kite lpsc 2018 poster v2 - UChicago...
Transcript of kite lpsc 2018 poster v2 - UChicago...
A N
ew G
lobal Database of M
ars River Dim
ensions
Acknowledgem
ents: Particular thanks to Jonathan Sneed and Sam H
olo for contributing to fieldwork.
Thanks to Marjorie Chan for logistic and intellectual support for fieldw
ork. Thank you to Sharon Wilson,
Caleb Fassett, Joel Davis, and M
arisa Palucis, who each shared unpublished w
ork. We acknow
ledge useful discussions w
ith Becky William
s, Robert Jacobsen, Ben Cardenas, Alan How
ard, Devon Burr, Tim
Goudge,
Alastair Hayden, Caleb Fassett, N
icolas Mangold, D
avid Mohrig, Ben Cardenas, Rom
an diBiase, and especiallyRoss Irw
in. Grants: N
ASA (NN
X15AM49G
, NN
X16AG55G
).
We have ruled out the possibilities that m
y observations result from lim
ited image resolution, postfluvial
modification, flash-snow
melt due to reentry heating from
distal impact ejecta, dam
-overtopping, karst-like m
odification of paleochannels, or misinterpretation of
debris-flow deposits. W
e might be m
easuring strath terraces or channel belts at som
e sites, but not most. Published w
ork on Earth perm
afrost-river hydraulic geometry does not support a large
permafrost correction. Tw
o possibilities remain:
Fine grain sizes, or extreme runoff production on Early M
ars?
Rivers on Mars w
ere wider than rivers on Earth for the sam
e drainage area
The main surprise so far: Channels are frequently too big (relative to their drainage area) to be
easily reconciled with a seasonal-snow
melt clim
ate. As expected from Earth data, scatter is
high. At Earth sites, the width of flat-topped ridges can record channel-belt w
idth (not channel width).
On M
ars, width-inferred and w
avelength-inferred paleodischarges agree, consistent with the
interpretation that well-preserved flat-topped sinuous ridges record channel w
idth.
Evidence for regional variations
Repeated ArcGIS traces are m
erged and analysed in MATLAB.
172 drainage areas are represented. ~83%
of sites have HiRISE coverage
(~60% of those w
ith HiRISE anaglyphs or H
iRISE DTM
s) an advance over the pioneering THEM
IS study of Irwin et al., Geology, 2005
Two m
ain biases in the database: (1) O
nly well-preserved channels and drainage areas are included.
(2) We m
easured the largest visible channels in a catchment.
Discharge Q
inferred from w
idth w:
(using the Ref. 24 scaling; the Ref. 23 scaling gives very sim
ilar results).
Discharge Q
inferred from w
avelength λ:
R:R:
Edwin S. Kite
1,* ([email protected]), D
avid P. Mayer 1,2, Casey J. D
uncan3, D
eirdre Edward
1
Rivers on Earth adjust their depths to just mobilize sedim
ent. Therefore, if grainsize on M
ars was sm
all, then modest
river depths could transport sediment, so discharge
could be small (consistent w
ith snowm
elt) for a given width.
Extremely high runoff production (rainfall?) on Early M
ars.
12
1. University of Chicago. 2. N
ow at U
SGS Astrogeology Center. 3. U
niversity of Utah. * poster author.
Motivations &
Findings:
Method:
The scale of ancient Mars rivers – their paleochannel w
idths and m
eander wavelengths – is a proxy for past river discharge.
Discharge, divided by drainage area, yields runoff production, w
hich is a key param
eter for selecting between clim
ate models (e.g rain
versus snowm
elt).
Gale region (1)
+ supraglacial channels (2,8)
SW M
elasChasm
a (9)
Colors correspond togeographic clusters
k-means clustering of geographic distribution of m
easured rivers
High-quality data onlyO
pen circles: widths
Closed circles: wavelengths
Do the flat tops of sinuous ridges m
easured from orbit corre-
spond to channel-belt widths, or channel w
idths? Sinuous ridges near G
reen River in SE Utah preserve channel deposits
and point-bar deposits. At this site, channel deposits preserved w
ithin sinuous ridges can be less than the width of the flat top
of the ridge, and in some interpretations the w
idth of the flat top of the ridge corresponds to channel-belt w
idth, not a channel w
idth. These Earth-analog data are a warning against
over-interpreting HiRISE D
TMs, because the decisive grain-size
and bedset-thickness measurem
ents are very difficult from
orbit. For m
any Mars river deposits, the sim
plest interpretation of sinuous-ridge w
idth is nevertheless that ridge-top width
corresponds to inverted channel width. This is because
0
3D view
of drone-derived Digital Terrain M
odel (DTM
) of SE Utah inverted
λ-only global trend(λ)
(w)
w-only global trend
yellow trend-line: all-data fit, high quality only
cyan trend-line: all-data fit, all qualities
Exploiting preservation of river channel properties in river deposits
Author contributions. E.S.K. analysed M
ars data and supervised fieldwork.
D.P.M. built the M
ars GIS, and the M
ars D
TMs, for the project. C.J.D
. collected the drone data and built the Earth D
TMs. D.E. analysed drone data.
(n = 577; 106 channels)
Automatic extraction from
hand-picked traces (Kite et al., EPSL, 2015)
centerlines picked in triplicate
R: runoff production (mm
/hr)
channel (Oct 2017). Flat top is ~20 m
wide. N
o vertical exaggeration.
(1) sandblasting-away of floodplain deposits allow
s diagnostic bedform
s, e.g. lateral-accretion deposits, to be recognized from
orbit; (2) agreement betw
een meander-w
avelengths and paleochannel w
idths allows cross-checking; (3) rivers can
transition from negative-relief valley floors to positive-relief
channel floors, which decreases the likelihood that either is an
artifact.
Earth data from Bieger
et al., JAWRA 2015