Imma Perfetto
Cosmos science journalist
A previously unknown phenomenon discovered deep inside the ice streaming from the Greenland ice sheet will change the way scientists model ice melt and rising sea levels.
The ice streams of Antarctica and Greenland are major contributors to sea level rise, carrying ice from inland ice sheets to the sea. So, accurately predicting their behaviour in a changing climate is of utmost importance.
Currently, simulations of ice stream movements assume they flow slowly and steadily like thick honey. But the results of these models do not align with satellite measurements.
Now, a team of researchers, including one from the Australian National University, has discovered the ice streams also move with a constant stick-slip motion.
This is driven by countless weak quakes deep within the ice that trigger one another, and propagate over hundreds of metres.
They found the quakes by drilling an almost 3km borehole in the Northeast Greenland Ice Stream (NEGIS) and lowering a fibre-optic cable 1.5km down to detect seismic data using distributed acoustic sensing (DAS).
The research is published in the journal Science.
“The fact that we’ve now discovered these ice quakes is a key step towards gaining a better understanding of the deformation of ice streams on small scales,” says Olaf Eisen of the Alfred Wegener Institute in Germany, one of the study’s co-authors.
The quakes are the origin of fault planes between ice crystals in cores taken from great depths, which have been known to scientists for decades but remained unexplained until now.
The ice quakes cannot be observed at the surface due to a layer of volcanic particles located 900m deep. Analysis of the ice core showed that these volcanic particles originate from a massive eruption of Mount Mazama 7,700 years ago, in what is now the US state of Oregon.
The triggers of the ice quakes can be traced back to volcanic eruptions too.
Traces of sulphate impurities that entered the atmosphere in volcanic eruptions and were deposited on the Greenland ice sheet in snowfall reduce the stability of the ice and favour the formation of micro fissures.
“We were astonished by this previously unknown relationship between the dynamics of an ice stream and volcanic eruptions,” says Professor Andreas Fichtner of ETH Zurich in Switzerland, lead author of the paper.
As ice quakes occur frequently over a wide area in the researchers’ measurements, Fichtner believes it is also plausible that they occur in ice streams everywhere, all the time.
To verify this, they plan to take seismic measurements in other boreholes.
