Transcript FLIR El Salvador, March 2008

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
AGU Fall Meeting
18 December 2008
Photo courtesy of La Prensa Gráfica
Santa Ana volcanic complex, El Salvador
Courtesy of USGS
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].
2005 eruptive crisis &
phreatic eruption
1 Oct. 2005
late Aug. 2005
Courtesy of El Diaro del Hoy
Eruption column to ~14km altitude
Courtesy of La Prensa Gráfica
Incandescent fumaroles—not magma (!)
Courtesy of SNET
Hot acidic lahar
Santa Ana crater
Before
3 Feb 2001
Orthorectified
ASTER image
31 August 2005
Courtesy of El Diaro del Hoy
After
28 June 2007
4 Feb 2007
Orthorectified
ASTER image
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
short-range precursors (weeks)
Hydrothermal activity
Aug & Sep 2005
1 Oct 2005 eruption
Oct 2005 – 2007
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
Comparison to other crater lakes
Lake
Name
Lake
Type
Representative Values
Temp.
pH
Size
(radius)
Power
Output
Eruption History
Santa Ana high activity,
pre-2005
cool acid
brine
16-30ºC 0.7 to
2
100 m
0.5-20
MW
Phreatic eruption Oct
2005.
Yugama,
Kusatsu
Shirane
8-33ºC
135 m
3-25
MW
Phreatic eruptions; cool
between eruption; hot
before and after
eruptions.
high activity,
cool acid
brine
1 to
1.8
Santa Ana peak activity/ 25-65ºC 0.4 to
post-2005 variable mass
1.2
Laguna
Caliente,
Poas
<100m 13-830
MW
peak activity/ 38-96ºC -0.87
140 m
variable mass
to 0.26
150-550
MW
Volcanic lake classification based on Varekamp et al. (2000).
Upwelling, several
lake evaporations &
minor phreatic eruption.
Phreatic activity, lake
disappears in April
1989 and liquid sulfur
pools form.
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.
Conclusions
• 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.
Acknowledgements
Funding Sources:
Dept. of Geological & Mining Eng. & Sciences, Michigan Tech Univ.
National Science Foundation
OISE & PIRE 0530109
EAR 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 University
Dr. Joop Varekamp
Servicio Nacional de Estudios Territoriales
Demetrio Escobar, Eduardo Gutierrez, Francisco Montalvo
Universidad de El Salvador
Rodolfo Olmos & students
LaGeo S.A. de C.V.
Carlos Pullinger, Marvin Garcia