Delisle, G.

Zeibig, M.

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Polarforschung 62 (2/3): 147-150,1992 (erschienen 1994)Drilling into Antarctic Ice - The New BGR Ice DrillBy Michael Zeibig and Georg Delisle*Summary: We describe a new ice drill consisting of an electrially heated pro-be that melts its way through the ice. The produced meltwater is recoveredperiodically with a bailer. The instrument is mounted in a cIosed container on asledge and is operable irrespective of weather conditions. 48 boreholes inAntarctic ice were drilled so far in two Antarctic seasons by this system. Thedeepest hole reached 102 m.Zusammenfassung: Ein neues Eisbohrgerät. bestehend aus einer elektrischbeheizten, sich durch das Eis schmelzenden Sonde, wird beschrieben. Das wäh-rend des Bohrvorganges entstehende Schmelzwasser wird periodisch abge-schöpft. Das Gerät ist fest in einem überdachten Schlitten montiert und kannwetterunabhängig betrieben werden. Mit dem Gerät wurden in zwei antarkti-schen Einsätzen 48 Bohrungen niedergebracht. Die bislang tiefste Bohrung er-reichte 102 m.INTRODUCTIONThe employment of commercially available conventional dril-ling techniques in Antarctica is very expensive and difficult tohandle from the logistic point of view. One available "cheap"method, the .Jiot water" drill, is not very well suited for theweather and, in particular, the wind conditions on the Antarc-tic Polar Plateau. To overcome these limitations, we have de-veloped a new ice drill:• that can be operated without putting unreasonably large strainon the logistic capabilities of Antarctic expeditions, and• that can be operated irrespective of weather conditions, whichminimizes the environmental impact on the ice.The new instrument was built as part of a BGR-research pro-ject supported by the Deutsche Forschungsgemeinschaft (DFG).The aim of the project was to measure terrestrial heat flow inboreholes sunk into almost stagnant Antarctic ice fields andspecifically along a profile across the Transantarctic Mountains.The results of this project will be discussed elsewhere. A sur-vey of potential drill sites in the season 1990/91 (GANOVEX-VI expedition of BGR) had demonstrated periodic fierce wea-ther conditions with high catabatic winds in the area. Given theexperience of the 1990/91 survey, the ice drill had to meet thefollowing specifications:• housed in a closed container on a sledge,• sufficiently compact for transport by helicopter 01' to be pul-led overland by snowmobiles,• operable independent of weather conditions.* Michael Zeibig and Georg DelisIe, Bundesanstalt für Geowissenschaften und Rohstoffe(BGR), 5 I 01 53, D-3063I Hannover, Postfach.Manuscript received 18 August, 1993; accepted 11 April 1994.THEDESIGNThe principle concept realized by our new drill is to let an elec-trially heated probe melt its way through the ice and recover theproduced meltwater periodically with a bailer. This techniqueminimizes the risk of environmental hazards. It does not requi-re the use of oil and/or antifreeze fluids, The only acting pol-lutant is the exhaust of the generator producing the electricalpower for the probe.Similar concepts have been realized in the past. IGNATOV (1965)describes in detail a melting device that penetrated Antarctic icenear the Vostok Station in Antarctica down to a depth of 52 m.PHILBERTH (1965) and AAMOT (1967, 1968a, b) discuss variousmelting devices with the emphasis on technical details to insu-re its vertical penetration through the ice. Of particular interestis the discussion by PHILBERTH (1984) of a non-retrievable pro-be. The lower end of its power supply cable was housed in theprobe and paid out according to the drilling progress. One pro-be of this type reached a depth of 1005 m in the Greenland icesheet.Fig. 1 shows the principal components of the new BGR-instru-ment. A tripod, an electrically driven winch and an electronicunit for operation of the winch are mounted on a 2 m • 3 m lar-ge platform that is kept by two runners 30 cm above the snowsurface. A 2 m high aluminum frame covered by canvass rai-ses from the edges of the platform. The floor under the tripodhas an opening through which the probe can be lowered into theice.The design of the probe is shown in Fig. 2. The thermal pene-trator contains a heating element with a power output of 2.5 kW.The penetrator is connected to a 1.3 m long pipe, whose princi-pal function is to collect the melted water. Four one-way val-ves are positioned at the upper end of the penetrator, throughwhich the meltwater enters the pipe. The interior of the pipe isequipped with a heater (160 W) to prevent premature freezingof the meltwater within the pipe and of the outer surface of thepipe to the ice wall. A second penetrator (400 W) rests on thetop section of the probe. Its function is to enable the probe tomelt its way out of the borehole, if for some reason the probebecomes jammed by newly formed ice along the borehole walls.The total weight of the probe is 12 kg.We have not added any device to insure a vertical attitude ofthedrill in ice as they were used in previous drill designs (i.e. AA-MODT 1967). The observation of our drill during the start of each147."l2;~-GJ-10Fig. 1: The sIedge with its principal components: I generator; 2 =electronic contro1unit; 3 =engine; 4, 5 =transmission and winch; 6 =winch speed controlunit; 7 =power supply regulator; 8 =tripod; 9 =.Keflar't-cable; 10 =thermal probe; I I =canvass of slcdge.Abb.l: Die Einzelkomponenten des Bohrschlittens: I =Generator, 2 =Elektronische Steuereinheit, 3 =Motor, 4 und 5 =Übersetzung und Winde, 6 =Winden-steuerung, 7 =Leistungsregler für Bohrsonde, 8 =Dreibock, 9 =Ketlar-Kabel, 10 =Sonde, 11 =Dachbespannung.POWER CABLETHERMAL PENETRATORIe--- HEATING ELEMENTSdrilling operation showed us that any deviation from the verti-cal is corrected immediately by preferential melting on the sideon which the device starts to lean. This process is greatly assi-sted by keeping a tight power cable between the winch and themelting device.The electric power cable connecting the probe with the powersupply is designed to resist prolonged wear and tear along theice walls during operation. It is made up of four 2.5 mm- leadssurrounded by a mantle made of .Kevlar". The diameter of thecable is 9.8 mm, the allowed maximum pull load is 200 kg.PIPE <COPPERl The need to bail out.the meltwater requires to lower and raisethe probe frequently. The winch is designed to permit a maxi-mum speed of 0.6 mJs of the probe through the borehole.FIELD OPERATIONSTHERMAL PENETRATOR1,--- HEATING ELEMENTFig. 2: Principal design of the thermal probe.Abb, 2: Prinzipskizze der Sondenkonstruktion.The instrument was used during the field season 92/93 to drillsuccessfully three boreholes through ice in Victoria Land, Ant-arctica. A first test of the probe on blue ice near Ambalada Peakfailed however, due to an unforeseen reason. The length of thepipe of the probe during this attempt was 3 m. The drilling pro-gress and the recoverable amount of meltwater were closelymonitored. We recovered about 5.7 liters of meltwater per me-ter borehole to a depth of -4 m. A sharp reduction down to lessthan 1 liter per m ocurred below that depth. The probe froze tothe borehole wall at -10m and was lost.148We interprete these observations as follows: The blue ice beingunder tension had developed numerous open fissures, which arenot obvious at the ice surface, Meltwater being produced duringthe summer season on the blue ice surface enters any developingfissure and reseals the ice apparently down to a depth of about-4 m. Fissures below this level are not reached by seasonalmeltwater and remain open. The permeability of the ice belowthis level is apparently sufficient to drain about 30 liter of wa-tel' within half a day from a borehole with a diameter of 8 cm.To prevent a further probe loss we shortened the pipe to 1.3 m(which trippled the effectivity of the internal heating element).This measure proved effective.The following boreholes were successfully completed:problem was most severe at the last drilling point, where the firn!ice was warrnest (-24° C).The recoverable amount of meltwater was about 5.7 liters permeter, which amounts to an average diameter of 8 cm of theborehole.The drilling speed in firn gradually decreased from an initialSmJh to about 2.8 m per hour. The typical drilling speed in denseice averaged around 2.2 mJh . The actual penetration speed washowever closer to 0.9 m per h due to the time needed for thebailing trips.OUTLOOKdrill pointRicker HillsMt BillingMt Howardboreholedepth- 51 m-102m- 83 mcoordinates75° 45.5' S75° 40.8' S75° 39.5' S158° 5004' E160° 48.2' E161012.8' EThis technique offers advantages and disadvantages. Negativeaspects are the relative low drilling speed (due to the frequentbailing trips) and the lack of recoverable drill cores at thisstage. Advantageous are mainly two factors:• The drilling process can be interrupted at any time.• The borehole stays open for a long time.The equipment housed on sledges was transported from Gond-wana Station (Terra Nova Bay, North Victoria Land) by heli-copter into the field and pulled by skidoo overland between alldrill points (Fig. 3) . The average speed over snow terrain was11 km per hour.RESULTSAll completed boreholes show a rather smooth borehole wall.The holes are almost vertical as judged from the almost unim-peded travel of the probe down to the bottom. Each boreholedeveloped one 01' several difficult spots through which the pro-be had to be sunk with special care. The greatest problemoccurred inadvertently at the firn-ice interface. The bottom ofthe firn had a tendency to move inward and to reduce the bore-hole diameter. This section had to be redrilled occasionally. ThisFig. 3: The drilling unit being pulled by snowmobile over Antarctic terrain.Abb. 3: Das von einem Motorschlitten gezogene Bohrgerät auf seinem Weg überantarktisches Eisgelände.The boreholes drilled so far have been measured in by GPS. Weplan to revisit some or all of them in the future. All boreholesare marked by poles. In the future we will attempt to realize inaddition an alternative concept that allows the recovery ofcores. The penetrator will be replaced by a heated ring that meltsits way through the ice, while the inner ice core enters a catcherlocated in the pipe. The lower end of the ice core will be sepa-rated from the borehole bottom by keeping the ring in a statio-nary location.Apart from the availability of an ice core we hope to reduce bythis way the number of required bailing trips. We also plan tobuild aseparate bailer to be lowered instead of the pipe abovethe probe to remove remaining meltwater out of the boreholebetween drilling trips.AddendumThe original system was employed for a second time on Antarc-tic ice in the season 1993/94 within the Italian Antarctic pro-gramme. 45 shot holes of depths varying between 18 m to 40 mwere drilled at foul' shot points in support of the seismic refrac-tion profile ACRUP-1 across the Transantarctic Mountains southofthe Drygalski Ice Tongue in Victoria Land. 20 boreholes weredrilled on the Polar Plateau at an elevation of 2000 m.ACKNOWLEDGMENTSWe gratefully acknowledge the financial support of this projectby the Deutsche Forschungsgemeinschaft (DFG) and by BGR.Likewise we thank the logistics officer J. Kothe (BGR) at Gond-wana Station for his untiring support of the drilling crew in the"Far South" in the season 1992/93 and the Italian Antarctic Pro-gramme for its generous logistic support in 1993/94.149ReferencesAamot, H. W C. (1967): Pendulum steering for thermal probes in glaciers.- J.Glaciol. 6: 935-938.Aamot, H. Wc. (1968a): Instrumented probes for deep glacial investigations.-J. Glaciol. 7: 321-328.Aamot, H. Wc. (I968b): A buoyancy-stabilized hot-point drill for glacier stu-dies.- J. Glaciol. 7: 493-498.Ignatov, V.S. (1965): Experiment in the thermal drilling of holes in the ice atVostok Station.- In: Information Bulletin Soviet Antarctic Expedition, Vol.III, 50-52 (Translation by Elsevier Publishing Company, Amsterdam, Lon-don, New York.).Philberth, K. (1965): Über zwei Elektro-Schmelzsonden mit Vertikalstabilisie-rung.- Polarforschung 34: 278-280.Philberth, K. (1984): Die thermische Tiefbohrung in Station Jarl-Joset und ihretheoretische Auswertung.- Polarforschung 54: 43-49.150

Drilling into Antarctic Ice - The New BGR Ice Drill

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