Ninth International Conference on Permafrost ... - IARC Research

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Contribution of Terrestrial Laser Scanning for Studying the Creep ofMountain PermafrostFrançois RiffGeographic Institute of Lausanne UniversityChristophe LambielGeographic Institute of Lausanne UniversityThierry OppikoferInstitute of Geomatics and Risk Analysis, University of LausanneIntroductionUp to now, differential GPS and triangulation usingtheodolite were the most used terrestrial techniques formeasuring the creep of permanently frozen sediment bodies.Recently, the studies of Bauer et al. (2003) and Bodin (2007)demonstrated that terrestrial laser scanning (TLS) offersgood opportunities to provide precise measurements onmountain permafrost creep.This abstract presents positive results of TLS measurementscarried out on two permafrost-related creeping landformslocated in the Swiss Alps: the tiny Lac des Vaux rockglacier, located in a wider complex slope, and on the Coldes Gentianes push moraine (cf. Lambiel 2006). First, thetwo principal stages of the methodology (data acquisitionand treatment) will be presented.Data AcquisitionTLS is based on the contactless and reflectorless acquisitionof a XYZ point cloud of the topography using a time-of-flightprinciple. The TLS data acquisition stage is relatively quickand easy. However, two recurrent problems were identifiedusing the Optech ILRIS 3D in alpine periglacial landforms:• The localization of ideal viewpoints is crucial in orderto avoid occlusion and too far distances to the object. At adistance shorter than 100 m and with a point cloud resolutionbetter than 5 cm, we were able to identify every object in aunique way. This allows the observation of the movement ofthe matrix and the bigger blocks. Beyond a distance of about300 m and a resolution higher than 10 cm, this advantage islost, but measurement of mass movement is still possible.• No points can be obtained from snow-coveredsurfaces, since snow does not reflect the TLS signal.mass loss or depletion.In addition, the following operations can be carried out:• Precise volume calculation by creation of parallelcross-sections or use of 3D point clouds.• Creation of movement vectors by point pairidentification. However, using real time kinematics GPS toobtain this kind of information is more practical, faster andmore precise than the TLS, but provides only information onselected monitoring points.• Easy integration of the results in a GIS, since allinformation is georeferenced.ResultsLac des Vaux rock glacierIn the upper part of the rock glacier, a distinct blue area (1)indicates a loss of elevation of about 35 cm (Fig. 1). Directlybelow (2), the light green to yellow colors correspond topositive values, which indicate a general slight increase(5–15 cm) in elevation. Several big blocks even show apositive displacement of about 50 cm. In the lower part(3), the increase in elevation is a bit lower. The GPS dataindicates slightly larger displacements.According to geomorphologic evidence, the successiveloss (1) and gain (2-3) in elevation may be the result ofData TreatmentThe longest stage in the TLS methodology is data treatmentwith the Polyworks software. The raw TLS point cloudsneed to be cleaned from unwanted objects, unified to a singlepoint cloud and finally georeferenced using GPS points.Sequential TLS point clouds, or TLS time-series, enablethe calculation of relative differences, which are related toslope movements (e.g., Oppikofer et al. in review). Positivedifferences (yellow to red colors in Figs. 1, 2) are related toadvances or elevation increases of the creep, while negativedifferences (blue to pink colors in Figs. 1, 2) are signs ofFigure 1. Topographic evolution of the Lac des Vaux rock glacierbetween 19 July and 16 October 2007, represented with a 50 cmscale. Top left are represented the D-GPS movements extrapolatedbetween the same dates.255
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFigure 2. Topographic evolution of the northeast and central parts of the “Col des Gentianes” push moraine between 19 July and 16 October2007 represented with a 100 cm scale.a landslide-like development process, as evidenced indestabilized rock glaciers (see Roer et al. 2008). The upperarea (1) corresponds to a scar, whereas the lower area (2-3)is the place of a rapid accumulation of materials, with higherdestabilization of metric blocks.Col des Gentianes push moraineAccording to geoelectrical measurements and directobservations, the ice content in the moraine is locallyimportant (Lambiel 2006). Generally speaking, all themoraine displays more or less marked movements (Fig. 2).For instance, we can recognize accumulation of materialsbelow a scar (U), a scar of debris flow (F) above an areawithout any data because of the presence of snow at the timeof the first survey (S) and settlement of the moraine due todead ice melting (I1, I2). C1 and C2 areas are more stable,even if a slight movement (creep) can be observed. Thedebris-covered glacier at the foot of the moraine is clearlyvisible (G); (E) is the result of excavation work; and finally,the data confirms the building stability (B).Discussion and ConclusionThe comparison TLS point clouds evidenced differentprocesses in both investigated landforms, like, for example,permafrost creep, sliding, and settlement due to meltingof massive ice. The measurements revealed also that themovement of metric blocks is more important than thedisplacement of smaller elements, like small rocks and thematrix. Thus, we can conclude that the creeping velocitiesmeasured with D-GPS may be slightly overestimated, since,with this technique, large boulders are normally chosen.Regarding the accuracy of the TLS method, the mean erroron sequential TLS point cloud comparisons can be estimatedto about 3 cm. This is in the same order of magnitude thanwith D-GPS. According to the high resolution and precisionof the data, the TLS appears to be an efficient technique forstudying the creep of mountain permafrost.ReferencesBauer, A., Paar, G. & Kaufmann, V. 2003. Terrestrial laserscanning for rock glacier monitoring. Proceedings ofthe Eighth <strong>International</strong> <strong>Conference</strong> on Permafrost,Zürich, Switzerland, June 2003, 1: 55-60.Bodin, X. 2008. Géodynamique du pergélisol de montagne:fonctionnement, distribution et évolution récente.L’exemple du massif du Combeynot (Hautes Alpes).Thesis. University of Paris-Diderot (Paris 7), 274 pp.Lambiel, C. 2006. Le pergélisol dans les terrains sédimentairesà forte déclivité: distribution, régime thermique etinstabilités. Thèse, Université de Lausanne, Institutde Géographie, coll. “Travaux et Recherches” No.33: 260 pp.Oppikofer, T., Jaboyedoff, M. & Keusen, H.-R. In review.Terrestrial laser scanner monitoring of the 2006 Eigerrockslide in the Swiss Alps. Nature Geosciences.Roer, I., Avian, M., Delaloye, R., Lambiel, C., Haeberli,W., Kääb, A. & Kaufmann, V. 2008. Observationsand considerations on collapsing active rockglaciersin the Alps. Proceedings of the <strong>Ninth</strong> <strong>International</strong><strong>Conference</strong> on Permafrost, Fairbanks, Alaska, 29June–3 July 2008.256
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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