Deflation acting on Pantelleria island (Sicily Channel) inferred through geodetic data

Pantelleria is a volcanic island situated at the centre of the Sicily Chann el continental rift. Since 1980, the island has been monitored by geodetic techniques (electro-optical distance measurements (EDM) and levelling) and gravimetry. After more than 10 years, the EDM network was re-measured in 19 95 and successively it has been improved and measured also with global posi tion system (GPS) techniques. It has therefore been possible to carry out a long-term analysis (1980-1996) of the deformation pattern. The levelling i n the 1980-1996 period revealed a marked lowering of the central-southern p art of the island with respect to the northern sector. The horizontal EDM m easurements all prove to be in contraction and suggest that a deflation is ongoing in the central-southern part. The effects of areal contraction and lowering are interpreted as being due to the volcanic field, which appears to predominate over possible stretching induced by the Sicily Channel dynam ics. We modelled the horizontal and vertical changes accumulated over 16 ye ars using a 3D ellipsoidal depressuring model which indicates a ca. 5 km de ep source located under the area within the most recent caldera. This model could explain a short term (tens of years) acting deflation. We also propo se an interpretive framework in the case where the deflation is acting over a long period (thousands of years). In this case, the deflation is interpr eted as readjustment following the loss of mass occurring with recent volca nism (18-3 kyr). (C) 2000 Elsevier Science B.V. All rights reserved.