See beneath the Greenland ice sheet through the noise of the Earth

Produced high-resolution images of the rocks beneath the Greenland ice sheet through seismic waves.Using the ‘noise’ generated by ocean storms to create a detailed model of the geological conditions underlying the Greenland ice sheet. This is the goal that an international team of researchers from Swansea University and University College London set themselves in collaboration with the Italian Istituto Nazionale di Geofisica e Vulcanologia (INGV), in the study “Uppermost crustal structure regulates the flow of the Greenland Ice Sheet” published in the journal Nature Communications.”The Greenland ice sheet”, explains Andrea Morelli, researcher at INGV and co-author of the study, “is the second largest freshwater reservoir on Earth. However, the rate of ice mass loss has increased sixfold since 1991, which represents about 10% of the recent global sea level rise”.The geological conditions of the ground under an ice sheet or glacier play a key role in determining the movements of the ice and identifying which areas are the most susceptible.”The main factors to consider”, continues Morelli, “include the geological composition of the rock layers, the temperature of the underlying earth’s crust and the amount of water present in liquid form between the rock and ice, since it acts as a lubricant accelerating the flow towards the ocean with the consequent rise in sea level”.The problem, however, is how to assess what is happening deep underground, as the rock is covered in a layer of ice about 2.5 kilometers thick.”By measuring the shape and speed of the seismic waves – called ‘Rayleigh’ – extracted from the earth’s noise”, adds the researcher, “we were able to map what is happening down to 5 kilometers below the Greenland ice sheet. These waves travel along the Earth’s surface and are sensitive to changes in the properties of the Earth”.The researchers, therefore, by analyzing the seismic waves were able to elaborate high resolution images which, as Andrea Morelli says, “showed that the low velocities in the upper crust tend to be associated with the main outlet glaciers along the edge of the ice cap and to the high flow of geothermal heat produced, over the course of geological history, by the same deep structure now responsible for volcanism in Iceland. Basal ice may affect the increase in ice flow velocity at the Petermann glacier and in the Northeastern Greenland Ice Stream”.“The research”, he concludes, “highlights the importance of the interaction between solid earth and the dynamics of the ice cap. These interactions control past, present and future flow dynamics and must be adequately explored and implemented in models of the ice sheet”. (font: Istituto Nazionale di Geofisica e Vulcanologia – INGV)