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Licancabur: exploring the highest lake on Earth. Oral exam, Hock Topic 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

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Licancabur exploring the highest lake on earth
Licancabur: exploring the highest lake on Earth.

Oral exam, Hock

Topic 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


    • Volcan Licancabur temperature anomaly observed at Licancabur Volcano crater lake.

    • 2250’S, 6753’W

    • Crater lake:

      • 5916 m

      • ~90 x 70 x 4 m

      • Twater~ 0-6 C

      • pH ~ 8.5

      • TDS ~ 1.05 ppt

    Map: de Silva and Francis 1991.


    Motivation
    Motivation temperature anomaly observed at Licancabur Volcano crater lake.

    • 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


    Motivation1
    Motivation temperature anomaly observed at Licancabur Volcano crater lake.


    Observations
    Observations temperature anomaly observed at Licancabur Volcano crater lake.

    • 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)


  • H 2 o physics

    Licancabur: T temperature anomaly observed at Licancabur Volcano crater lake. max~3.74

    Licancabur: Tobs~6.00

    Sea level freshwater: Tmax~4.00

    …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


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

    • The site: Volcan Licancabur

    • Hypotheses & tests

      1. Measurement error

      2. Heliothermic

      3. Volcanic

      • Analysis

  • Modeling lake mass, energy balance

  • Proposed future work


  • Hypotheses temperature anomaly observed at Licancabur Volcano crater lake. Measured bottom water temperature at Licancabur is ~2 °C warmer than predicted Tρmaxfor lake water

    • Measurement error – there is no temperature anomaly.

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

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


    1. Measurement error? temperature anomaly observed at Licancabur Volcano crater lake.

    • 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 ice

        cover, the bottom temperature of this ~4 m deep lake

        in 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


    3. Volcanic temperature anomaly observed at Licancabur Volcano crater lake.

    • 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

    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/


    Analysis
    Analysis temperature anomaly observed at Licancabur Volcano crater lake.

    T(zmax): ~4 °C

    T(zmax): ~6 °C

    n/a

    n/a

    Seasonally-dependent heat flow

    Heat flow sufficient to drive water column convection

    S(z): salinity-based stratification

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

    n/a

    Isothermal profile

    Seasonally-independent mixing

    Acidic bottom water

    Tw(z): increase w/o mixing

    Volcanic inputs as unknowns…

    Net outflow

    No determinable net flow, net inflow

    Elevated heat flow

    Low heat flow w/o observed thermal fluid input


    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 balance temperature anomaly observed at Licancabur Volcano crater lake.

    Wmet = Wevap + Wout

    Energy balance

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

    Solar/atmospheric

    radiation

    Radiative

    cooling

    Evaporation

    Evaporation, conduction

    Precipitation

    Groundwater,

    snow

    Seepage, outflow

    Volcanic input?

    “Drainage” loss

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

    Lake waters


    Term temperature anomaly observed at Licancabur Volcano crater lake.

    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

    Eevap

    Brown et al. 1991

    Emet

    Ac, I, (Tw-Tprecip)

    Tprecip=0 C; Pasternack and Varekamp 1997

    Eout

    Wout, H

    Wout=0

    Terms in the balance…


    2002 results hock et al 2002 hock et al 2003
    2002 Results temperature anomaly observed at Licancabur Volcano crater lake. [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


    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 data

    • Mass outflux by seepage and outflow = 0 temperature anomaly observed at Licancabur Volcano crater lake.

    • Air temperature and cloud cover average functions of latitude and elevation (Linacre 1992)

      • Readout temperature loggers

    • All meteoric input at 0 C

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

    • The lake remains unfrozen

      • Readout surface water temperature logger

    • Vapor pressure approximation assumes year-round temperatures <0 C

      • Readout temperature loggers

    • Average crater wind speed was estimated ~6.7 m/s

      • Log wind speed in crater

    Constrain model using field data


    2003 campaign
    2003 campaign temperature anomaly observed at Licancabur Volcano crater lake.

    • 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 station

      1) quantify analogy between the Licancabur summit environment and paleoenvironments on Mars

      2) 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
    Summary temperature anomaly observed at Licancabur Volcano crater lake.

    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 terms

    Term temperature anomaly observed at Licancabur Volcano crater lake.

    Term

    Expression

    Expression

    Reference

    Reference

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

    Precipitation mass flux [m3/day]: Wmeteoric

    185+5.9φ-0.22φ2+0.00167φ3

    IAc

    Linacre 1992

    Pasternack and Varekamp 1997; Nunez et al. 2002

    Evaporative mass flux [m3/day]: Wevap

    Eevap/ab

    Pasternack and Varekamp 1997

    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

    Energy balance terms

    Mass balance terms


    • 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.


    • Volcanic lake systematics 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.

    • 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.

    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.


    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.


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