Scientists in the summer of 2002 watched in amazement as the Larsen B Ice Shelf splintered and collapsed in just over one month. Never before had such a large area — 1,250 square miles (3,250 square km) disintegrated so quickly. And with climate change accelerating its environmental impact, NASA glaciologists have made a last-ditch attempt to understand exactly how global warming affects ice.
Thousands of earthquakes are recorded every day on the Antarctic ice shelf.
These ice quakes, a process also known as cryoseisms, occur when ice re-forms after melting during the day.
And it is thought the phenomenon will help explain the breakup of large ice shelves.
“In these areas we would record tens, hundreds, up to thousands of these per night,” explains Professor Douglas MacAyeal, co-author of the NASA-funded study.
“It’s possible that seismometers may be a practical way for us to remotely monitor glacier melting.”
Professor MacAyeal’s University of Chicago team were interested in the role of “quakes” on the floating ice shelves.
But the study led the team to consider whether the phenomenon was occurring in ice in the Antarctic, and what role it plays in the melting and breakup of ice.
The University of Chicago team set up seismometers – instruments recording ground motions – for two months 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.
And they found the wetter location 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,” Professor 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 is recorded by seismometers.
While some of the cracks can re-heal, others will not, Professor MacAyeal said.
The phenomena may explain why icebergs actually break off more frequently during colder times of the year.
“Perhaps this is happening at longer, slower scales,” Professor 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.