Sea Ice Ridging and Rafting Sea Ice Ridging and Rafting Structures on Mars and EarthStructures on Mars and Earth

Laboratory for Remote Sensing and Geoinformatics

Department of Earth and Environmental Science

University of Texas at San Antonio

Stephen F. Ackley, Penelope Wagner, and Hongjie Xie

IntroductionIntroduction

Similarities found with sea ice features on Mars Similarities found with sea ice features on Mars and Earth and Earth (Murray et al 2005).(Murray et al 2005).

2 Types Examined Further Here2 Types Examined Further Here Pile-up behaviorPile-up behavior Ridging and Rafting FeaturesRidging and Rafting Features

Mechanisms of transition of Ductile to Brittle Mechanisms of transition of Ductile to Brittle Behavior Observed on EarthBehavior Observed on Earth

Sinusoidal Ridging: Comparison Earth and MarsSinusoidal Ridging: Comparison Earth and Mars Compositional similarities and differences?Compositional similarities and differences?

Baltic Sea Pile-upBaltic Sea Pile-up

Pile up with longer flow area behind (Lepparanta, 2005) Pileup thickness is a multiple of the ice sheet thickness, related to the area of cleared channel

Mars Pile-upMars Pile-up

20m20m

Martian pile-up followed by clear area flow (Murray et al., 2005) Same orientation of flow direction Variable ratio of clear area to pile-up area up to 7:1

(HRSC, ESA, Mars Express)

20m20m

Martian Pile-up/Clear Area Ratio

0

1

2

3

4

5

6

7

8

Pile-up 1 Pile-up 2 Pile-up 3 Pile-up 4 Pile-up 5 Pile-up 6 Pile-up 7

Pile-up Feature

Rat

io

Discrete Element Pile-up Simulation Discrete Element Pile-up Simulation ModelModel

Pile-up at Earth’s gravity (~1.0) Pile-up at Mars gravity (0.38g)

Similar Mechanism – 2 Differences (Hopkins et al., 1999) Lower gravity potential energy proportional to increased pile-up height Lower normal force reduces friction proportional to gravity, increasing pileup height on Mars

Pile upPile up

Pile-up height related:Pile-up height related:Horizontal forces necessary to supply Horizontal forces necessary to supply

potential forcepotential forceSquare root of sheet ice thicknessSquare root of sheet ice thicknessDifferent Mars Pileup Height also due to 1/3 Different Mars Pileup Height also due to 1/3

gravity to that of Earth affecting Potential gravity to that of Earth affecting Potential Energy and FrictionEnergy and Friction

Mars Potential Mechanism: 1 Main Event Mars Potential Mechanism: 1 Main Event possibly from an outburst flood (single possibly from an outburst flood (single direction of the pileups) direction of the pileups)

Transition: Ductile BrittleTransition: Ductile Brittle

~10m – 20m ductile over thrusts of adjacent sheets~10m – 20m ductile over thrusts of adjacent sheets Lower temperature or hydraulic transformation leads Lower temperature or hydraulic transformation leads

to decrease in brine volumeto decrease in brine volume Precipitated salts decreases fluid volumePrecipitated salts decreases fluid volume Ice sheet pushed out of fluid and onto solid surface causing Ice sheet pushed out of fluid and onto solid surface causing

drainage through porous structure drainage through porous structure Loss of fluid leads to stiffening to increase brittle behaviorLoss of fluid leads to stiffening to increase brittle behavior Ductile sheets create curved formations during deformationDuctile sheets create curved formations during deformation

Arctic Rafting FeaturesArctic Rafting Features

Over thrusting sheetsOver thrusting sheets Higher brine volumes Higher brine volumes

related to higher related to higher ductile materialductile materialAccommodate large Accommodate large

strain w/o breaking strain w/o breaking for tens of metersfor tens of meters

Plastic deformation Plastic deformation at low stressat low stress

““Finger raftingFinger rafting””

Arctic Ridging FeaturesArctic Ridging Features

High brine volume gives High brine volume gives high angle plasticity initiallyhigh angle plasticity initially

Lower brine volumes from Lower brine volumes from freezing related leads to freezing related leads to brittle material that then brittle material that then Fractures at low strain by Fractures at low strain by own weight of sheetown weight of sheet

Brittle Ridges Outline outer Brittle Ridges Outline outer edges of Ductile thrustsedges of Ductile thrusts

From above can look like a From above can look like a Sinusoidal formationSinusoidal formation

Ridging and Rafting Features: Ridging and Rafting Features: ArcticArctic

Finger Rafting

Linear Ridging

Sinusoidal Ridging

Sinusoidal RidgingSinusoidal Ridging

100m 100m

HiRise Mars images (25cm per pixel)

Arctic images

Sinusoidal RidgingSinusoidal Ridging

100m

50m

HiRise Mars images (25cm per pixel) Arctic images

Mars and Arctic Ridging ComparisonMars and Arctic Ridging Comparison

Mars/Arctic Side Length

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10.0

20.0

30.0

40.0

50.0

Average

Per

cen

tag

e

Mars Side Length

Arctic Side Length

Mars/Arctic Width

0.010.020.030.040.050.060.070.080.0

Average

Per

cen

tag

e

Mars width

Arctic Width

Mars/Arctic Amplitude

0.0

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0-5051-100

101-150

151-200

201-250

251-300

Average

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rce

nta

ge

Mars Amplitude

Arctic Amplitude

Mars values higher at lower distances

Arctic values evenly distributed

Mars and Arctic Ridging ComparisonMars and Arctic Ridging Comparison

Similar processesSimilar processes Two phase mixture required to form these Two phase mixture required to form these

featuresfeaturesMarsMars

Lower amplitude indicates faster transition of ductile to Lower amplitude indicates faster transition of ductile to brittle behaviorbrittle behavior

Colder weather conditions (accelerated freezing)Colder weather conditions (accelerated freezing) Water ice less saturated with brine (different composition?)Water ice less saturated with brine (different composition?)

ArcticArcticEvidence more ductile material due to finger rafting Evidence more ductile material due to finger rafting

featuresfeatures

Mars Thermal StiffeningMars Thermal Stiffening

Small temperature changes (<5C) cause Small temperature changes (<5C) cause large phase changes and mechanical large phase changes and mechanical behaviors of these features found in the behaviors of these features found in the ArcticArcticFreezing temperatures Freezing temperatures (Mean T -63°C, range -

140° C to -20° C) Dry and thin atmosphere Dry and thin atmosphere (~6 mbar CO2, 4%

Earth)

Additional PossibilitiesAdditional Possibilities

Composition?Composition?Spectrometer instrument necessary to determine Spectrometer instrument necessary to determine

mineral compositionmineral compositionObservations from McMurdo area in Antarctica – Observations from McMurdo area in Antarctica –

Salts precipitating out of sea iceSalts precipitating out of sea iceTemperature decrease below eutectic area to form salt Temperature decrease below eutectic area to form salt

precipitates “Salt Flower”precipitates “Salt Flower”Mirabilite (NaMirabilite (Na2SOSO4··10H10H2O)O) – Salt dune formations – Salt dune formations

from precipitated saltsfrom precipitated salts

Discussion and ConclusionsDiscussion and Conclusions

Similar pile-up and ridging structures found on Mars Similar pile-up and ridging structures found on Mars and Earth indicative of sea ice formationand Earth indicative of sea ice formation

Earth ridging features exhibits increased ductile Earth ridging features exhibits increased ductile behavior to create larger thrusting featuresbehavior to create larger thrusting features

Mars features are consistently smaller due to a faster Mars features are consistently smaller due to a faster transition following the 2-phase system from ductile transition following the 2-phase system from ductile to brittle behaviorto brittle behavior Potential differences in mineralogyPotential differences in mineralogy Apparent differences in climate and gravitational potential Apparent differences in climate and gravitational potential

energyenergy

ReferencesReferences Hopkins, Mark A.Hopkins, Mark A. (1998) Four stages of pressure ridging. (1998) Four stages of pressure ridging. JGR vol. JGR vol.

103, pp. 21,883-21,891103, pp. 21,883-21,891.. Hopkins, Mark A.Hopkins, Mark A. (1999) Rafting and ridging of thin ice sheets. JGR (1999) Rafting and ridging of thin ice sheets. JGR

vol. 104, pp. 13,605-13,614.vol. 104, pp. 13,605-13,614. Murray, J.B., Muller, J., Neukum, G., Werner, S., Gasselt, S., Murray, J.B., Muller, J., Neukum, G., Werner, S., Gasselt, S.,

Hauber, E., Markiewicz, W., Head, J., Foing, B., Page, D., Mitchell, Hauber, E., Markiewicz, W., Head, J., Foing, B., Page, D., Mitchell, K., Portyankina, G., (2005) K., Portyankina, G., (2005) Evidence from the Mars Express High Evidence from the Mars Express High Resolution Stereo Camera for a frozen sea close to Mars’ equator. Resolution Stereo Camera for a frozen sea close to Mars’ equator. Nature vol. 434, pp. 352-355Nature vol. 434, pp. 352-355..

Neukum, G., Jaumann, R., HRSC Co-Investigator and Experiment Neukum, G., Jaumann, R., HRSC Co-Investigator and Experiment Team. HRSC: the High Resolution Stereo Camera of Mars Team. HRSC: the High Resolution Stereo Camera of Mars Express.Express.