Studies of Volcanic Plumes with Spectroscopic Remote Sensing Techniques

Volcanism is a widespread phenomenon on Earth and other planetary bodies. Terrestrial volcanoes are shallow manifestations of deep and complex mechanisms of heat and mass transport and play an important role in the formation and change of the atmosphere and the natural landscape. Moreover, volcanic eruptions represent one of the most important natural threats for humans, whose civilizations have for ages lived and thrived in the fertile and beautiful volcanic lands, but also have sometimes succumbed after major eruptive outbursts.Active volcanoes constitute important sources of molecular species emitted to the atmosphere, such as H2O, CO2, SO2, HCl, HF, H2S, CO, which participate in several geochemical processes. Although present at relatively small concentrations in their parental magmas, the segregation of these volatiles is crucial for controlling the dynamics of shallow magma transport and thus the style of volcanic eruptions. Quantifying the source strength and the fate of volcanic gaseous emissions is therefore a highly desirable, but unfortunately not always feasible goal, due mainly to present technological, logistical or economical limitations. In this context, the development of remote sensing techniques applied to the measurement of volcanic emissions constitutes an endeavor of high scientific and societal interest.The main focus of the work presented in this thesis is the study of active volcanism by measuring emission rates and molar ratios of volcanic gases via two passive spectroscopic remote sensing techniques: Differential Optical Absorption Spectroscopy (DOAS) of sky-scattered ultraviolet solar radiation and Fourier Transform Infra-Red (FTIR) spectroscopy of direct solar radiation and passive thermal emission. The thesis presents some developments in the techniques that have been used during field campaigns in Popocat\ue9petl, Karymsky and Tungurahua volcanoes, principally, as well as the results of the evaluation and interpretation of long-term gas emission data from Tungurahua and Nyiragongo volcanoes.This work aims at contributing to a better understanding of volcanic activity by advancing the methods for accurate, simple, robust, and safe monitoring of volcanogenic gas emissions. Increasing this understanding is very helpful to take informed decisions for reducing the risks posed by volcanic eruptions, which despite their implied potential danger, constitute some of the most fascinating, widespread and far-reaching natural phenomena on Eart