Seasonally active slipface avalanches in the north polar sand sea of Mars: Evidence for a wind-related origin
Co-authored with Jim Bell.
Geophysical Research Letters, 39, L09201, doi:10.1029/2012GL051329
Meter-scale MRO/HiRISE camera images of dune slipfaces in the north polar sand sea of Mars reveal the presence of deep... more Meter-scale MRO/HiRISE camera images of dune slipfaces in the north polar sand sea of Mars reveal the presence of deep alcoves above depositional fans. These features are apparently active under current climatic conditions, because they form between observations taken in subsequent Mars years. Recently, other workers have hypothesized that the alcoves form due to destabilization and mass-wasting during sublimation of CO2 frost in the spring. While there is evidence for springtime modification of these features, our analysis of early springtime images reveals that over 80% of the new alcoves are visible underneath the CO2 frost. Thus, we present an alternative hypothesis that formation of new alcoves and fans occurs prior to CO2 deposition. We propose that fans and alcoves form primarily by aeolian processes in the mid- to late summer, through a sequence of aeolian deposition on the slipface, over-steepening, failure, and dry granular flow. An aeolian origin is supported by the orientations of the alcoves, which are consistent with recent wind directions. Furthermore, morphologically similar but much smaller alcoves form on terrestrial dune slipfaces, and the size differences between the terrestrial and martian features may reflect cohesion in the near-subsurface of the martian features. The size and preservation of the largest alcoves on the martian slipfaces also support the presence of an indurated surface layer; thus, new alcoves might be sites of early spring CO2 sublimation and secondary mass-wasting because they act as a window to looser, less indurated materials that warm up more quickly in the spring.
Download (.pdf) Widespread weathered glass on the surface of Mars
Briony Horgan and Jim Bell, published in Geology, May 2010
Low albedo sediments cover >107 km2 in the northern lowlands of Mars, but the composition and origin of these... more Low albedo sediments cover >107 km2 in the northern lowlands of Mars, but the composition and origin of these widespread deposits have remained ambiguous despite many previous investigations. Here we use near-infrared spectra acquired by the Mars Express OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité) imaging spectrometer to show that these sediments exhibit spectral characteristics that are consistent with both high abundances of iron-bearing glass and silica-enriched leached rinds on glass. This interpretation is supported by observations of low-albedo soil grains with possible rinds at the Phoenix Mars Lander landing site in the northern lowlands. By comparison with the extensive glass-rich dune fields and sand sheets of Iceland, we propose an explosive volcanic origin for these glass-rich sediments. We also propose that the glassy remnant rinds on the sediments are the result of postdepositional alteration, as these rinds are commonly formed in arid terrestrial volcanic environments during water-limited, moderately acidic leaching. These weathered, glass-rich deposits in the northern lowlands are also colocated with the strongest concentrations of a major global compositional surface type previously identified in mid-infrared spectra, suggesting that they may be representative of global processes. Our results provide potential confirmation of models suggesting that explosive volcanism has been widespread on Mars, and also raise the possibilities that glass-rich volcaniclastics are a major source of eolian sand on Mars and that widespread surficial aqueous alteration has occurred under Amazonian climatic conditions.
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Recent aeolian dune changes on Mars
by Ken Edgett
(2008)
M. C. Bourke, K. S. Edgett, and B. A. Cantor
Geomorphology, 94, 247–255. doi:10.1016/j.geomorph.2007.05.012
Previous comparisons of Martian aeolian dunes in satellite images have not detected any change in dune form or... more Previous comparisons of Martian aeolian dunes in satellite images have not detected any change in dune form or position. Here, we show dome dunes in the north polar region that shrank and then disappeared over a period of 3.04 Mars years (5.7 Earth years), while larger, neighboring dunes showed no erosion or movement. The removal of sand from these dunes indicates that not only is the threshold wind speed for saltation exceeded under present conditions on Mars, but that any sand that is available for transport is likely to be moved. Dunes that show no evidence of change could be crusted, indurated, or subject to infrequent episodes of movement.
Volcaniclastic aeolian dunes: Terrestrial examples and application to martian sands
by Ken Edgett
(1993) **SELF ARCHIVED PDF AVAILABLE HERE**
K. S. Edgett and N. Lancaster
Journal of Arid Environments, 25, 271–297. doi:10.1006/jare.1993.1061
On Earth, most aeolian dunes are quartz rich; others are composed of evaporites, carbonates, or clay/silt aggregates.... more On Earth, most aeolian dunes are quartz rich; others are composed of evaporites, carbonates, or clay/silt aggregates. Dunes made of wind-reworked volcaniclastic sediment comprise a less-commonly recognized fifth dune composition. Terrestrial volcaniclastic aeolian dunes are found in (1) arid to semi-arid volcanic regions and (2) coastal areas on volcanic islands. Their sediments can be formed by explosive volcanism or by erosion of lava flows and other lithified volcanic material. Commonly, these sediments have been transported by volcanic and/or fluvial processes before being reworked by wind. Their compositions range from malic to sialic, depending on local volcanic sources. Volcaniclastic dunes, especially those of basaltic composition, may be the best compositional analog for aeolian dunes on Mars. Martian dunes are typically dark-hued and their sands may be derived from erosion of volcanic materials.
Geology and Geomorphology of Coral Pink Sand Dunes State Park, Utah
For a reprint copy, please contact: kathleen.nicoll@gmail.com
Citation: Richard L. Ford, Shari L. Gillman, David E. Wilkins, William P. Clement, and Kathleen Nicoll, 2010. "Geology and Geomorphology of Coral Pink Sand Dunes State Park, Utah," in Geology of Utah’s Parks and Monuments: 2010 Utah Geological Association Publication 28 (third editiion), D.A. Sprinkel, T.C. Chidsey, Jr., and P.B. Anderson, editors.
ABSTRACT Coral Pink Sand Dunes State Park, located in southwestern Kane County, Utah, contains a variety of geologic... more
ABSTRACT Coral Pink Sand Dunes State Park, located in southwestern Kane County, Utah, contains a variety of geologic features, including one of the largest areas of freely migrating dunes in the Colorado Plateau. The semiarid climate, strong prevailing southerly winds, sparse vegetation, and abundant supply of sand-sized sediment make this area susceptible to eolian processes. Picturesque exposures of Jurassic rocks are present within the park. The stratigraphic sequence ranges from the Triassic-Jurassic Moenave Formation to the Middle Jurassic Carmel Formation. The most widespread bedrock unit exposed within the park is the Navajo Sandstone (Lower Jurassic). The Navajo Sandstone is also widely exposed across the Moccasin Terrace southwest of the park and is the most likely source for the sand that comprises the dune field. The “coral pink” color of the dune sand is the result of iron-oxide stains on the surface of the sand grains inherited from the source sandstones.
Migrating dunes, whose morphology is primarily a function of wind characteristics, include transverse ridges, barchanoid ridges, and a solitary star dune. Dunes influenced or impeded by topographic obstacles or vegetation include climbing dunes, echo dunes, parabolic dunes, vegetated linear dunes, and nebkhas. We divide the dune field into major geomorphic units based on the dominant dune type. A largely stabilized (vegetated) sand sheet and partially stabilized, poorly organized dunes are present at the southern (upwind) end of the dune field. The active core of the dune field contains transverse ridges and barchanoid ridges. Barchanoid ridges at the northern (downwind) end of the active core grade into climbing dunes that ramp up the bedrock escarpment associated with the Sevier fault. The climbing dunes in turn grade into large parabolic dunes that dominate the downwind end of the dune field.
Coral Pink Sand Dunes lies within the structural transition zone between the Great Basin section of the Basin and Range province to the west, and the core of the Colorado Plateau to the east. The north-south-trending Sevier fault cuts through the length of the park. The fault trace is marked by a west-facing bedrock escarpment that divides the park into two topographic units (a forested plateau to the east and a relatively low-lying valley floor to the west) and acts as a major control over the accumulation of sand within the dune field.
Important events recorded in the geologic features of the park include the Triassic and Jurassic depositional history of the Glen Canyon Group, the Cretaceous to Cenozoic structural history of the Colorado Plateau, and the late Holocene history of the active dunes. Optically stimulated luminescence dates from the active core of the dune field indicate that Holocene eolian deposition began at least 4,000 years ago. Radiocarbon dating of organic materials from an exhumed soil surface suggests a period of landscape stability approximately 500-200 years ago, coincident with the Little Ice Age. Dendrochronologic data from the ponderosa pines in the park, along with historic photos, indicate the dunefield has experienced alternating wet periods and drought since the end of the Little Ice Age, which have influenced vegetation coverage and dune activity in the area.