Sea Ice Ridging and Rafting
Structures on Mars and Earth
Stephen F. Ackley, Penelope Wagner, and Hongjie Xie
Laboratory for Remote Sensing and Geoinformatics
Department of Earth and Environmental Science
University of Texas at San Antonio
Introduction

Similarities found with sea ice features on Mars
and Earth (Murray et al 2005).

2 Types Examined Further Here





Pile-up behavior
Ridging and Rafting Features
Mechanisms of transition of Ductile to Brittle
Behavior Observed on Earth
Sinusoidal Ridging: Comparison Earth and
Mars
Compositional similarities and differences?
Baltic 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-up
20m
20m
 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)
20m
20m
Martian Pile-up/Clear Area Ratio
8
7
6
Ratio
5
4
3
2
1
0
Pile-up 1
Pile-up 2
Pile-up 3
Pile-up 4
Pile-up 5
Pile-up Feature
Pile-up 6
Pile-up 7
Discrete Element Pile-up Simulation
Model
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 up

Pile-up height related:
Horizontal forces necessary to supply
potential force
 Square root of sheet ice thickness
 Different Mars Pileup Height also due to 1/3
gravity to that of Earth affecting Potential
Energy and Friction
 Mars Potential Mechanism: 1 Main Event
possibly from an outburst flood (single
direction of the pileups)

Transition: Ductile


Brittle
~10m – 20m ductile over thrusts of adjacent sheets
Lower temperature or hydraulic transformation leads
to decrease in brine volume




Precipitated salts decreases fluid volume
Ice sheet pushed out of fluid and onto solid surface causing
drainage through porous structure
Loss of fluid leads to stiffening to increase brittle behavior
Ductile sheets create curved formations during deformation
Arctic Rafting Features


Over thrusting sheets
Higher brine volumes
related to higher
ductile material
 Accommodate large
strain w/o breaking
for tens of meters
 Plastic deformation
at low stress

“Finger rafting”
Arctic Ridging Features




High brine volume gives
high angle plasticity
initially
Lower brine volumes from
freezing related leads to
brittle material that then
Fractures at low strain by
own weight of sheet
Brittle Ridges Outline
outer edges of Ductile
thrusts
From above can look like a
Sinusoidal formation
Ridging and Rafting Features:
Arctic
Linear Ridging
Finger Rafting
Sinusoidal Ridging
Sinusoidal Ridging
HiRise Mars images (25cm per pixel)
100m
Arctic images
100m
Sinusoidal Ridging
50m
100m
HiRise Mars images (25cm per pixel)
Arctic images
Mars and Arctic Ridging Comparison
Mars/Arctic Side Length
Mars/Arctic Width
40.0
30.0
Mars Side Length
20.0
Arctic Side Length
10.0
0.0
050
51
-1
00
10
115
0
15
120
0
20
25
1125
30
0
0
Percentage
60.0
50.0
40.0
30.0
20.0
10.0
0.0
Arctic Amplitude
00
10
1-
15
0
Arctic Width
51
-1
00
10
115
0
15
120
0
 Mars values higher at lower
distances
Mars Amplitude
51
-1
Mars width
Average
Mars/Arctic Amplitude
50
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
050
Average
0-
Percentage
Percentage
50.0
15
1-
20
0
Average
20
1-
25
0
25
130
0
 Arctic values evenly distributed
Mars and Arctic Ridging Comparison
Similar processes
 Two phase mixture required to form these
features


Mars
 Lower
amplitude indicates faster transition of ductile to
brittle behavior



Colder weather conditions (accelerated freezing)
Water ice less saturated with brine (different composition?)
Arctic
 Evidence
features
more ductile material due to finger rafting
Mars Thermal Stiffening

Small temperature changes (<5C) cause
large phase changes and mechanical
behaviors of these features found in the
Arctic
Freezing temperatures (Mean T -63°C, range 140° C to -20° C)
 Dry and thin atmosphere (~6 mbar CO2, 4%
Earth)

Additional Possibilities

Composition?
Spectrometer instrument necessary to determine
mineral composition
 Observations from McMurdo area in Antarctica –
Salts precipitating out of sea ice

 Temperature
decrease below eutectic area to form salt
precipitates “Salt Flower”
 Mirabilite (Na2SO4·10H2O) – Salt dune formations
from precipitated salts
Discussion and Conclusions



Similar pile-up and ridging structures found on Mars
and Earth indicative of sea ice formation
Earth ridging features exhibits increased ductile
behavior to create larger thrusting features
Mars features are consistently smaller due to a faster
transition following the 2-phase system from ductile
to brittle behavior


Potential differences in mineralogy
Apparent differences in climate and gravitational potential
energy
References




Hopkins, Mark A. (1998) Four stages of pressure ridging. JGR vol.
103, pp. 21,883-21,891.
Hopkins, Mark A. (1999) Rafting and ridging of thin ice sheets. JGR
vol. 104, pp. 13,605-13,614.
Murray, J.B., Muller, J., Neukum, G., Werner, S., Gasselt, S.,
Hauber, E., Markiewicz, W., Head, J., Foing, B., Page, D., Mitchell,
K., Portyankina, G., (2005) Evidence from the Mars Express High
Resolution Stereo Camera for a frozen sea close to Mars’ equator.
Nature vol. 434, pp. 352-355.
Neukum, G., Jaumann, R., HRSC Co-Investigator and Experiment
Team. HRSC: the High Resolution Stereo Camera of Mars Express.