A huge flood triggered by the rapid draining of a lake beneath the Greenland Ice Sheet occurred with such force that it fractured the ice above and burst out across its surface.
This phenomenon, observed for the first time in Greenland and detailed in research published today in the journal Nature Geoscience, sheds new light on the destructive potential of meltwater stored beneath the ice sheet.
It reveals how, under extreme conditions, water flooding underneath the ice can force its way upwards through the ice and escape at the ice sheet surface.
This phenomenon is not considered by numerical models that aim to predict the future evolution of the Greenland Ice Sheet, and this new work raises questions about whether this type of mechanism deserves greater attention in the future.
The international team of researchers led by Jade Bowling and Malcolm McMillan from Lancaster University’s Centre of Excellence in Environmental Data Science and The UK Centre for Polar Observation and Modelling, studied a previously undetected lake beneath the ice sheet (known as a subglacial lake) in a remote region of northern Greenland, using state-of-the-art satellite data and numerical models.
The team also includes other colleagues from Lancaster University, colleagues from The Geological Survey of Denmark and Greenland, The University of Edinburgh, The University of Liege, Utrecht University, DTU Space (Technical University of Denmark), The University of California, Universite Grenoble, The University of Leeds, The Alfred Wegener Institute and The University of Bremen.
Using detailed three-dimensional representations of the ice sheet surface from the ArcticDEM project, alongside data from a number of European Space Agency (ESA) and NASA satellite missions, they monitored the sudden drainage of this lake.
The researchers discovered that over a period of 10 days in summer 2014, an 85 metre-deep crater appeared across a 2 km² area in the ice surface, as 90 million cubic meters of water flooded out of the underlying lake. This represents one of the largest Greenland subglacial floods in recorded history.
However, what the researchers found further downstream was even more surprising.
In a region of previously unblemished ice, they observed the sudden appearance of an area the size of around 54 football pitches (385,000 square metres) of fractured and distorted ice; comprising deep cracks and 25 m high uprooted ice blocks, together with a freshly water-scoured ice surface of around 6 km².
Dr Andrew Sole said: “Observations of subglacial lake drainages are rare, and for us to see such clear and dramatic evidence of the flood re-emerging at the ice surface is really exciting. The knock-on effects on ice motion and iceberg calving highlight how large individual events can induce a cascade of downstream processes increasing their impact on the environment.
“Observing the lake drainage from field data would require a huge amount of luck, but satellites which frequently image large areas of the ice surface enable us to identify and investigate these important and intriguing phenomena.”
Although it had been previously assumed that meltwater flows from the surface to the base of the ice sheet, and then onwards to the ocean, this research provides clear evidence that water can also travel upwards, in the opposite direction.
It also surprised the scientists to find that the flood occurred in a region where models predicted that the ice was frozen at the bed, leading the researchers to propose a mechanism whereby pressure-driven fracturing of ice along the ice bed created a pathway for the water to then flow.
These mechanisms are not something that are considered by the models that aim to simulate how the ice sheet might evolve in the future, as Earth’s climate warms and the ice sheets experience increasing rates of melting.
As such, these discoveries highlight the complexity of water flow, and the need to better understand how the ice sheet responds to extreme inputs of meltwater; something which is likely to become more common as our climate warms, and surface melting intensifies and expands into new areas.
The research was primarily funded by the UK Natural Environment Research Council (NERC), the European Space Agency (ESA), and UK Research and Innovation (UKRI).