Active lava lakes present a rare opportunity to observe directly the complex processes occurring within a magma body. Situated on Ross Island, Antarctica, the 3794-m-high crater of Erebus volcano has hosted a phonolite lava lake for decades. Previous studies have shown that many of the lake’s characteristics, such as surface velocity, gas flux and gas composition, exhibit a pronounced pulsatory behaviour on a time-scale of ∼10 min. Focusing primarily on the analysis of infra-red (IR) imagery acquired from the crater rim, this dissertation considers how the periodic behaviour of the Erebus lava lake evolves over decadal time periods, how the cyclic fluctuations of the different properties are interrelated and what can be inferred about the mechanisms occurring beneath the surface of the lake from these observations. Creation of new hardware, software and methodologies to facilitate these types of observations is a strong focus of this work. Chapter 1 introduces the nature of active lava lakes, reviews previous studies of Erebus and presents in detail the research objectives that are addressed by the subsequent chapters. In Chapter 2, a new thermal camera system that was developed as part of this study is described. Designed to run autonomously at the crater-rim of Erebus, this system was installed in December 2012 and has enabled, for the first time, extended time-series of images to be acquired. Chapter 3 briefly describes some of the other hardware and software that was developed as part of this study and outlines how it has been utilised for volcano monitoring. In Chapter 4, a dataset of IR images collected between 2004–2011 is used to assess inter-annual variability in the pulsatory behaviour of the surface motion of the Erebus lava lake. The cyclic behaviour is found to be a sustained feature of the lake, and no obvious changes are observed across the time period analysed. Data collected with the camera system described in Chapter 2 are analysed in Chapter 5 and combined with measurements from other instruments to assess the correlation between the cyclic behaviours of different lake properties. Cycles in surface speed, surface elevation, gas flux and gas composition are found to be highly correlated with each other. In Chapter 6, the surface velocities calculated in the preceding chapters are revisited, and the two-dimensional structure of the flow field is analysed. Chapter 7 demonstrates how the motion tracking methodologies developed for studying the Erebus lava lake can be used to improve high time resolution sulphur dioxide flux estimates - a significant challenge faced in the study presented in Chapter 5. Finally, Chapter 8 presents a synthesis of the key findings and conclusions from the preceding chapters.