New very high resolution radar studies of the Moon

As part of an effort to further understand the geologic utility of radar studies of the terrestrial planets, investigators at the Hawaii Institute of Geophysics are collaborating with NEROC Haystack Observatory, MIT and the Jet Propulsion Laboratory in the analysis of existing 3.8 and 70 cm radar images of the Moon, and in the acquisition of new data for selected lunar targets. The intent is to obtain multi-polarization radar images at resolutions approaching 75 meters (3.8 cm wavelength) and 400 meters (70 cm wavelength) for the Apollo landing sites (thereby exploiting available ground truth) or regions covered by the metric camera and geochemical experiments onboard the command modules of Apollos 15, 16 and 17. These data were collected in both like- and cross-polarizations, and, in the case of the 70 cm data, permit the phase records to be used to assess the scattering properties of the surface. The distribution of surface units on the Moon that show a mismatch between the surface implied by like- and cross-polarized scattering data is being analyzed, based on the scattering models of Evans and Hagfors

Late-stage intrusive activity at Olympus Mons, Mars:summit inflation and giant dike formation

By mapping the distribution of 351 lava flows at the summit area of Olympus Mons volcano on Mars, and correlating these flows with the current topography from the Mars Orbiter Laser Altimeter (MOLA), we have identified numerous flows which appear to have moved uphill. This disparity is most clearly seen to the south of the caldera rim, where the elevation increases by >200 m along the apparent path of the flow. Additional present day topographic anomalies have been identified, including the tilting down towards the north of the floors of Apollo and Hermes Paterae within the caldera, and an elevation difference of >400 m between the northern and southern portions of the floor of Zeus Patera. We conclude that inflation of the southern flank after the eruption of the youngest lava flows is the most plausible explanation, which implies that intrusive activity at Olympus Mons continued towards the present beyond the age of the youngest paterae ~200 – 300 Myr (Neukum et al., 2004; Robbins et al., 2011). We propose that intrusion of lateral dikes to radial distances >2,000 km is linked to the formation of the individual paterae at Olympus Mons. Two specific dikes to the SE of the volcano are inferred to have volumes of ~4,400 km3 and ~6,100 km3, greater than the volumes of individual calderas and implying triggering of both caldera collapse and lateral dike injection by the arrival of large inputs of magma from the mantle. A comparable disparity between lava flow direction and current topography, together with a tilted part of the caldera floor, has been identified at Ascraeus Mons

Post Eruption Hazards at Mt. Pinatubo, Philippines

Our project focused on the investigation of the post-eruption hazards at Mt. Pinatubo (Philippines) using remote sensing data, and field observations of the 1991 eruption deposits. Through the use of multiple satellite images, field work, and the 1996/2000 PacRim data sets, we conducted studies of the co- and post-eruption hazards of the volcano due to erosion and re-deposition of the extensive pyroclastic flow deposits. A major part of this project was the assembly and analysis of a database of over 50 high resolution (1 - 50 m/pixel) images that will facilitate this study. We collected Ikonos, SPOT, SIR-C/X-SAR, Landsat, ERS, RADARSAT, and ASTER images of the area around Mt. Pinatubo. An example of the changes that could be seen in these data is shown. Our investigation focused on a retrospective analysis of the erosion, redeposition, and re-vegetation of the 1991 pyroclastic flow deposits of Mt. Pinatubo. The primary geologic goal of our work was the analysis of the spatial distribution and volume change of the sources and sinks of materials associated with mudflow ('lahar') events. This included the measurement of river valley gradients and cross-sections using TOPSAR digital elevation data, as we are participating in the PacRim 2000 deployment to the Philippines specifically so that we can collect a second set of TOPSAR data that can then be used to create a topographic difference image of the volcano. The main results from this multi-sensor study have been published as Torres et al.. A discussion of the methodology that we used to assemble an appropriate database was included in Mouginis-Mark and Domergue-Schmidt. As part of an educational outreach effort, we also helped the Philippine Institute of Volcanology and Seismology (PHIVOLCS) in the Philippines to use NASA data to study Mt. Pinatubo and other Filipino volcanoes

MERC:a fortran iv program for the production of topographic data for the planet Mercury

MERC provides the capability to construct cross sections or topographic maps for parts of the surface of the planet Mercury. The photometric theory that permits digital image brightness measurements from the Mariner 10 spacecraft to be converted into changes in surface topography elevations is described. Techniques for leveling or readjusting the slope of specific portions of a cross profile by multiple surface albedo estimates are discussed. We present several examples of crater cross sections and a topographic map

Phreatomagmatic explosive origin of Hrad Vallis, Mars

Hrad Vallis is a ∼370 m deep, ∼800 km long depression located at 34°N, 218°W, in Elysium Planitia, Mars. A distinctive deposit, present on both sides of the source area of Hrad Vallis, has a maximum width of ∼70 km along the strike of the depression, a lower unit extends for nearly 100 km away from the depression on either side, and an upper unit extends for ∼50 km. Viking and Mars Orbiter Camera (MOC) images show lobate deposit boundaries, rheomorphic deformation, and numerous craters 270-580 m in diameter within the deposit. The deposit coincides with a broad topographic rise ∼30 km wide and ∼100-150 m high extending along the sides of the valley for at least 100 km along strike. We propose that these features formed when a dike underlying the axis of the valley generated a shallow sill, which in turn is partly responsible for the rise topography. The remainder of the rise consists of a mud-like deposit of ejecta from a large-scale phreatomagmatic explosion due to violent mechanical and thermal mixing between the central part of the sill and ice-rich rock layers in the upper few hundred meters of the crust in a fuel-coolant-type interaction. The observed range and thickness of ejecta and the depth of the Hrad depression imply explosion steam pressures up to 360 MPa, ejecta speeds of ∼400 m s-1, and a sill at least 150 m thick intruded at a depth of ∼350-400 m below the original surface

Volcanic input to the atmosphere from Alba Patera on Mars

With the recent increased interest in the evolution of volcanism, tectonism and volatiles on Mars, several studies have been initiated to infer the mass of water vapour and carbon dioxide that might have been released from magmas erupted on the martian surface over geological time (see refs 1,2). Such studies are complementary to investigations of the global volatile inventory for Mars3,4, which trace a constant mass of volatiles to various sinks in the regolith, atmosphere and polar caps. Of necessity, these volatile distribution models are generalizations of Mars-wide averages. Here we present what we believe to be the first estimates for the amount of water vapour and/or carbon dioxide released, together with the corresponding release rates, from specific volcanic deposits on a relatively young martian volcanic construct (Alba Patera)

Dynamics of a fluid flow on Mars:lava or mud?

A distinctive flow deposit southwest of Cerberus Fossae on Mars is analyzed. The flow source is a similar to 20 m deep, similar to 12 x 1.5 km wide depression within a yardang associated with the Medusae Fossae Formation. The flow traveled for similar to 40 km following topographic lows to leave a deposit on average 3-4 km wide. The surface morphology of the deposit suggests that it was produced by the emplacement of a fluid flowing in a laminar fashion and possessing a finite yield strength. We use topographic data from a digital elevation model (DEM) to model the dynamics of the motion and infer that the fluid had a Bingham rheology with a plastic viscosity of similar to 1 Pa s and a yield strength of similar to 185 Pa. Although the low viscosity is consistent with the properties of komatiite-like lava, the combination of values of viscosity and yield strength, as well as the surface morphology of the flow, suggests that this was a mud flow. Comparison with published experimental data implies a solids content close to 60% by volume and a grain size dominated by silt-size particles. Comparison of the similar to 1.5 km(3) deposit volume with the similar to 0.03 km(3) volume of the source depression implies that similar to 98% of the flow material was derived from depth in the crust. There are similarities between the deposit studied here, which we infer to be mud, and other flow deposits on Mars currently widely held to be lavas. This suggests that a re-appraisal of many of these deposits is now in order

Phreato-magmatic dike-cryosphere interactions as the origin of small ridges north of Olympus Mons, Mars.

Using images from the Mars Orbiter Camera, we have identified several linear ridges located 10–60 km north of the volcano Olympus Mons, Mars, at the edge of the Olympus Mons aureole materials. These ridges appear to be made of unconsolidated material by virtue of the many dust avalanche scars seen on their upper slopes. Based upon their morphology (several ridges have crater-like central depressions) and superposition relationships, the ridges appear to have formed very recently and post-date the formation of the youngest lava flows spilling over the northern escarpment of Olympus Mons. Several possible origins for the ridges, including an eolian, periglacial, or depositional origin have been considered, but we favor a ridge origin by a series of small explosive eruptions initiated by the intrusion of a dike into a volatile-rich substrate. To explore this process, we develop a numerical model for dike intrusion into a volatile-rich substrate that yields plausible dike widths between 2.4–3.5 m. The total volume of a single ridge system is 65×106 m3, and we calculate that it may have taken only a few minutes to form. Viable solutions only exist when the thicknesses of the ice-rich layer is less than 1000–2000 m. This strongly suggests that the ice-rich region is limited in its vertical extent to a value of this order