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USGS1999

Debris-flow origin for the Simud/Tiu deposit on Mars

A late Hesperian smooth plains deposit on Mars interpreted as a debris flow extends more than 2000 km from Hydraotes Chaos, through Simud and Tiu Valles, and into Chryse Planitia. The Simud/Tiu deposit widens out to >1000 km and embays streamlined landforms and knobs made up of sedimentary and perhaps volcanic deposits that were carved by earlier channeling activity. Morphologic features of the Simud/Tiu deposit observed in Viking and Pathfinder images are generally consistent with a debris-flow origin, but some of the deposit's salient features are not readily explained by catastrophic flooding or ice flow. Internal depressions appear to be bounded by linear scarps along flow margins where differential shearing may have occurred and in areas where flow spreading may have produced zones of extensional breakup and thinning within the flow. Possible flow lobes within the deposit may have formed by successive flow surges within the flow unit. The Pathfinder landing site is on the Simud/Tiu deposit, and the observations there are consistent with debris flow. The low, longitudinal ridges at the site may have formed by clast interactions as the flow ground to a halt. Imbricated, planar rocks on the ridges, such as in the Rock Garden, also may have been emplaced by debris or ice flow. However, stream energy calculations at Ares Vallis and channel geology indicate that flooding probably was incapable of emplacing the meter-size boulders observed at the Pathfinder site. Dewatering of pressurized zones in the debris flow or underlying material may be responsible for mud eruptions that formed a couple of patches of low pancakelike shields up to 5 km in diameter and for probable water flows that formed two small rille channels a few kilometers long. Local irregular grooves may be cracks that resulted from later desiccation and contraction of the flow material. The debris-flow unit apparently coalesced from outflows of water-fluidized debris originating from beneath chaotic and hummocky terrains within and along the margins of Simud and Tiu Valles. The deposit is onlapped from the north by another flow deposit originating from Acidalia Planitia. If the Simud/Tiu debris flow had entered a standing body of water, a turbidity current may have arisen from the debris flow and then backflowed over the debris flow to account for the Acidalia deposit.

Journal of Geophysical Research E: Planets↗

USGS2014

Methane hydrates in nature - Current knowledge and challenges

Recognizing the importance of methane hydrate research and the need for a coordinated effort, the United States Congress enacted the Methane Hydrate Research and Development Act of 2000. At the same time, the Ministry of International Trade and Industry in Japan launched a research program to develop plans for a methane hydrate exploratory drilling project in the Nankai Trough. India, China, the Republic of Korea, and other nations also have established large methane hydrate research and development programs. Government-funded scientific research drilling expeditions and production test studies have provided a wealth of information on the occurrence of methane hydrates in nature. Numerous studies have shown that the amount of gas stored as methane hydrates in the world may exceed the volume of known organic carbon sources. However, methane hydrates represent both a scientific and technical challenge, and much remains to be learned about their characteristics and occurrence in nature. Methane hydrate research in recent years has mostly focused on: (1) documenting the geologic parameters that control the occurrence and stability of methane hydrates in nature, (2) assessing the volume of natural gas stored within various methane hydrate accumulations, (3) analyzing the production response and characteristics of methane hydrates, (4) identifying and predicting natural and induced environmental and climate impacts of natural methane hydrates, (5) analyzing the methane hydrate role as a geohazard, (6) establishing the means to detect and characterize methane hydrate accumulations using geologic and geophysical data, and (7) establishing the thermodynamic phase equilibrium properties of methane hydrates as a function of temperature, pressure, and gas composition. The U.S. Department of Energy (DOE) and the Consortium for Ocean Leadership (COL) combined their efforts in 2012 to assess the contributions that scientific drilling has made and could continue to make to advance our understanding of methane hydrates in nature. COL assembled a Methane Hydrate Project Science Team with members from academia, industry, and government. This Science Team worked with COL and DOE to develop and host the Methane Hydrate Community Workshop, which surveyed a substantial cross section of the methane hydrate research community for input on the most important research developments in our understanding of methane hydrates in nature and their potential role as an energy resource, a geohazard, and/or as an agent of global climate change. Our understanding of how methane hydrates occur in nature is still growing and evolving, and it is known with certainty that field, laboratory, and modeling studies have contributed greatly to our understanding of hydrates in nature and will continue to be a critical source of the information needed to advance our understanding of methane hydrates.

Journal of Chemical and Engineering Data↗

USGS2005

Volcanic-ash hazard to aviation during the 2003-2004 eruptive activity of Anatahan volcano, Commonwealth of the Northern Mariana Islands

Within the Commonwealth of the Northern Mariana Islands (CNMI), Anatahan is one of nine active subaerial volcanoes that pose hazards to major air-traffic routes from airborne volcanic ash. The 2003-2004 eruptive activity of Anatahan volcano affected the region's aviation operations for 3 days in May 2003. On the first day of the eruption (10 May 2003), two international flights from Saipan to Japan were cancelled, and several flights implemented ash-avoidance procedures. On 13 May 2003, a high-altitude flight through volcanic gas was reported, with no perceptible damage to the aircraft. TOMS and MODIS analysis of satellite data strongly suggests that no significant ash and only minor amounts of SO2 were involved in the incident, consistent with crew observations. On 23 May 2003, airport operations were disrupted when tropical-cyclone winds dispersed ash to the south, dusting Saipan with light ashfall and causing flight cancellations there and at Guam 320 km south of the volcano. Operational (near-real-time) monitoring of ash clouds produced by Anatahan has been conducted since the first day of the eruption on 10 May 2003 by the Washington Volcanic Ash Advisory Center (VAAC). The VAAC was among the first groups outside of the immediate area of the volcano to detect and report on the unexpected eruption of Anatahan. After being contacted about an unusual cloud by National Weather Service forecasters in Guam at 1235 UTC on 10 May 2003, the VAAC analyzed GOES 9 images, confirming Anatahan as the likely source of an ash cloud and estimating that the eruption began at about 0730 UTC. The VAAC issued its first Volcanic Ash Advisory for Anatahan at 1300 UTC on 10 May 2003 more than 5 h after the start of the eruption, the delay reflecting the difficulty of detecting and confirming a surprise eruption at a remote volcano with no in situ real-time geophysical monitoring. The initial eruption plume reached 10.7-13.4 km (35,000-44,000 ft), well into jet cruise altitudes; thereafter, the maximum plume height decreased and during the rest of the eruption usually did not exceed ???5 km (???17,000 ft), which lessened the potential hazard to aircraft at higher cruise altitudes. Drifting ash clouds commonly extended hundreds of kilometers from the volcano, occasionally as far west as the Philippines. Over the course of the eruptive activity in 2003-2004, the VAAC issued 323 advisories (168 with graphical depictions of ash clouds) for Anatahan, serving as a reliable source of ash-cloud information for aviation-related meteorological offices and air carriers. With a record of frequent eruptions in the CNMI, continued satellite and in situ real-time geophysical monitoring is needed at Anatahan and other Marianas volcanoes so that potential hazards to aviation from any future eruptive activity can be quickly and correctly assessed. 2005 Elsevier B.V. All rights reserved.

Northern Mariana Islands↗

USGS2012

Lithology and evolution of the crust-mantle boundary region in the southwestern Basin and Range Province

Mantle and crustal xenoliths from volcanic rocks in the southwestern Basin and Range province and Colorado Plateau Transition Zone reveal histories of episodic magmatism and deformation that have profoundly influenced the crustal structure of this region. Seismic transects in this area show a strongly reflective Moho of generally low relief, which, in the area of modern transects, consists of a thin zone (<2 km thick) of short reflectors. The upper mantle is transparent and has a P n of 7.8–8.0 km/s similar to much of the western United States. A lower crustal zone, 2–13 km thick, has variable internal reflectivity and a relatively low velocity of 6.6–6.8 km/s. Upper mantle peridotite xenoliths show both ductile and brittle deformational features and have structures and compositions affected by magmatic intrusion; intrusions form complex dike systems and extensive zones of grain boundary infiltration in peridotite xenoliths. Whereas melt infiltration preceded and followed ductile deformation, brittle deformation, represented by closely spaced joint systems and faults, followed ductile deformation and is related to the youngest magmatic episodes. These structural characteristics and high uppermost mantle temperature (∼1000°C) may combine to explain the relatively low P n . Alternating layers of ductily deformed and undeformed peridotites, with or without igneous intrusions, may contribute to the reflectivity of the Moho. Lower crustal xenoliths are dominantly igneous-textured pyroxenites and mafic to intermediate gabbros identical to the dikes in peridotite xenoliths. The crustal xenoliths also commonly are jointed, and in addition many show partial melting and have abundant cavities that probably were filled with CO 2 -rich fluids. These rocks are interpreted as products of underplated magmas that were fed through the mantle dike systems and may represent the lowest crustal unit identified in the seismic records. The mafic compositions and high densities of the crustal xenoliths indicate that the low velocity of the lower crust may be caused in part by fracture systems, partial melts, and high temperatures. Garnet granulite xenoliths from a locality with no mantle peridotite xenoliths probably represent crust of the region before late Miocene extension. Felsic granulite xenoliths from two localities have velocities like those of the two lower crustal units identified seismically and could be present in the modern crust as unequilibrated remnants of old crust. The preferred model for the evolution of the lower lithosphere is one in which extension affects the upper mantle as well as the crust and is overlapped in time by multiple magmatic episodes. The earliest magmatic events preceded extension, and later events accompanied and followed extension.

Arizona, California, Nevada↗

USGS2000

Geologic mapping of Europa

Galileo data enable the major geological units, structures, and surface features to be identified on Europa. These include five primary units (plains, chaos, band, ridge, and crater materials) and their subunits, along with various tectonic structures such as faults. Plains units are the most widespread. Ridged plains material spans a wide range of geological ages, including the oldest recognizable features on Europa, and appears to represent a style of tectonic resurfacing, rather than cryovolcanism. Smooth plains material typically embays other terrains and units, possibly as a type of fluid emplacement, and is among the youngest material units observed. At global scales, plains are typically mapped as undifferentiated plains material, although in some areas differences can be discerned in the near infrared which might be related to differences in ice grain size. Chaos material is composed of plains and other preexisting materials that have been severely disrupted by inferred internal activity; chaos is characterized by blocks of icy material set in a hummocky matrix. Band material is arrayed in linear, curvilinear, wedge-shaped, or cuspate zones with contrasting albedo and surface textures with respect to the surrounding terrain. Bilateral symmetry observed in some bands and the relationships with the surrounding units suggest that band material forms by the lithosphere fracturing, spreading apart, and infilling with material derived from the subsurface. Ridge material is mapped as a unit on local and some regional maps but shown with symbols at global scales. Ridge material includes single ridges, doublet ridges, and ridge complexes. Ridge materials are considered to represent tectonic processes, possibly accompanied by the extrusion or intrusion of subsurface materials, such as diapirs. The tectonic processes might be related to tidal flexing of the icy lithosphere on diurnal or longer timescales. Crater materials include various interior (smooth central, rough inner, and annular massif) and exterior (continuous ejecta) subunits. Structural features and landforms are shown with conventional symbols. Type localities for the units are identified, along with suggestions for portraying the features on geological maps, including colors and letter abbreviations for material units. Implementing these suggestions by the planetary mapping community would facilitate comparisons of maps for different parts of Europa and contribute to an eventual global synthesis of its complex geology. On the basis of initial mapping results, a stratigraphic sequence is suggested in which ridged plains form the oldest unit on Europa, followed by development of band material and individual ridges. Band materials tend to be somewhat older than ridges, but in many areas the two units formed simultaneously. Similarly, the formation of most chaos follows the development of ridged plains; although chaos is among the youngest materials on Europa, some chaos units might have formed contemporaneously with ridged plains. Smooth plains generally embay all other units and are late-stage in the evolution of the surface. C1 craters are superposed on ridged plains but are crosscut by other materials, including bands and ridges. Most c2 craters postdate all other units, but a few c2 craters are cut by ridge material. C3 craters constitute the youngest recognizable material on Europa. Copyright 2000 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2003

Temperature-pressure conditions in coalbed methane reservoirs of the Black Warrior basin: Implications for carbon sequestration and enhanced coalbed methane recovery

Sorption of gas onto coal is sensitive to pressure and temperature, and carbon dioxide can be a potentially volatile supercritical fluid in coalbed methane reservoirs. More than 5000 wells have been drilled in the coalbed methane fields of the Black Warrior basin in west-central Alabama, and the hydrologic and geothermic information from geophysical well logs provides a robust database that can be used to assess the potential for carbon sequestration in coal-bearing strata.Reservoir temperature within the coalbed methane target zone generally ranges from 80 to 125 ??F (27-52 ??C), and geothermal gradient ranges from 6.0 to 19.9 ??F/1000 ft (10.9-36.2 ??C/km). Geothermal gradient data have a strong central tendency about a mean of 9.0 ??F/1000 ft (16.4 ??C/km). Hydrostatic pressure gradients in the coalbed methane fields range from normal (0.43 psi/ft) to extremely underpressured (<0.05 psi/ft). Pressure-depth plots establish a bimodal regime in which 70% of the wells have pressure gradients greater than 0.30 psi/ft, and 20% have pressure gradients lower than 0.10 psi/ft. Pockets of underpressure are developed around deep longwall coal mines and in areas distal to the main hydrologic recharge zone, which is developed in structurally upturned strata along the southeastern margin of the basin.Geothermal gradients within the coalbed methane fields are high enough that reservoirs never cross the gas-liquid condensation line for carbon dioxide. However, reservoirs have potential for supercritical fluid conditions beyond a depth of 2480 ft (756 m) under normally pressured conditions. All target coal beds are subcritically pressured in the northeastern half of the coalbed methane exploration fairway, whereas those same beds were in the supercritical phase window prior to gas production in the southwestern half of the fairway. Although mature reservoirs are dewatered and thus are in the carbon dioxide gas window, supercritical conditions may develop as reservoirs equilibrate toward a normal hydrostatic pressure gradient after abandonment. Coal can hold large quantities of carbon dioxide under supercritical conditions, and supercritical isotherms indicate non-Langmiur conditions under which some carbon dioxide may remain mobile in coal or may react with formation fluids or minerals. Hence, carbon sequestration and enhanced coalbed methane recovery show great promise in subcritical reservoirs, and additional research is required to assess the behavior of carbon dioxide in coal under supercritical conditions where additional sequestration capacity may exist. ?? 2003 Elsevier Science B.V. All rights reserved.

International Journal of Coal Geology↗

USGS2012

The mechanics and three-dimensional internal structure of active magmatic systems: Kilauea volcano, Hawaii

Interpretation of abundant seismic data suggests that Kilauea's primary conduit within the upper mantle is concentrically zoned to about 34-km depth. This zoned structure is inferred to contain a central core region of relatively higher permeability, surrounded by numerous dikes that are in intermittent hydraulic communication with each other and with the central core. During periods of relatively high magma transport, the entire cross section of the conduit is utilized. During periods of relatively low to moderate transport, however, only the central core is active. As the conduit penetrates the oceanic crust and enters the volcanic shield, it simultaneously supplies the deeper sections of the rift zones (6-to 10-km depth) and the roots of the summit reservoir with picritic magma. The rift zones at depth are inferred to be almost wholly molten and to possess a high degree of fluid continuity from Heiheiahulu in the East Rift Zone, 45 km westward through the roots of the summit magma reservoir, and well into the Southwest Rift Zone. Higher in the shield, the subcaldera magma reservoir and the shallow rift zones occupy the 2-to 4-km depth interval. Summit-differentiated olivine tholeiite (ρ ≈ 2.62 g cm −3 ) is periodically injected laterally along a horizon of neutral buoyancy within the rift zones, where the density of the magma is just balanced by the in situ density of the shield (Ryan, 1987 a , b ). Deep rift zone intrusions push seaward the deep tectonic blocks of the volcano's south flank. Shallow rift intrusions build a sheeted dike complex, inferred to be in isostatic equilibrium with the higher-density deep rift cores below. General finite element analyses are presented for the deformation and stress fields surrounding such dikes in the horizontal and vertical planes. The dike tip in two and three dimensions is surrounded by a tubular core of tensile (σ 1 , σ 2 ) and shear stress (τ max ). The displacement field is characterized by counterrotating cells on either side of the dike tip which, in vertical orientation, produce the characteristic subsidence above the dike complex, with uplift on either side, forming a ridge-trough-ridge structure. A finite element model of Kilauea's shield computes the displacement fields and principal stress (σ 1 ) distributions resulting from intrusive activity on each or both of the rift zones. Within the summit region, tensile stress lobes produced by the three-dimensional upward extension of the intrusions superpose constructively to produce calderawide regimes of tensile stress, conducive to caldera development. Parametric studies of (1) intrusion in the East Rift Zone only, (2) intrusion in the Southwest Rift Zone only, and (3) intrusion in both rift zones demonstrate their unique kinematic contributions. For case 1, the caldera undergoes a counterclockwise rotation (torque up state) conducive to the development of rightstepping en echelon eruptive fissures, as exemplified by the August 14, 1971, eruption. For case 2, the caldera undergoes a clockwise rotation (torque down state) conducive to the development of left-stepping eruptive fissures, as occurred during the December 31, 1974, eruption. For case 3, the caldera substructure is driven due southward, producing the southward migration of the upper portions of the summit magma reservoir.

Journal of Geophysical Research Solid Earth↗

USGS2012

Television observations from Surveyor 3

A total of 6315 pictures were taken by the television camera on Surveyor 3 after the lunar landing. These pictures have provided much new information about the location of the landing site on the moon, the detailed topographic and geologic characteristics of the lunar surface, and the appearance of the earth as seen from the moon, both during eclipse of the sun and during partial direct illumination by the sun. Surveyor 3 landed in a subdued crater slightly more than 200 meters in diameter, which has a low rounded rim and is about 15 meters deep. The spacecraft is situated on the east wall of the crater, about half way between the center of the crater and the rim crest. The spacecraft is inclined 14.7° ± 1.0° toward the west. The selenographic coordinates of the landing site are 2.94°S latitude, 23.34°W longitude, relative to selenodetic control adopted by the Aeronautical Chart and Information Center. Small morphologic elements of the landing site include small craters, linear ridges and troughs, and fragmental debris. The craters and fragmental debris resemble those observed at the Surveyor 1 landing site, both in distribution of shape and in distribution of size. Most of the craters in Surveyor 1 and 3 pictures are inferred to be of impact origin. Their size-frequency distribution corresponds to the distribution that would be produced by repetitive bombardment by meteoroids, a bombardment sufficiently prolonged that the crater population has reached a steady state or has come to equilibrium. Some of the craters observed at the Surveyor 3 landing site are inferred to be of secondary impact origin, and some probably have been formed either by subsidence or by drainage of fragmental debris into cracks or fissures in the subsurface. Fragmental debris at the landing site is inferred to have been derived primarily by the same process of repetitive bombardment that produced the majority of craters. The inferred volumetric size-frequency distribution of fragments, derived from the observed size distribution of fragments on the surface, is similar to the distribution that would be produced by repetitive bombardment of coherent rocks by meteoroids with a mass-frequency distribution like that found from observed meteors and recovered meteorites on earth. Two prominent strewn fields of blocky debris were observed around two craters, 13 and 15 meters across, at the Surveyor 3 site. The 13-meter crater has a sharp raised rim, and the 15-meter crater has a more subdued rounded rim. The blocks associated with the subdued crater have twice as high a mean roundness as the blocks associated with the raised-rim crater, and they are much more deeply buried. The size-frequency distribution function for the fragments in each of the strewn fields of blocks resembles the size-frequency distribution for fragments ejected by impacts in strong rock, such as Meteor Crater, Arizona. Most of the fragments at the surface of the Surveyor 3 landing site are evidently part of a layer of fragmental material of low cohesion that is at least 1 meter thick along the upper parts of the wall of the crater in which Surveyor 3 landed and may be much thicker near the center of the crater. The evidence from the Surveyor 3 pictures suggests that this layer of debris, or regolith, is subject to downslope creep or mass movement. Creep is probably caused by seismic shaking, due mainly to near and far impact events and perhaps due partly to internal lunar seismicity. Disturbances of the lunar surface produced by Surveyor 3, like those produced by Surveyor 1, exposed material at depths of a few centimeters or less that was darker than the material at the surface. The albedo of the fine-grained fragmental debris is probably 20 to 30% lower at depths of only a fraction of a millimeter than it is at the optically observed surface. All coarse fragments protruding above the general level of the surface have a higher albedo than the fine-grained matrix of the surface. These general photometric relationships can be explained if it is assumed that the surfaces of the particles in the shallow lunar subsurface tend to become coated with a dark substance; the term proposed for this hypothetical substance is ‘lunar varnish’ On the protruding surface of blocks and coarse fragments the lunar varnish is scrubbed off by the processes that cause rounding. The exposed surfaces of fine particles on the lunar surface are similarly affected, but, because they are mixed relatively rapidly with particles just beneath the surface, the process is incomplete and the fine-grained material exposed at the lunar surface, therefore, has a lower albedo than blocks and other large fragments. Coating of particles by lunar varnish evidently takes place just beneath the surface. The estimated normal luminance factor (normal albedo) of an undisturbed part of the lunar surface next to footpad 2 of the Surveyor 3 spacecraft is 8.5%. An area of the lunar surface disturbed by the surface sampler has an estimated normal luminance factor of 6.6%, and fine-grained material placed on footpad 2 by the surface sampler has an estimated normal luminance factor of 7.6%. The errors in all these estimates may be as high as 25% because of uncertainties of correction required for light scattered from the camera mirror. Preliminary search for color differences, by color reconstitution methods, revealed no determinable differences in color among various coarse blocks, the fine-grained matrix of the surface, or fine-grained material disturbed by the surface sampler. Surveyor 3 pictures of the eclipse of the sun by the earth revealed a bright region in the refraction halo surrounding the earth, which was correlated with the position of the sun, and a series of bright beads that occurred over regions of the earth largely clear of clouds. Clouds tend to occult the refracted rays of the sun, most of which pass through the lower part of the atmosphere at the limb; the beads occurred in the depressions in the optical silhouette of the earth. Preliminary reduction of the color of the refracted light showed that the brightest region, near the position of the sun, exhibited a correlated color temperature close to 4800°K. The color temperature tended to be lower for light that followed paths of greater atmospheric absorption. Preliminary analysis of Surveyor 3 pictures of the partly illuminated earth revealed colors similar to the colors recorded from orbit by the Mercury and Gemini astronauts.

Journal of Geophysical Research↗