Licancabur: Exploring the highest lake on Earth
Andrew N. Hock
Field Examination Written Proposal
10 October, 2003
This work proposes the continued study of the physical environment of the Licancabur
Volcano summit lake (22°50’S 67°53’W). At 5916 m above sea level, it is one of the highest
lakes on Earth, and persists despite annual precipitation of <200 mm y-1 and sub-freezing
average air temperature. In 1984, a high-altitude diving expedition measured an
anomalously warm bottom water temperature beneath ~80 cm of ice. We suggest that this
observation may be explained by a) solar heating of dense, mineralized bottom water or b)
the presence of a volcanic heat input. In the following, we present work from the 2002 field
season and outline the rationale and experiments for future work.
Introduction
Volcan Licancabur is located at 22°50’S latitude by 67°53’W longitude on the southwest
border of Bolivia with Chile (Figure 1). Its simple conical structure interrupts the surrounding
altiplano with a 1500 m edifice. Post-glacial lava flows and young pyroclastic deposits implicate
a geologically young age for this volcano, although there have been no eruptions in recorded
history (Marinovic and Lahsen 1984, de Silva and Francis 1991). The region at the base of the
volcano (~4300 m elevation) is still geothermally active, with springs ranging from ~17-37 °C
and hypersaline lagunas (Hock et al. 2002).
Fig. 1. Context images for Licancabur
Volcano, whose location is indicated
by the red triangle in (A). (B) shows
Licancabur to the right of its neighbor,
Volcan Juriques in the distance.
Some parts of the Bolivian Altiplano,
pictured here in the foreground, have
never seen precipitation in recorded
history. (C) is an image of the summit
lake of Licancabur, taken during the
austral spring of 2002. Note the clarity
and green color, as well as the fact
that there is no ice cover, despite the
predicted average air temperature of
nearly -13 centigrade. Map adapted
from de Silva and Francis (1991).
2
Motivation
At 5916 meters above sea level, the small crater lake of Licancabur Volcano is the
highest perennial lake on Earth and represents an end member of the spectrum of liquid water
habitats for life, but has been explored by only two widely reported scientific expeditions.
Rudolph (1955) conducted the first published expedition to the summit of Licancabur, as part of
a Geographical Review study of the area. They noted that the lake was unfrozen at the time of
their visit in the austral summer and suggested that it had once been deep enough to overflow
through the spillway at the southwest side of the crater (~130 feet above the lake’s current level,
visible in the upper portion of Fig. 1c). In November 1984, Leach and others sought the world
altitude record for SCUBA diving at the Licancabur crater lake. Despite an 80 cm ice cover,
their team measured the depth (4 m) and bottom water temperature (6 C) of the lake during their
dive. Delmelle and Bernard cite only the presence of the lake, and no chemical or physical data
exists to classify it with respect to other terrestrial volcanic lakes (Pasternack and Varekamp
1997, Varekamp et al. 2000). As such, this site represents a tremendous opportunity for
terrestrial limnology, volcanology, and biology. The results of this work will provide the first
thorough characterization of the physical environment at the Licancabur Volcano crater lake and
the surrounding environment.
Observations
The thermal condition of the lake is anomalous: most lakes above 5200 m on Chile’s
volcanoes are perennially frozen, and the average air temperature at the summit of Licancabur is
approximated to be –13 C (e.g. Rudolph 1955, Linacre 1992). The region receives less than
200 mm precipitation year-1 (Nunez 2002), yet the summit crater contains a ~90 m wide, ~4 m
deep lake which is ice-covered only part of the year. The predicted temperature of maximum
density for freshwater at that altitude is ~4 C (Eklund 1963), and if we take in to account the
salinity of the lake (Hock et al. 2002), the predicted temperature of maximum density is
depressed further to 3.74 C (Fig. 2). The source of this ~2 C temperature discrepancy is not
known. We suggest several hypotheses that may account for this difference, described in detail
below..873bar, not .4…?
1. 0015
1.001
1. 001
( 0  t  1 )
1000
Density [g/cc]
Densit y [g/cc ]
1. 0005
1
 ( 1. 05 t  0. 873)
1000
0. 9995
0. 999
0. 9985
0. 9982521618 0. 998
0.998
0
0
0
5
10
t
Temperature
[C]
Tem perat ure [C]
15
20
20
20
Fig. 2. Water density [g cc-1] as a function of salinity expressed in ~parts per thousand [ppt], temperature [C], and
pressure [bar] (from Gill 1982). The black curve represents the density of freshwater at sea level as a function of
temperature (zero salinity, 1 bar); a black arrow indicates the ~4.0 C temperature of maximum density for these
conditions. The blue curve represents the expected conditions within the Licancabur crater lake, where pressure ~
0.873 b at 5900 m altitude and lakewater salinity is ~1.05 ppt (Hock et al. 2002). The blue arrow indicates the
3
predicted temperature of maximum density there. Last, the red arrow indicates the 6 C bottom water temperature
measured by Leach (1986).
Hypotheses
The goal of our proposal is to provide a quantitative physical explanation for the
observed ~2 C water temperature anomaly of the Licancabur Volcano crater lake. Candidate
explanations for that observation are as follows:
 Measurement error – the measured temperature value is incorrect. According to Leach’s
1986 account, the temperature measurement was made under very difficult conditions.
Divers were on site to establish a world record for high altitude SCUBA, the bottom survey
was limited by an ~80 cm ice cover, and no information is given as to the accuracy of the
depth or temperature measurement.

Heliothermic – saline bottom waters are heated by direct insolation and radiative cooling of
bottom sediments. Fluid may acquire increased salinity (and thereby density) by several
mechanisms: a) groundwater interaction with soil, b) direct diffusion of solutes in to lake
waters through bottom sediments, c) leaching of salts in to surface waters below a developing
ice cover, d) input from a saline water source (e.g. saline springs, streams, etc.; Wetzel 2001).
These salty waters flow by density gradients to deeper portions of the lake, where thermaldensity instability (mixing) is prevented by the resulting salinity and density gradient (Fig.
3).
a
b
ρS=1.05=1.00086
ρS=1.05=1.00082
ρS=2.0=1.002
Fig. 3. Hypothetical temperature profiles for lake waters under a 0 C ice cover. Calculated values in black represent
the density of water at the given temperature and salinity—for example ρS=1.05 in (a) is the density of water with 1.05
parts per thousand (ppt) salt content at ~4 C. (a) Heliothermy: relatively fresh water (1.05 ppt) beneath the ice cover
is warmed to its temperature of maximum density and mixes freely in the upper water column. Salty (2.0 ppt) bottom
water is isolated by a chemical density gradient and heated by radiative cooling of shallow bottom sediments; the
density increase due to salinity in this case outweighs the density decrease due to thermal buoyancy and the bottom
water remains stagnant, as compared to (b), a well-mixed case.
It is not unusual for bottom water temperature to exceed the predicted temperature of
maximum density in these systems (Wetzel 2001). One example of this process is Hot Lake,
Washington, whose bottom waters at 2-3 m depth are heated to nearly 30 C despite subfreezing air temperatures and a thin seasonal ice cover (after Anderson 1958). A minor
increase in salinity could account for the observed temperature anomaly. Water at 6 C
becomes more dense than freshwater at 4 C by the addition of only 0.05 parts per thousand
(ppt) salt.
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
Volcanic hydrothermal – the lake waters are heated above that predicted by the temperature
of maximum density either by the conductive input from a shallow magma body or by the
enthalpy of volcanic hydrothermal fluid input. Fig. 4 illustrates the major physical processes
occurring in two hypothetical scenarios. Fig. 4a is a typical freshwater reservoir, with no
volcanic input, while the lake in Fig. 4b is the surface manifestation of a volcanic
hydrothermal system, where heating is a function of volcanic activity (e.g. Brown et al.
1991). We propose that the physical processes occurring at Licancabur place it between
these two end member scenarios: we do not observe any fumaroles or direct outgassing from
the volcano and the lake is not a hot, acidic brine (e.g. the crater lakes of Keli Mutu,
Indonesia; Varekamp and Rowe 1997), yet we do observe a ~2 C anomaly and active
geothermal springs at the base of the volcano (Hock et al. 2002).
To the first order, a small volcanic input may explain the observed thermal anomaly. If we
approximate the lake volume by an elliptic sinusoid (Wetzel 2001) with maximum depth of 4
m (Leach 1986), then heating the entire volume of the lake by 2 C requires ~70000 MJ of
energy. If we then assume that Licancabur (surface ≈ 5000 m2) receives the same amount of
volcanic input per unit area as Crater Lake, Oregon ~0.2-0.6 W m-2 (Delmelle and Bernard
2000), we find that the average volcanic input of 1-3 MW would supply the required energy
in < 1 day.
a
b
Fig. 4. Schematic diagram of (a) dominant physical processes of a simple freshwater reservoir: blue
terms indicate mass flux, while yellow and red arrows indicate energy flux. (b) physical processes that
may occur in a volcanic hydrothermal system: additional heating of the lake may occur through
conduction or by influx of hot fluids and gases.
Research tasks
We propose three lines of investigation: 1) Analyze the chemical and physical properties
of the water column, including basic water chemistry and temperature as a function of depth. 2)
Determine conductive heat flow through the lake bottom sediments. 3) Develop a mass and
energy balance model for the lake; acquire field data to validate and constrain the model. The
objectives, experiments, and requirements of our proposed research are described below. Table
1 illustrates the relevance of this work as it pertains to the hypotheses developed earlier.
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Task
Hypothesis
Measurement error
Heliothermic
Volcanic
Water column
analysis
Conductive heat
flow
Mass, energy
balance
T(zmax): ~4 °C
T(zmax): ~6 °C
S(z): salinity-based
stratification
S(z): well mixed.
Low bottom water
salinity
n/a
n/a
Seasonallydependent heat flow
Heat flow sufficient
to drive water
column convection
n/a
Isothermal T(z)
Elevated heat flow
Low heat flow w/o
observed thermal
fluid input
Volcanic inputs as
unknowns…
Net outflow
No determinable net
flow, net inflow
Acidic bottom water
T(z): increase
without mixing
Table 1. Analysis matrix. Three candidate hypotheses for the temperature anomaly versus the three lines of
proposed research described below. In the body of the table, green type indicates a potential supporting result, while
red type indicates a result that would argue against the hypothesis indicated. For the water column task, T(zmax) is
the water temperature at maximum depth, S(z) is salinity as a function of depth, and T(z) is water temperature as a
function of depth. For example, if a measurement of bottom water temperature gives ~4 C, it would support the
measurement error hypothesis.
Water column analysis
We will perform several analyses as a function of depth in the water column to provide
redundant data on previous measurements, investigate mixing processes in the water column, and
search for evidence of hydrothermal fluid input to the lake’s bottom waters. The following
experiments will be performed:
 Temperature. We will measure water temperature at the surface, and as a function of depth;
dataloggers will be installed at different depths in the lake to monitor the time-dependent
variation of water temperature. If the lake is heliothermic, the upper water column will
remain isothermal for periods of time while a temperature gradient will be established below
a gradient in salinity. If not, we will likely observe mixing to depth once or more throughout
the year. In turn, the volcanic hydrothermal hypothesis will be supported if the lake is well
mixed throughout the year—in particular if the entire water column in winter is isothermal
and warmer than expected under the ice. Frequent surface water temperature data will also
allow us to determine the presence and longevity of ice cover.
 Salinity. Measurements of salinity as a function of water depth will be taken and used to
recalculate the predicted temperature of maximum density as shown in Fig. 2. We will also
rigorously determine the maximum depth of the lake. Observation of salinity-based
stratification would lend support to the heliothermic hypothesis (e.g. Wetzel 2001).
 pH. Low pH bottom waters may indicate the influx of acidic volcanic hydrothermal fluids
(Varekamp et al. 2000).
Conductive heat flow
We will determine the conductive heat flow from temperature gradient measurements in
Licancabur lake bottom sediments (e.g. Williams and Von Herzen 1983), and use the results of
this study to differentiate between the heliothermic and volcanic hydrothermal hypotheses as
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described in Table 1. The determined average heat flow will be compared with that predicted by
diurnal temperature variations. Since our measurements will be made under several meters of
water, and the diurnal skin depth of water is ~6 cm, these effects should be minimized,
depending on the amount of direct insolation the bottom of the lake recieves. First, we will
construct an instrument capable of measuring temperature gradients in lake bottom sediments.
Where conductive heat flux is given by Fourier’s law (e.g. Schubert and Turcotte 2002)
q = -k(dT/dy)
(1)
with k is the coefficient of thermal conductivity and y is in the direction of temperature variation,
we will directly measure dT/dy. If possible, we will determine the value for k in the field, but
otherwise for this preliminary work we will assume values on the order of Crater Lake, Oregon
sediments ~0.84 W m-2 K-1 (Williams and Von Herzen 1983).
Results of this experiment alone may be ambiguous. Low heat flow may be indicative of
no volcanic heating, but the conduction from hot rock is not significant in most volcanic lakes
where the magmatic heat source is > 1 km below the lake (Pasternack and Varekamp 1997).
Additionally, conductive heat flow is commonly low near hydrothermal systems, where
subsurface temperature gradients are depressed by the onset of convection (Williams and Von
Herzen 1974). High heat flow may be indicative of volcanic geothermal input, but may also
represent the effects of solar heating. For this reason, we will log temperature profile data over
one day if possible, to minimize diurnal variations in heat flow.
Mass, energy balance
We will develop a model of mass and energy balance for the Licancabur crater lake. The
results of this effort will allow us to quantitatively assess the role of hydrothermal fluid input and
volcanic heat flow in the lake’s stability and thermal behavior (e.g. Henderson-Sellers 1986,
Brown et al. 1991, Pasternack and Varekamp 1997). This experiment has two tasks: first,
quantify the role of volcanic fluid and heat input to Licancabur crater lake using a model of mass
and energy balance, and second, collect in situ environmental data to constrain model terms.
 Given that the crater can hold water, a volcanic lake in steady state requires mass and energy
balance.
The mass balance [kg s-1] for a volcanic lake is given by
Wvolc + Wprecip = Wout + Wevap
(2)
where Wvolc is the volcanic hydrothermal mass influx, which we will treat as an unknown.
Wprecip = IAc is the precipitation mass influx, where I is the precipitation rate [m day-1] and Ac
is the area of the catchment basin [m2]. Wout is the mass outflux term for outflow (e.g. stream
runoff) and seepage through the crater floor. Wevap is the mass loss through evaporation,
which is simply the energy outflux divided by the enthalpy of the water vapor ≈ 2.27 MJ kg-1
(Pasternack and Varekamp 1997).
Energy balance [W m-2] for a volcanic lake follows
Evolc + Esw + Elw = Erad + Eevap + Econd + Eprecip
(3)
where Evolc is the volcanic energy influx from conduction plus the enthalpy of volcanic fluid
and gas input, which we will treat as an unknown. The shortwave (solar) and longwave
(atmospheric) energy influx are approximated by global annual climate data (Linacre 1992)
Esw = 185 – 5.9φ – 0.22φ2 + 0.00167φ3
(4)
Elw = (208 + 6Tair)(1 + 0.0034C2)
(5)
7
where φ is latitude [degrees], Tair is the average air temperature [C], and C is the average
cloud cover [octos]. Tair and C are Linacre’s (1992) average fits to climate data, and are
functions of φ and elevation and φ, respectively. Erad is radiative loss from the lake surface,
given by the Stefan-Boltzmann law.
The next term in (2) is energy outflux by evaporation (after Ryan and Harlemann 1973)
Eevap = [μ(Tl – Tair )1/3 + bW](es – e2)A
(6)
where:
μ is constant = 2.7 W m-2 mbar-1 K-1/3
Tl is lake temperature [K]
b is constant = 3.2 W m-2 mbar-1 (m s-1)-1
W is wind speed at 2 m above the lake surface [m s-1]
es is saturation water vapor pressure at Tl [mbar]
e2 is water vapor pressure 2 m above the lake [mbar]
A is lake surface area [m2].
Conductive heat loss, Econd, is given by the ratio Econd/Eevap = 0.61[(Tl – Tair)/( es – e2)]
(Brown et al. 1991). Eprecip constitutes the heat flux to/from incoming precipitation, given by
aWprecip(Tl - Tprecip)cp where a is constant = 55555.6 mol m-3, Tprecip is temperature of
precipitation [C], and cp is the heat capacity of water.
Mass input to the lake is from volcanic-hydrothermal fluid and meteoric water derived from
precipitation and groundwater inflow. Mass output is from evaporation, overflow, and seepage
through the lake floor. Energy inputs are volcanic heating (conduction and the enthalpy of hot
fluid input), and solar and atmospheric radiation. Energy outputs are evaporation and radiation
from the lake surface, overflow and seepage, and heating incoming meteoric waters. By treating
the volcanic terms in this model as unknowns, any net loss of mass or energy is interpreted as
volcanic input.

The second objective is to collect in situ environmental data which will constrain model
terms. On site measurements of precipitation, solar radiation, lake temperature, atmospheric
temperature, wind speed, humidity, soil heat flux will be used to improve initial assumptions
made for the model (described in detail below). Last, GPS data will be collected to provide
redundant measures of lake location, size, and altitude. This will allow us to accurately
measure the size of the lake; over time, we will have the opportunity to observe changes in
water level annually and extract some information water level stability. Additionally,
determining lake surface area is an important factor in the energy budget (e.g. evaporative
flux and the effect of insolation).
Using observed temperatures of the lake water and other parameters recorded in the field, we
will determine values of Wvolc and Evolc using the model described above as a primary
constraint on the volcanic hydrothermal hypothesis. If steady state balance requires a net
input of mass and energy, then that hypothesis will be favored; otherwise, it will be
questioned further.