Bulletin of Volcanology

, Volume 50, Issue 2, pp 86–105 | Cite as

Structural, stratigraphic, and petrologic aspects of the Arenal-Chato volcanic system, Costa Rica: Evolution of a young stratovolcanic complex

  • Andrea Borgia
  • Clark Poore
  • Michael J. Carr
  • William G. Melson
  • Guillermo E. Alvarado


Geologic mapping on a scale of 1:10000 and detailed stratigraphic studies of lava flows and tephra deposits of the Arenal-Chato volcanic system reveal a complex and cyclic volcanic history. This cyclicity provides insight into the evolution of magma batches during the growth of the andesitic volcanic system. The Arenal and Chato volcanoes have a central zone comprised of a lava armor and a distal zone comprised of a tephra apron. During Arenal's last two eruptive periods major craters formed near intersections of regional fractures at the lava armortephra apron transition. We suggest that such intersections are potential sites for future major explosions. The earliest rocks, i.e., the Chato lava flows, range in composition from basaltic andesite to andesite. These rocks, except for the andesitic domes of Chatito and La Espina, appear to have evolved from a common parental magma. The last active period of Chato volcano occurred 3550 B. P. The earliest known activity of Arenal volcano is 2900 B. P. Arenal lava flows have 54–56 wt% SiO2 and may be subdivided into a high-alumina group (HAG, Al2O3 = 20 wt%) and a low-alumina group (LAG, Al2O3 = 19 wt%). Compared to the HAG, the LAG also has smaller amounts of incompatible elements and higher amounts of FeO and MgO. Arenal tephra deposits were emplaced by Plinian-Sub-Plinian explosions occurring at 300±150-yr intervals. These deposits are compositionally zoned and alternate between dacite and basalt. The stratigraphy reveals an apparent magmatic cycle consisting of (a) dacitic-andesitic tephra, (b) HAG lava flows, (c) LAG lava flows, and (d) andesitic-basaltic tephra. This magmatic cycle is repeated four times during Arenal's history and is interpreted to have developed by the crystal fractionation and crystal redistribution of a single magma batch. The period of this cycle, and consequently the “life” of a magma batch, is about 800 years. If the cyclic pattern continues, a basaltic explosive phase may occur in the next 250 years.


Tephra Lava Flow Basaltic Andesite Tephra Deposit Magma Batch 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1988

Authors and Affiliations

  • Andrea Borgia
    • 1
  • Clark Poore
    • 2
  • Michael J. Carr
    • 3
  • William G. Melson
    • 4
  • Guillermo E. Alvarado
    • 5
  1. 1.Centro de Investigaciones GeofisicasUniversidad de Costa RicaCosta Rica
  2. 2.Department of GeologyOklahoma State UniversityStillwaterUSA
  3. 3.Department of Geological SciencesRutgers UniversityNew BrunswickUSA
  4. 4.Division of Petrology and VolcanologySmithsonian InstitutionWashington, D. C.USA
  5. 5.Departamento de GeologiaInstituto Costarricense de ElectricidadSan JoseCosta Rica

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