3D SURFACE DEFORMATION DURING THE MAY 2008 FLANK ERUPTION OF MT. ETNA FROM AIRBORNE STEREO IMAGING

Mapping ground deformation caused by dike intrusions associated with volcanic eruptions can reveal substantial information on volcanic feeding systems, but is often limited by the number of ground geodetic stations or benchmarks available and by loss of correlation for SAR interferometry due to modification of the surface by the eruption. We report on an experimental application of a specifically designed photogrammetric mapping technique for this task. Analysis of optical images from repeated stereo imaging campaigns provides high potentials for obtaining a dense set of displacement measurements (due to high spatial resolution and strictly local correlation techniques) and the capability of measuring all 3 displacement components.

We mapped the displacements between 2007-2008 in the summit area of Etna and Valle del Bove based on sub-pixel image correlation of multi-temporal data (airborne HRSC multi-line scanner images, resolution ~15 cm). Displacement components are filtered by a RANSAC-type procedure and mapped to a regular grid of smaller resolution to reduce uncertainty. Comparison with ground GPS displacement data, and observed variance on stable surfaces, point to a precision of 5-10 cm (10-15 cm for height) on a 5 m grid. The results show that displacements could be determined in close vicinity to active volcanic vents and new lava flows. Lateral continuity also allows us to identify strong displacement gradients most likely related to fault movements.

Eruptive activity at Mt. Etna in recent years was accompanied by short phases of intensified ground deformation, in particular in conjunction with the opening of an eruptive fissure on May 13, 2008. The displacements we observe reveal an extensive deformation field that requires important interior processes as causative mechanisms. The displacements locally attain values of more than 1 m for both horizontal components and subsidence of more than 3 m. While the deformation pattern observed along the eruptive fissure, according to an Okada source model, is compatible with extension associated with dike intrusion below the upper western slope of Valle del Bove, the pattern observed on the upper NE-flank of Etna shows more complex characteristics and suggests interaction with structures related to the boundary of the instable eastern sector of the volcano.