Chuck Bednar for redOrbit.com – @BednarChuck
Glacial earthquakes have been pretty poorly understood. However, the recent discovery that some chunks of ice rapidly move backwards and downwards after breaking off into the ocean during calving events could shed new light on this phenomenon.
Writing in Thursday’s edition of the journal Science Express, Swansea University Professor Tavi Murray and colleagues from Newcastle University and the University of Sheffield explained that the discovery could enable researchers to remotely measure glacier calving while improving the reliability of models used to predict future sea-level rise in a warming climate.
Over the past 20 years, glacial earthquakes have increased seven-fold and experienced a northward migration. This appears to indicate an increase in the mass loss rate at the Greenland Ice Sheet as a result of calving, Professor Murray’s team said. To investigate, they installed wireless GPS devices on Helheim Glacier, one of the largest glaciers in southeast Greenland.
The goal was to measure the velocity and displacement of the glacier surface. The UK team, along with collaborators from the US, was able to determine the unexpected movements of a glacier in the moments immediately after a calving event.
Mechanism linking earthquakes, calving events discovered
“The specific source of glacial earthquakes has been under debate since they were first discovered in 2003,” Dr. Timothy James from the Glaciology Group at Swansea University, told redOrbit via email. “Part of the difficulty has been a lack of data of real calving events. The front of a calving glacier is a very dynamic environment and difficult to instrument and measure.”
“Our paper has combined three key sources of data: unique GPS data and camera imagery from the glacier itself providing detailed information about the glacier’s movement during a calving event; earthquake data from the Global Seismic Network; and scale models in the lab which gives us the force exerted by the iceberg on the calving front (which would be impossible to measure in real life),” he added.
While Dr. James said that he and his fellow researchers already knew that there was a link between glacial earthquakes and glacier calving events, they previously did not know the exact mechanism through which they were caused. Using the aforementioned three sources of data, he said they were able to document the actual forces that are active during large, backward-rotating calving events, and thus the causes of glacier earthquakes themselves.
“Now that we know how to interpret the seismic signal from the Global Seismic Network, we are much closer to being able to estimate physical characteristics (like size/volume) from just the seismic signal,” Dr. James told redOrbit. “Data from the Global Seismic Network is very cheap compared to actually visiting a glacier to measure the same thing, and it can record calving events from all over the world – and it is available continuously, year-round, in all weather.”
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