Abstract.
The crater lake of Licancabur Volcano (2250’S, 6753’W) is the highest lake on Earth.
As an end-member in terms of the physical environment on Earth where lakes and liquid
water are stable, the site is of considerable interest in terrestrial limnology, biology, and
volcanology. It is also believed that by studying the environment and biota in this arid,
high-UV, low pressure, low temperature environment, we may be able to better target our
search for potentially habitable (or once-habitable) environments and for life elsewhere in
the solar system.
In particular, hydrothermal systems on Mars may have provided a source of heat energy
and liquid water in an environment otherwise ill suited for life. In order to: a)
quantitatively characterize this unique terrestrial environment for the first time, and b)
develop the analogy to ancient lacustrine environments on Mars, we present an
investigation of the hypothesis that the Licancabur Volcano crater lake is supported by a
deep magmatic hydrothermal system.
Basic geophysical models of mass- and energy-balance show that lake stability requires
additional fluid and heat influx of approximately 6.74 m3/day and 1.81106 W,
respectively. Ion Chromatography (IC) and Inductively Coupled Mass Spectrometry
(ICP-MS) of water samples show that the summit lake is enriched in some major rock
forming elements (e.g. Na, K, Mg, Ca, Al, Fe) compared with local meteoric and
geothermal spring waters. The bulk properties of the lake, as well as the aforementioned
geophysical and geochemical analyses continue to lead us toward the conclusion that the
Licancabur Volcano crater lake is a low-activity volcanic lake, which is supported by a
small geothermal heating term and may host a diffuse hydrothermal system.
Background.
1. Volcanic Lakes.
Often sitting within an actively degassing crater, volcanic lakes host unique
physical, chemical, and biological environments and serve as reservoirs for
volcanic heat, fluids, and volatiles (Figure 1). However, only 16% of young
terrestrial volcanoes contain a lake according to the Catalog of Active Volcanoes
of the World due to the energetically and hydrologically unstable niche they
reside in. The small lake at the summit of Volcan Licancabur has seen only a few
recorded scientific expeditions, and remains one of the least explored places on
Earth.
2. Licancabur.
Volcan Licancabur is located at 2250’S latitude by 6753’W longitude on the
southwest border of Bolivia with Chile (Figure 2A). Its simple conical structure
(Fig 2B) interrupts the surrounding altiplano with a 1500 m edifice, post-glacial
lava flows and minor pyroclastic deposits (Marinovic and Lahsen 1984). The
area at the base of the volcano (~4300 m elevation) is geothermally active, with
springs ranging from ~17-37 C and hypersaline lagunas. The summit at ~6000
m above sea level houses a small crater lake, which is currently the highest in the
world at 5867 m (Fig. 2C). Due to the decreased atmospheric pressure (~ 430
mb), increased UV flux (~85 W/m2), and arid climate (< 200mm precipitation/yr),
this region and the surrounding terrain are excellent terrestrial analogs to ancient
Mars.
This work focuses on supporting or refuting the hypothesis that the summit lake is
supported (energetically and hydrologically) by a magmatic hydrothermal system.
Previously, in situ measurements (Hock et al 2002) showed that the surface water
at the summit lake has near-neutral pH, and dissolved solids content similar or
less than typical fresh water reservoirs. However, the measured values
(Tsurface~4.9°C, pH~8.5, and TDS~0.1%) also fit the classification (as per
Pasternack and Varekamp 1997) of a “low-activity” volcanic lake, with a diffuse
hydrothermal input. The first motivation for this work is to gain a better
understanding of the physical processes at work within the lake that may constrain
endemic biology. Second, hydrothermal environments associated with volcanism
on Earth and Mars (Farmer 1996) are particularly interesting because they are
likely sites for the early evolution of life (Shock 1996); therein, an associated
motivation of this study is to extend and quantify the analogy between this site
and hydrothermal systems (e.g. paleolakes, hot springs, and impact crater lakes)
on Mars.
Physical Classification.
1. Temperature of maximum density.
A high-altitude diving expedition measured the temperature of the summit lake’s
bottom waters at ~4 m depth to be 6 °C (Leach 1984). However, calculation of
the temperature of maximum density for freshwater using the adiabatic and
isothermal compressibility (as per Eklund 1983) suggests that bottom waters
should be no warmer than 4 °C. This discrepancy suggests that we seek out an
explanation for the lake’s anomalous warmth.
2. Mass and energy balance.
Following Pasternack and Varekamp (1997), we assume that a volcanic lake in
equilibrium will obey the following simplified hydrologic mass
Wvolc + Wmet = Wevap + Wout + Wseep
and energy
Evolc + Esw + Elw = Erad + Eevap + Econd +Emet
balance equations. We set out to model the system at Licancabur by solving these
equations for the net mass and energy flux, treating Wvolc—the magmatic
hydrothermal fluid influx—and Evolc—the combined volcanic
conductive/hydrothermal energy flux—as unknowns. Briefly, the other terms
(illustrated in the energy balance box model, Figure 3):
* mass flux reported in m3 H2O/day; energy flux in W.
 Wmet – meteoric water flux in to the lake. Annual precipitation in the Chilean
Altiplano is typically less than 200 mm per year (Nunez et al. 2002).
 Wevap – evaporative loss.

Wout – comprised of runoff and overflow. Assumed zero here, as there are no
topographic outlets from the summit lake.
 Wseep – seepage through the bottom sediments of the crater lake; often a
nonzero term due to fractured volcanic bedrock, but set to zero for a
conservative first analysis.
 Esw, Elw – short wave solar flux and long wave radiation from the
atmosphere: functions of latitude and cloud cover from Linacre (1992).
 Erad – thermal blackbody radiation from the lake (T~4.9 C) surface.
 Eevap, Econd – evaporative energy loss from lake surface and sensible heat
loss from water vapor to the atmosphere. Average wind speed in the crater
was estimated at ~6.7 m/s, and for the average air temperature (from Linacre
1992) of –12.6 C, ice saturation water vapor pressure (Buck 1981) was used.
 Emet – heat flux required to bring local precipitation/runoff to the temperature
of lake waters. As a first-order assumption, we allowed all precipitation at the
summit to be liquid water; future work will account for the latent heat of
melting snowfall.
Results from this model are presented in Table 1, below.
Chemical Classification.
Water samples were taken from several geothermal springs, two saline lagunas, as well as
the summit lake for chemical analysis. Inductively-Coupled Mass Spectrometry (ICPMS, Activation Laboratories, Tucson, AZ, USA) was employed to determine elemental
concentrations across much of the periodic table to the ppb level, and Ion
Chromatography (IC) was used to determine anion (F-, Cl-, NO2-, NO3-, PO4--, SO4--)
concentrations to the ppm level (as per EPA method 300.0). Results from this work are
presented in Table 2, below.
References.
Buck 1981. J. Atmos. Sci., 20, 1527.
de Silva S.L. and P.W. Francis 1991. Volcanoes of the Central Andes, SpringerVerlag:Berlin.
Eklund H. 1963. Science, 142, 1457.
Farmer J.D. 1996. in Evolution of Hydrothermal Ecosystems on Earth (and Mars?), John
Wiley & Sons:Chichester.
Leach J.W.P. 1986. Underwater Technology, 12, 27.
Marinovic N. and A. Lahsen 1984. Carta Geologica de Chile, no. 58. SNGM, Santiago.
Nunez L., M. Grosjean, and I. Cartajena 2002. Science, 298, 821.
Pasternack G.B. and J.C. Varekamp 1997. Bull. Volcanol., 58, 528.
Shock E.L. 1996. in Evolution of Hydrothermal Ecosystems on Earth (and Mars?), John
Wiley & Sons:Chichester.
Varekamp J.C., G.B. Pasternack, and G.L. Rowe, Jr. 2000. J. Volc. Geoth. Res., 97, 161.
Acknowledgements.
First thanks go to all members of the 2002 Licancabur Expedition Team, listed
individually below. Training and time on the Ion Chromatograph were kindly made
available by Edward Ruth and Dr. Sim Lin Lau, Department of Civil and Environmental
Engineering, UCLA. ICP-MS samples were run by Craig Hansen, Actlabs, inc.
Affiliations. The 2002 Licancabur Expedition Team is: Guillermo Chong4, Christopher
P. McKay2, Marcus Murbach2, E. Imre Friedmann2, Cecilia Demargasso4, Roseli
Friedmann2, Keeve Kiss5, Istvan Grigorsky6, Brian H. Grigsby7, Edna DeVore8, Lorena
Escudero4, and Cristian Tambley4.
1
Dept. of Earth and Space Sciences, UCLA, Los Angeles, CA 90095-1567 and the NASA
Ames GSRP. 2Space Sciences Division, NASA Ames Research Center, Moffett Field,
CA. 3Earth Resources Laboratory, MIT, Cambridge, MA. 4Universidad Catolica del
Norte, Chile. 5Hungarian Academy of Sciences, Hungary. 6Kossuth Lajos University,
Hungary. 7Project ARISE, Shasta Co., CA. 8SETI Institute, Mountain View, CA.
*to whom correspondence should be addressed: e-mail: ahock@ucla.edu