Licancabur: exploring the highest lake on Earth.

Oral exam, HockTopic 1, v.1.0

9 Sept. 2003

GOAL: provide a quantitative physical explanation for a temperature anomaly observed at Licancabur Volcano crater lake.

• The site: Volcan Licancabur• Motivation

• Observations—water temperature anomaly– H2O physics

• Hypotheses & tests

• Modeling lake mass, energy balance

• Proposed future work

Map: de Silva and Francis 1991.

Volcan Licancabur• 2250’S, 6753’W• Crater lake:

• 5916 m• ~90 x 70 x 4 m• Twater~ 0-6 C• pH ~ 8.5• TDS ~ 1.05 ppt

Motivation• Terrestrial

– Unexplored (e.g. Rudolph 1955; Leach 1986)– One of the highest (~5916 m) lakes on Earth– Volcanology/Limnology

• Unclassified wrt world’s volcano lakes

• Martian– Terrestrial analog to ancient paleolakes?

• intense UV flux (~85 W/m2) and a cold (-13 °C), dry (< 200 mm/yr), oxygen-depraved (~48% pO2(0)) atmosphere

– Harsh physical environment—Survival strategies of endemic organisms

Motivation

Observations

– No eruptions in recorded history.– Evidence of recent activity

• youthful lava flows, well-preserved summit crater, absence of glacial geomorphic features (de Silva and Francis 1991).

– The region surrounding the volcano is geothermally active

• springs ranging from ~17-37 C and elevated heat flow (Hock et al. 2002).

• Despite sub-freezing air temperature and a 80 cm ice cover, summit lake has ~6 C bottom water (Leach 1986)– Summer surface water ~4.9 C , salinity ~1.05 ppt

(Hock et al. 2002)

…H2O physics…bottom water temperature should equal the temperature of maximum

density for water under these conditions.

(S,T,p)

• freshwater has max~1.00 g/cc at ~4 °C

• T max(S,p)

• Licancabur (~4 m depth) waters have predicted T max~3.74 °C

1.0015

0.9982521618

0 t 1( )

1000

1.05 t 0.873( )

1000

200 t

0 5 10 15 200.998

0.9985

0.999

0.9995

1

1.0005

1.001

Temperature [C]

Den

sity

[g/

cc]

Licancabur: Tmax~3.74

Sea level freshwater: Tmax~4.00

Licancabur: Tobs~6.00

GOAL: provide a quantitative physical explanation for a temperature anomaly observed at Licancabur Volcano crater lake.

• The site: Volcan Licancabur

• Hypotheses & tests1. Measurement error

2. Heliothermic

3. Volcanic

• Analysis

• Modeling lake mass, energy balance

• Proposed future work

1. Measurement error – there is no temperature anomaly.

2. Heliothermic – saline bottom waters are heated by solar insolation and sediment radiative cooling.

3. Volcanic – the lake hosts a diffuse hydrothermal system that supplies energy and fluid to the system.

HypothesesMeasured bottom water temperature at Licancabur is ~2 °C warmer

than predicted Tρmax for lake water

1. Measurement error?• Leach 1986:

– Difficult conditions• Diver, early spring• Overlying 80 cm ice cover

– Instrument accuracy (d, T) unknown

2. Heliothermic?• Saline bottom waters heated by sun

– Thermal-density instability is prevented by an increased solute concentration (Wetzel 2001).

– Only a very small increase in salinity is required to explain the observed temperature anomaly

Example: Hot Lake, Washington. Even under icecover, the bottom temperature of this ~4 m deep

lakein a salt mine reaches 30 °C! (after Kirkland et al. 1983)

ρS=1.05=1.00086

ρS=2.0=1.002

ρS=1.05=1.00082

Simplified model of a crater lake atop a passively degassing volcano. From the International Association of Volcanology and Chemistry of the Earth’s Interior Committee on Volcanic Lakes website: : http://www.ulb.ac.be/sciences/cvl/

• As a surface expression of terrestrial degassing and the interaction between the Earth’s mantle and hydrosphere, volcanic lakes host unique physical, chemical, and biological environments.

• “Neutral-dilute” problem:• Volcanic lakes within dormant craters,

--may be virtually indistinguishable from a typical freshwater reservoir (e.g. Crater Lake, OR)

• No fumaroles• Diffuse, not discrete (seafloor-type)

venting.• Low T, neutral pH, low dissolved

solids content• Address with physical modeling

3. Volcanic

AnalysisAnalysis

Hypothesis

Water column Conductive heat flow

Mass, energy balance model

Measurement error

Heliothermic

Volcanic

T(zmax): ~4 T(zmax): ~4 °C°C

T(zmax): ~6 T(zmax): ~6 °C°C

n/a n/a

S(z): salinity-based S(z): salinity-based stratificationstratification

S(z): well mixed. Low S(z): well mixed. Low bottom water salinitybottom water salinity

Seasonally-dependent Seasonally-dependent heat flowheat flow

Heat flow sufficient Heat flow sufficient to drive water column to drive water column convectionconvection

n/a

Isothermal profileIsothermal profile

Seasonally-independent Seasonally-independent mixingmixing

Acidic bottom waterAcidic bottom water

Tw(z): increase w/o mixingTw(z): increase w/o mixing

Elevated heat flowElevated heat flow

Low heat flow w/o Low heat flow w/o observed thermal observed thermal fluid inputfluid input

Volcanic inputs as unknowns…

Net outflowNet outflow

No determinable net No determinable net flow, net inflowflow, net inflow

GOAL: provide a quantitative physical explanation for a temperature anomaly observed at Licancabur Volcano crater lake.

• The site: Volcan Licancabur

• Hypotheses & tests

• Modeling lake mass, energy balance• Terms, equations

• Results

• Proposed future work

• Mass balanceWmet = Wevap + Wout

• Energy balance

Esw + Elw = Erad + Eevap + Econd + Emet + Eout

Lake waters

PrecipitationEvaporation

Seepage, outflow Volcanic input?

Solar/atmospheric radiation

Radiative cooling Evaporation, conduction

Groundwater,snow

“Drainage” loss

Observations of stability on ~10 year timescale: assume hydrologic and energetic steady state.

Terms in the balance…

Term Dependence Assumptions

Wmet I, Ac I~200 mm y-1; Pasternack and Varekamp 1997; Nunez et al. 2002

Wevap Eevap

Pasternack and Varekamp 1997

Wout  Wout=0

Esw φ Linacre 1992

Elw Tair, C C(φ,z); Linacre 1992

Erad Tw Tw~5 ºC; Davies et al. 1971, Henderson-Sellers 1986

Eevap (Tw-Tair), W, (es-e2) Tw~5 ºC; W~6 m s-1; Ryan and Harleman 1973

Econd EevapBrown et al. 1991

Emet Ac, I, (Tw-Tprecip) Tprecip=0 C; Pasternack and Varekamp 1997

Eout Wout, H Wout=0

2002 Results [Hock et al. 2002, Hock et al. 2003]

• Model:

– May support volcanic hypothesis—input on the order of ~106 W and a few m3 H2O/day. Field data needed.

• Water chemistry– first measurements!– pH~8.5, TDS~1.05 ppt– Rock forming elements (Fe, Al, Mg, others)

enriched wrt local geothermal, meteoric waters– Also enriched in SO4, Cl, F—principal anions

found in magmatic hydrothermal fluids

Mass Balance

Input Term: Mass Influx (m3 H2O/day) Output Term: Mass Outflux (m3 H2O/day) Net Mass Flux (m3 H2O/day)

Precipitation 28.94 Evaporation 35.68 -6.74Outflow 0Seepage 0

Energy Balance

Input Term: Energy Influx (106 W) Output Term: Energy Outflux (106 W) Net Energy Flux (106 W)Solar radiation 1.13 Radiative loss 1.55 -1.81Atmospheric radiation 0.691 Evaporation 0.938

Conduction 1.13Precipitation 0.0146

GOAL: provide a quantitative physical explanation for a temperature anomaly observed at Licancabur Volcano crater lake.

• The site: Volcan Licancabur

• Hypotheses & tests

• Modeling lake mass, energy balance

• Proposed future work• Constrain model using field data

• 2003 field campaign, beyond

Constrain model using field data1) Mass outflux by seepage and outflow = 02) Air temperature and cloud cover average functions of latitude and elevation

(Linacre 1992)

• Readout temperature loggers3) All meteoric input at 0 C

• Install meteorology station; measure precipitation and account for latent heat of melting in model

4) The lake remains unfrozen

• Readout surface water temperature logger5) Vapor pressure approximation assumes year-round temperatures <0 C

• Readout temperature loggers6) Average crater wind speed was estimated ~6.7

m/s

• Log wind speed in crater

2003 campaign• Collect all of the deployed data loggers

– Investigate mixing with time-dependent T(d) profiles

• CTD probe– Investigate heliothermic hypothesis with

• Deploy a simple meteorological station1) quantify analogy between the Licancabur summit environment and

paleoenvironments on Mars2) validate data for wind speed (a critical term in evaporative flux estimates) and

precipitation (critical to meteoric input estimates)

• Model the equilibrium chemistry of a pH 8.5 freshwater body in contact with andesitic sediments

• Analog to Mars – quantify the environmental parameters that underlie the analogy to ancient Mars

and, in particular, martian paleolakes—compare with climate models?

• Scout additional sites; adaptations of biology; human physiology; education and public outreach…

Summary

As one of the highest lakes on Earth and an end-member of the physical environments on Earth where lakes and liquid water are stable, the Licancabur crater lake is of considerable interest to terrestrial limnology, biology, and volcanology. My proposal represents the first thorough characterization of this environment and a quantitative physical explanation for the anomalous warmth of its waters.

Energy balance termsTerm Expression Reference

Incident shortwave radiation (solar) [W/m2]: Esw

185+5.9φ-0.22φ2+0.00167φ3 Linacre 1992

Incident longwave radiation from atmosphere [W/m2]: Elw

(208+6Tair)(1+0.0034C2) Linacre 1992

Longwave radiative (blackbody) loss [W/m2]: Erad

εwσTw4 Davies et al. 1971; Henderson-Sellers 1986

Evaporation energy flux [W/m2]: Eevap [2.7(Tlv-Tav)1/3+3.2W2](es-e2) Ryan and Harleman 1973

Conductive heat loss [W/m2]: Econd 0.61[(Tlake-Tair)/(es-e2)]Eevap Brown et al. 1991

Precipitation energy flux [W/m2]: Emeteoric aI(Tlake-Tprecip)cp Pasternack and Varekamp 1997

Mass balance termsTerm Expression Reference

Precipitation mass flux [m3/day]: Wmeteoric IAc Pasternack and Varekamp 1997; Nunez et al. 2002

Evaporative mass flux [m3/day]: Wevap Eevap/ab Pasternack and Varekamp 1997

Name Licancabur Volcano crater lake Thermales Hot Spring Laguna Blanca Cold Spring Snow

Elevation (m) 5867 4328 4340 5700Temperature (°C) 4.9 36.2 17.7 --pH 8.5 8 7.3 --TDS 1050 2120 2740 --Li 0.0395 4.17 7.46 0.0168B 7.16 26.9 28.8 1.39Na 67.5 422 57.2 1.59Mg 39.6 22.9 48.1 0.229Al 1.75 0.00592 0.0387 0.188Si 11.9 97 53.1 0.433K 26.2 72 38.9 0.32Ca 230 104 107 1.72Mn 0.0427 0.000234 0.0031 0.0139Fe 0.902 0.125 0.175 0.0719As 0.0276 0.519 1.56 0.0125Rb 0.02 0.292 0.211 0.00117Cs 0.000398 0.29 0.25 0.000434SO4 588.97 545.44 233.57 4.37F 0.56 0.33 0.2 --Cl 57.79 203.72 381.37 0.54

• If we assume that the source water for these features have similar composition, then enrichment in rock forming elements may be representative volcanic hydrothermal fluid input as fluid flowing up to the summit is allowed more time to react with local lithologies.

• Since solute enrichment is not uniform across the analytes in the summit lake waters, it is unlikely that this chemistry is a result of evaporative concentration alone.

Schematic “box model” of energy and mass balance in a volcanic crater lake; the terms represent those used for this model. The two volcanic input arrows at the bottom of the lake represent unknowns, and are solved for in the model. Wout and Wseep are set to zero as a conservative estimate.

Physicochemical classification scheme for volcanic lakes (from Pasternack and Varekamp 1997). Dashed lines indicate

physically-imposed thresholds; representative temperature (T) and total dissolved solids (TDS) values are given.

Volcanic lake systematics• Physical and chemical differences between lakes reflect the complex interaction between

volcanic (e.g. the timescale and intensity of volcanic heat and fluid input) and nonvolcanic (e.g. atmospheric conditions, precipitation) phenomena

• Given a crater that can hold water, a volcanic lake in steady state requires an energetic and hydrologic balance between volcanic heat and mass input and output to the environment.

Thermopile temperature gradient probe deployment (buried probe top indicated by red arrow). Surface and underwater soil heat flux measurements were made using this lightweight, high-sensitivity probe at lower elevation lagunas and hot springs. Preliminary calculations show conductive heat flux values ranging from near global average (~0.06 W/m2) to nearly two orders of magnitude greater near the hot spring.