Spatio-Temporal Variations of Rockfall Activity Into Forests: Results from Tree-Ring and Tree Analysis

AUS DEM DEPARTEMENT FÜR GEOWISSENSCHAFTEN - GEOGRAPHIE UNIVERSITÄT FREIBURG (SCHWEIZ) Spatio-temporal variations of rockfall activity into forests - results from tree-ring and tree analysis INAUGURAL - DISSERTATION zur Erlangung der Würde eines Doctor rerum naturalium der Mathematisch - Naturwissenschaftlichen Fakultät der Universität Freiburg in der Schweiz Markus STOFFEL aus Visperterminen (VS, Schweiz) Dissertation Nr. 1480 Multiprint, Fribourg, 2005 Die vorliegende Arbeit wurde an der Mathematisch - Naturwissenschaftlichen Fakultät der Universität Freiburg, Schweiz, im Juni 2005 aufgrund der Gutachten von Prof. Michel Monbaron, Prof. Hans Kienholz, Prof. Horst Strunk und Dr. Hugo Raetzo angenommen. Als Jurypräsident waltete Prof. Martin Beniston. The Faculty of Science of the University of Fribourg, Switzerland, accepted the present work as dissertation in June 2005 based on the experts’ reports of Prof. Michel Monbaron, Prof. Hans Kienholz, Prof. Horst Strunk and Dr. Hugo Raetzo. President of the Jury: Prof. Martin Beniston Fribourg, 27 June 2005 The PhD thesis’ director: The Dean: Prof. Michel Monbaron Prof. Marco Celio Zitierung (Citation): Stoffel M., 2005: Spatio-temporal variations of rockfall activity into forests – results from tree-ring and tree analysis. PhD thesis No. 1480, University of Fribourg. GeoFocus 12, 188 pp. GeoFocus is the publication series of the Dept. of Geosciences, University of Fribourg, Switzerland, and can be ordered at Department of Geosciences - Geology University of Fribourg 1700 Fribourg Table of contents - 1 TABLE OF CONTENTS TABLE OF CONTENTS 1 2.2 STUDIES DEALING WITH TREE RINGS AND PAST ZUSAMMENFASSUNG 5 ROCKFALL ACTIVITY - A STATE OF THE ART 31 ABSTRACT 7 ABBREVIATIONS 9 3 AIMS AND STRUCTURE OF THIS THESIS ACKNOWLEDGEMENTS 11 4 STUDY SITES CHAPTER A: OVERALL INTRODUCTION 4.1 INTRODUCTORY COMMENTS AND LOCALIZATION OF STUDY SITES 35 1 ROCKFALL 4.2 TÄSCHGUFER (TÄSCH, VS) 35 4.2.1 Geology 35 1.1 UNDERSTANDING THE PROCESS 17 4.2.2 Topography 37 1.1.1 What is rockfall - some defi nitions 17 4.2.3 Temperature, precipitation and perma- 1.1.2 Triggers of rockfall activity 18 frost 37 1.1.3 Departure, transit and deposition zone of 4.2.4 Forest cover 38 rockfall 19 4.2.5 Rockslides, large rockfalls and rockfall 1.1.4 Rocks and boulders ‘traveling down- processes 38 slope’ 20 4.2.6 Other processes 42 1.2 ROCKFALL INTO FORESTS 21 4.3 ALTDORFER BANNWALD (ALTDORF, UR) 42 1.2.1 Infl uence of forest stands on rockfall propagation 21 1.2.2 Reactions of trees to rockfall 22 CHAPTER B: ASSESSING PAST ROCKFALL 1.2.3 Protection forests - dreams and reality 23 ACTIVITY WITH TREE RINGS 1.3 FREQUENCY AND VOLUMES OF PAST ROCKFALL ACTIVITY 24 1 THE SEASONAL TIMING OF ROCKFALL 1.4 MODELING ROCKFALL IN LABORATORY TESTS, ACTIVITY ON SLOPES AND IN FORESTS 25 1.4.1 Empirical rockfall models 25 ABSTRACT 47 1.4.2 Process-based rockfall models 25 ZUSAMMENFASSUNG 48 1.4.3 GIS-based rockfall models 26 RÉSUMÉ 48 1.4.4 Combined modeling approaches and the 1.1 INTRODUCTION 49 integration of trees 26 1.2 STUDY SITES 49 1.5 HAZARD ANALYSIS AND RISK ASSESSMENT IN 1.3 MATERIAL AND METHODS 51 ROCKFALL RESEARCH 27 1.3.1 Dendrochronological analysis of rockfall activity 51 2 DENDROGEOMORPHOLOGY 1.3.2 Seasonal timing of rockfall 52 1.4 RESULTS 53 2.1 A GENERAL INTRODUCTION TO TREE-RING 1.4.1 Rockfall activity and construction works 54 ANALYSIS IN THE FIELD OF GEOMORPHOLOGY 29 1.4.2 Natural rockfall activity 55 2 - Table of contents 1.5 DISCUSSION 57 1.3.1 Height distribution of scars on stems 92 1.6 CONCLUSION 58 1.3.2 Radial distribution of scars on stems 93 ACKNOWLEDGEMENTS 58 1.3.3 Visible injuries vs. overgrown scars 94 1.3.4 Scars at ‘test height’ vs. injuries to the 2 SPATIO-TEMPORAL FLUCTUATIONS IN entire tree 95 ROCKFALL ACTIVITY (1600-2002) 1.3.5 Growth disturbances at ‘test height’ vs. injuries to the entire tree 96 ABSTRACT 59 1.4 OVERALL DISCUSSION AND CONCLUSIONS 96 2.1 INTRODUCTION 60 ACKNOWLEDGEMENTS 99 2.2 STUDY AREA 60 2.3 MATERIAL AND METHODS 63 CHAPTER E: OVERALL CONCLUSIONS 2.3.1 Sampling strategy 63 2.3.2 Tree-ring analysis and rockfall 63 2.3.3 Spatial visualization of single tree data 65 1.1 SUMMARY OF MAIN RESULTS AND OVERALL 2.4 RESULTS 66 CONCLUSIONS 103 2.4.1 Age structure of the forest stand 66 1.2 OUTLOOK AND FURTHER RESEARCH NEEDS 104 2.4.2 Visible defects and growth reactions to 1.2.1 Traumatic rows of resin ducts: where do rockfall impacts 67 they occur? 104 2.4.3 Spatial distribution of growth disturban- 1.2.2 Vertical distribution of scars on trees: Did ces 68 we largely underestimate bounce heights 2.4.4 Rockfall magnitudes and frequencies 69 so far? 105 2.4.5 Decadal variations in rockfall activities 70 1.2.3 Does seismic activity in Valais trigger 2.5 DISCUSSION 74 rockfall(s) at Täschgufer? 105 2.6 CONCLUSION 76 1.2.4 Are there correlations between rockfall ACKNOWLEDGEMENTS 76 and climate at Täschgufer? 105 CHAPTER C: HEIGHT DISTRIBUTION AND CHAPTER F: APPENDICES THE PERSISTENCE OF ROCKFALL REVIEW OF STUDIES DEALING WITH TREE SCARS ON STEM SURFACES 1 A RINGS AND ROCKFALL ACTIVITY SUMMARY 79 ABSTRACT 109 ZUSAMMENFASSUNG 79 1.1 INTRODUCTION 109 RÉSUMÉ 80 1.2 DENDROGEOMORPHOLOGICAL APPLICATIONS AND 1.1 INTRODUCTION 80 METHODS 110 1.2 STUDY SITE 80 1.3 CASE STUDIES FOCUSING ON TREE RINGS AND 1.3 METHODS 81 PAST ROCKFALL ACTIVITY 112 1.4 RESULTS 81 1.3.1 The beginnings 112 1.4.1 Tree data and rockfall scars 81 1.3.2 Later works 113 1.4.2 Vertical distribution of scars on stems 82 1.3.3 Studies on the spatial distribution of 1.4.3 Visible and hidden scars 83 rockfall activity 115 1.5 DISCUSSION AND CONCLUSIONS 84 1.3.4 Studies on the seasonal timing of rockfall ACKNOWLEDGEMENTS 85 activity 116 1.4 DISCUSSION AND CONCLUSIONS 118 ACKNOWLEDGEMENTS 118 CHAPTER D: SOME LIMITATIONS OF TREE- 2 SPATIAL AND TEMPORAL ROCKFALL ACTIVITY RING ANALYSIS IN ROCKFALL IN A FOREST STAND IN THE WISS REALPS A RESEARCH S P - DENDROGEOMORPHOLOGICAL CASE STUDY SUMMARY 89 ABSTRACT 119 1.1 INTRODUCTION 90 2.1 INTRODUCTION 120 1.2 MATERIAL AND METHODS 91 2.2 MATERIAL AND METHODS 120 1.3 RESULTS 92 2.2.1 Study site and sampling 120 Table of contents - 3 2.2.2 Recording past rockfall events 121 3.5 CONCLUSIONS 142 2.2.3 Spatial and temporal data analysis 122 ACKNOWLEDGEMENTS 143 2.3 RESULTS 123 2.3.1 Characteristics of trees and their rockfall 4 TÄSCHGUFER - A ‘PICTURESQUE’ JOURNEY injuries 123 2.3.2 Spatial rockfall distribution 124 PLATE 1: BEDROCK 146 2.3.3 Temporal rockfall activity 124 PLATE 2: DISCONTINUIETES AND FISSURES 148 2.4 DISCUSSION 127 PLATE 3: LOOSE DEBRIS AND REMOBILIZATION 2.5 CONCLUSIONS 129 OF ROCKS AND BOULDERS 150 ACKNOWLEDGEMENT 130 PLATE 4: TALUS SLOPE AND FOREST FRINGE 152 PLATE 5: PROTECTION DAMS 154 3 QUANTIFYING THE PROTECTIVE EFFECT OF PLATE 6: INJURIES CAUSED TO TREES GROWING MOUNTAIN FORESTS USING A 3D SIMULATION AT TÄSCHGUFER 156 MODEL PLATE 7: CROSS-SECTIONS AND MICRO-CUTS 158 ABSTRACT 131 5 METHODS USED TO STUDY PAST ROCKFALL 3.1 INTRODUCTION 132 ACTIVITY 3.2 METHODS 133 3.2.1 The Rockyfor model 133 5.1 SAMPLING TREES AND SAMPLE PREPARATION 161 3.2.2 Study sites 133 5.2 COUNTING TREE RINGS, SKELETON PLOTS AND 3.2.3 Model input data 135 TREE-RING MEASUREMENT 163 3.2.4 Simulation set-up 135 5.3 BUILDING A REFERENCE CHRONOLOGY WITH 3.2.5 Assessment of model accuracy 135 UNDISTURBED TREES 164 3.2.6 Assessment of the protective effect of the 5.4 ASSESSING PAST EVENTS IN INCREMENT RINGS different stands 137 OF DISTURBED TREES 165 3.3 RESULTS 137 5.5 PREPARING MICRO-CUTS FROM CROSS-SECTIONS 169 3.3.1 Model accuracy 137 3.3.2 Protective effect 139 3.4 DISCUSSION 141 BIBLIOGRAPHY 171 3.4.1 Model accuracy 141 CURRICULUM VITAE 187 3.4.2 Protective effect 142 ***** 4 Zusammenfassung - 5 ZUSAMMENFASSUNG Steinschlag stellt einen der am häufi gsten in der winterlichen Wachstumspause zugeordnet werden, Gebirgsregionen auftretenden geomorphologischen welche lokal von Mitte Oktober bis Ende Mai andauert. Prozesse dar und wurde daher in der Vergangenheit Direkte Beobachtungen am Hang bestätigen diese ausgiebig studiert. Trotzdem bleiben detaillierte Kenntnisse Resultate und deuten überdies darauf hin, dass die zur Steinschlagfrequenz (wie häufi g), zu Steinschlag- Aktivität im April und Mai am ausgeprägtesten volumen (wie gross), zu räumlichen Mustern (wo ) oder sein dürfte. Während dieser Periode nimmt die zur Jahreszeitlichkeit (wann) der Steinschlagaktivität globale Sonneneinstrahlung am westexponierten Hang die Ausnahme und Angaben zumeist nur sehr fragmen- des Täschgufer kontinuierlich zu und vermag so tarisch. Ebenso wurden Jahrringanalysen bislang nur in die Eislinsen aufzutauen, die durch das Gefrieren wenigen Ausnahmen herangezogen, um die vergangene von Schmelzwasser in den Spalten und Rissen der Steinschlagaktivität zu untersuchen. Es ist daher das Anrisszonen gebildet werden konnten. Im Gegensatz Ziel dieser Arbeit, (i) saisonale Unterschiede in der dazu scheint die Steinschlagaktivität im Täschgufer Steinschlagaktivität festzulegen und (ii) räumlich- weder durch Sommergewitter noch durch anhaltende zeitliche Variationen in der Steinschlagaktivität mit Niederschläge im Herbst beeinfl usst zu werden. dendrochronologischen Untersuchungen zu durchleuch- ten. Daneben wurden die vertikale Verteilung und In einer zweiten Untersuchung wurden im Täsch- die Sichtbarkeit von Steinschlagverletzungen auf gufer an 135 stark verletzten Lärchen 564 Bohrkerne der Stammoberfl äche betrachtet, bevor Stärken und gezogen, um langfristige Veränderungen in räumlich- Schwächen der Dendrochronologie im Bereich der zeitlichen Steinschlagmustern festzustellen.

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