  We present the first density model of Stromboli volcano (Aeolian Islands,
Italy) obtained by simultaneously inverting land-based (543) and sea-surface
(327) relative gravity data. Modern positioning technology, a 1 * 1 m digital
elevation model, and a 15 * 15 m bathymetric model made it possible to obtain a
detailed 3-D density model through an iteratively reweighted
smoothness-constrained least-squares inversion that explained the land-based
gravity data to 0.09 mGal and the sea-surface data to 5 mGal. Our inverse
formulation avoids introducing any assumptions about density magnitudes. At 125
m depth from the land surface, the inferred mean density of the island is 2380
kg m-3, with corresponding 2.5 and 97.5 percentiles of 2200 and 2530 kg m-3.
This density range covers the rock densities of new and previously published
samples of Paleostromboli I, Vancori, Neostromboli and San Bartolo lava flows.
High-density anomalies in the central and southern part of the island can be
related to two main degassing faults crossing the island (N41 and N64) that are
interpreted as preferential regions of dyke intrusions. In addition, two
low-density anomalies are found in the northeastern part and in the summit area
of the island. These anomalies seem to be geographically related with past
paroxysmal explosive phreato-magmatic events that have played important roles
in the evolution of Stromboli Island by forming the Scari caldera and the
Neostromboli crater, respectively.
