An international group of scientists has discovered that numerous small ice quakes happen in one of Greenland’s largest ice streams. This revelation will improve the accuracy of estimates regarding the movement of the ice sheet and the resulting changes in sea levels.
The significant ice streams found in Antarctica and Greenland resemble frozen rivers, transporting ice from the vast inland ice sheets to the ocean. Changes in their behavior can greatly impact sea-level rise. To predict how much sea levels will increase, climate scientists utilize computer models of these ice streams. Previously, these models were built on the premise that ice streams move slowly and consistently into the ocean, similar to thick honey flowing.
However, satellite data tracking the speed of ice streams indicates that these models are flawed and do not accurately represent reality. This leads to significant uncertainties in projections concerning the mass loss from ice streams and the speed and extent of sea-level rise.
Ice streams both shake and flow
Recently, a research team headed by Professor Andreas Fichtner from ETH Zurich made a surprising finding: within these ice streams, numerous small quakes are occurring that trigger one another and can extend over distances of hundreds of meters. This new insight bridges the gap between existing models of ice streams and satellite observations, influencing how future simulations will be conducted.
“The idea that ice streams only flow like viscous honey is no longer valid; they also exhibit a continuous stick-slip movement,” states Fichtner. He is optimistic that this new understanding will be incorporated into ice stream simulations, leading to more precise projections of sea-level changes.
New insights into ice core mysteries
Moreover, the ice quakes provide explanations for many fault planes found within ice cores collected from deep within the ice. These fault planes, a result of tectonic movements, have puzzled scientists for years, but this new discovery sheds light on their formation.
“The discovery of these ice quakes is a critical advancement in understanding the small-scale deformation of ice streams,” comments Olaf Eisen, a Professor at the Alfred Wegener Institute and a co-author of the study.
The recent research led by ETH Zurich has been published in the journal Science and included collaboration from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the University of Strasbourg, the Niels Bohr Institute (NBI), the Swiss Federal Institute WSL, and additional academic institutions.
Connections between fire and ice
The inability to detect these ice quakes at the surface, allowing them to go unnoticed until now, is attributed to a layer of volcanic particles that sits 900 meters beneath the ice surface. This layer prevents the quakes from reaching the surface. Analyses of the ice core indicated that these volcanic particles resulted from a significant eruption of Mount Mazama in present-day Oregon (USA) around 7,700 years ago. “We were surprised to find this previously unknown connection between ice stream behavior and volcanic activity,” recalls Fichtner.
Professor Fichtner also observed that these ice quakes originate from impurities within the ice. These impurities are remnants from volcanic activity: tiny amounts of sulfates that were released into the air during eruptions and traveled halfway around the world before settling on Greenland’s ice sheet as snow. These sulfates compromise the ice’s stability and promote the formation of micro-fissures.
A 2,700-meter borehole in the ice
The ice quakes were detected using a fiber-optic cable lowered into a 2,700-meter-deep borehole, capturing seismic data from within a massive ice stream for the first time. This borehole was drilled by researchers from the East Greenland Ice-core Project (EastGRIP), led by the Niels Bohr Institute with strong support from the Alfred Wegener Institute, which involved retrieving a 2,700-meter-long ice core. Once the drilling concluded, researchers took the opportunity to drop a fiber-optic cable 1,500 meters down the borehole to continuously record signals from the ice stream for a duration of 14 hours.
The research site and borehole are situated on the North East Greenland Ice Stream (NEGIS), about 400 kilometers from the shore. NEGIS is the largest ice stream of the Greenland ice sheet, which plays a significant role in the ongoing rise of sea levels. Near the research facility, the ice is advancing toward the ocean at an approximate speed of 50 meters per year.
Given the frequent occurrence of ice quakes over a wide area in their measurements, researcher Fichtner believes it is likely that such quakes happen in ice streams globally and continuously. However, further seismic measurements in other boreholes will be necessary to confirm this theory, and there are plans in place to do so.
