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Photographs of cracking and faulting that occurred below the surface during a series of experiments designed to simulate the intusion of magma along a dike. The dark area at the bottom of image is the dike. The dark layers are corn meal and light layers consist of a 3:1 mixutre by volume of granualted sugar and white flour. Obvious cracks (solid black lines) and less obvious cracks (dashed lines) were mapped during the experiment. Note scale in lower right of photographs (2 cm scale). The solid black line at the top of each photograph represents the original location of the surface before the experiment began.
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As fissures form at the surface (location a), indistinct vertical fractures and zones of disaggregation develop below the surface around the tip of the dike (location b). |
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Growth of shallow trough (called a syncline) directly above the dike plane and surface fissures along the limbs of the trough. Subsurface fractures develop (locations c and d) as vertical movement begins to occur. |
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Vertical movement along faults increases as fractures in adjacent layers are connected (location e) and fissures at the surface are connected to subsurface fractures (location f). Near the base of the faults, vertical movement is distributed within a braod zone of shearing and extension along the limbs of the syncline above the dike. |
