depending on how much of the beach in that area is now covered with water, or isn't covered with water. I'm not buying it.
If i dig out a huge chunk of land and it fills in with sea water, the ocean level didn't rise at all. I didn't just raise the ocean level. By the same logic I can't put a barrier, 50 feet into the ocean, drain the water creating new land area, and say that the ocean level dropped.
This is what is happening in a different form when land mass is sinking or rising. I would guess people area interchanging ocean level with ocean surface area.
To objectively measure if ocean level is rising I would think you would go out to several spots all around the globe and measure the depth of the water.
To correctly do what people describe happening. You need multiple terms. Not just one grab all. Ocean depth, surface area, and volume. There might be more, but those make the most sense to me.
(Score: 2) by c0lo on Wednesday December 05 2018, @05:20PM (1 child)
I disagree. It's not like there's an infinite amount of water so that sinking a volume of solid lets the water level unmodified. in fact, the volume of water on the entire Earth is surprisingly small as a proportion of entire Earth [usgs.gov]
The terminology that would scientifically describe the phenomenon is "redistribution of water volume, resulting in a different area of dry land".
If you include the post glacial rebound into account, you need to speak of "redistribution of water/crust/Earth's mantle volumes". Not very common-sensical for anybody unprepared to visualize the thing globally.
Or forget the "sea level" completely and deal in terms of "available area of dry land before and after glacier meltdown" - not only it's objective, but that is actually the metric that matters.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by IndigoFreak on Wednesday December 05 2018, @06:22PM
So yes, displacing water most likely will cause the water level to rise(but the earth is varied and there are many factors where it might ultimately stay the same like if the short period of extra height causes the crust to compress back to the original height). But then how can NY be sinking because that means its displacing water causing it to rise?? So it's rising but sinking faster? I get physics. Their language is all wrong when speaking of this.
We are mostly on the same page here.
(Score: 2) by hendrikboom on Thursday December 06 2018, @03:10AM (1 child)
Maybe not easy, but it *is* possible to measure the diameters of the Earth in different directions usinf satellite radar.
(Score: 2) by c0lo on Thursday December 06 2018, @03:29AM
What use do you have for that measure, given that is not constant (over 24h period or at any moment over 2π rads) within the precision of interest (few centimeters/inches)?
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 1) by kiffer on Wednesday December 05 2018, @12:48PM
Average global sea levels rise as more water is added to the oceans from land ice, e.g. Greenland, and Antarctica.
However "local" apparent sea level can fall, as isostatic rebound changes the height of the land.
Basically where all the ice was was pushed down by the weight of the ice, when the ice melts the land pops* up... when some land pops up, other land pops down.
The crust is a complex dynamic system, lots of stuff is happening all the time. It's just slow... then fast... then slow.
*I say pops... but obviously that's over geological time, though it doesn't happen smoothly, it can happen in sudden eathquake level movements and then stick for a while.
https://en.wikipedia.org/wiki/Post-glacial_rebound [wikipedia.org]
(Score: 4, Interesting) by HiThere on Wednesday December 05 2018, @05:56PM
When the ice over land melts, the water runs quickly into the ocean, but it takes multiple thousands of years for the land to rebound due to the removal of weight. Both are happening, but they're happening on different time scales.
OTOH, most of the current rise in the ocean is due to the oceans getting warmer, and warm water takes up a bit more space than cold water. (This is true while above about 4 degrees Centigrade, when colder water starts expanding to make ice that floats.)
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