New remote methods as alternatives and complements to ground-based surveys, e.g., satellite-based thermal alarms, measurements of varying gas composition and output as indicators of pending eruptions, radar, and the global positioning system (GPS), will all help to revolutionize prediction and hazard assessment in future years. New radar interferometry techniques are under development and have been used to produce high resolution (10--25 m spatial resolution, 2--5 m vertical accuracy) digital elevation models (DEMs) of volcanoes. Using an aircraft interferometric radar, DEMs have been constructed for Hekla ( Evans et al., 1992) and Vesuvius ( Mouginis-Mark and Garbeil, 1993), as well as the volcanoes in the western Galapagos islands (Fernandina and Isabela islands). These DEMs may prove to be particularly useful for the prediction of lava flow paths ( Wadge et al., 1994) or the hazards posed by pyroclastic flows ( Dobran et al., 1994). Orbital radar interferometry has also been done for Mt. Unzen (using JERS-1 radar images) and for the analysis of post-seismic deformation following the 1992 Landers earthquake in California ( Massonnet et al., 1993, 1994; Zebker et al., 1994), indicating that it could be used to detect ground motions on active volcanoes. Depending on the location of the volcano (which has to be within the field of view of a radar ground station), comparable radar observations of volcanoes undergoing inflation or deflation could also be made using orbital radar data obtained from the ERS-1 spacecraft. Alternatively, tape recorders on the JERS-1 and RADARSAT spacecraft could provide coverage anywhere around the world provided that the radar data are requested.
Very long baseline interferometry (VLBI) and GPS measurements made by Dixon et al. (1993) have been used to constrain the regional tectonic setting of Long Valley caldera, California, site of a volcanic crisis following seismic activity in the late 1980's, as well as measuring strain associated with the growth of the resurgent dome.
At Vesuvius, a volcano posing considerable hazard to a very populous region, a concerted effort has been mounted to combine eruption models with field data to better understand the threat from future activity ( Dobran, 1993). At Galeras and Unzen, pioneering work has been done that involves the field determination of volcanic gas emissions, including HCl for the first time, using Fourier-transform infrared spectral radiometer (FTIR) techniques ( Mori et al., 1993; Notsu et al., 1993; Stix et al., 1993). These methods have the distinct advantage that measurements can be made from several hundred meters away from the active crater, providing an important element of safety for the field volcanologist.