How are the water signals on a polythermal Glacier? MRS pilot study on Hansbreen Glacier, Hornsund, SW Spitzberguen (Norway)

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Information about How are the water signals on a polythermal Glacier? MRS pilot study on...

Published on November 14, 2016

Author: Igeotest

Source: slideshare.net

1. • In 2007 for the IPY activities was possible to visit different glaciers: • 1-Elisebreen on Kaffioyra (Forlandsundet) • 2-Ebbabreen on Petunia-bukta (Billefjorden), • 3-Scottbreen and Renarbreen on Calypsobyen (Bellsund) • 4- Hansbreen (Hornsund) • Piotr Glowacki offer me the possibility to came to Spizberguen if the scientific project could be related to a • Polish project. • Once accepted on spring 2009 the best site to do a large surface NMR survey was in Hansbreen. This experience was done between half august and half september 2009. HOW ARE THE WATER SIGNALS ON A POLYTHERMAL GLACIER?, MRS PILOT STUDY ON HANSBREEN GLACIER, HORNSUND, SW SPITZBERG (NORWAY) Valenti Turu Igeotest Ltd (Marcel Chevalier Foundation Project) Av. Príncep Benlloch 66-72, Edifici Interceus Dptx 308, AD 500, Principality of Andorra, (www.igeotest.ad)

2. Who we are? http://www.igeotest.ad

3. From were com from? • Andorra is independent until 1288 • 80.000 persons are living (30% Andorrans) and more than the 50% lives in 5 Km2 • Surface: 465 Km2 and 2000m mean altitude • « Modus vivendi »: Skiing & shopping • Is considered as a fiscal paradise

4. What is our main work?, Where we work? • The intense construction in the country let us work on few disciplines that are related: • Geology and geotechnics • Geophysics and hydrogeology • Natural hazards and landscape impacts • Our main place of work is Andorra and the Pyreenees • But also in West Europe (Spain, France and Germany basically)

5. What we study? • Usualy we study paleoglalcial environments and paraglacial process that are related with geotechnical problems, the safety of infrastructures and population related, water supply and groundwater vulnerability • One of our goals is to publish the scientific results almost once in a year. • We don’t look for impact ratios but the direct contact with scientist that are regionally involved. Is for that we usually present our results in open scientific meetings.

6. Why Spitzberguen? The glacial sediments that we study shows that subglalcial groundwater had an important imprint. So for extension to ours investigations, the opportunity to do some experiments on an actual glacier in Hornsund arises as an interestening project, now completed. But first of all let me expose what we found in the Pyrenees in cooperation with other scientist from Spanish Universities (Barcelona, Zaragoza, Valladolid), French Universities (Grenoble, Toulouse) and Scottish (Edinburgh University).

7. Evidences from hydro & geotechnical data Synthetic stratigraphic profile from the Andorra la Vella basin showing the geophysical and hydrogeotechnical data. Sedimentary units 1a/1b and 2a/2b are generally massive. At building outcrops tractive structures (imbrication) can be observed. Sedimentary units 3a/3b and 4a/4b are interpreted as subglacial till. Rythmites and turbidites are also present. A subglacial till facies occurs in the most consolidated upper layers (1a & 2a layers).

8. Evidences from geophysic data

9. Subglacial groundwater imprints

10. Load-Unload cycles on subglacial sediments a) Using a Modified Cam-Clay diagram of increasing or decreasing load-unload (L-UL) cycles. In a increasing strain/stress evolution, load and unload cycles with a constant pervasive shear stress can produce a critical state of consolidation. b) Using a MCC diagram in a decreasing stress/strain evolution the soil can show more than one preconsolidations. c) Behaviour evolution from the pressuremeters diagrams in depth. Stiffening diminishes the slope of the stress/strain diagram and kinematic hardening produce the migration of the locus yield

11. Is there subglacial water on Hansbreen? Report results:

12. Hansbreen polythermal glacier Hansbreen is located on the SW part of Spitsberguen, and it is a a typical subartic glacier. Such glaciers had a polythermal structure, that is a cold-ice layer overlaying a temperatet-ice layer one.    Latitude: 77ºN Longitude: 18ºE Earth magnetic field: 54389 - 5488 nT Larmor frequency: 2312 - 2317 Hz Noise conditions 176 nv for a 120x120 loop  Migala et al. 2006 Polish polar station Polythermal layers

13. Surveyed area

14. Locations

15. Hansbreen similarities with the andorran paleoglacier TT 1992 α Isbjornhamna 33514 33515 33516 33517 8546- 8547- 8548- 8549- 8550- 8551- 8552- Crystal Cave 546 m 541 m 568 m 733 m 626 m 390 m 415 m 264 m Tuva Fugleberget Vesletuva Fannytoppen 200 m 176 m 118 m 95 m 53 m 175 m 33511 33512 33513 33518 2009 1 km Ice-cored moraine Polish Polar Station

16. But first of all, what is a MRS survey?

17. Method

18. Tests

19. Tests

20. Execution

21. Obtained data

22. Interpretation

23. Interpretation

24. Applying the MRS method Latitude: 77ºN Longitude: 18ºE Earth magnetic field: 54389 - 5488 nT Larmor frequency: 2312 - 2317 Hz Noise conditions 176 nv for a 120x120 loop The best conditions are met here, a resistive body (glacier), ice is not a magnetic environments, high latitudes, non sea water below the ice (low resistivity), low electronic noise and large antennas can be done. MRS 19: (q15), noise = 14,7 nV

25. Knowing the thermal structure: The thermistors From Jania et al. (1994) we know that the boundary between the Internal Refraction Horizont (IRH) and the boundary between cold and tempered ice not always are coincident. The direct implication is that can be temperate ice with lower water content and perhaps below the background of the MRS device.

26. Knowing the water content. The GPR CMP

27. From such data is possible to locate the substratum and also to distinguish some structures on it. It is known that marine terrace sediments are present beneath the glacier, so a potential acuifer is there present Marine terrace Recent studies: Benn et al (2009) in Crystal Cave Grabiec (2009) with GPR

28. Karstic type conduits were recognised at Crystal cave. Benn et al. (2009) followed vertical shafts through more than 70 m to subglacial conduit. Deep hydrofracturing occurred at this site due to a combination of extensional ice flow and abundant surface metwater at a glacier confluence. The surface-to-bed drainage can occur wherever high meltwater supply coincides with ice large tensile stresses. Here at 60m depth the boundary between cold ice and tempered ice was found. In Hansbreen it has been observed that the ablation depends on daily mean and maximum air temperatures, but also in wind speed conditions (Migala et al., 2006). So the water flow through crevasses and moulines can change quickly from one day to other on the first decameters on ice. So the MRS signals in the cold ice can vary quickly and the method can be used to know how much and how is the recovery.

29. On the middle of the glacier we obtain from small loop a water content of the subsurface reaching values above 2% of water content (Eo= 24 nV), and a general decreasing pattern in water content can be observed with depth until 36 m. Decays of the signals are above 200 ms. Bigger loops reaching depths below 90 m, low water signals still appears (<2%, Eo<20 nV). Finally the the biggest done loop (120x120 m) high amplitude of water signals are obtained (Eo > 30 nV) and relative large decays are also observed (150 - 300 ms) MRS 8: 30x30 two turns Crevassed Cold Ice Eo = 12 nV; T2*= 570 ms; Freq = 2318,9 Hz; St.N = 10,6 nV Eo = 19 nV; T1*= 1000 ms; Freq = 2318,6 Hz; Noise =117nV MRS 11: 120x120 m (Q16/Q20) Temperated ice Eo = 18 nV; T2*= 125 ms; Freq = 2318,7 Hz; St.N = 18,7 nV Eo = 13 nV; T1*= 150 ms; Freq = 2312,1 Hz; Noise = 427 nV Eo = 31 nV; T2*= 132 ms; Freq = 2312,3 Hz; St.N = 19,4 nV Eo = 30 nV; T1*= 204 ms; Freq = 2311,9 Hz; Noise = 414 nV MRS 11: 120x120 (Q18/Q20) Aquifer beneath the glacier Water signals

30. 1D synthetic model and conclusions Three types of water signals are possible to distinguish, from top to bottom are: 1) Relatively high amplitudes and very high time decays, when the weather conditions permits surface melting (full karstic aquifer conditions). Is the Cold-ice: Superficial signal with high water contents, until 8% on water content. Here a general decreasing water content shape is observed from tthe surface to the bottom and medium decays can also be obtained (more than 100 ms). 2) Low amplitudes and very low time decays or water content below the threshold of the device. Some times is possible to detect relatively high amplitudes but low decays, possibly by the presence of stagned water bodys (aquiclude). Temperate ice: Deeper signal with low to very low or no water contents, less than 2% on water content. In general the water content increase with depth but here some equivalences arise and should we compare the results with normal GPR data. Depth and low decays are always obtained (less than 150 ms). 3) Moderate to relatively high amplitudes and moderate time decays to relatively large time decays. Bottom aquifer: A high water than 2%) are present at the deepest depths had and also large decays can be observed (more than 200 ms).

31. Subglacial groundwater and permafrost In situation 1 the drainage of the system permit that the subglacial water flows at the base of the glacier and in the aquifer. Here the pressure of the subglacial water is below from those of the glacier pressure melting boundary. That is the case on the upper part of the MRS surveyed zone in Hansbreen. In situation 2 a bad drainage of the system makes that the water level on ice arise. Close to the margins of the glacier the pressure of the subglacial water is above the pressure melting boundary from the ice and permafrost can be formed on the aquifer. That is the case on the lower part of the MRS surveyed zone in Hansbreen and close to the ice cliff.

32. Implications for the Pyrenees In fact the different subglacial consolidated layers represent four main cycles of bad subglacial drainage or high meltwater imput. The chronology of those sediments is < 27 Ka BP, after the main glacial phase in the Pyrenees that is well known is before de LGM, so those cycles are related with the deglaciation in the Pyrenees and each level represents a glacier advances, each one less important than the previous.

33. Interpreted data and link with GPR

34. Thank you

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