Analysis and Modelling of Tree Succession on the 1991 Randa Rockslide (Switzerland)
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FACULTEIT WETENSCHAPPEN Vakgroep Geologie en Bodemkunde Analysis and modelling of tree succession on the 1991 Randa rockslide (Switzerland). Liesbet Van der Burght Academiejaar 2009–2010 Scriptie voorgelegd tot het behalen van de graad Van Master in de Geologie Promotor: Prof. Dr. F. Mostaert Co-promotor: Dr. M. Stoffel Leescommissie: Prof. Dr. P. Jacobs, Prof. Dr. J. Nyssen, Prof. Dr. P. Goetghebeur . Judging from the surprised looks on the faces of some people and the moderate enthusiasm of others, this thesis subject might not have been the most logical choice for a Belgian geology student, with only minor background knowledge on Alpine geology and dendrochronology. Personally however, I have always seen studying abroad as a major advantage in many aspects of life, an experience worth to be stimulated. Moreover, I have always been fascinated by the Alpine geology, and even when a couple of months and a lot of interest are most certainly not enough to understand all aspects of it, nor to grasp its full complexity, I found my passion even more awakened and stimulated. As so, this thesis subject has always seemed a very sensible choice to me, and despite the numerous administrational, meteorological, lingual, and logistic problems, I would most happily make the same choice tomorrow. I would like to thank my parents and grandmother, I’m sure it wasn’t always easy to them to see their only child roam off again, nevertheless they have always been uttermost supportive. A warm and grateful word also to Charlotte and her family in Gasenried, and to Georgette in Stettlen, for indulging and taking care of me, as if I were their own daughter. Michelle and Markus, thanks for giving me the opportunity to work on this subject and for being an incredible support and motivation, again and again and again! Christof, thanks for the time and effort you put into explaining me statistical methods, all of your suggestions were very much of use. Prof. Mostaert, thanks for your support, critical point of view and honest fascination. A grateful word also goes to Igor, Estelle, Dirk, and Valentin. And finally, Lina, Oliver, David, Glenn, and Ben, thanks a lot for your support and helping out whenever possible. Table of contents Foreword 1 Introduction ...................................................................................................... 5 1.1 Natural hazards in the Alps ....................................................................................... 5 1.2 Aim of this study ......................................................................................................... 5 1.3 Cooperation with Swiss researchers ........................................................................ 7 2 Study site description ........................................................................................................ 9 2.1 Regional Geography ................................................................................................... 9 2.2 Geomorphology .......................................................................................................... 10 2.3 Climate ......................................................................................................................... 11 2.4 Soil ............................................................................................................................... 13 2.5 Vegetation ................................................................................................................... 13 2.6 Geology........................................................................................................................ 13 2.6.1 Alpine geology ........................................................................................................... 15 2.6.1.1 Penninic palaeogeography ..................................................................................... 15 2.6.1.2 Penninic basement ................................................................................................. 17 2.6.1.3 Penninic sedimentary rocks .................................................................................... 17 2.6.2 Folding ....................................................................................................................... 19 2.6.3 Local geology ............................................................................................................. 22 2.6.4 Rockslide event ......................................................................................................... 23 2.6.4.1 The situation before 1979 ....................................................................................... 23 2.6.4.2 The rockslide event of 18.4.1991 and its foreplay .................................................. 23 2.6.4.3 19.4.1991 – 22.4.1991 ............................................................................................ 24 2.6.4.4 23.4.1991 – The rockslide event from 9.5.1991 ..................................................... 24 2.6.4.5 Development since 1991 ........................................................................................ 26 2.6.4.6 Erosion, relaxation processes ................................................................................ 26 2.6.4.7 Hydrogeology .......................................................................................................... 27 2.6.4.8 Seismicity ................................................................................................................ 28 2.6.4.9 Cubature, dust, settlement, interstices ................................................................... 28 2.6.4.10 Kinematics ............................................................................................................ 29 2.6.4.11 Possible causes .................................................................................................... 30 2.6.5 The rockslide area today ........................................................................................... 30 3 Literature study ............................................................................................... 32 3.1 Dendrochronology ...................................................................................................... 32 3.1.1 Introduction ................................................................................................................ 32 3.1.2 Dendrochronological principles ................................................................................. 33 3.1.3 Primary succession .................................................................................................... 35 3.1.4 Species found in Randa ............................................................................................ 36 3.1.4.1 Larix decidua .......................................................................................................... 36 1 Inhalt 3.1.4.2 Betula pendula ........................................................................................................ 38 4.1.4.3 Picea abies ............................................................................................................. 39 4.1.4.4 Acer pseudoplatanus .............................................................................................. 40 4.1.4.5 Alnus viridis ............................................................................................................. 40 4.1.4.6 Salix purpurea ......................................................................................................... 42 4.1.4.7 Salix caprea ............................................................................................................ 42 4.1.4.8 Sambucus racemosa .............................................................................................. 43 4.1.4.9 Populus tremula ...................................................................................................... 44 4.1.4.10 Other plants .......................................................................................................... 45 3.2 Previous work ............................................................................................................. 47 3.2.1 Natural succession on the Randa rockslide deposit (Gasser, 1995) ........................ 47 3.2.1.1 Procedure ............................................................................................................... 47 3.2.1.2 Relevant results ...................................................................................................... 48 4 Methods and Material ...................................................................................... 49 4.1 Fieldwork and sample preparation ........................................................................... 49 4.1.1 Standard dendrochronological methods .................................................................... 49 4.1.2 Field and sampling procedures ................................................................................. 51 4.1.3 Topographical survey ................................................................................................ 55 4.2 Data processing .......................................................................................................... 56 4.2.1 Geographical data processing with ArcGIS ............................................................... 56 4.2.2 Statistical data processing ......................................................................................... 57 4.2.2.1