The Advanced Spaceborne Thermal Emission and Relection and Radiometer (ASTER) will have a comprehensive ability to gather digital imaging data across the visible, near, and thermal infrared parts of the spectrum, as well as stereophotogrammentric capability. This simultaneous multiband data, combined with a repeat interval of several times per month, off-track pointing capability, and high spatial resolution (e.g., 15 min visible bands), will provide an unprecedented opportunity to observe a variety of transient phenomena globally (e.g., volcanic eruptins, progressive slope instabilities, flood damege). For some larger events, data from the Multi-angle Imaging SpectroRadiometer (MISR), and the Moderate Resolution Imaging Spectroradiometer (MODIS), both of which have lower spatial resolution, can be effectively combined with ASTER data for more frequent temporal coverage. ASTER will be particularly effective in establishing base level radiometric and topographic descriptions of sites which are undergoing perennial activity or for where activity is suspected in the future, and monitoring crescendo styles of activity before or after an event. More problematic are situations where an expected event finally occurs, or an isolated unexpected event happens. In these latter cases, ASTER's ability to capture the event will depend mainly on shrewd planning, intuition, or more likely in the latter case, luck. Given its spectral flexibility, high spatial resolution, and dynamic range, ASTER will be particularly well-suited for observations of volcanic precursor activity (e.g., monitoring summit crater and fumarole thermal emissions and aerosol, particulate, and SO2 emission levels), surface activity during eruptions (e.g., progression and thermal emissions of active lava flows), and eruption plume morphology and composition.