Abstract:    In strongly nonlinear flow fields, material volumes are not only advected by the flow but also tend to be strongly deformed as time progresses. This advection-driven deformation enhances mixing both by steepening gradients of passive scalar fields and by increasing the size of material surfaces relative to material volumes. I will present recent experimental work aimed at understanding the dynamics of shape changes of material areas in a quasi-two-dimensional weakly turbulent laboratory flow. I will focus on the shape distortion of Lagrangian triangles, minimal parameterizations of material areas, and on the spatial distribution of strongly nonlinear deformation. Host:  Prof. Eckart Meiburg