Download - AGU Fall Meeting 18 December 2008
AGU Fall Meeting18 December 2008 Photo courtesy of La Prensa Gráfica
Crater lake evolution during volcanic unrest: case study of the 2005 eruption
at Santa Ana volcano, El Salvador.
Anna Colvin, Bill Rose, Demetrio Escobar, Eduardo Gutierrez, Francisco Montalvo, Rodolfo Olmos, Joop Varekamp, Matt
Patrick, & Jose Luis Palma
Santa Ana volcanic complex, El Salvador
Most active volcano in El Salvador
High risk: 1 million people live within a 25 km radius (17% total population of El Salvador) [Pullinger, 1998], [DIGESTYC, 2008].
Courtesy of USGS
2005 eruptive crisis &phreatic eruption
Incandescent fumaroles—not magma (!)
Hot acidic lahar
Eruption column to ~14km altitude
1 Oct. 2005
late Aug. 2005
Courtesy of La Prensa Gráfica
Courtesy of SNET
Courtesy of El Diaro del Hoy
Santa Ana crater
4 Feb 2007Orthorectified ASTER image
After28 June 2007
Before31 August 2005
3 Feb 2001
Orthorectified
ASTER image
Courtesy of El Diaro del Hoy
Crater lake evolution, 2000-2007
Low level activity early 2000
[Bernard et al., 2004]
Hydrothermal activity May 2000 - Feb 2002
[Bernard et al., 2004]
Low level activity Feb 2002 - Jun 2004
Hydrothermal activity Jun 2004 - Aug 2005
long-range precursors (months) Fumarolic activity Aug & Sep 2005
short-range precursors (weeks) Hydrothermal activity Oct 2005 – 2007
1 Oct 2005 eruption
Geochemical trends
Seismic and gas flux trends
Relative contributions to degassing from lake and fumaroles
Pre-2005:
Majority of degassing escapes through subaerial fumaroles
Post-2005:
Sulfur scrubbing by precipitation of native sulfur
Schematic model:
Post-eruption
Sulfur spherules
LakeName
Lake Type
Representative Values
Temp. pHSize
(radius)
Power Output
Eruption History
Santa Ana pre-2005
high activity,cool acid brine
16-30ºC 0.7 to 2
100 m 0.5-20 MW
Phreatic eruption Oct 2005.
Yugama, KusatsuShirane
high activity, cool acid brine
8-33ºC 1 to 1.8
135 m 3-25MW
Phreatic eruptions; cool between eruption; hot before and aftereruptions.
Santa Ana post-2005
peak activity/variable mass
25-65ºC 0.4 to 1.2
<100m 13-830MW
Upwelling, several lake evaporations & minor phreatic eruption.
Laguna Caliente, Poas
peak activity/ variable mass
38-96ºC -0.87 to 0.26
140 m 150-550MW
Phreatic activity, lake disappears in April 1989 and liquid sulfur pools form.
Comparison to other crater lakes
Volcanic lake classification based on Varekamp et al. (2000).
Conclusions
• Analysis of crater lake evolution 2000-2007 & integration with gas emission and seismic data has allowed for identification of eruption precursors and interpretation of a possible eruption triggering mechanism.
• Long-range precursors (Jun 2004-Aug 2005): — crater lake warming, LP seismicity, geochemical
constancy.
• Short-range precursors (Aug & Sept 2005):— fumarole incandescence, high gas emissions, VT
swarms, banded tremor.
• Likely eruption triggering mechanism: magmatic intrusion does not reach the surface but induces overpressure in the hydrothermal system and triggers a phreatic eruption.
• On-going intrusion (?) more plausible with sustained high lake temperatures and may yet trigger a phreatomagmatic/magmatic eruption.
• Satellite & ground-based remote sensing will be vital for future monitoring.
Conclusions
AcknowledgementsFunding Sources:Dept. of Geological & Mining Eng. & Sciences, Michigan Tech Univ.National Science Foundation
OISE & PIRE 0530109EAR 0732632
DeVlieg Foundation Fellowship
Collaborations:Michigan Technological University
Dr. Bill Rose, Dr. Matt Patrick (now at USGS/HVO), Dr. Ann Maclean, Dr. John Gierke, Dr. Jose Luis Palma,Dr. George Robinson, RS4Haz graduate students
Wesleyan UniversityDr. Joop Varekamp
Servicio Nacional de Estudios TerritorialesDemetrio Escobar, Eduardo Gutierrez, Francisco Montalvo
Universidad de El SalvadorRodolfo Olmos & students
LaGeo S.A. de C.V.Carlos Pullinger, Marvin Garcia