Our understanding of the dynamics of ice sheet movement is limited due to the harsh and difficult-to-access nature of the environment.

However, knowing how meltwater actually moves through glaciers is essential for helping coastal populations adapt to climate change, understanding how coastal ecosystems are transforming, and accurately predicting the rise in global sea level, writes Maarja Kruusmaa, professor of biorobotics at the Tallinn University of Technology (TalTech) together with her Estonian and Norwegian colleagues in a newly published research article.

The way into the unknown

Large and intricate networks of waterways transport the surface meltwater of glaciers both inside and beneath them. These channels resemble mighty waterslides at a large amusement park; they have a significant impact on the glacier's stability and rate of decay. Such under-surface water systems are poorly understood since it is difficult, if not impossible, to monitor the water flow in them.

Researchers from the University of Oslo (UiO), the Tallinn University of Technology (TalTech) and the Norwegian University of Science and Technology (NTNU) have developed a technique for mapping subsurface water channels using small, sensor-equipped drifters carried by the water flow.

The small floating drifters are fitted with motion sensors and inertial measurement devices for registering the float's motion, as well as a satellite receiver and radio bacon for registering its position when it disappears into the glacier and reappears at the glacier outlet.

Because GPS signals do not penetrate ice, a GPS receiver cannot determine the location of the drifter. The only data recorded by the drifter are the acceleration and rotation of its own body in relation to the Earth's magnetic field.

Laura Piho, a mathematician at TalTech, analyzed these signals using AI techniques. Her system, which is based on research in the fields of human motion analysis and robot navigation, looks for discrete sensor signals as these drifters traverse meanders, slide and drop waterfalls.

She then calculates how they must be aligned in order for the drifter to move from one location to the next and creates the most likely path the drifter could have taken between recording its GPS coordinates at the entry and exit of the channel.

"We can now directly measure how water rushes through those channels at sometimes dizzying speeds and pressurizes the glacier's base," Andreas Alexander, a glaciologist from UiO, said.

What is the hardest part?

The deployment and retrieval of equipment is usually the most difficult part of glaciology fieldwork. The team have spent many summers conducting tests, climbing glaciers or sending drones to drop gadgets onto them.

The design of the devices, developed originally at TalTech for a completely different application (measuring pressure in hydropower turbines), is especially rugged to tolerate drops from gigantic waterfalls in large glaciers and they are equipped with satellite receivers and radio beacons to locate them at the glacial front.

Nevertheless, many of the devices get smashed in moulins (deep vertical shafts though which water enters into the glacier) or stay stuck in the gigantic hidden network of glacial rivers and lakes.

Professor Maarja Kruusmaa (TalTech and NTNU) said, "The drifter hunt has been our most exciting and expected entertainment every summer."

The research article "Topology and spatial-pressure-distribution reconstruction of an englacial channel" was published in the European Geosciences Union (EGU) scientific journal.

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