Alluvial Fan Science Alluvial Fan Science PotentialPotential

Kelin X. Whipple and Kelli WakefieldKelin X. Whipple and Kelli Wakefield

School of Earth and Space School of Earth and Space ExplorationExploration

Arizona State UniversityArizona State University

Holden CraterHolden Crater

from Moore and Howard (2005)

Bajada: Apron of Bajada: Apron of Coalescing Coalescing

Alluvial Fans Alluvial Fans

Common Common Elevation Elevation Alluvial Alluvial

Fan Fan Margins Margins

(~2000m)(~2000m)::

Top LTLD Top LTLD

Bajada Traverse: Scientific BonusBajada Traverse: Scientific BonusDiversity, Context, Clay Source?, Diversity, Context, Clay Source?,

Depositional Environment through Time, Depositional Environment through Time,

Duration Wet ConditionsDuration Wet Conditions

Science Value: Bajada Science Value: Bajada TraverseTraverse

Source-Area (Crater Wall) Materials Source-Area (Crater Wall) Materials Lithology, Mineralogy (clast/matrix), WeatheringLithology, Mineralogy (clast/matrix), Weathering

Context for LTLDContext for LTLD Depositional Environment (relation to LTLD)Depositional Environment (relation to LTLD) Paleoclimatic Conditions (hydraulics, Paleoclimatic Conditions (hydraulics,

weathering)weathering) Plausible Water Source(s)Plausible Water Source(s) Duration of Active Sediment TransportDuration of Active Sediment Transport

Depositional ProcessDepositional Process Mudflow / Debris Flow – composition (water Mudflow / Debris Flow – composition (water

content)content) Other Mass Flow?Other Mass Flow? Fluvial (gravel – boulder) – flow depth, grain sizeFluvial (gravel – boulder) – flow depth, grain size Fluvial (sand – granule)Fluvial (sand – granule) Intermittency?Intermittency?

Relation to LTLDRelation to LTLDLayers exposed in every Layers exposed in every

fresh crater fresh crater Layers exposed in every Layers exposed in every

channel ridgechannel ridgeContact/transition Contact/transition

exposed in cliffs (see exposed in cliffs (see Full Res HiRise)?Full Res HiRise)?

Fans Common in Fans Common in CratersCraters

Late Noachian, Late Noachian, Widespread within Widespread within Latitudinal BandLatitudinal Band

Excellent Excellent Context: Context:

Understand LTLD in Understand LTLD in GeneralGeneral

Fluvial Fans Best Fluvial Fans Best AnalogAnalog

But Mixed Stream But Mixed Stream and Mudflow Fans and Mudflow Fans Can be Less SteepCan be Less Steep

2uC fb rfC 2/1

ghSb

ncssq )(

DgDq

q ss R

gDb

R

sR

Flow and Sediment Transport RelationsFlow and Sediment Transport Relations

Constraining Constraining Environmental Environmental

Conditions (Fluvial Fans)Conditions (Fluvial Fans)

Sandy Sandy channels channels

Gravel Gravel channels channels

c

Expanding Expanding Flow Flow

c 3.1

12/3/12

)(]})ˆ11

[({ rDgD

Q

rDgD

rQS w

rcnso

s

RR

w

so

s

r

Q

QS

R32 S

Q

Q

w

so

3

2

Expanding Flow Model Expanding Flow Model (bedload) Parker et al. (bedload) Parker et al.

(1998)(1998)

Reduce: n = 3/2 (bedload); Reduce: n = 3/2 (bedload); c

Terrestrial Fans (Stock et al., 2008), Terrestrial Fans (Stock et al., 2008), Experimental Fans Experimental Fans

No Dependence on g, D, or Flow No Dependence on g, D, or Flow Width! Width!

)

ˆ1()(

22/3112/1

w

sonc

brbsc Q

rQS

R

R

w

so

wsc

r

Q

Q

cS

132

R

42 c 1.0wc

S

Q

QS

w

so

3

2

3

1

3

2

5

1

Equilibrium Channel Model Equilibrium Channel Model (bedload)(bedload)

Reduce: n = 3/2 (bedload); Critical Stress Reduce: n = 3/2 (bedload); Critical Stress DominantDominant

w

so

sc

r

Q

QS

1

32R 2 5.1c

S

Q

Q

w

so

3

23

Equilibrium Channel Model Equilibrium Channel Model (suspended load, n = 5/2)(suspended load, n = 5/2)

w

f

w

so

V

V

Q

Q

Required Water Volume Required Water Volume (Fluvial)(Fluvial)

SQ

QS

w

so 27

1 S

Q

Q

w

so

3

2

so

wfw Q

QVV

Required Water Volume Required Water Volume (Mudflow)(Mudflow)

45.1 w

so

Q

Q ~40x ~40x Less!Less!

1

w

sofw QQ

VV

15-15-250(50)250(50)VVff

fC

ghSu uhwQw

ww

soso Q

Q

QQ

so

f

Q

VT

w

f

w

f

QS

VT

QS

V7

21

Water Volume -> Formation Water Volume -> Formation TimeTime

w

w

Q

VT

~10’s – 1000 years minimum ~10’s – 1000 years minimum (200 – 20000) [5% (200 – 20000) [5%

intermittency]intermittency]

Weakest Weakest linklink

Relation to LTLDRelation to LTLDLayers exposed in every Layers exposed in every

fresh crater fresh crater Layers exposed in every Layers exposed in every

channel ridgechannel ridgeContact/transition Contact/transition

exposed in cliffs (see exposed in cliffs (see Full Res HiRise)?Full Res HiRise)?

Calculation of QCalculation of Qww

Empirical method by Irwin et al. Empirical method by Irwin et al. (2005)(2005) Q Q 22= 1.9= 1.9ww1.221.22

Correction for Mars: multiply by factor Correction for Mars: multiply by factor of of

0.76 (1.250.76 (1.25-1.22-1.22) to account for lower ) to account for lower velocity on Mars for same dischargevelocity on Mars for same discharge

0.00

0.04

0.08

0.12

0.16

0.0 0.5 1.0 1.5

Norm. Distance (r/L)

Norm

. Ele

vation (z/

L)

0.016

0.033

0.063

0.016

0.033

0.063

Qso/Qw

0.00

0.04

0.08

0.0 0.5 1.0 1.5

Norm. Distance (r/L)

Norm

. Ele

vation (z/

L)

0.016

0.033

0.063

0.016

0.033

0.063

Qso/Qw

Suspension-Dominated SandBedload-Dominated Sand

Straight to Concave Profiles Convexo-Concave Profiles

Lines are Theoretical Prediction (no tuning of parameters)

Bedload-Dominated Sand Experiments

Vary Qw

Lines are Theoretical Prediction (no tuning of parameters)

0.00

0.04

0.08

0.12

0.16

0.00 0.02 0.04 0.06 0.08 0.10

Qso/Qw

Slo

pe

Qw, 270 um

160 um

270 um

460 um

550 um

Qw, 550 um