Volcanic Stratigraphy Southwest of the Active Crater

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Volcanic Stratigraphy Southwest of the Active Crater

Field photographs --- Summit photomosaic --- Summit crater photographs

The volcanic sequence exposed along the southwestern flank of Rincon de la Vieja volcano has been subdivided into four stratigraphic groups based primarily on the relative proportions of lava and tephra. The only stratigraphic division distinguished by a widespread unconformity is between Groups 1 and 2. Other unconformities exist but could not be correlated over a broad area.

In the geologic map shown above, the oldest deposits, Group 4, are dominated by voluminous two-pyroxene andesitic lavas. Lavas are increasingly less voluminous in Group 3 while intercalated tephra deposits increase in thickness. Tephra deposits dominate Group 2 volcanic products, although intercalated small-volume lavas are common. Group 1 deposits include the last major tephra deposit, the Rio Blanco tephra, and all subsequent tephra deposits erupted from the Active Crater. A schematic profile of the complete stratigraphic sequence shows the relative increase in tephra / lava through time.

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