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Aerial Photomosaic of the Western Summit Region
photomosaic compiled from 1:35,000 USAF aerial photographs, taken in 1977.
An extraordinary feature at Rincon de la Vieja is a triangular-shaped dead zone (zone of devegetation SW of the Active Crater) delineated by the yellow line on the above photomosaic. Barren, steep-walled canyons in this area provide unusual access to the prehistoric eruptive deposits of the volcano. The dead zone is formed by acid rains, which are produced by the mixing of steady ENE prevailing trade winds and acidic vapors rising from the Active Crater. The high degree of erosion in the dead zone and historical records of activity indicate that this process has been ongoing for several centuries.
The last major eruption at Rincon occurred at approximately 3500 ybp and formed the Rio Blanco tephra deposit. In the photomosaic above, this deposit blankets the Von Seebach cone, the West Crater, and many of the ridges in the dead zone. The Active Crater is interpreted as the eruptive source of this deposit.
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