Friday , November 27 2020

An antarctic ice shelf is shaken by thousands of "icebergs" but only at night



As the frozen Antarctic landscape at the bottom of the world adapts to an ever warmer planet, we continue to find more mysterious phenomena beneath and in the ice. Now there is "ice cold" to add to this list.

It was not so long ago that earthquakes did not appear to exist on this irreconcilable continent. Scientists know better now, and have just reported another tedious anomaly: ice quake that shakes the frozen landscape … but only at night.

When the darkness falls, for a 6-12 hour period in the evening, scientists studying the behavior of the ice at McMurdo Ice Shelf fetched these mysterious ice-cold vibrations thanks to seismometers planted across the shelf landscape.

765 Antarctic Ice Cakes 1(Alison Banwell)

"In these areas, we would record tens, hundreds, up to thousands of these per night," said glaciologist Douglas MacAyeal of the University of Chicago.

It is MacAyeal's business to study how melt water and melting processes affect the Antarctic region; While it may sound surprising, it actually melts that is responsible for averting this nocturnal cavalcade of quakes.

During Austral's summer melting season (November 2016 to January 2017), researchers set up seismometers at two different locations 20 kilometers apart (just over 12 miles apart) at McMurdo Ice Shelf.

They called the places "dry station" and "wet station", in relation to how much melting behavior the exhibited areas.

On the wet station, the dark ice-cream produced pools of water on the ground during the day, whereas the dry station was particularly less prone to melting water despite the sunlight's heat.

But that was not the only difference between these two environments.

Each night, the wet station became alive with hundreds or thousands of fleeting ice quakes generated by natural activity and lasting less than a second each time.

In contrast, the seismic activity detected at the dry station was markedly different and appeared to be caused by human activity (probably vehicles on a nearby road used by the research group).

As for the quakes on the wet station, it is not the first time scientists have observed 24-hour cycles of seismicity on an ice shelf this way – but it has never been associated with ice shelf melting and surface hydrology, as the scientists suggest is going on here.

"In these ponds there is often a layer of ice on the top of molten water below, as you see with a lake that is only frozen upstairs," says MacAyeal.

"When the temperature cools at night, the ice on the top contracts, and the water underneath expands as it freezes. It makes the top cover until it finally breaks with a snap."

The seismic phenomenon could ultimately help scientists monitor glacier melting extremely, the scientists hypothesize because where the melting processes are the strongest, where the ice quakes spring up.

By backing up their admittedly "modest seismometer implementation" with models simulating the same phenomenon, the team concludes that "thermally regulated seismicity can exist on any ice shelf that undergoes surface melting and freezing, especially those that have lost their protective insulating anniversary. ".

Of course, the team's explanation is probably best seen as a hypothesis until further evidence comes to support it in one way or another.

Tragically, however, we cannot wait too long.

With Antarctica now rapidly melting everywhere, there has never been a better time exploring the origin of these dark tremors.

The results are reported in Annunciation of Glaciology.


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