P34A-01 INVITED
The Great Basin and Mojave Desert as a hydrological analog to the Martian highlands
The western United States has numerous enclosed drainages caused by an arid climate in conjunction with active tectonic deformation. The highlands of Mars likewise feature numerous enclosed depressions, although the cause is primarily impact cratering rather than tectonics. During the early history of the red planet, these crater basins behaved much like their terrestrial analog, featuring lakes which expanded and contracted depending upon the water balance and channel systems whose degree of integration likewise waxed and waned with climatic variations. The Great Basin hydrological analog is explored using a spatially-explicit routing model that balances runoff and evaporation to predict the size and location of lakes and flows through the channel system under both modern and Pleistocene conditions. The model is parameterized using a spatial database of modern precipitation and elevation as well as regression estimates of runoff and evaporation as a function of precipitation, mean annual temperature, elevation, and latitude. The model reproduces the modern distribution of lakes as well as the extent of Pleistocene lakes (e.g., Bonneville, Lahontan, and Manly) under reasonable changes in average runoff and lake evaporation. The hydrological model has been adapted to the Martian highlands to explore the degree of drainage integration and location of lake basins as a function of the ratio of lake evaporation to runoff depth. Comparison of the spatial distribution of valleys, basin overflows, and incision depths permits the estimation of relative evaporation and runoff during early Martian history. Simulation modeling of landform evolution also is used to explore differences in pattern of erosion and deposition on the Martian highlands as a function of the evaporation/runoff ratio.
P34A-02 INVITED
Orbital and Ground-penetrating Radar Studies of Mars-analog Terrain in Egypt
Several study groups have endorsed the concept of flying an imaging synthetic aperture radar (SAR) in orbit that would penetrate areas of thin surface cover revealing underlying terrain and providing additional information on surface roughness, physical properties and composition. Egypt provides many excellent terrestrial field sites to study both the processes that we expect to be revealed in a Mars SAR Mission, as well as the stratigraphic setting of past depositional environments that are similar to those seen in southern Egypt. We have used terrestrial orbital radar data for southern Egypt, comparing geologic materials and boundaries mapped in the field and with visible wavelengths (from Landsat) to those discerned via Shuttle Imaging Radar (SIR) -C, and field checking key sites to determine the depth, physical characteristics and types of geologic boundaries that contribute to the radar returns. In addition to stratigraphic mapping of the thickness and extent of near-surface units in the field, we have used ground-penetrating radar (GPR) to determine the lateral extent and depth of subsurface interfaces. In this manner, we expect to learn more about the capabilities and limitations of orbital and ground-based systems, the trade-offs between frequency, polarization and resolution in Mars-like terrain for detecting buried interfaces and structures, and more about the geologic history of southern Egypt. Several studies have concentrated on one of the areas of prominent radar-detected channels near Bir Safsaf in the southwest desert, we have concentrated on the Bir Kiseiba region, an area where the mixture of gravel spreads, buried paleochannels, and alluvium creates a setting that may mimic outflow deposit locations on Mars. While bedrock incised channels may stand out in SAR images because of a near-surface, sharp dielectric interface (such as those at Safsaf and in northern Sudan), the more complex problem of distinguishing fluvial patterns in Mars-like alluvial environments requires additional study.
P34A-03 INVITED
Icelandic Rootless Volcanic Cone Eruptions as Analogs to Explosive Lava-Water Interactions on Mars
Rootless volcanic cones form by explosive lava-water interaction when a lava flow moves over a water-bearing substrate, such as lake deposits, riverbeds, or marshes. Rootless cones are common in the Holocene lava flows of Iceland, where they form groupings of hundreds of structures within a host lava flow. Since the late 1990's, high-resolution Mars Orbiter Camera and Thermal Emission Imaging System images have revealed in great detail fields of cones in the northern volcanic plains of Mars. In this case, it has been postulated that the cones are produced by interactions of lava with ice contained at shallow depths within the martian regolith. In the Cerberus region, the co-location of extensive young effusive volcanism with repeated aqueous flood events would provide a mechanism for rootless eruptions. Hundreds of cones have been identified in this area, implying the presence of low-latitude water/ice stores in geologically recent times. Our work involves detailed field studies of Icelandic rootless cones aimed at elucidating the formation mechanism of rootless explosions and developing models of the lava-water interaction. Furthermore, we have devised statistical methods for the unequivocal identification rootless cone fields on Mars, and mapped their occurrence on a number of young lava flows. Our presentation will include new insights into cone formation processes gleaned from our field campaigns, and discuss the implications for regolith ice stores on Mars.
P34A-04
Morphology and Emplacement of Long Lava Flows in the Tharsis Volcanic Province, Mars
Lava flows, 10's to 100's of kilometers in length, dominate the lower plains surrounding the Tharsis Montes volcanoes (Ascraeus Mons, Pavonis Mons, and Arsia Mons) on Mars. An analysis of the morphology and emplacement of a 690-km-long lava flow on the southwest perimeter of Ascraeus Mons indicates that effusion rates on the order of 104 m3 s-1 and eruption durations of 3 to 7 Earth-months are needed to emplace a flow of this scale. We will present an analysis of the morphology and emplacement, including effusion rates, eruption durations, and style of flow (e.g. channeled or non-channeled) for 10 lava flows with flow lengths traceable for >100 km in the Tharsis Montes region, Mars identified in a mosaic of Thermal Infrared Imaging System (THEMIS) infrared images (256 m/pixel). The source areas for these flows are typically obscured, but the center-lines of the flows trend back toward the aprons on the northeast and southern flanks of each of the volcanoes. Lava flows in Hawaii and New Mexico serve as terrestrial analogs for the lava flows we are studying on Mars. We have combined mapping of Ikonos images (2 m/pixel) with Differential Global Positioning System (DGPS) transects to interpret the emplacement of channeled a'a flow from the 1907 eruption on Mauna Loa volcano, Hawaii. Downstream changes in flow morphology are similar between the 1907 Mauna Loa flow and the ~690-km-long lava flow from Ascraeus Mons, though the 1907 flow has a shorter eruption duration, flow length, and lower calculated eruption rate. We will also present a preliminary analysis of research on a lava flow in New Mexico as an analog for non-channeled lava flows. Additional studies of lava flows >100 km long in the Tharsis region will constrain eruption parameters along the lower plains and provide insight into late-stage eruption periods of these three large volcanoes.
P34A-05
Martian Gullies: H2O or CO2 snow?
The theories proposed to try to explain the origin of the Martian gullies involve either liquid water, liquid carbon dioxide or flows of dry granular material. We propose another processes that can be favorable for the origin of the Martian gullies, with our model by gaseous fluidification of CO2. We propose that on the Martian slopes, CO2 snow and dust transported by winds, are accumulate. During the Martian spring, sublimation of carbonic snow starts because of heat and weigth of the frezze layer, causing that the material mixed its fluidifized and slide downslope by gravity. By experimental work with dry granular material, we simulated the development of the Martian gullies injecting air inside the granular material. We also present the characteristics of some terrestrial gullies forms at cold environment, sited at Nevado de Toluca Volcano near Toluca City, México. We compared them with some Martian gullies, to identify possible processes evolved in its formation. We measured the lengths of those Martian gullies and the range was from 24 meters to 1775 meters. Finally, we present results of our experimental work at laboratory with dry granular material and our field trip to Nevado de Toluca Volcano.
P34A-06
Barchan and Linear Dunes on Earth and Mars - Comparative Research
High resolution images from MGS and MRO reveal, in detail, ripples and dunes on Mars that were not discerned in old Viking images. The two basic dune types known on Earth, barchan (and transverse) and seif (linear), are also common on Mars, although seif dunes are quite rare on that planet. Some Martian barchan and seif dunes have a different morphology, particularly as evident in the Martian north polar region. Some of the barchans have an elongated, elliptical shape, while some of the linear dunes lack the sinuosity commonly associated with terrestrial seif dunes. These barchan and linear dunes occur together, side-by-side, and in some cases are merged to create a single bed-form. Induration of the dunes, or crust formation, can explain the occurrence of these dunes of unusual morphology in the Martian north polar region. Crusts may form as water vapor diffuses into and out of the fine-grained materials on the planet's surface. Salts would be deposited as intergranular cement. Because these bedforms occur in the polar region, the cementing agent could be ice instead of salts; indeed, the dunes spend more than half each Martian year beneath a covering of seasonal frost, mostly frozen carbon dioxide. Elliptical shaped barchans were created artificially in Saudi Arabia by spraying advancing barchan dunes with crude oil to stabilize them until the dunes reached a streamlined body shape. Simulation work indicates that the same process can occur on the indurated Martian barchans, but by cementation of grains rather than introduction of oil. Short lee dunes that have a linear shape with a sharp-edged crest are known to form from sand accumulation at the lee side of obstacles. Once a dune is stabilized by induration or crust, it functions as an obstacle to the wind. Linear lee dunes stabilized by ice (water or carbon dioxide) or mineral crust may elongate and form a long linear dune that aligns parallel to the wind. Melting of the ice will set up a straight linear dune, with loose sand, parallel to the dominant wind. Field observations on terrestrial deserts show that such a dune can only be formed when it is covered by vegetation. If vegetation is removed the bare linear dune disintegrates into small barchans. Simulation also shows that linear dune is unstable and deforms until it takes the shape of a string of barchans, which are the stable shape under unidirectional winds.
P34A-07
Dunes Versus Ripples: Topographic Profiling Across Terrestrial Examples, With Application to the Interpretation of Features on Mars
Topographic profiles were collected for several aeolian bedform types throughout the western United States, ranging from sand ripples to transverse dunes. Profiles were measured perpendicular to bedform crests for features ranging over three orders of magnitude in wavelength, including sand ripples, granule-covered sand ripples, granule ripples, active transverse dunes, and partially stabilized transverse dunes. The data collection technique used depended on the size of the bedform. When the terrestrial topographic profiles are normalized by the measured wavelength of the features, in both horizontal and vertical dimensions, the profiles show a progression of shapes from sand ripples to granule ripples to transverse dunes. Current sampling does not allow a determination of whether the observed profile changes represent a smooth progression of profile shape or that the profiles fall into discreet classes. As a test of the use of the scaled profile approach to features on Mars, topographic information was derived through simple photoclinometry on the first publicly-released, full- resolution HiRISE image, which happens to reveal an abundance of aeolian bedforms. When scaled by the feature wavelength, as was done for the terrestrial examples, the profile across a 50-m-wavelength martian bedform has the characteristic shape of a granule ripple. However, the scaled height of the martian feature (0.17) is greater than the largest scaled height of any of our measured terrestrial features (0.13, for a sand ripple). If the heights from the martian profile are reduced by a factor of 0.38, the ratio of martian to terrestrial gravity, the martian profile then conforms very closely to the scaled profile of a terrestrial granule ripple. Numerous granule ripples have been imaged by both the Spirit and Opportunity rovers during more than 3 years of operation on Mars, but to date the rovers have not investigated a feature of 50 m wavelength. Topographic profiles should be obtained for additional terrestrial and martian aeolian bedforms, but our initial results imply that scaled topographic profiles can be of great assistance in evaluating whether 10- to 100-m-wavelength martian bedforms are more likely to be either small sand dunes or large granule-coated ripples.
P34A-08
Geophysical evidence of an impact crater in northwestern South America
A prominent positive terrain correlated free-air gravity anomaly over regionally depressed topography may identify a mascon centered on (4.15 N, 69.5W) in the Vichada plain, Guiana Shield in Northwestern South America. The topographic depression was recognized by LANDSAT images, showing a complex crater with two rings of 30 km and 50 km of diameter. Being one third of the size of the Chibxulub's impact crater, the 50 km-wide impact crater is the first meteor impact found in Colombia and the biggest impact crater of South America. This structure has been partially eroded by the Vichada River and its topographic expression is obscured by dense vegetation and erosion. Free air gravity anomalies at 20 km altitude from EGM-96 do not show any significant signature. However, concentric positive terrain-correlated free-air gravity anomalies are superposed to the impact crater. Also negative Terrain decorrelated free air gravity anomalies are located at the impact crater structure. MOHO estimates from inverse modeled compensated terrain gravity effects show a shallower MOHO below the impact crater, with a thinning of the continental crust, that could be created as a result of the mantle rebound after the shock waves generated by the impact, creating a mascon, typical of an impact crater structure, with a 40 km-wide, 3 km-high plug of mantle material that had risen up into the Earth's crust. Concentric negative total field magnetic anomalies superposed to the gravity anomalies also support the impact crater model.