The internal structure of lava flows—insights from AMS measurements I: Near-vent a'a

摘要: Abstract Two small near-vent a'a flows (one from Xitle, Mexico and the other Mauna Kea, Hawaii) showing a conspicuous pattern of concentric vesicle foliation were used to investigate how anisotropy magnetic susceptibility (AMS) measurements relates internal structure lava flows. The results show an almost perfect match between plane containing maximum intermediate principal susceptibilities, or foliation. Both types can be explained by variations in relative magnitudes local shear stresses, assuming unidirectional velocity within attitude provides three-dimensional picture dynamic behavior flowing lava, might applicable also instances when no is observable. A strong imbrication occurs, marked distribution parallel family nested cones axis which coincides with flow axis, apices point down-flow. Flow having, at least part, stationary roof possessing yield strength consistent profiles inferred orientation foliations. model based on its fluid proposed explain origin AMS lava. At variance existing qualitative models, our allows semi-quantitative systematic explanation different circumstances under any direction.