Bulletin of Volcanology

, Volume 70, Issue 6, pp 655–673 | Cite as

The 2005 eruption of Sierra Negra volcano, Galápagos, Ecuador

  • Dennis J. Geist
  • Karen S. Harpp
  • Terry R. Naumann
  • Michael Poland
  • William W. Chadwick
  • Minard Hall
  • Erika Rader
Research Article


Sierra Negra volcano began erupting on 22 October 2005, after a repose of 26 years. A plume of ash and steam more than 13 km high accompanied the initial phase of the eruption and was quickly followed by a ~2-km-long curtain of lava fountains. The eruptive fissure opened inside the north rim of the caldera, on the opposite side of the caldera from an active fault system that experienced an mb 4.6 earthquake and ~84 cm of uplift on 16 April 2005. The main products of the eruption were an `a`a flow that ponded in the caldera and clastigenic lavas that flowed down the north flank. The `a`a flow grew in an unusual way. Once it had established most of its aerial extent, the interior of the flow was fed via a perched lava pond, causing inflation of the `a`a. This pressurized fluid interior then fed pahoehoe breakouts along the margins of the flow, many of which were subsequently overridden by `a`a, as the crust slowly spread from the center of the pond and tumbled over the pahoehoe. The curtain of lava fountains coalesced with time, and by day 4, only one vent was erupting. The effusion rate slowed from day 7 until the eruption’s end two days later on 30 October. Although the caldera floor had inflated by ~5 m since 1992, and the rate of inflation had accelerated since 2003, there was no transient deformation in the hours or days before the eruption. During the 8 days of the eruption, GPS and InSAR data show that the caldera floor deflated ~5 m, and the volcano contracted horizontally ~6 m. The total eruptive volume is estimated as being ~150×106 m3. The opening-phase tephra is more evolved than the eruptive products that followed. The compositional variation of tephra and lava sampled over the course of the eruption is attributed to eruption from a zoned sill that lies 2.1 km beneath the caldera floor.


Caldera Basalt Galápagos Tephra Lava flow emplacement Volcano deformation Magma chamber processes 



We would like to extend our thanks to the Galápagos National Park and the Charles Darwin Research Station, who made our observation of the Sierra Negra eruption possible, particularly Srs. O. Carvajal, W. Tapia, F. Cruz, and G. Watkins. We are also grateful to individuals who have provided us with images from the early phases of the eruption, including G. Estes, F. Cruz, and A. Voigt. Thanks to J. Normandeau of UNAVCO for his heroic patience in helping us get the GPS receivers working again during the eruption. This work was supported by NSF grants EAR-0207425 to KSH and EAR-0207605, 0538205, and 0004067 (which supported the installation of the GPS network) to DJG. ENVISAT ASAR data are copyrighted 2004–2006 by the European Space Agency, and were obtained via Category-1 Proposal 3493. Thanks to W. Tater for his help with the SEM. We thank B. Cousens and especially S. Rowland for review and J. Stix for his editorial help.


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Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  • Dennis J. Geist
    • 1
  • Karen S. Harpp
    • 2
  • Terry R. Naumann
    • 3
  • Michael Poland
    • 4
  • William W. Chadwick
    • 5
  • Minard Hall
    • 6
  • Erika Rader
    • 2
  1. 1.Department of Geological SciencesUniversity of Idaho 3022MoscowUSA
  2. 2.Geology DepartmentColgate UniversityHamiltonUSA
  3. 3.Geology DepartmentUniversity of AlaskaAnchorageUSA
  4. 4.USGS-HVOHawai’i National ParkUSA
  5. 5.Hatfield Marine Science CenterOregon State UniversityNewportUSA
  6. 6.Instituto GeofisicoEscuela Politecnica NacionalQuitoEcuador

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