One of the most important volatiles in magma is water. In magma, water is incorporated in both the melt and in crystals, including hydrous and nominally anhydrous minerals (NAMs). The purpose of this study is to determine the role of magmatic water content in controlling volcano explosivity especially at Merapi volcano, Indonesia, which is one of the most active volcanoes in the world. Here I apply clinopyroxene from two types of eruption products, lava and ash, to test the magmatic water content in the Merapi 2010 eruption. Both oriented and unoriented crystals were analysed using Fourier-Transformed Infrared (FTIR) spectroscopy to establish the clinopyroxene’s crystal water content. By combining the water content of clinopyroxene and geochemical data obtained from EPMA analysis, the magmatic water content is then estimated by inserting the data into the equation of O’Leary et al. (2010) [lnD= -4.2(60.2)16.5(60.5) VI[Al3+]-1.0(60.2) [Ca2+]]. I also investigated clinopyroxene crystals that were experimentally rehydrated, including four oriented crystals from a Merapi 2010 eruption ash sample annealed at a temperature of 700°C and pressure of 1 atm. Magmatic water contents of Merapi 2010 from rehydration experiments were then compared to the Merapi 2006 magmatic water content which were treated under the same conditions. The results revealed a wide variation between samples and among crystals taken from the same sample. However, oriented samples yielded a smaller variation between minimum and maximum clinopyroxene crystal water content and, overall, ash samples yielded higher water content in clinopyroxene than lava samples. The rehydration experiment significantly amplified clinopyroxene crystal water content by 3 to 7-fold compared to the result without the rehydration procedure. Comparison of data between the 2006 and 2010 Merapi eruptions demonstrates that there was a significant difference in magmatic water contents with the 2010 eruption displaying more than twice as much magmatic water than the 2006 eruption. The result implies that magmatic water plays potentially a crucial role in controlling explosivity of Merapi eruptions. / Indonesien är det land i Världen som har den största befolkningen som lever inom 100 km av en aktiv vulkan. Merapi är en av de mest farliga vulkanerna i Indonesien, som också är en av de mest aktiva vulkanerna i Världen och ligger på ön Java runt 15-25 km från Yogyakarta med en total befolkningstäthet på 1000 personer per kvadratkilometer. Utbrott från Merapi har dödat cirka 5000 personer under de senaste 500 åren. Således är det viktigt att studera hur vulkanen beter sig och orsaken till utbrotten för att kunna vita förebyggande åtgärder för att minska antalet dödsfall eller till och med undvika dödsfall helt. Vulkanutbrott kontrolleras av många faktorer, en av faktorerna är flyktiga ämnen i magman och en av de viktigaste flyktiga ämnen är vatten. Det här projektet syftar till att ta reda på vattnets roll på explosiviteten hos utbrotten genom att undersöka eruptiva produkter från utbrotten av Merapi under 2006 och 2010 med hjälp av Fourier-Transformed Infrared (FTIR) spektroskopi. Experimentet använder normalt vattenfria mineraler (NAMs) så som klinopyroxen men vatten kan införlivas i NAMs genom att binda väte i kristallgitteret under kristalltillväxten. Tidigare studier har visat att vattenhalten i klinopyroxenkristall skulle kunna användas för att beräkna magmatisk vattenhalt och därmed jämföra den magmatiska vattenhalt mellan olika utbrott med olika explosivitet i samma vulkan, vilket kan indikera hur vattenhalten påverkar vulkanutbrotten. Magmatiskt vatteninnehåll beräknat utifrån klinopyroxenvattenhalten visade en variation mellan de undersöka proverna från samma utbrott, varför ytterligare undersökning genom rehydreringsexperiment gjordes genom annealing av proverna vid en temperatur av 700 °C och tryck vid 1 atm. Även om det var variation i magmatisk vattenhalt mellan proverna, så har utbrotten av Merapi under 2010 högre magmatiskt vatteninnehåll än utbrottet under 2006 med 3-7 gånger. Sammantaget har Merapi 2010 utbrottet högre explosivitet och högre magmatisk vattenhalt än 2006 utbrottet, vilket innebär att högre vattenhalt ger högre explosivitet. På detta sätt kontrollerade vattnet vulkanens explosivitet för Merapivulkanen.Nyckelord: Merapi vulkan, NA

Neste trabalho estudam-se alguns novos métodos de seleção de variáveis no contexto da regressão linear que surgiram nos últimos 15 anos, especificamente o LARS - Least Angle Regression, o NAMS - Noise Addition Model Selection, a Razão de Falsa Seleção - RFS (FSR em inglês), o LASSO Bayesiano e o Spike-and-Slab LASSO. A metodologia foi a análise e comparação dos métodos estudados e aplicações. Após esse estudo, realizam-se aplicações em bases de dados reais e um estudo de simulação, em que todos os métodos se mostraram promissores, com os métodos Bayesianos apresentando os melhores resultados. / In this work, some new variable selection methods that have appeared in the last 15 years in the context of linear regression are studied, specifically the LARS - Least Angle Regression, the NAMS - Noise Addition Model Selection, the False Selection Rate - FSR, the Bayesian LASSO and the Spike-and-Slab LASSO. The methodology was the analysis and comparison of the studied methods. After this study, applications to real data bases are made, as well as a simulation study, in which all methods are shown to be promising, with the Bayesian methods showing the best results.

Neste trabalho estudam-se alguns novos métodos de seleção de variáveis no contexto da regressão linear que surgiram nos últimos 15 anos, especificamente o LARS - Least Angle Regression, o NAMS - Noise Addition Model Selection, a Razão de Falsa Seleção - RFS (FSR em inglês), o LASSO Bayesiano e o Spike-and-Slab LASSO. A metodologia foi a análise e comparação dos métodos estudados e aplicações. Após esse estudo, realizam-se aplicações em bases de dados reais e um estudo de simulação, em que todos os métodos se mostraram promissores, com os métodos Bayesianos apresentando os melhores resultados. / In this work, some new variable selection methods that have appeared in the last 15 years in the context of linear regression are studied, specifically the LARS - Least Angle Regression, the NAMS - Noise Addition Model Selection, the False Selection Rate - FSR, the Bayesian LASSO and the Spike-and-Slab LASSO. The methodology was the analysis and comparison of the studied methods. After this study, applications to real data bases are made, as well as a simulation study, in which all methods are shown to be promising, with the Bayesian methods showing the best results.

The aim of this thesis is to increase our knowledge and understanding of trace water concentrations in nominally anhydrous minerals (NAMs). Special focus is put on the de- and rehydration mechanisms of clinopyroxene crystals in volcanic systems, how these minerals can be used to investigate the volatile content of mantle rocks and melts on both Earth and other planetary bodies (e.g., Mars). Various analytical techniques for water concentration analysis were evaluated. The first part of the thesis focusses on rehydration experiments in hydrogen gas at 1 atm and under hydrothermal pressures from 0.5 to 3 kbar on volcanic clinopyroxene crystals in order to test hydrogen incorporation and loss from crystals and how their initial water content at crystallization prior to dehydration may be restored. The results show that extensive dehydration may occur during magma ascent and degassing but may be hindered by fast ascent rates with limited volatile loss. De- and rehydration processes are governed by the redox-reaction OH- + Fe2+ ↔ O2- + Fe3+ + ½ H2. Performing rehydration experiments at different pressures can restore the water contents of clinopyroxene at various levels in the volcanic systems. Subsequently water contents of magmas and mantle sources can be deduced based on crystal/melt partition coefficients. This thesis provides examples from the Canary Islands, Merapi volcano in Indonesia and the famous Nakhla meteorite. Using NAMs as a proxy for magmatic and mantle water contents may provide a very good method especially for planetary science where sample material is limited. The thesis’ second part focusses on analytical methods to measure the concentration of water in NAMs. Specifically the application of Raman spectroscopy and proton-proton scattering are tested. The hydrated mineral zoisite is thoroughly analyzed in order to be used as an external standard material. Polarized single crystal spectra helped to determine the orientation of the OH-dipole in zoisite. Further, Transmission Raman spectroscopy and a new method for the preparation of very thin samples for proton-proton scattering were developed and tested. The results provide new possibilities for the concentration analysis of water in NAMs such as three dimensional distribution and high spatial resolution.