GROUND DEFORMATION STUDIES AT SOUFRIERE HILLS VOLCANO, MONTSERRAT I -ELECTRONIC DISTANCE METER STUDIES

Frequent occupation of a network of instrument and target sites using an Electronic Distance Meter (EDM) over 21 months has led to the recog nition of two distinct patterns of ground deformation. Corrected slant distances to reflector targets involve either continuous shortening o r an oscillatory pattern of shortening and recovery. These mio pattern s are considered to reflect the response of the volcanic edifice at ne ar-field and far-field positions, respectively. At near-field location s non-elastic deformation is predominant over elastic deformation and rebound associated with changes in the magma conduit pressure are not detectable. At far-field locations elastic deformation is dominant all owing recognition of relaxation in the conduit magma pressure. Recogni tion of the two patterns assists monitoring of crater stability and ma y aid long-range forecasting of future activity at the volcano.