Structures controlling volcanic activity within Masaya caldera, Nicaragua

Geophysical and geological observations collected in 2007-2012 shed light on the mechanisms controlling thestyle and location of eruptions within the Las Sierras-Masaya Caldera complex, Nicaragua. These results confirm ahypothesised∼3.5 km diameter structure with features compatible with the presence of a ring fracture (50–65°, withinward-dipping bounding walls). A central block is bound by this fracture and defines an incipient nested calderarelated to the emptying of the magma chamber following the last Plinian eruption (1.8 ka). The prolongation of theCofradías fault from the Managua graben represents the most significant structure on the floor of Masaya caldera.Current activity, including a convecting lava lake, largely depends on the interplay between the extensional stressregime associated with the Managua graben and deformation along the inner caldera bounding fault. This highspatial resolution survey uses a novel combination of geophysical methodologies to identify previously overlookedfoci for future volcanic activity at Masaya