Moulin SeismicsMoulins are deep vertical shafts on a glacier/ice-sheets that helps drain meltwater f

Moulin SeismicsMoulins are deep vertical shafts on a glacier/ice-sheets that helps drain meltwater from the surface. Meltwater streams and supraglacial lakes (lakes on the surface of the glacier/ice-sheet) drain their water into moulins and make their way right to the bottom where they help lubricate the path of the glacier, thereby accelerating its flow (watch this clip for an example - http://bit.ly/2coiqHL). Since these drainage systems directly influence the basal motion of glaciers and ice-sheets an understanding of these systems are essential for calculating glacier mass balances and thereby global sea level rise.The geometry of moulins and their changes owing to continuous meltwater flow are barely known since they are difficult to investigate due to their accessibility. However, recently for the first time, scientists working on the Russell glacier in Greenland have used seismics to understand the geometry of these structures. The vibrations emitted as large amounts of water draining through a moulin can be measured as ground displacement by an array seismometers installed at the surface (along with a few seismometers lowered into boreholes). The analysis of the seismic wavefield can help constrain the geometry of these structures.The walls of the moulins act as resonators to the acoustic waves produced by the inflowing water as they reach the collected water at the base. The tremor waveform has two different sources: one from the bottom of the resonator, and the other from the solid icewalls. The waveform patterns were similar to the resonance from an organ pipe that is plugged at one end. Just as the resonance from an organ pipe depends on the length of the tube, the resonance in the moulin depends on the level of water collected at the base.NateImage Credit:Alex Buisse - http://bit.ly/2cow1OxIan Joughin - http://bit.ly/2ct2MM4Source: http://bit.ly/2cc2ngoOriginal Paper: http://bit.ly/2cWvHtd -- source link

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