Systems and methods are described to identify motion events on a sloped surface, such as a mountainside, using transmitted and received radio frequency (RF) chirps. A one-dimensional array of receive antennas can be digitally beamformed to determine azimuth information of received reflected chirps. Elevation information can be determined based on time-of-flight measurements of received reflected chirps and known distances to locations on the sloped surface. Motion events may be characterized by deviations in return power levels and/or return phase shifts. The systems and methods may, for example, be used to provide real-time detection of avalanches and/or landslides.