Document Actions

IJEGE-11_BS-Palucis-et-alii

background image
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
243
DOI: 10.4408/IJEGE.2011-03.B-029
THE ROLE OF DEBRIS FLOWS IN THE ORIGIN AND EVOLUTION
OF GULLY SYSTEMS ON CRATER WALLS: MARTIAN ANALOGS IN
METEOR CRATER, ARIZONA (USA)
m
aRisa
C. PALUCIS
(*)
, w
illiam
e
. DIETRICH
(**)
& a
lan
HOWARD
(***)
(*) Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA
(**) Department of Earth and Planetary Science, University of California, Berkeley, California 94720-4767, USA
(***) Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22904, USA
INTRODUCTION
The discovery of geologically-recent gullies on
Mars by m
alin
& e
dGett
(2000) has lead to numerous
studies on gullies across Mars (e.g. t
Reiman
, 2003;
m
aRQuez
et alii, 2005; H
ead
et alii, 2008; l
anza
et
alii, 2010) and on terrestrial analogues (e.g. C
ostaRd
et alii, 2002; H
aRtmann
et alii, 2003; H
uGenHoltz
,
2008). The morphology of these gully systems varies,
but most commonly they have a well-defined source
alcove, channels or chutes, and a depositional apron.
Despite the abundance of high-resolution imaging and
morphometric characterization that has occurred over
the last decade, the processes creating these features
remains unknown.
Proposed mechanisms for flow generation on
Martian gullies span a wide range of processes. t
Rei
-
man
(2003) pointed to the similarity between Mar-
tian gullies and terrestrial snow avalanches and sug-
gested that they could have formed similarly, from
dry granular flows. Experiments performed by s
Hin
-
bRot
et alii (2004) showed that dry granular material
could produce weakly channelized flows if the set-
tling velocity of the grains is less than the flow veloc-
ity. The lower Martian gravity coupled with partially
mantled slopes of superposed material, thought to
be mainly fine sediment and ice, may encourage dry
flows, but thus far it has not been shown that such
flows can produce deep channels, natural levees or
hummocky terminal deposits.
A second set of hypotheses involves the emer-
ABSTRACT
In 1999, the Mars Global Surveyor acquired im-
ages of young gully features on the walls of impact
craters. From these and subsequent images, numerous
theoretical and physical models have been developed
based primarily on three competing theories about the
origin of the gullies: 1) scour and deposition by dry
granular flows, 2) debris flow driven gully incision
due to the sudden release of gases or fluid from the
subsurface, or 3) fluid incision via debris flows due to
the release of surface volatiles or the melting of ice. To
contribute insights and possible constraints on these
competing mechanisms, we are performing an inten-
sive investigation of the origin and evolution of the
gullies in Meteor Crater, a well-preserved terrestrial
analogue. The location of the gullies along radial frac-
tures in the crater wall and the presence of lake sedi-
ments on the crater floor have lead researchers to con-
clude that groundwater seepage and fluvial incision
formed the gullies. However, from initial field obser-
vations and inspection of high-resolution LiDAR data,
we have observed that the gullies: 1) show evidence
of multiple events, 2) do not cross the crater floor, 3)
have modest size levees, and 4) terminate on an ~8-
15
o
slope. As an alternative to current interpretations,
we suggest that gully incision was caused by debris
flows driven by periodic snowmelt during the cooler
and wetter Pleistocene.
K
ey
worDS
: Meteor Crater, Mars, Gully erosion
background image
m.c. P
AluciS
, w.e. D
ietrich
, & A. h
owArD
244
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
Lastly, surficial fluid sources have been proposed
from the release of seasonal or epochal accumulations
of volatiles, or from the melting of ice collected in
alcoves or mixed in with fine material that has been
atmospherically deposited on crater slopes (C
ostaRd
et alii, 2002; H
eCHt
, 2002; C
HRistensen
, 2003; m
an
-
Gold
et alii, 2003; d
iCkson
and
H
ead
, 2009). Based
on the model of P
aRsons
& n
immo
(2010), solar in-
solation cannot melt ice at rates fast enough to pro-
duce the discharges estimated to have flowed through
the gully systems. Observations of repeated erosional
and depositional activity in Martian gullies over the
past two years may suggest that seasonal CO2 frost
accumulations can fail and flow through the gully net-
works, perhaps with sufficient force to entrain debris
(d
undas
et alii, 2010). It has also been proposed that
debris flows could be generated by the saturation of
surface layers by slow melting or in the generation of
excess pore water pressures beneath a frozen surface
layer, thereby creating a slushflow (C
oleman
et alii,
2010; d
ixon
et alii, 2010).
Careful analysis of terrestrial analogues, where
specific mechanisms can be identified or tested in-
situ, is required to provide insight and possible con-
straints to the proposed mechanisms for Martian gully
formation. Meteor Crater, also known as Barringer
Meteorite Crater, is an ideal place to perform such
a study. While one of the best-preserved craters on
Earth, its interior walls are etched with gullies that
closely resemble the widely investigated “typical”
gully systems on Mars (i.e. those that involve source
gence of gas or fluid from the subsurface. m
ellon
&
P
HilliPs
(2001) hypothesize that oscillations in the
Martian orbit can lead to freeze-thaw cycles at depth,
potentially forcing water to the surface under freez-
ing pressure, similar to springs that emerge from ter-
restrial pingos, a periglacial landform in which rock
and soil cover a large mound of ice. m
usselwHite
et
alii (2001) suggest a similar mechanism to M
ellon
& P
HilliPs
(2001), only under the action of liquid
CO2. Groundwater seepage has been proposed as a
transporting agent by several authors (e.g. m
alin
&
e
dGett
, 2000; G
ilmoRe
& P
HilliPs
, 2002; H
eldman
& m
ellon
, 2004; m
aRQue
Z et alii, 2005) based on
observations of similar elevations of alcoves on cra-
ter walls, exposure of layered rock in alcoves, and the
fact that the present day climate on Mars does not al-
low for mobilizing appreciable quantities of surface
water.
Fig. 1 - (left) Shaded relief map (left) of Meteor Crater derived from lidar provided by the National Center for Air-
borne Laser Mapping and (right) slope map (on 0.25 m gridded data) (North up). Note access trail is visible
in northern part of slope map
background image
THE ROLE OF DEBRIS FLOWS IN THE ORIGIN AND EVOLUTION OF GULLY SYSTEMS ON CRATER WALLS: MARTIAN ANALOGS IN
METEOR CRATER, ARIZONA (USA)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
245
placements of only several meters (s
HoemakeR
, 1960;
C
onley
, 1977). A majority of these faults are paral-
lel with a north-westerly regional joint set, and these
joints may have led to the ‘squarish’ shape of the cra-
ter, as mapped by s
HoemakeR
(1960). R
oddy
(1978),
and subsequently k
umaR
& k
RinG
(2008), measured
the azumuthal bearings of the joints surrounding the
crater and the faults in the crater wall.
s
HoemakeR
(1960, 1987), s
HoemakeR
& k
ief
-
feR
(1974), k
RinG
(2007), and k
umaR
et alii, (2010)
provide a detailed description of the bedrock, ejecta
and surface deposits at Meteor Crater, which we only
briefly summarize here. The rocks exposed in the cra-
ter range from the Coconino Sandstone of the Perm-
ian age to the Moenkopi formation of the Triassic
age, which are units in the upper portion of the Grand
Canyon Sequence (G
RotzinGeR
et alii, 2007). A cross-
section is shown in Fig. 3. The lowest exposed unit
in the crater is the Coconino sandstone, composed of
well-sorted quartz eolian sands (m
C
k
ee
, 1945). This
is overlain by 3 m of Toroweap Formation, composed
of sandstone and dolomite. The Kaibab Formation, an
~80 m thick unit, is composed of dolomite, dolomitic
limestone, and thin calcareous sandstone horizons,
and overlies the Toroweap. The Kaibab is exposed
along the steep upper wall of the crater. Two beds
of the Moenkopi Formation rest disconformably on
the Kaibab. The bottom bed is the Wupatki Member,
which is 2-6 m thick and composed of very-fine sand-
stone. Atop the Wupatki is the Moqui Member, which
is 2-10 m and is composed of siltstone. The crater rim
is underlain by a sequence of Quaternary debris and
alluvium, resting on the previously described strata.
The ejecta debris units in the rim consist of angular
fragments ranging from 1 micron to 30 m (s
Hoemak
-
eR
, 1987). Beneath the crater floor lies about 1.6 m of
Holocene sediments resting on ~30 m of Pleistocene
lake sediment that overlie 10.5 m of thoroughly mixed
(by source) bedrock debris, which is most likely fall-
out debris (Fig. 3). Beneath this mix layer is brecci-
ated bedrock, locally over 150 m thick.
Breccia produced by the impact consists of three
units: authigenic (breccias produced by shattering ap-
proximately in situ), allogenic (breccias formed by
major displacement), and mixed debris. k
RinG
(2007)
notes that the authigenic breccias at Meteor Crater are
located along the faults that cross-cut the crater walls
and rim, and the allogenic breccias, which are com-
alcoves, chutes, and depositional aprons), as shown in
Fig. 1. In addition to sharing morphologic similarities
to Martian craters, Meteor Crater also has an appar-
ent history of an elevated water table hosting a lake,
which raises the issue of groundwater seepage influ-
ences. Also, it is a well-studied crater in regards to its
basic geology (s
HoemakeR
, 1960; s
HoemakeR
& k
i
-
effeR
, 1974), post-impact geophysical characteristics
(k
umaR
& k
RinG
, 2008), and recently, even its ero-
sional features been described in some detail (k
umaR
et alii, 2008; k
umaR
et alii, 2010).
Currently, the key issue at Meteor Crater regarding
post-impact erosional processes is the role of ground-
water in forming the gully networks. k
umaR
et alii
(2010) suggest that groundwater seepage and fluvial
processes may have dominated, but our observations,
based both on an initial field campaign and more im-
portantly, high-resolution topographic data recently
obtained from the National Center for Airborne Laser
Mapping (NCALM), now suggest an alternative hy-
pothesis. In what follows, we argue that the gullies may
be the result of repeated debris flows that have no clear
connection to groundwater seepage. Furthermore, es-
sential to the formation of these mass flows is not just
the occurrence of water (either from surface runoff or
groundwater seepage), but also the presence of fine ma-
terial from the impact, which when mixed with water
serves to mobilize and sustain debris flow motion.
.
GEOLOGICAL SETTING
GEOLOGY
Meteor Crater is located in the Colorado Plateau
in north central Arizona (35°03´N, 111°02´E). The
crater is a bowl-shaped depression, about 180 m deep
and 1.2 km in diameter, and is encompassed by a rim
of ejecta that rises 30 to 60 m above the surround-
ing plain (s
HoemakeR
, 1960). Independent dating us-
ing
10
Be-
26
Al measurements (n
isHiizumi
et alii, 1991),
cosmogenic
36
Cl measurements (P
HilliPs
et alii, 1991)
and thermoluminescence dating of shock-metamor-
phosed dolomite and quartz (s
utton
, 1985), places
the age of the impact at about 50,000 years. In the vi-
cinity of the crater, the Colorado Plateau is underlain
by nearly flat-lying beds of Permian and Triassic age
(FOOS, 1999). The crater lies near the anticlinal bend
of a gentle monoclinal fold and the strata are broken
by wide-spaced, north-west trending normal faults,
which are typically kilometers in length but have dis-
background image
m.c. P
AluciS
, w.e. D
ietrich
, & A. h
owArD
246
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
parently began deposition immediately after impact
(s
HoemakeR
& k
ieffeR
, 1974).
CURRENT AND PALEO-CLIMATE
Precipitation at Meteor Crater is 300 to 450 mm
annually, with approximately equal amounts of rain and
snow. k
umaR
et alii (2010) report mean annual rainfall
of 200 mm and snowfall of 290 mm at the Winslow sta-
tion (about 30 km away) for the past 100 years.
At Meteor Crater, grasslands dominate the vegeta-
tion. To the east of the crater, at lower elevations, there
is a sagebrush ecosystem and to the west, at higher el-
evations, the grassland turns to woodland, dominated
by juniper and pinyon (some of which is observed on
the south rim of Meteor Crater) and pine (a
ndeRson
et
posed of material from multiple formations as well
as shock-melted Coconino and meteoritic debris, are
located on the upper crater walls and in a thick lens on
the crater floor.
The steepest and highest part of the crater wall
consists of exposed bedrock with local patches of
breccia. This is bordered by material mapped as talus
by s
HoemakeR
& k
ieffeR
(1974), downslope of which
lies sediment referred to as Pleistocene and Holocene
alluvium and lake deposits (and Holocene playa beds)
(Figs. 2 and 3). The talus is located in a similar po-
sition to the “pasted-on” deposits in Martian gullies
(m
ustaRd
et alii, 2001; C
HRistensen
, 2003) and the
older alluvium is similar to the “apron” deposits on
Mars. The 30 m of lake sediments in the crater ap-
Fig. 2 - (above) Conceptual sketch of materials and
surface features in crater. Note the covaria-
tion in slope gradient, materials and process.
Bedrock is exposed in the upper wall (slopes
>~32°). Deep canyons are cut through the
equivalent of “pasted-on” materials (~20 -
32°) found on Mars and the channels terminate
in lobate or tongue-shaped deposits, which
through successive events cross each other
(corresponding mostly to the 8 to 15° slopes
in Figure 1). water sorted sediments (wash
and lake deposits) occupy the lowest regions.
The fan is the cartoon is based on comments
found in K
umAr
et alii (2010) and has not yet
been detected from the LIDAR images or the
brief initial field work. The numbers refer to
three general sources of water: 1) local re-
charge and crater wall discharge associated
with impact fractures [based on K
umAr
et alii
(2010)], 2) surface moisture runoff (snow melt
or rain), and 3) regional groundwater rise and
discharge to crater wall (not shown). Compare
cartoon with Figure 3
Fig. 3 - Lithologic cross-section of Meteor crater (S
hoemAKer
, 1960)
background image
THE ROLE OF DEBRIS FLOWS IN THE ORIGIN AND EVOLUTION OF GULLY SYSTEMS ON CRATER WALLS: MARTIAN ANALOGS IN
METEOR CRATER, ARIZONA (USA)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
247
north of the point of impact, was 186 m below the
ground surface (or 1500 m MSL), putting the water
table about 60 m below the current crater floor. P
ilon
et alii (1991) used ground-penetrating radar to locate
the water table, and found it to be ~65m below the
crater bottom (or 1440 m MSL), in good agreement
with the well reading. Based on the immediate forma-
tion of lake deposits post impact, s
HoemakeR
& k
i
-
effeR
(1974) proposed that at the time of impact, the
water table was 30-40 m higher (1536-1546 m MSL)
than the current water level. R
oddy
(1978), however,
pointed out that shock compression of the Coconino
sandstone could have induced high pore pressures
which forced water to flow upward into the crater,
allowing for a lake to form without the crater floor
intersecting the local groundwater table.
In the Black Mesa basin in northeast Arizona, z
Hu
et alii (1998) used
14
C dating of groundwater in com-
bination with numerical simulations of groundwater
flow to look at groundwater levels from 40,000 years
ago to present, and found that around 15,000 years
ago the groundwater levels reached a maximum (55
m higher than present) and then steadily declined.
Though Meteor Crater is not in the Black Mesa ba-
sin, it does share a similar climate and geology, and
perhaps experienced similar groundwater levels. If so,
at the time of impact, assuming the impact occurred
50,000 years ago, the groundwater levels may have
been 35-40 m higher than present. k
RinG
(2007) sum-
marizes studies of the fossil record in the lake sedi-
ments, which suggest sustained lake levels (not sea-
sonally dry) that may have been supported by springs.
The intensive fracturing associated with the mete-
orite impact may also have created “enhanced permea-
bilities on the crater wall rocks” (k
umaR
et alii, 2010).
As illustrated in Fig. 2, if such fracturing were to lead
to water directed to the walls, then perhaps very local
seepage could occur there. Given that the bedrock was
already relatively permeable before impact, it is not
clear if a perched water table within the fractured rock
and above the regional water table would occur, or if
it would drain to the crater walls.
.
OBSERVATIONS AND DISCUSSION
Meteor Crater serves as an analogue to Martian
gullies for several reasons. Firstly, it shares morpho-
logical similarities to Martian gullies. In addition to
having erosional features with the classic “alcove-
alii, 2000; k
RinG
, 2007). Packrat middens have been
observed in the crater wall and burrowing animals are
still present at the crater, as indicated by the burrow sys-
tem on the crater floor (k
RinG
, 2007).
C
oats
et alii (2008) collected sixty packrat mid-
dens across the Colorado Plateau that ranged from
>48,000 years BP to present and found that differ-
ences in elevation distributions for trees and shrubs
ranged from 1200 m to no change. This study also
found that at some times Wisconsinan climates must
have had greater monsoon precipitation than today in
order to support certain conifer populations north of
their current distributions. k
RinG
(2007) found pollen
deposited in the lake sediments at Meteor Crater, sug-
gesting that woodlands might have been established
near or at the impact site. However, the diversity and
concentration of pollen is low, indicating it travelled
from long-distances and supporting the hypothesis
that sagebrush may have dominated during the late
Pleistocene.
More specific paleo-climate inferences have been
made for the nearby Black Mesa basin (Zhu et alii,
1998; z
Hu
et alii, 2010). Direct dating, numerical mod-
elling and tracing of noble gases suggest that 14,000
to 17,000 years ago the recharge rates increased by
three times relative to today. Rainfall intensity may
have also been higher. z
Hu
et alii (1998) propose the
pulse of high recharge was due to a northward migra-
tion of the southern branch of the split jet stream and
that water level fluctuations rose by as much as 60 m
relative to current levels. Recently, w
aGneR
et alii
(2010), reported the results of a high-resolution analy-
sis of a speleothem from a cave in Arizona. They dem-
onstrate that the record tracks the pattern of millennial
variability seen in diverse locations throughout the
Northern Hemisphere between 54 and 30 kyr BP. The
record continues to about 11, 000 BP. Taken together,
these studies show that a systematic wetter and cooler
climate existed in the late Pleistocene, but significant
climatic oscillations occurred during the period of ac-
tive gully development in Meteor Crater. Snow may
have been a greater proportion of the total precipita-
tion, potentially generating snowmelt, or more intense
rain may have occurred, leading to surface runoff.
CURRENT AND PALEO-HYDROLOGY
In 1978, R
oddy
(1978) reported that the wa-
ter level in the Meteor Crater well, located 1050 m
background image
m.c. P
AluciS
, w.e. D
ietrich
, & A. h
owArD
248
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
channel-apron” shape, the crater also has thick talus
deposits that the gullies have eroded into, similar to
the “pasted-on” terrain into which Martian gullies
have eroded. Secondly, it is a well-studied crater, from
its formation mechanism to its geology to its past hy-
drology and ecology, data which are almost impos-
sible to obtain about any crater on Mars. Thirdly, it
has evidence of a paleo-lake that may have been sup-
ported by an elevated water table. This fairly raises
the question about groundwater influences, which is
a central question concerning Martian gullies, since
many craters on Mars also show signs of past lake
deposits. And lastly, it is young enough that its full
erosional history can be deciphered.
For these reasons, we have obtained a high-reso-
lution topographic data set from the National Center
for Airborne Laser Mapping (NCALM), which allows
us to detect detailed morphology of the gullies, includ-
ing their levees. With this dataset and an initial field
campaign we have observed that the Meteor Crater
gullies: 1) cut through talus, 2) show evidence of mul-
tiple events, 3) do not cross the crater floor, 4) mostly
terminate on an apron that has a slope between 8 to 15
degrees, 5) are 1 to 10 m wide across the top of the al-
cove, and 6) have modest-sized, but distinctive, levees.
As mentioned previously, most Martian gullies
occur on slopes that are partially mantled with mate-
rial that has most likely been atmospherically depos-
ited.. The scarcity of large boulders in HiRISE images
of the depositional region and the abundance of large
boulders in the wall rock exposed in alcoves seems to
indicate that gully forming processes entrain and trans-
port pasted-on material, not material derived from wall
rock. Also, it is likely that the pasted-on material is
largely composed of fine material, ranging from sand
to dust-sized particles, and it is this size range that is
important for forming flows capable of deep channels,
natural levees or hummocky terminal deposits. Many
of the gullies on Meteor crater, which cut through de-
posited terrain (i.e. talus), may work in the same way.
k
umaR
et alii (2010) describe in detail the “al-
cove-like” headwater areas to the gullies. They note
that the alcoves occur on the bedrock exposures on
the upper to middle crater walls, either originating
from the rim crest or below the contact of the Kaibab
dolomite and Coconino sandstone. The alcoves in the
Coconino sandstone tend to be wider and deeper than
those in the Kaibab, most likely due to the differences
in weathering between the hard Kaibab dolomites and
the soft Coconino sandstone. k
umaR
et alii (2010)
also note that the larger gullies incise down into the
bedrock and the smaller gullies incise only talus and
alluvial deposits. The crater also has an extensive net-
work of fractures, which have been grouped into three
categories by k
umaR
& k
RinG
(2008): radial, concen-
tric, and conical. Based on the observations of k
umaR
et alii (2010), most of the gullies occur preferentially
along the radial fractures, which strike more or less
perpendicularly to the bedding planes. Based on our
inspection of one alcove area, there was no evidence
that seepage had occurred. There was no staining, or
coarse lag deposits, and the channels below showed
no sign of sustained fluvial wash.
We observed at our site (and it has been observed
on Mars) that portions of the aprons are not connected
to their chutes and are generally smoother in appear-
Fig. 4 - A. Photograph (above left) of Meteor Crater showing upper bedrock, lowered mantled (pasted-on) slope fol-
lowed by hummocky apron of crossing levee deposits down to white playa lake area. B. Photograph (above
right) looking upslope in apron area showing boulder levees
background image
THE ROLE OF DEBRIS FLOWS IN THE ORIGIN AND EVOLUTION OF GULLY SYSTEMS ON CRATER WALLS: MARTIAN ANALOGS IN
METEOR CRATER, ARIZONA (USA)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
249
from the observation that the gullies occur preferen-
tially along the fracture-fault system in the crater wall,
there is no other quantitative or qualitative data that
exists to support the inference that fluvial processes
(e.g. surface runoff producing overland flow or small
creeks) are the erosive and transporting agent.
Our observations suggest that an alternative ex-
planation to the previously proposed seepage erosion
and fluvial incision and deposition scenario may be
needed. From the point of view of modeling gully
formation processes on Mars, it is important to distin-
guish river incision and deposition (fluvial processes)
from that done by debris flows (mass transport). Riv-
er transport of coarse sediment on steep slopes is a
subject of active research in terrestrial channels (e.g.
y
aGeR
et alii, 2007; l
amb
et alii, 2008). Field obser-
vations suggest that shallow flows on steep slopes of-
ten cannot generate sufficient boundary shear stresses
to mobilize coarse sediment (i.e. cobbles and boul-
ders) as bedload. Instead, sweeping of coarse sedi-
ment downslope and incision into underlying bedrock
is driven by periodic debris flows (s
toCk
& d
ietRiCH
,
2003 and 2006). This distinction is important: much
more water is needed to transport sediment, and erode
bedrock, (e.g. s
klaR
& d
ietRiCH
, 2004) at the rela-
tively low concentrations of bedload transport than is
necessary to produce a mass flow that can scour and
mobilize large particles. Experimental work by H
su
et alii (2008) demonstrates the effectiveness of debris
flow incision into bedrock. Hence, it is important if the
Meteor Crater gullies are to be used to test models like
those of P
aRsons
& n
immo
(2010) that we quantify
the relative role of fluvial versus debris flow processes
in the incision, transport and deposition of sediment.
As an alternative to current interpretations, we
propose that debris flows, perhaps driven by periodic
snowmelt during the cooler, wetter Pleistocene drove
gully incision into the talus and led to interlacing
channels downslope (Fig. 2). An essential ingredient
was not just water, but the presence of fines, that when
mixed with water served to mobilize and sustain the
debris flow motion. We hypothesize that the fines are
derived in part from the crushed rock and dust that is
patchily found around the crater. The talus has some
strength so that it can support cuts into it, and yet,
through erosion, it may provide the necessary fines for
debris flow mobilization. If our future work finds this
to be correct, it will provide an additional constraint
ance. In addition, chutes disconnected from source
alcoves, degraded chutes, terraces along chutes, and
apron-head trenching indicate multiple flow events. It
is plausible that the formation of the Meteor Crater
alcoves, chutes, and aprons (as well as the Martian
ones) requires many flow events to form.
Another feature that both Meteor Crater and Mar-
tian gullies share is the abrupt termination of chutes
and hummocky deposits. Photogrammetric measure-
ment of depositional aprons on Mars indicates that
most exhibit nearly linear profiles inclined 8 to 15
degrees (H
owaRd
et alii, 2008a; P
aRsons
& n
immo
,
2010). At Meteor Crater, we observed that the chan-
nels do not form an integrated network, and com-
monly they either terminate abruptly without a fan or
end in a lobate, or tongue-like, deposit of debris. This
apron transition from the talus incision to the termina-
tion point, lying in the ~8 to 15 degree slope range (the
same as on Mars), corresponds to an elevation drop
from 1580 m to 1570 m. The lower elevation is about
the height of the highest mapped lake sediments in the
crater [the bottom of crater is at about 1561 m above
mean sea level (MSL)].
Modest sized levees were seen on foot and are
detectable with the 25 cm contour-interval LiDAR
data, and are characteristic of mass wasting, not flu-
vial processes. Exposure in the levee walls show that
the levees are cored by matrix supported material.
However, locally, well-sorted boulder levees do oc-
cur. We have not yet detected features that suggest a
delta transition into standing water. Also, if sustained
seepage occurred due to the intersection of the crater
wall with the water table, we would expect that al-
luvial fans would be present at the mouth of the chan-
nels, but inspection of the LiDAR data does not detect
such features.
.AN ALTERNATIVE HYPOTHESIS TO
GROUNDwATER SEEPAGE
k
umaR
et alii (2010) argue that the gullies at Me-
teor Crater are associated with the radial fractures and
tear faults exposed in the crater walls and suggest this
association is due in part to groundwater discharge.
This discharge could be derived from local recharge
in the fractured rock surrounding the crater. They con-
clude that “fluvial processes eroded the materials from
the crater walls and deposited them as Pleistocene al-
luvium… inter-fingered with lake sediments”. Aside
background image
m.c. P
AluciS
, w.e. D
ietrich
, & A. h
owArD
250
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
on the essential elements for debris flow initiation and
mobilization on Mars (i.e. fines from impact waste).
CONCLUSIONS AND FUTURE WORK
Key observations and data are still needed to
resolve the difference between the previous ground-
water seepage model coupled to fluvial incision and
our debris flow model from surface water (perhaps
from snow melt). Our goal for this paper was merely
to add to the observations of k
umaR
et alii (2010)
and propose an alternative way of interpreting these
observations. It is now necessary to: 1) identify mor-
phologic, sedimentologic and weathering features
that would support a seepage versus surface water
origin of the channels via field observation and care-
ful analysis of LiDAR data, 2) determine the maxi-
mum height of the ground water table during the late
Pleistocene through the use of numerical groundwa-
ter models, 3) obtain cosmogenic dating of the most
recent debris flows to find out if they were active in
the Holocene (when the water table was presumably
near current levels), and 4) document of the role of
crushed rock fines in debris flow generation through
large scale experimentation in a vertically rotating
drum [similar to the work of H
su
(2010)].
ACKNOWLEDGEMENTS
This research is supported by the National Center
for Earth-surface Dynamics and the Barringer Fam-
ily Fund for Meteorite Impact Research. The LiDAR
coverage was provided through a seed grant to the
senior author by the National Center for Airborne
Laser Mapping. The authors would also like to thank
Ionut Iordache, for his help with processing the raw
LiDAR data, and David Kring, for valuable discus-
sions regarding Meteor Crater and its geologic history.
REFERENCES
a
ndeRson
R.s., b
etanCouRt
J.l, m
ead
J.i., H
evly
R.H. & a
dam
d.P. (2000) - Middle- and late-wisconsin paleobotanic and
paleoclimatic records from the southern Colorado Plateau, USA, Paleo, 155, 31-57.
C
HRistensen
P.R. (2003) - Formation of recent Martian gullies through melting of extensive water-rich snow deposits, Nature,
422, 45-48.
C
oats
l.l., C
ole
k.l & m
ead
J.i. (2008) - 50,000 years of vegetation and climate history on the Colorado Plateau, Utah and
Arizona, USA, Quaternary Research, 70, 322-338.
C
oleman
k.a., d
ixon
J., H
owe
k.l. & C
HevRieR
v.f. (2010) - Slushflows as analogs for Martian gully formation, Lunar and
Planetary Science Conference 41, Abstract 2741.
C
onley
J.n. (1977) - Subsurface Structure Maps G-6A, G-7, G-8 Eastern Mogollon Slope, Region, East Central Arizona, Ari-
zona Oil and Gas Conservation Commission, Pheonix, AZ.
C
ostaRd
f., f
oRGet
f., m
anGold
n. & P
eulvast
J.P. (2002) - Formation of Recent Martian Debris Flows by Melting of Near-
Surface Ground Ice at High Obliquity, Science, 295, 110-113.
d
iCkson
J.l. & H
ead
J.w. (2009) - The formation and evolution of youthful gullies on Mars: Gullies as the late-stage phase of
Mars’ most recent ice age, Icarus, 204, 63-86.
d
ixon
J.C., H
owe
k.l. & C
oleman
k.a. (2010) - Periglacial hillslope analogs for Martian gully formation, Lunar and Planetary
Science Conference 41, Abstract 2392.
d
undas
C.m., m
C
e
wen
a.s, d
inieGa
s., b
yRne
s. & m
aRtinez
-a
lonso
s. (2010) - New and recent gully activity on Mars as seen
by HiRISE, Geophysical Research Letters, 37, L07202, doi:10.1029/2009GL041351.
f
oos
a. (1999) - Geology of the Colorado Plateau, 6 pp.
G
ilmoRe
m.s. & P
HilliPs
e.l. (2002) - Role of aquicludes in formation of Martian gullies. Geology, 30 (12), 1107-1110.
G
RotzinGeR
J., J
oRdan
t.H., P
Ress
f. & s
ieveR
R. (2007) - Understanding Earth, 5
th
Edition, W.H. Freeman and Company, New
York, NY.
H
aRtmann
w.k., t
HoRsteinsson
t. & s
iGuRdsson
t. (2003) - Martian hillside gullies and Icelandic analogs, Icarus, 162: 259-
277.
H
ead
J.w., m
aRCHent
d.R. & k
Reslavsky
m.a. (2008) - Formation of gullies on Mars: Link to recent climate history and inso-
lation microenvironments implicate surface water flow origin, Proc. Natl. Acad. Sci., 105 (36): 13258-13263.
H
eCHt
m.H. (2002) - Metastability of Liquid water on Mars, Icarus, 156: 373-386.
H
eldmann
J.l. & m
ellon
m.t. (2004) - Observations of martian gullies and constraints on potential formation mechanisms,
background image
THE ROLE OF DEBRIS FLOWS IN THE ORIGIN AND EVOLUTION OF GULLY SYSTEMS ON CRATER WALLS: MARTIAN ANALOGS IN
METEOR CRATER, ARIZONA (USA)
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
251
Icarus, 168: 285-304.
H
owaRd
a.d., m
ooRe
J.m., d
ietRiCH
w.e. & P
eRRon
J.t. (2008a) - Martian Gullies: Morphometric properties and flow charac-
teristics, Lunar and Planetary Science Conference, 39: Abstract 1629.
H
uGenHoltz
C.H. (2008) - Frosted granular flow: A new hypothesis for mass wasting in martian gullies, Icarus, 197, 65-72.
HSU L. (2010) - Bedrock erosion by granular flow. Ph.D. diss., Department of Earth and Planetary Science, University of Cali-
fornia, Berkeley.
H
su
l., d
ietRiCH
w.e. & s
klaR
l.s (2008) - Experimental study of bedrock erosion by granular flows, Journal of Geophysical
Research, 113: F02001, doi: 10.1029/2007JF000778.
k
RinG
d.a. (2007) - Guidebook to the Geology of Barringer Meteorite Crater, Arizona, Lunar and Planetary Institute, Houston,
TX, 150 pp. (LPI Contribution Number 1355).
k
umaR
P.s., H
ead
J.w. & k
RinG
d.a. (2008) - Structural and lithologic controls on gully formation on the inner wall of Meteor
Crater, Arizona: Implication for the origin of mars gullies. Workshop on Martian Gullies: Theories and Tests, Abstract 8011.
k
umaR
P.s., H
ead
J.w. & k
RinG
d.a. (2010) - Erosional modification and gully formation processes at Meteor Crater, Arizona:
Insights into crater degradation processes on Mars. Icarus, 208: 608-620.
k
umaR
P.s & k
RinG
d.a. (2008) - Impact fracturing and structural modification of sedimentary rocks at Meteor Crater, Arizona,
J. Geophys. Res., 113: p. E09009 10.1029/2008JE003115.
lanza n.i., meyeR G.a., okuba C.H., newson H.e. & wiens R.C. (2010) – Evidence for debris flow gully formation
initiated by shallow subsurface water on Mars, Icarus, 205: 103-112.
l
amb
m.P., d
ietRiCH
w.e., a
CieGo
s.m., d
e
P
aolo
d.J. & m
anGa
m. (2008) - Formation of Box Canyon, Idaho, by Megaflood:
Implications for Seepage Erosion on Earth and Mars, Science, 320. doi: 10.1126/science.1156630.
m
alin
m.C. & e
dGett
k.s. (2000) - Evidence for Recent Groundwater Seepage and Surface Runoff on Mars, Science, 288:
2330-2335.
m
anGold
n., C
ostaRd
f. & f
oRGet
f. (2003) - Debris flows over sand dunes on Mars: Evidence for liquid water, Journal of
Geophysical Research (Planets), 108. DOI: 10.1029/2002JE001958.
m
áRQuez
a.,
de
P
ablo
m.a., o
yaRzun
R. & v
iedma
C. (2005) - Evidence of gully formation by regional groundwater flow in the
Gorgonum Newton region (Mars). Icarus, 179: 398-414.
m
C
k
ee
e.d. (1945) - Small-Scale Structures in the Coconino Sandstone of Northern Arizona. The Journal of Geology, 53 (5),
313-325.
m
ellon
m.t. & P
HilliPs
R.J. (2001) - Recent gullies on Mars and the source of liquid water, Journal of Geophysical Research,
Planets, 106: 23165-23180.
m
usselwHite
d.s., s
windle
t.d. & l
unine
t.i. (2001) - Liquid CO2 breakout and the formation of recent small gullies on Mars,
Geophysical Research Letters, 28 (7): 1283-1285.
m
ustaRd
J.f., C
ooPeR
C.d. & R
ifkin
m.k. (2001) - Evidence for recent climate change on Mars from the identification of youth-
ful near-surface ground ice, Nature, 412: 4111-4114.
n
isHiizumi
k., k
oHl
C.P., s
HoemakeR
e.m., a
Rnold
J.R., k
lein
J., f
ink
d. & m
iddleton
d. (1991) - In situ
10
Be–
26
Al exposure
ages at Meteor Crater, Arizona, Geochim. Cosmochim. Acta, 55: 2699–2703.
P
aRsons
R.a. & n
immo
f. (2010) - Numerical modeling of Martian gully sediment transport: Testing the fluvial hypothesis,
Journal of Geophysical Research, 115, E06001, doi:10.1029/2009JE003517.
P
HilliPs
f.m., z
Reda
m.G., s
mitH
s.s., e
lmoRe
d., k
ubik
P.w., d
oRn
R.i. & R
oddy
d.J. (1991) - Age and geomorphic history
of Meteor Crater, Arizona, from cosmogenic
36
Cl and
14
C in rock varnish, Geochim. Cosmochim. Acta, 55: 2695-2698.
P
ilon
J.a., G
Rieve
R.a.f. & s
HaRPton
v.l. (1991) - The subsurface character of Meteor Crater, Arizona, as determined by
ground-probing radar, Journal of Geophysical Research, 96 (1): 15563-15576.
R
oddy
d.J. (1978) - Pre-impact geologic conditions, physical properties, energy calculations, meteorite and initial crater dimen-
sions and orientations of joints, faults, and walls at Meteor Crater, Arizona, Proc. Lunar Planet. Sci. Conf., 9: 3891-3930.
s
HinbRot
t., d
uonG
n.H., k
wan
l. & a
lvaRez
m.m. (2004) - Dry granular flows can generate surface features resembling those
seen in Martian gullies. Proceedings of the National Academy of Science, 101: 8542-8546.
s
HoemakeR
e.m. (1960) - Penetration mechanics of high velocity meteorites. illustrated by Meteor Crater, Arizona, 21
st
Interna-
tional Geological Congress, Int. Union of Geol. Sci., 418-434.
background image
m.c. P
AluciS
, w.e. D
ietrich
, & A. h
owArD
252
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
s
HoemakeR
e.m. (1987) - Meteor Crater, Arizona, Geological Society of America Centennial Field Guide – Rocky Mountain
Section, 6 pp.
s
HoemakeR
e.m. & k
ieffeR
s.w. (1974) - Guidebook to the Geology of Meteor Crater, Arizona. Arizona State University,
Tempe, Arizona, p. 66 (Publication No. 17).
s
klaR
l.s. & d
ietRiCH
w.e. (2004) - A mechanistic model for river incision into bedrock by saltating bedload. Water Resources
Research, 40, doi: 10.1029/2003WR002496.
s
toCk
J.d. & d
ietRiCH
w.e. (2003) - Valley incision by debris flows: Evidence of a topographic signature. Water Resources
Research, 39 (4), doi: 10.1029/2001WR001057.
s
toCk
J.d. & d
ietRiCH
w.e. (2006) - Erosion of steepland valleys by debris flows. GSA Bulletin, 118: 1125-1148.
s
utton
s.R. (1985) - Thermoluminescence measurements on shock-metamorphosed sandstone and dolomite from Meteor Crater,
Arizona. 2. Thermoluminescence age of Meteor Crater, J. Geophys. Res., 90: 3690–3700.
t
Reiman
a.H. (2003) - Geologic settings of Martian gullies: Implications for their origins, Journal of Geophysical Research,
108 (E4), 8031, doi:10.1029/2002JE001900.
w
aGneR
J.d.m., C
ole
J.e., b
eCk
J.w., P
atCHett
P.J., H
endeRson
G.m. & b
aRnett
H.R. (2010) - Moisture Variability in the
Southwestern United States linked to abrupt glacial climate change. Nature Geoscience, 3: 110-113.
y
aGeR
e.m., k
iRCHneR
J.w. & d
ietRiCH
w.e. (2007) - Calculating bed load transport in steep boulder bed channels. Water
Resources Research, 43. doi: 10.1029/2006WR005432.
z
Hu
C., w
addell
R.k., s
taR
i., & o
stRandeR
M. (1998) - Responses of ground water in the Black Mesa basin, northeastern
Arizona, to paleoclimatic changes during the late Pleistocene and Holocene. Geology, 26 (2): 127-130.
z
Hu
C. & k
olf
R. (2010) - Noble gas signatures of high recharge pulses and migrating jet stream in the late Pleistocene over
Black Mesa, Arizona, United States. Geology, 38 (1): 83-86.
Statistics