Heidy Mader was born at RAF Cosford and was schooled in the UK and at secondary level in Germany where she became passionate about physics. After a first-class degree in Physics at the University of York in 1985, Heidy was employed as Research Physicist in the Technical Development Department of Cadbury Schweppes Ltd, Bournville, Birmingham. She investigated the flow of bubbly molten chocolate and worked on developing Wispa bars and the manufacture of Crunchie. This experience proved to be highly relevant to her later fundamental research on flow of complex multiphase fluids.
She started a PhD at Bristol in 1987 in the Department of Physics on the physics of ice supervised by Professor John Nye FRS, who pioneered understanding the physics of glaciers. Her work concerned how water veins and micropores of liquid water developed in polycrystalline ice, and she demonstrated the profound effects of the veins on ice physics and distribution of impurities. The existence of water veins had been predicted by John Nye and Sir Charles Frank FRS, on the basis of thermodynamic reasoning, and Heidy documented their occurrence, geometries and importance.
Her interest changed to volcanoes as she joined the then Department of Geology as a postdoctoral research fellow collaborating with Professor Brad Sturtevant, from Caltech, and me. She was tasked with replicating the explosive volcanic flows of liquid rock and gas using analogue fluids. These were difficult experiments carried out in shock tubes designed by Heidy in which carbonate solutions and acids were rapidly mixed to produce very dynamic expanding flows due to the chemical reaction. They were pioneering, being among the first to measure the pressures and speeds of expanding explosive flows of bubbly liquids to simulate volcanic eruptions in the lab. This work displayed Heidy’s many strengths as a scientist including a very systematic and rigorous approach, meticulous attention to detail, innovation in experimental design and an ability to make insightful interpretations of the data.
Her prowess was quickly recognised with a move to a lectureship at Lancaster University (1992-1996) in the Institute of Environmental and Biological Sciences. Here her attention turned to the behaviour of bubbles in magmas. She returned to Bristol to take up a lectureship in 1996 and quickly established an outstanding research group on the rheology of magmas, which was destined to produce seminal research on the effects of bubbles and crystals suspended in very viscous liquids on rheology, motivated by advancing understanding of magma and volcanic eruption dynamics. She built up a state-of-the-art rheology laboratory to undertake tricky experiments on mixtures of bubbles and viscous liquids where rheological behaviour was complicated by the dependency of the bubble on strain rate and size. Together with some exceptionally able PhD students and postdoctoral fellows she established herself as the leading international researcher in magma rheology with a legacy of several very highly cited publications. This success owed a great deal to her deep understanding of the underlying physics of multiphase fluids, her outstanding skill as an experimentalist and her ability to inspire and motivate very bright young researchers.
In the mid-1990s, she returned to her interests in glaciology to study veins in glaciers as a habitat for microbial organisms (‘life in ice’) with some highly influential research papers. The research theme included fieldwork in Svalbard, where she learned to climb out of crevices and to shoot a rifle (in case of attack by polar bears).
Promotion to Reader followed in 2006. In 2007 she demonstrated another side of her abilities and personal qualities when she became Graduate Dean for the Faculty of Science, a post she held until 2013. Here her organisational skills became legendary among senior management. She brought rigour and compassion to this exacting role and her flair in academic administrative leadership were on a par with her excellence as a research scientist and teacher. With a personal chair bestowed in 2012 Heidy returned to research and teaching, leading a major new multi-institutional NERC-funded project on the role of crystal and bubble growth in volcanic eruptions.
Heidy’s outside interests included hiking, swimming, baking, and music: she baked superb cakes, using her experience at Cadbury’s working with chocolate, and she played the bassoon to a high standard. Her main passion, though, was for her family. She spoke movingly at her retirement party about the importance family played in her life. Indeed, research students and postdoctoral researchers speak particularly warmly and affectionately about her wisdom and kindness, playing an informal role in supporting them to balance work with personal life and in welcoming those from overseas to help them settle into a new culture.
Heidy will be greatly missed by her students, friends and colleagues in Bristol and around the world. She leaves her beloved partner Jon and children Rob and Miranda.