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Comets, often referred to as cosmic time capsules, serve as invaluable repositories of information from the nascent phases of our solar system. Varying significantly in size, with nuclei ranging from a few kilometers to tens of kilometers in diameter, these celestial bodies are complex, porous aggregates of organic molecules, silicate particles, and entrapped volatile gases. Their orbits, which can be categorized into the Main Belt, the Kuiper Belt, and the Oort Cloud, offer distinct insights into their origins and the early conditions of the solar system. Understanding the physical processes occurring within these nuclei is critical, particularly in the context of comet outbursts—sudden increases in brightness accompanied by the release of gas and dust. These outbursts are the consequence of intricate internal mechanisms triggered when the comet approaches the Sun, leading to the sublimation of ice and subsequent gas production. Existing theories attribute outbursts to a buildup of internal stress, often facilitated by thermodynamic factors, such as temperature and pressure gradients, or mechanical factors, such as changes in angular momentum. However, one of the least understood aspects of these celestial bodies is the interaction of heat energy with their porous structure. This study aims to shed light on this very phenomenon, focusing on how heat energy from the Sun penetrates the surface of the comet and diffuses into its sub-layers, subsequently impacting phase transitions, gas production, and ultimately, the formation of outbursts. To accomplish this, we employ a multidisciplinary approach that combines thermodynamics, heat transfer equations, and computational modeling. We introduce a novel pore network model based on percolation theory to simulate the behavior of gas within the comet’s porous structure, allowing us to probe the intricate dynamics of gas movement and pressure build-up. Our work is validated against observational data, specifically from the European Space Agency’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko. Our models have yielded preliminary results that emphasize the role of the formation of a first cluster in the porous network as a critical point for outburst occurrence. Particularly for comets approaching the perihelion position, the internal pressure and temperature dynamics become increasingly complex, and our findings contribute to a nuanced understanding of these dynamics. These insights not only advance our understanding of the comet nucleus but also offer a robust theoretical framework for investigating similar phenomena in other celestial bodies.

Lihir Gold Mine in Papua New Guinea is one of the largest gold mines in the world situated in a seismically sensitive zone. The gold deposit is located in an extinct volcano in close proximity to the sea shore and presents a series of geohazards. Some geohazards are uncommon and include: geothermal outbursts, cavities, water inrush and earthquake/ tsunami. After a major multi-batter (5 benches high) slope failure that occurred on the 1st of October 2009, a team of engineers, lead by the author investigated the incident and made series of recommendations. Arising out of these recommendations, a comprehensive Geohazard Management Plan was formulated by revisiting, revising and putting together all the individual geohazard management plans as a single document. This thesis describes the outcomes of the investigation and presents an overview and systematic approach in formulation of the Geohazard Management Plan, apart from a summary of the gaps that were identified in the existing system, major contributions that were made as well as the expected improvements and constraints in managing these geohazards. / Mining Engineering

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No description available.