The Batamote Mountains represent a 14-16-million-year-old eroded shield volcano complex in the Basin and Range province near Ajo, Arizona. Analysis of Landsat 7 Enhanced Thematic Mapper “Plus” data and fieldwork enabled mapping the geology at 1:24,000 scale. Volcanic deposits and field relations indicate that mid-Tertiary eruptions initially involved mild explosions from at least six vents, evidenced by near-surface intrusive units surrounded by ash, oxidized cinders, and spatter deposits. The associated lava flows partly cover the pre-Batamote basement silicic volcanic rocks. At least three subsequent effusive phases emplaced multiple flows from a minimum of six vents on the cinder cone deposits and earlier lava flows. The last volcanic event involved fire-fountains that produced several short, thin, agglutinated flows, forming the steeper summit of the volcano. Extension and normal faulting caused rocks in the central portion of the Batamote Mountains to collapse; subsequent erosion of summit material left the amphitheater morphology seen today.

Introduction: Some linear, curved and "curlicue" albedo features on Mars are attributed to the tracks left by the passage of dust devils. Most such features are lower in albedo than the surrounding terrain, and result from the removal of bright dust from the surface by atmospheric vortexes, exposing a darker substrate. Some dust devil tracks, however, are of higher albedo than the surrounding terrain (Figure 1).

EVOLUTION OF A MARTIAN SHIELD VOLCANO. D. A. Williams, J. E. Bleacher, D. Shean, P. K. Byrne, R. Greeley, K. L. Tanaka, and S. Musiol, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-1404 (David.Williams@asu.edu), Planetary Geodynamics Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland (Jacob.E.Bleacher@nasa.gov), Malin Space Science Systems, Inc., San Diego, California (dshean@msss.com), Trinity College, Dublin, Ireland (byrnepk@gmail.com), Astrogeology Science Center, U.S. Geological Survey, Flagstaff, Arizona (ktanaka@usgs.gov), Institute of Geosciences, Free University, Berlin, Germany.

THRESHOLD WIND SPEED AND TRAJECTORY RESULTS. D.M. Burr 1,2 , J.F. Aliaga-Caro 3 , B.R. White 3 , J.R. Marshall 2 , R. Greeley 4 , and N.T. Bridges 5 , 1 Earth and Planetary Sciences Department and Planetary Geosciences Institute, University of Tennessee, Knoxville TN 37996-1410 (dburr1@utk.edu) 2 Carl Sagan Center, SETI Institute, 3 University of California, Davis, 4 Arizona State University, 5 Jet Propulsion Laboratory

Introduction Mars Transverse Mercator (MTM) -30262 and -30267 quadrangles cover the summit region and east margin of Hadriaca Patera, one of the Martian volcanoes designated highland paterae. MTM -30262 quadrangle includes volcanic deposits from Hadriaca Patera and Tyrrhena Patera (summit northeast of map area) and floor deposits associated with the Dao and Niger Valles canyon systems (south of map area). MTM -30267 quadrangle is centered on the caldera of Hadriaca Patera. The highland paterae are among the oldest, central-vent volcanoes on Mars and exhibit evidence for explosive eruptions, which make a detailed study of their geology an important component in understanding the evolution of Martian volcanism. Photogeologic mapping at 1:500,000-scale from analysis of Viking Orbiter images complements volcanological studies of Hadriaca Patera, geologic investigations of the other highland paterae, and an analysis of the styles and evolution of volcanic activity east of Hellas Planitia in the ancient, cratered highlands of Mars. This photogeologic study is an extension of regional geologic mapping east of Hellas Planitia. The Martian highland paterae are low-relief, areally extensive volcanoes exhibiting central calderas and radial channels and ridges. Four of these volcanoes, Hadriaca, Tyrrhena, Amphitrites, and Peneus Paterae, are located in the ancient cratered terrains surrounding Hellas Planitia and are thought to be located on inferred impact basin rings or related fractures. Based on analyses of Mariner 9 images, Potter (1976), Peterson (1977), and King (1978) suggested that the highland paterae were shield volcanoes formed by eruptions of fluid lavas. Later studies noted morphologic similarities between the paterae and terrestrial ash shields and the lack of primary lava flow features on the flanks of the volcanoes. The degraded appearances of Hadriaca and Tyrrhena Paterae and the apparently easily eroded materials composing their low, broad shields further suggest that the highland paterae are composed predominantly of pyroclastic deposits. Analyses of eruption and flow processes indicate that the distribution of units at Hadriaca and Tyrrhena Paterae is consistent with emplacement by gravity-driven pyroclastic flows. Detailed geologic study of the summit caldera and flanks of Hadriaca Patera is essential to determine the types of volcanic materials exposed, the nature of the processes forming these deposits, and the role of volcanism in the evolution of the cratered highlands that are characteristic of the southern hemisphere of Mars.

Dust devils on Earth and Mars: Extension of particle threshold laboratory simulations Conference Item How to cite: Neakrase, Lynn D. V.; Greeley, Ronald; Haan, Frederick L.; Sarkar, Partha; Iversen, James D.; Balme, Matthew R. and Eddlemon, Eric E. (2006). Dust devils on Earth and Mars: Extension of particle threshold laboratory simulations. In: 37th Lunar and Planetary Science Conference, 13-17 March 2006, Houston, Texas, USA.

Electric field strengths can grow quite large during terrestrial dust devils, ∼ 10 kVm−1 [1]. This compares to the breakdown electric field on Earth (∼ 3000 kVm−1 in the laboratory, but 300 kVm−1 within thunderstorms [2]), and exceeds the breakdown electric field in the martian atmosphere, ∼ 5 kVm−1 [3]. Electrical discharge in martian dust devils is therefore a distinct possibility, with consequences for atmospheric chemistry on Mars (e.g., nitrogen fixation [4]) and human exploration of Mars. Charging of dust may affect its ability to coat solar panels [5], and it is worth noting that a nighttime winds probably dislodged dust adhered to the solar panels of the MER Spirit on Sol 420. For these reasons it is important to understand how dust is electrically charged, and transported, in dust devils on Earth and Mars. In this abstract we describe: a model for charging of saltating and wind-blown particles; an experimental design to test this model; and a numerical simulations of dust dynamics and electrical charge in dust devils. The ultimate aim of these investigations is to determine whether electrical discharge can take place in terrestrial or martian dust devils.

Introduction: Terrain analyses are commonly used to study the geomorphic processes that have modified surfaces [1]. Our approach is based on analysis of slopes, which are the irregular surface expressions of the processes responsible for shaping landscapes [2]. Slope distributions likely represent unique surface forming processes and can be used to characterize entire landscapes at a given scale [3]. Because terrestrial slopes are constantly changing due to the influence of exogenic agents this approach is typically used to examine erosional processes. However, it is reasonable to utilize slope distributions to identify different lava flow emplacement processes and therefore volcanic style, when the overall surface construction rate is higher than the surface modification rate or when the opposing processes are separable upon analysis. The final form of a lava flow is dependent, in part, on the physical properties of the lava and the effusion conditions [4]. Thus the slope distributions displayed by different volcanic terrains should be unique to their emplacement conditions. We present slope distributions for the shield volcanoes on the island of Hawaii as a possible comparative approach to characterize martian volcanic provinces. Background: The volcanoes of Hawaii satisfy the criteria presented above allowing quantitative characterization of their constructional processes based on slope distributions. The island of Hawaii consists of five Quaternary shield volcanoes at various stages of their eruptive sequence [5]. Kohala and Mauna Kea are thought to be extinct and have undergone some erosion, Hualalai is likely dormant, and both Mauna Loa and Kilauea are active [5]. The general shield morphology of Hawaiian volcanoes evolves from a broad, gently sloping structure composed of long, thin, overlapping tholeiitic basalts, to a steeper structure surrounding the vent when lavas become more silicic [5] and eruption volumes and duration diminish as the volcano becomes inactive [6,7]. With a range of eruptive stages and emplacement conditions present, Hawaii presents an ideal location to test the validity of characterizing terrestrial basaltic shields according to slope distributions. The availability of the MOLA topographic dataset [8] provides the opportunity for comparisons between terrestrial slope distribution trends and trends displayed by martian volcanoes. Results: The complete Hawaiian USGS 10 m/pixel DEM grid (mosaiced in ArcView GIS 3.2 by ESRI) is used to calculate slopes over each volcano.

Introduction: A large concentration of seemingly collapsed features and associated outflow channels are found between western Lunae Planum and western Arabia Terra in the cratered highlands (units Npl1 and Npl2 [1]) and the volcanic plains (unit Hr [1]). Comparisons with terrestrial flood channels, such as those of Channeled Scablands in eastern Washington, suggest that the Martian channels were eroded by catastrophic floods [2,3,4]. Most of the Martian channels originate from chaotic terrains interpreted to represent areas where the ground collapsed as water (confined under the permafrost) was released under high hydrostatic pressures within artesian basins [5,6]. Understanding the geologic history of the Shalbatana Valley System (SVS) can improve our knowledge of groundwater recharging and extraction mechanisms, and the derivation of the history of valley formation in the highlands. Shalbatana Vallis was interpreted as an outflow channel excavated by water flow from an icecovered paleolake in Ganges Chasma [7] and from catastrophically releases from confined aquifers as the permafrost seal [8] was disrupted at three locations, forming chaotic regions [9]. Palmero and others [10] proposed that the excavation of SVS also involved water released from an extensive underground cavern system. They also proposed an alternative hypothesis for the origin for the Shalbatana upstream chaotic region; they suggest that a highly degraded late Hesperian impact crater (SE part) collapsed over the putative cavernous system. In this work, we have used 128 pixels/degree MOLA DEMs to derive alternative hypotheses for the origin the Basin-A and its chaotic material, as well as for the origin of the flanking Valley system III (Fig.1). The Basin A: The abrupt widening of the main Shalbatana Valley occurs at the junction between VS-I and B-A (Fig.2). This is also the transition of the main valley from incision into the Noachian plateau (bounded by unit Npl2 to the east) and to the West by VSIII (Hesperian highland unit Hr). The chaotic terrain in B-A was used as evidence that this basin resulted from collapse over an aquifer [9]. The east margin of the main SVS valley shows a change in orientation where it bounds B-A, which resemble intercepted craters. The topographic region TL1 partly bounds the basin at an elevation of about 700 meters above TL2 and TL3 (Fig.2). A channel (Chn) extends from VSI into B-A, the margins of which are partly bounded by TL1-A and TL1-B. This suggests that the topography was continuous prior to channel formation. The topographic and roughness characteristics of these terrains resemble those of Crater A (Fig.2 and Fig.3). Moreover, unit TL1-C occurs along the flanks of the arcuate cliff section. These observations are consistent with this unit representing the floor of collapsed craters intercepted by SVS. The karst-like features (seen on the top edges of B-A [11]), are consistent with collapse processes for this part of the valley. Structural control [9] over the main valley determined the deep and narrow U-shaped VSI, which is incised into the Noachian highlands. Structural control along the eastern flank of the main valley is suggested by the orientation, depth and slope characteristics and we propose that the abrupt widening of the main valley resulted from a change in lithologies. This hypothesis is consistent with the distribution of the chaotic terrain, which is rougher, more abundant, and topographically higher on the flanks of VSIII. This suggests that the chaotic material was shed from the VSIII upland. The position of the deepest and smoothest topographic unit (TL3) is consistent with its being a depositional area for material carried by the channel (Chn). We propose that flow from VS-I intercepted a series of collapsed craters in this region and possibly formed a crater-lake system, which might have extended as far as the end of VS-II. The geological materials composing the western margin of this lake system were apparently volatile rich.

The goal of the proposed work was to determine the origins of small volcanic cones observed in Mars Global Surveyor (MGS) data, and their implications for regolith ice stores and magma volatile contents. For this 1-year study, our approach involved a combination of: Quantitative morphologic analysis and interpretation of Mars Orbiter Camera (MOC) and Mars Orbiter Laser Altimeter (MOLA) data; Numerical modeling of eruption processes responsible for producing the observed features; Fieldwork on terrestrial analogs in Iceland. Following this approach, this study succeeded in furthering our understanding of (i) the spatial and temporal distribution of near-surface water ice, as defined by the distribution and sizes of rootless volcanic cones ("pseudocraters"), and (ii) the properties, eruption conditions, and volatile contents of magmas producing primary vent cones.