New insights into the characteristics and dynamics of rhyolite long-lasting volcanic eruptions Dissertation zur Erlangung des Grades ―Doktor der Naturwissenchaften‖ Im Promotionsfach Geologie/Paleontologie am Fachberich Chemie, Pharmazie und Geowissenschften der Johannes Gutenberg-Universität Mainz Pablo Brian Forte geb. in Buenos Aires Mainz, 2018 II 1. Berichterstatter: 2. Berichterstatter: Tag der mündlichen Prüfung: 06.05.19 III IV Table of Contents Table of Contents .......................................................................................................... V List of Figures ............................................................................................................... VIII List of Tables ................................................................................................................. X Preamble ........................................................................................................................ XI Zusammenfassung ....................................................................................................... 1 Abstract ......................................................................................................................... 3 1. Introduction… ........................................................................................................... 5 1.1 Pre-2008 state of knowledge of rhyolite eruptions. ............................................... 7 1.1.1 Bubble nucleation and growth ....................................................................... 9 1.1.2 The fate of rising magma. .............................................................................. 12 1.2 Witnessing rhyolite eruptions in the southern Andes, Chile ................................... 13 1.2.1 2008-2010 eruption of Chaitén volcano, Chile. .............................................. 14 1.2.2 2011-2012 eruption of Cordón Caulle, Chile. ................................................. 16 1.3 What have we learned after these eruptions? ....................................................... 17 1.4 Thesis structure .................................................................................................... 20 2. H2O evolution in rhyolite systems: the case of the 2008-2010 Chaitén volcano eruption, Chile ............................................................................................................... 21 2.1 Introduction ........................................................................................................... 23 2.1.1 H2O: main characteristics .............................................................................. 23 2.1.2 Primary versus secondary H2O ..................................................................... 25 2.1.3 H2O contents in rhyolite deposits................................................................... 26 2.1.3.1 Recent rhyolite eruptions ....................................................................... 29 2.2 Methodology ......................................................................................................... 29 2.2.1 Sampling strategy ......................................................................................... 29 2.2.2 H2O content determination. ........................................................................... 31 2.2.2.1 FTIR measurements. ............................................................................. 32 2.2.2.2 DSC-TGA measurements ...................................................................... 33 2.2.3 Electron Probe Microanalysis (EPMA) ........................................................... 33 2.3 Results ................................................................................................................. 34 2.4 Discussion ............................................................................................................ 39 2.4.1 H2O: magmatic or secondary?. ..................................................................... 39 2.4.1.1 Hydrous speciation. ............................................................................... 40 2.4.1.2 2008 vs. 2016 ash fallout deposits ......................................................... 43 2.4.1.3 DSC-TGA measurements ...................................................................... 44 V 2.4.2 H2O evolution during 2008 Chaitén eruption. ................................................ 45 2.5 Conclusions .......................................................................................................... 48 3. High temperature – 0.1 MPa experiments with rhyolitic glasses ........................... 51 3.1 Introduction ........................................................................................................... 53 3.2 Methodology ......................................................................................................... 54 3.2.1 Samples ........................................................................................................ 54 3.2.2 Experimental and Analytical Methods ............................................................ 54 3.2.2.1 Sample characterization and preparation............................................... 54 3.2.2.2 Experimental procedure ......................................................................... 56 3.3 Results. ................................................................................................................ 59 3.4 Discussion ............................................................................................................ 66 3.4.1 Onset of vesiculation ..................................................................................... 66 3.4.2 Vesiculation regimes. .................................................................................... 68 3.5 Conclusions .......................................................................................................... 74 4. Explosive fragmentation of rhyolite magma: an experimental perspective .......... 77 4.1 Introduction ........................................................................................................... 79 4.2 Methodology ......................................................................................................... 80 4.2.1. High Temperature-0.1 MPa experiments ...................................................... 80 4.2.2 High Pressure-variable temperature shock-tube experiments ....................... 82 4.2.2.1 Sample characterization ........................................................................ 82 4.2.2.2 Experimental procedure. ........................................................................ 82 4.2.3 Post-experimental analysis ........................................................................... 84 4.3 Results ................................................................................................................. 85 4.3.1 High Temperature-0.1 MPa experiments ....................................................... 85 4.3.2 High pressure experiments ........................................................................... 88 4.4 Discussion ............................................................................................................ 93 4.4.1 High Temperature-0.1 MPa experiments ....................................................... 93 4.4.1.1 From Foam to Fragments: why samples of the 1.4 wt.% H2O series explode? ......................................................................................................................... 93 4.4.1.2 Foam expansion as an analogous of magma decompression ................ 96 4.4.2 Fragmentation experiments and the 2008 Chaitén eruption .......................... 99 4.5 Conclusions .......................................................................................................... 102 5. Long-lasting impacts of rhyolite volcanic eruptions: ash resuspension events .. 105 5.1 Introduction ........................................................................................................... 107 5.2 Area of study. ....................................................................................................... 111 5.2.1 Social and economic aspects ........................................................................ 111 5.2.2 Meteorological and environmental aspects.................................................... 113 VI 5.2.3 Volcanic activity and its impacts .................................................................... 114 5.2.3.1 2008-2010 Chaitén eruption .................................................................. 114 5.2.3.2 2011-2012 Cordón Caulle eruption ........................................................ 115 5.2.3.3 2015 Calbuco eruption. .......................................................................... 116 5.3 Methodology ......................................................................................................... 116 5.4 Results ................................................................................................................. 118 5.4.1 Farmers: main demographics ........................................................................ 118 5.4.2 Ash resuspension events .............................................................................. 119 5.4.3. Impacts: ash resuspension events vs. primary tephra fallout ....................... 124 5.4.4 The influence of 2015 Calbuco eruption ........................................................ 129