The geological evolution of Merapi volcano, Central Java, Indonesia

Merapi is an almost persistently active basalt to basaltic andesite volcanic complex in Central Java (Indonesia) and often referred to as the type volcano for small-volume pyroclastic flows generated by gravitational lava dome failures (Merapi-type nuées ardentes). Stratigraphic field data, published and new radiocarbon ages in conjunction with a new set of ⁴⁰K–⁴⁰Ar and ⁴⁰Ar–³⁹Ar ages, and whole-rock geochemical data allow a reassessment of the geological and geochemical evolution of the volcanic complex. An adapted version of the published geological map of Merapi [(Wirakusumah et al. 1989), Peta Geologi Gunungapi Merapi, Jawa Tengah (Geologic map of Merapi volcano, Central Java), 1:50,000] is presented, in which eight main volcano stratigraphic units are distinguished, linked to three main evolutionary stages of the volcanic complex—Proto-Merapi, Old Merapi and New Merapi. Construction of the Merapi volcanic complex began after 170?ka. The two earliest (Proto-Merapi) volcanic edifices, Gunung Bibi (109?±?60?ka), a small basaltic andesite volcanic structure on Merapi’s north-east flank, and Gunung Turgo and Gunung Plawangan (138?±?3?ka; 135?±?3?ka), two basaltic hills in the southern sector of the volcano, predate the Merapi cone sensu stricto. Old Merapi started to grow at ~30?ka, building a stratovolcano of basaltic andesite lavas and intercalated pyroclastic rocks. This older Merapi edifice was destroyed by one or, possibly, several flank failures, the latest of which occurred after 4.8?±?1.5?ka and marks the end of the Old Merapi stage. The construction of the recent Merapi cone (New Merapi) began afterwards. Mostly basaltic andesite pyroclastic and epiclastic deposits of both Old and New Merapi (<11,792?±?90 ¹⁴C years BP) cover the lower flanks of the edifice. A shift from medium-K to high-K character of the eruptive products occurred at ~1,900 ¹⁴C years BP, with all younger products having high-K affinity. The radiocarbon record points towards an almost continuous activity of Merapi since this time, with periods of high eruption frequency interrupted by shorter intervals of apparently lower eruption rates, which is reflected in the geochemical composition of the eruptive products. The Holocene stratigraphic record reveals that fountain collapse pyroclastic flows are a common phenomenon at Merapi. The distribution and run-out distances of these flows have frequently exceeded those of the classic Merapi-type nuées ardentes of the recent activity. Widespread pumiceous fallout deposits testify the occurrence of moderate to large (subplinian) eruptions (VEI 3–4) during the mid to late Holocene. VEI 4 eruptions, as identified in the stratigraphic record, are an order of magnitude larger than any recorded historical eruption of Merapi, except for the 1872?AD and, possibly, the October–November 2010 events. Both types of eruptive and volcanic phenomena require careful consideration in long-term hazard assessment at Merapi.     

Restoration of wadi aquifers by artificial recharge with treated waste water

Fresh water resources within the Kingdom of Saudi Arabia are a rare and precious commodity that must be managed within a context of integrated water management. Wadi aquifers contain a high percentage of the naturally occurring fresh groundwater in the Kingdom. This resource is currently overused and has become depleted or contaminated at many locations. One resource that could be used to restore or enhance the fresh water resources within wadi aquifers is treated municipal waste water (reclaimed water). Each year about 80 percent of the country's treated municipal waste water is discharged to waste without any beneficial use. These discharges not only represent a lost water resource, but also create a number of adverse environmental impacts, such as damage to sensitive nearshore marine environments and creation of high-salinity interior surface water areas. An investigation of the hydrogeology of wadi aquifers in Saudi Arabia revealed that these aquifers can be used to develop aquifer recharge and recovery (ARR) systems that will be able to treat the impaired-quality water, store it until needed, and allow recovery of the water for transmittal to areas in demand. Full-engineered ARR systems can be designed at high capacities within wadi aquifer systems that can operate in concert with the natural role of wadis, while providing the required functions of additional treatment, storage and recovery of reclaimed water, while reducing the need to develop additional, energy-intensive desalination to meet new water supply demands.     

Analysis of sediment stability on the Peru‐Chile continental slope

Abstract

Potential sediment mass movement was analyzed at ten locations on the continental slope off Peru and northern Chile, using samples obtained from up to 3 m below the seafloor. Shear strength parameters were obtained from consolidated‐undrained triaxial compression tests. Sediment behavior in these tests reflects the influence of organic matter, which is concentrated in the slope deposits by coastal upwelling. High water content of the organic‐rich sediments and the high de‐formability of organic matter contribute to the prevalent ductile behavior. Aggregation of clays by organic matter is apparently responsible for the high friction angles, up to 44°, displayed by the slope deposits. Sediment stability was assessed using infinite slope analyses. These analyses indicate that gravitational forces alone are not sufficient to cause sediment failure at any of the slope locations. Sediment accumulation on the slope is not rapid enough to generate excess pore pressure and reduce the resistance to gravitational sliding. Effects of earthquakes on slope stability were evaluated by modeling earthquake‐induced inertia forces as static forces and estimating pore pressures developed during cyclic loading. This analysis shows that sediments of the lower slope off Peru possess the highest susceptibility to failure during earthquakes. Earthquake accelerations on the order of 0.2 gravity are sufficient to trigger slumping at all ten slope locations. Indirect evidence suggests that creep and mass flows initiated at shallower water depths are factors that might contribute to sediment failure on the slope.     

Detecting potential changes in the meridional overturning circulation at 26˚N in the Atlantic

We analyze the ability of an oceanic monitoring array to detect potential changes in the North Atlantic meridional overturning circulation (MOC). The observing array is ‘deployed’ into a numerical model (ECHAM5/MPI-OM), and simulates the measurements of density and wind stress at 26^°N in the Atlantic. The simulated array mimics the continuous monitoring system deployed in the framework of the UK Rapid Climate Change program. We analyze a set of three realizations of a climate change scenario (IPCC A1B), in which – within the considered time-horizon of 200 years – the MOC weakens, but does not collapse. For the detection analysis, we assume that the natural variability of the MOC is known from an independent source, the control run. Our detection approach accounts for the effects of observation errors, infrequent observations, autocorrelated internal variability, and uncertainty in the initial conditions. Continuous observation with the simulated array for approximately 60 years yields a statistically significant (p < 0.05) detection with 95 percent reliability assuming a random observation error of 1 Sv (1 Sv = 10⁶ m³ s^?1). Observing continuously with an observation error of 3 Sv yields a detection time of about 90 years (with 95 percent reliability). Repeated hydrographic transects every 5 years/ 20 years result in a detection time of about 90 years/120 years, with 95 percent reliability and an assumed observation error of 3 Sv. An observation error of 3 Sv (one standard deviation) is a plausible estimate of the observation error associated with the RAPID UK 26^°N array.     

NOS study of applied photobathymetry

Classical hydrographic mapping in shallow waters with surface craft is slow, hazardous, and expensive. The remarkable water penetration capability of several currently used film emulsions and their dramatic presentation of submerged detail provides an alternative tool and supplement for mapping the seabed in shoals and waters of moderate depth. Photogrammetric bathymetric surveys preceding hydrography can show many of the rocks, reefs, shallow areas, photogrammetrically observed depth measurements and depth curves, and other features and thereby assist the hydrographers whose work is more difficult because they do not have the overall view of the bottom to guide their operations in developing important details. The objective of this paper is to advance the comprehension of the potential of photogrammetric bathymetry to provide the following benefits: (1) improve the accuracy and completeness of the hydrographie survey; (2) reduce the cost and time of the field hydrographie survey; and, (3) reduce ship requirements for a particular hydrographic survey, thereby releasing some of the craft for other assignments and/or enlarging the size of the coastal water areas that can be surveyed within a given time frame. The investigation of the potential for accomplishing photogrammetric bathymetry was restricted to ten regions of high priority along the East Coast and the Gulf of Mexico. A five‐year photobathymetry program is envisaged that will require a maximum of 10,765 man‐days of work and cost $1,154,750. These figures can be substantially reduced by employing digitized stereoscopic plotting instruments and developing advanced, sophisticated photogrammetric analytic aerotriangulation procedures.     

A crustal-scale integrated geophysical and tectonic study of the Snake River Plain region,northwestern U.S.A.

The Pacific Northwest region of North America is a site of very complex tectonomagmatic activity. This activity is due to subduction of the Pacific plate, the associated Cascade chain of volcanoes, micro-plate interactions, and mantle plume activity to the east of the plate margin that produced the Yellowstone hotspot track along the Eastern Snake River Plain (ESRP). A number of recent geophysical and geological studies have produced new results that have drawn attention to the complex tectonic setting of the region east of the Cascade Range, and its tectonic evolution is the subject of considerable scientific interest and debate. Numerous seismic studies have specifically focused on the crustal and upper mantle structure of the ESRP and Yellowstone area. However, crustal-scale studies of the Western Snake River Plain (WSRP) are limited. We undertook an integrated analysis of new and existing geophysical data and geologic constraints to study the crustal structure of the WSRP and generated two-dimensional crustal models across it. We observed both differences and similarities in the structural and tectonic evolution of the eastern and western arms of the SRP based on our integrated analysis. From a broader perspective based on recent geological and geophysical studies in the surrounding region, the intersection of the two arms of the SRP emerges as a major element of a complex tectonic intersection that includes the High Lava Plains of eastern Oregon, the Northern Nevada rift, a southwestern extension of the ESRP into northern Nevada, as well as, faulting and volcanism extending north-westward to connect with the Columbia River basalt plateau region. Thus, the goal of this study is to advance our understanding of the tectonomagmatic evolution of the region and to encourage further studies in the region.     

The Wajid Sandstone around Abha/Khamis Mushayt and in its type area: lithostratigraphic architecture and correlations

The Wajid Sandstone of southeastern Saudi Arabia is a prolific aquifer and a recent target for hydrocarbon exploration, but a sedimentologic model and the stratigraphic architecture of the sediments have only recently been presented for the type area of the Wajid Group around Wadi Dawasir. Farther to the west, the Wajid Sandstone was also recognized, but stratigraphic architecture and sedimentology are poorly known. This paper presents the preliminary results of investigations targeted at the outcrops west and south of the type area, covering the area between Wadi Dawasir, Najran in the south, and Abha in the west. Two successions are recognized, a lower red one and an upper beige one. Although the lower one sedimentologically shares several features with the lowermost unit in the type area, the marine Dibsiyah Formation, a correlation remains doubtful. The red succession lacks the Skolithos fauna of the Dibsiyah Formation, and its facies associations point to a fluvial depositional environment. From its stratigraphic position and from its lithology, the red succession is similar to the Siq Formation of the northern Kingdom and it will be discussed whether the red succession might be a yet unrecognized equivalent of the Siq Formation. The lower red unit is bounded by a major unconformity, separating it from the underlying basement. This pan-African unconformity developed during a latest Neoproterozoic–Cambrian episode of intensive weathering and peneplanation. It is characterized by a thick weathering zone and an overlying coarse but thin quartz pebble breccia to conglomerate, which together represent a regolith. The beige succession is definitely correlated to the Khusayyayn Formation. Both successions are characterized by macro-scale to giant 2D and 3D submarine dunes and share many other phenomena. The basal unconformity also shows regolith development with a quartz pebble conglomerate, whose clasts seem to have been reworked from the pan-African regolith.     

Interpretation of HMC images by a combined thermal and gasdynamic model

Images of comet Halley's nucleus taken by the HMC camera during the GIOT-TO encounter in 1986 show that a major part of the total dust production is localized in a few active areas which are the sources of gas-dust jets. The global dust distribution in the inner coma is dominated by two main jets roughly directed to the sun. A combination of a 1D thermal nucleus model with an axisymmetric continuum model of the jet outflow was used to investigate the properties of the inner coma. Detailed investigations show that the characteristics of the observed jets can be reproduced by outgassing from free sublimating active areas of a few km in diameter, a dust to gas ratio of 1–2.5 and a size distribution dominated by the larger grains. It is further shown that most of the observational constraints provided by the HMC data can be met simultaneously by a model of three jets superimposed on a weak background.     

On the importance of dust in cometary nuclei

The icy conglomerate model introduced by Whipple more than 40 years ago has been widely accepted in cometary science because it is able to describe numerous cometary phenomena. In this model comets are described as a conglomerate of ices and dust where the ices represent the major component. However, some recent observations seem to favour dust rich comets. The purpose of this paper is to summarize the observational facts supporting the dominance of refractories in comets and to discuss the consequences of a dust dominated nucleus for cometary physics.     

Application of a spherical FFT approach in airborne gravimetry

The basic idea of this paper is to modifyPoisson's integral for harmonic downward continuation into a convolution formula in the space domain. In this manner, the Fast Fourier Transform can be applied. The method is applied to airborne gravimetry, motivated especially by the Greenland survey. The accuracy of data continuation from the flight-level to the ground is analysed. In particular, the influence of latitudinal extension is investigated, since the introduced convolution formula is exact only for the mid-parallel of the analysed area. The results obtained justify the conclusion that the introduced method is applicable to processing of real data. Extended quadratic areas (up to 2500km × 2500km) in equatorial areas and up to 500km × 500km in regions with latitudes about 75°) can effectively be processed in one single procedure.