Early Holocene Edifice Failure And Sector Collapse of Volcán Barú, Panama

What: This research project will use a multidisciplinary approach to investigate the early Holocene eruption and sector collapse of Volcan Barú which may have produced up to 100km3 of ejected material – possibly one of the largest Holocene collapses in the Western Hemisphere. However, there may be multiple collapses extending back into the Pleistocene, confounding volume estimates. Our work will utilize geologic mapping, volcanic stratigraphy, geochemical analyses and radiometric dating to explore the eruptive history of this volcano.

When: July 1-30

Where: Volcan, Panama; in western Panama along the Costa Rica border.

Who: 3 students; Project Director: Thomas Gardner (Trinity University) Project Assistant: Kristin Morell (Penn State)

Project Description and Goals

Many of us do not associate Panama with impressively large, active volcanoes, perhaps because no historic eruptions have occurred in Panama. Thus, there are no newsworthy images of Panamanian eruptions as are common from other volcanoes within the “Pacific Ring of Fire”. Despite this fact, it appears that Panama may have played host to one of the largest edifice and sector collapses in Central America during the Holocene. It has been hypothesized that Volcán Barú experienced an early Holocene or Late Pleistocene eruption with estimates of ejected material ranging from ~25 km3 to ~100 km3. Debris-avalanche deposits and lahars extend as much as 90 km away from the collapsed edifice, reaching the Pacific Ocean. Our recent preliminary mapping and dating of these deposits tightly constrains the age of this eruption to between ~8.7 ka and ~9.2 ka. However, our recent mapping also indicates that there have probably been multiple Quaternary eruptive events that confound volume estimates for the early Holocene eruption. Volcán Barú lies along a complex plate boundary inboard of the Panama Triple Junction (PTJ) located in southern Central America, near the border with Panama and Costa Rica (Fig. 2). The evolution of the PTJ has controlled, to a large degree, the eruptive history of Volcán Barú throughout the last ~3 Ma.

The active volcanic arc of Central America continues unbroken from Guatemala to central Costa Rica. However, the last active volcano in Costa Rica is Volcán Turrialba. Southeast of Volcán Turrialba and inboard of the Cocos Ridge, the arc is extinct and ~8-10 Ma granitic plutons that formed the core of the old volcanic arc [de Boer et al., 1995;] are exposed in the highest range on the Central American isthmus, the Cordillera de Talamanca (Fig. 2). Southeast of the PFZ and the PTJ, active volcanism resumes at Volcán Barú (Fig. 2) which has not erupted in historic times, but it is an “active” volcano. There have been 4 eruptive episodes within the last 1300 years (Sherrod et al., 2007) consisting of small lapilli and ash eruptions with accompanying pyroclastic surges. Compositionally these eruptions are andesite to basaltic andesite with minor dacite. The most recent eruptive episode occurred between 420 and 540 cal yr BP. There was an earthquake swarm under the volcano several years ago.

Field mapping on the southern flank of Barú has identified an eruption that produced debris – avalanche and lahar deposits (Siebert et al., 2006, Sherrod et al., 2007, Frels, 2008) that are spectacular in their estimated volumes and extent (Fig. 3). Volume estimates range from ~25 – ~30 km3 for the debris avalanche deposits (Siebert et al., 2006; Sherrod et al., 2007) to as much as 60 – 100 km3 for the combined debris – avalanche and lahar deposits (Fig. 3a; Sherrod et al., 2007; Frels, 2008). Restoration of inferred pre-failure contours within the ~45 km2 avalanche at Barú suggests that the pre-failure summit could have reached ~4000 m elevation and that as much as 30 km3 may have collapsed (Siebert et al., 2004).

Our most recent field mapping and dating indicates that these deposits may be very tightly constrained to between 8.7 -9.2 ka. Importantly, we have recently identified two older lahars and debris avalanche deposits, one around 40 ka and another > ~45 ka that will complicate mapping, but may explain the large volume estimates for the early Holocene eruption.

There will be an extensive radiocarbon dating campaign in this project that will attempt to tightly constrain the ages of the 2 youngest eruptive events. To help constrain the eruptive history that exceeds ~>45 ka, we have 13 samples undergoing analysis for Ar-Ar ages. We will use standard geochemical analyses of major and trace element and HREE’s to see if there are any significant chemical differences that may help distinguish different age deposits or possibly deposits from different eruptive centers, Fabrega or Cerro Pecon (Fig. 2). We will sample lahar and debris-avalanche matrix if thin sections show that eruptive components, such as euhedra crystals, welded ash or pumice fragments are present.

This summer research project has two main goals. First, we will describe and map the facies, composition (field descriptions), internal relationships, and extent of the volcanic deposits. Second, we will undertake extensive petrographic and geochemical analyses, supplemented by a radiometric dating campaign. These analyses will allow us to determine the Quaternary eruptive history of the Barú volcano, and the synchroniety of the volcanic deposits. More specifically, we will determine if the deposits originated from the same “early Holocene eruption” or from multiple Quaternary eruptions.

Student Projects

Three students will be engaged in this month-long, summer research effort. All three projects have flexibility to develop in numerous directions to accommodate student interests.

  • Edifice area: One project will involve fieldwork in the region proximal to the eruptive center (Fig 3a). Here we hope to obtain fresh samples of datable (Ar-Ar) volcanic rocks that may help constrain the older eruptive phase (s). We will also be able to map in detail the proximal facies of the early Holocene debris avalanche deposits and the structural features of the sector collapse of the edifice (Fig. 4a and b).
  • Lahar plain: A second project will study the lahar plain (Fig 3b) which extends from the southern flank of the edifice to the Carretera Interamericana and probably to the Pacific Ocean. The lahars are very well exposed in construction sites at a new dam and hydroelectric plant on the Río Piedra (Fig. 4f). Important exposures also occur along other major river valleys throughout the lahar plain. We plan to collect numerous samples for radiocarbon dating and petrographic/geochemical analysis. We want to determine if all of the lahars are coeval with the debris avalanche and attempt to estimate the contribution from fresh magmatic material in the lahars. We will also describe detailed stratigraphic sections for facies analysis and volume estimates.
  • Debris-Avalanche deposits: The third project will explore the intriguing debris – avalanche deposits (Fig. 4c, d, and e) which extend from the edifice region to the Pacific Ocean and possibly the Burica Peninsula. There are superb exposures in a new hydroelectric project on the Río Chiriquí Viejo that offer unprecedented access to the medial portion of the debris – avalanche. Additionally, there are numerous active quarries that are used for road and construction materials. Our approach here will be similar to the lahar plain.

Field Conditions

Panama is a tropical rain forest, except where deforested. July is the early part of the rainy season, so it will rain some days, a lot some days! There will be thunderstorms and fog some days. The sun will shine brightly with incredibly blue sky some days. There will be double and triple rainbows!!! Near the volcanic edifice at 2000-3000 m it can get damp and cool. Down near sea level it will be humid and hot. So we will experience a variety of weather conditions, to say the least.

Weathering profiles are deep and clay-rich. It will be muddy in some places. We will be hiking up streams far from civilization on some days. The solitude can be awesome. Insects and all kinds of crazy critter love to live there. I won’t even mention snakes!! If that makes you squeamish, then this may not be for you. We will be working on road outcrops and in hydroelectric plant construction sites. Maybe we’ll go white water rafting on a day off! I’ve done that and it’s a wild ride.

Course Preparation:

  • Required: Geomorphology or equivalent; Earth Materials or equivalent;
  • Recommended: Volcanology or Stratigraphy or Spanish

References

  • de Boer, J. Z., M. J. Defant, R. H. Stewart, J. F. Restrepo, L. F. Clark, and A. H. Ramirez (1988), Quaternary calc-alkaline volcanism in western Panama; regional variation and implication for the plate tectonic framework, Journal of South American Earth Sciences, 1, 275-293.
  • de Boer, J. Z., M. Drummond, M. Bordelon, M. Defant, H. Bellon, R. Maury (1995), Cenozoic magmatic phases of the Costa Rican island arc (Cordillera de Talamanca), in Geologic and tectonic development of the Caribbean Plate boundary in southern Central America, edited by P. Mann, pp. 131-157, Geological Society of America Special Paper 295, Boulder, Colorado.
  • Frels, Jason (2009), Thrust Belt Propagation in Response to Panama Triple Junction Migration, Southwest Panama, 36p, Bachelor’s Thesis, Trinity University. Instituto de Recursos Hidraulicos y Electrificacion (IRHE), 1987, Final report on the reconnaissance study of geothermal resources in the Republic of Panama: Instituto de Recursos Hidraulicos y Electrificacion-Inter-American Development Bank-Organización Latinoamericana de Energía (IRHE-IDB-OLADE), 72 p.
  • Sherrod, D.R., Vallance, J. W., Espinosa, A. T., and McGeehin, J. P. (2007), Volcán Barú – Eruptive History and Volcano-Hazards Assessment. Open File Report 2007- 1401, 33 p.
  • Siebert, L., Kimberly, P., and Pullinger, C.P. (2004), The voluminous Acajutla debris avalanche from Santa Ana volcano, western El Salvador, and comparison with other Central American edifice-failure events, in Rose, W.I., Bommer, J.J., Lopez, D.L., Carr, M.L., and Major, J.J., eds., Natural hazards in El Salvador: Geological Society of America Special Paper 375, 5-23.
  • Siebert, L. Alvarado, G., Vallance, J., van Wwk de Vries (2006), Large – volume volcanic edifice failures in Central America and associated hazards, Geological Society of America Special Paper 412, 1-26

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