As we learnt from Young and Laplace, the cohesion of fluids makes them choose specific shapes, in particular spheres at a small scale. We discuss several ways to maintain this ideal shape on a solid, which leads to unique dynamical situations: water pearls do not stick, they run easily and they bounce - a little bit as if they were solid marbles. (But they are not. And the liquid nature of these pearls has interesting consequences on the dynamical shapes they adopt, for example.) The high mobility of liquid pearls implies that tiny forces are sufficient to move them, and we plan to present recent achievements where some asymmetric patterns at a solid surface permit the self-propulsion of the liquid. We would also like to discuss the effects of various fields to control these elusive drops.

Precise measurements of ground deformation have become increasingly common as large networks of GPS receivers and borehole strainmeters have been established over the last decade. Complementing this continuous record are comparatively infrequent but spatially dense images of ground deformation from radar satellites, and a long historical record of leveling, Electronic Distance Meter, triangulation, and tilt data. Deformation can arise from tectonic and volcanic forces and from human activities such as aquifer withdrawal or geothermal exploitation. Mathematical models of how the crust deforms in response to different physical processes are required to characterize driving processes and constrain source location, size, orientation, and strength. This information is valuable for hazards forecasting and mitigation.