Cashman studies links between chemical and physical factors that control magma ascent, eruption, and emplacement on the Earth's surface. She has studied volcanoes on all seven continents and explored a wide range of eruption styles. She is best known for her work that links the kinetics of bubble and crystal formation to the behaviour of volcanic materials, but has worked on problems that span from the chemical to physical to social aspects of volcanism. She has worked with all the US volcano observatories and served on the scientific advisory committee for the island of Montserrat. Her research uses a combination of volcanology, igneous petrology, kinetics, microscopy and fluid dynamics with a focus on mafic volcanoes. This includes channel development in Hawaiian lava flows and volcanic ash formation in eruptions. She also has interests in intermediate composition and silicic volcanoes, particularly at Mount St. Helens.