The study of gravity-driven flows (avalanches, landslides, etc.) has made significant progress in the last decade, mainly in the field of numerical models. However, these models rely on a speculative basis and, for lack of field data, modeling the internal dynamics of these flows remains a key issue. The main challenge to obtaining appropriate field data is the tremendous difficulty of monitoring the flow dynamics inside the bulk, especially when the material flows at high speed. This project is aimed at filling this gap using the sensor network paradigm. The key to reliable, accurate, and fast monitoring is a local positioning system enabling every node to determine its own position at an arbitrary point in space and time. Unlike existing local positioning systems, in this approach, nodes are transmitters. A small number of fixed high sensitivity receivers determine a fix to each sensor node independently via high resolution time-of-flight. The respective position may then be downloaded to the nodes in real time or recoded to build a time-varying position map during the course of the phenomenon. To ensure a reliable link even in hostile environments, the nodes utilize ultra-wideband communication techniques with omni-directional antennas and relatively low transmission power. Relatively long-range radios enable deployment over large instable fields, thus potentially serving as reliable warning systems.