A University of Chicago press release reports on the discovery of an unknown phenomenon that occurs on the marine extensions of land glaciers in Antarctica, they are known as ice shelves and they experience thousands of tiny quakes when meltwater refreezes at night. The discovery might allow scientists to remotely study and predict ice shelf collapse.
Updates on Brunt and Thwaites below the fold.
From the University of Chicago News:
Stay overnight on an Antarctic ice shelf, and you may feel the shaking from thousands of tiny quakes as the ice re-forms after melting during the day.
In a recent study, UChicago scientists placed seismometers on the McMurdo Ice Shelf and recorded hundreds of thousands of tiny “ice quakes” that appear to be caused by pools of partially melted ice expanding and freezing at night. The phenomenon may be able to help scientists track glacier melting—and to help explain the breakup of large ice shelves.
snip
MacAyeal and the team were interested in the role of “quakes” on the floating ice shelves. (You may remember reports of ice or frost quakes around Chicago and the Midwest during the cold snap caused by the polar vortex weeks ago, when residents reported booms or cracking sounds at night; this is the same mechanism.) But they wondered how often the phenomenon was occurring in ice in the Antarctic, and what role it might play in the melting and breakup of ice.
The team set up seismometers for 60 days during the melt season in two locations near seasonal meltwater lakes on the McMurdo Ice Shelf. One was drier; the other was slushier, with pools of melted water forming and refreezing. The wetter location, they found, was alive with seismic activity at night.
“In these ponds, there’s often a layer of ice on top of melted water below, like you see with a lake that’s only frozen on top,” MacAyeal explained. “As the temperature cools at night, the ice on the top contracts, and the water below expands as it undergoes freezing. This warps the top lid, until it finally breaks with a snap.”
The energy vibrates out into the surroundings, where it’s picked up by seismometers. Some of the cracks re-heal, but some do not, MacAyeal said.
It may explain why icebergs actually break off more frequently during colder times of the year. “Perhaps this is happening at longer, slower scales,” MacAyeal said.
The discovery adds an important piece to our understanding of the physics and processes around melting ponds on ice shelves—especially if it can help researchers remotely keep track of Antarctic melting. “It may be very useful to add this to our other ways of monitoring ice,” MacAyeal said.
Updates
Brunt Ice Shelf
Tensile strength is defined as "the resistance of a material to breaking under tension".
The red dot is the location of the Chasm 1 crack. IIRC, the crack is with .4 miles from the Halloween Crack, and when they meet it will break off a massive block of ice about the size of Delaware.
Thwaites Glacier
Ocean
Ice shelf collapse from being pummeled by ocean waves due to the loss of sea ice.
“Sea ice acts as a protective buffer to ice shelves, by dampening destructive ocean swells before they reach the ice shelf edge,” Dr Massom said.
“But where there is loss of sea ice, storm-generated ocean swells can easily reach the exposed ice shelf, causing the first few kilometres of its outer margin to flex.”
“Over time, this flexing enlarges pre-existing fractures until long thin ‘sliver’ icebergs break away or ‘calve’ from the shelf front.”
“This is like the ‘straw that broke the camel’s back’, triggering the runaway collapse of large areas of ice shelves weakened by pre-existing fracturing and decades of surface flooding.”
Meanwhile in the Pacific