Obituary for Heidy Mader

My colleague, mentor, and friend Heidy Mader, who died of cancer at the age of 61, was an outstanding experimental scientist. She applied what she learned developing the Wispa chocolate bar as a research physicist at Cadbury to lead a revolution in understanding lava and magma flow as a professor at Bristol University.

Heidy was born in Cosford, Shropshire to Renate (née Pitz) and Eric Mader. Eric was an officer in the RAF and Renate, who was from Germany, later became a teacher. The family moved frequently within the UK due to Eric’s postings.

They settled in Germany for Heidy’s secondary school, where she became fluent in German and became passionate about physics. Ignoring the clear statement from her teachers that “girls can’t do physics”, she took the Abitur – the only girl in her year. This was the first of many times in her life that Heidy would encounter and shed a lazy stereotype of female limitation.

After a first class degree in Physics from the University of York, Heidy moved to Cadbury’s Technical Development department where she studied the rheology of effervescent melted chocolate as part of the Wispa development team. Little known to the general public, rheology, which describes how materials flow and deform when subjected to a force, permeates all aspects of our lives and determines how blood flows around our bodies, like all types of products – food , medicines, plastics – are made and how materials like ice and magma flow through the natural environment.

Heidy returned to Bristol in 1996 after completing a PhD at Bristol University on the physical properties of ice, a post-doctoral position studying explosive processes in volcanic eruptions and a teaching position at the University of Lancaster. There she set up a rheology laboratory, conducting painstaking experiments with bubble- and particle-laden fluids — proxies for lava and magma.

Like the chocolate intended to become Wispa bars, Magma consists of a crystallizing liquid containing bubbles; Heidy’s big discovery was that the same rheological techniques she had used at Cadbury could be applied to understand magma flow during volcanic eruptions. The results changed the understanding of magma flows and led to mathematical models that allowed more accurate predictions of volcanic eruption behavior.

Heidy was a generous mentor to dozens of younger scientists, sharing her skills and knowledge and always offering wise advice, even when it came to speaking uncomfortable truths. She has been seen as a role model for women in science, in part because she showed that “family first” need not mean “career second” at a time when many in academia still expected women to make that choice .

She and her longtime partner, mathematician Jon Keating, had three children – the first, Alex, sadly died shortly after birth. In her free time, Heidy played bassoon, swam, knitted, made stained glass, baked wonderful cakes and walked her beloved dog Tess.

Heidy is survived by Jon, whom she married in 2009, and their children, Rob and Miranda, and their mother.

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