Figure 4
From: Contrasting catastrophic eruptions predicted by different intrusion and collapse scenarios
Structural evolution of deformation pattern 3. t0: stage before beginning the experiment; t1 and t2: stages at minutes 5 and 10 respectively. (a) X-ray cross-sections of the volcano (see b for sections location) of a representative experiment (Experiment 4: see Table 1). Faults are imaged as darker linear trends and syrup intrusion as a homogeneous dark grey area. Note at t1 image the development of an inward-dipping fault from near the cone summit. At t2 image a conjugate system of faults has developed near summit zone inside the displaced block. (b) Sketched structural interpretation in cross-sections and map-view of the main deformation features common at experiments showing this deformation pattern (see text for an explanation). f1, f2, f3: faults, in chronological order. Dashed lines: diffuse shear zones. Grey areas: changes at volcano topography (dark grey: subsidence; light grey: bulging). Black zones: magma bodies. Large arrows: movement of the volcano blocks (i.e., subsidence, lateral displacement or tilting). Thin arrows: relative movement along fault planes and basal shear zones. Circle: tube location. Dots: volcano centre. (c) Map-views showing the variation of the cone topography detected by MDCT between times t1 and t0 (t1-t0), and between t2 and t1 (t2-t1), over a shaded relief image of the cone. Contour interval: 1 mm. Colour scale at right. Note how at t1 the entire flank delimited by the first fault has been displaced, subsiding at the summit area and bulging at the lower flank. At t2 two complementary deformation zones have developed inside the displaced block, and oblique to the first trend: a summit subsidence zone and a lower bulge delimited by the inward-dipping fault visible at t2.
