Abstract

In the inner rift valley of the active spreading center within the Panama Basin, narrow lava plains occur between the axial ridge of pillow basalt (the central high) and the fault scarps of the inner walls. These nearly horizontal flows are decorated with small-scale forms typical of subaerial pahoehoe, although they are at a water depth of 2.5 km. In particular, large (1- to 4-m diameter) coils of ropy pahoehoe have been mapped during a deep-tow survey and are believed to mark shear zones at the edges of individual streams of mobile lava. Eruption of plain-forming pahoehoe probably modifies the magnetic signature as well as the geomorphology of the axial zone.

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