Towards a thermodynamics of immiscible two-phase steady-state flow in porous media

We propose that steady-state two-phase flow in porous media may be described through a formalism closely resembling equilibrium thermodynamics. This leads to a Monte Carlo method that will be highly efficient in studying two-phase flow under steady-state conditions numerically. This work was partially supported by the Norwegian Research Council through grants nos. 154535/432 and 180296/S30.     

The wavelength dependence of granulation (0.38–2.4 μm)

Using 2 pinhole photometers the intensity of the undisturbed photosphere was recorded simultaneously in 6 and in 4 wavelength regions. The rms value of the intensity variation in each of the 10 wavelength regions decreases slightly with increasing value of the heliocentric angle; this result confirms recent observations by other authors and supports the critique of the results given by Edmonds (1964).We report the detection of a secondary maximum in the wavelength dependence of the intensity variation at 1.5 m.     

The depositional architecture and facies variability of shelf deltas in the Eocene Battfjellet Formation,Nathorst Land,Spitsbergen

Deltas are commonly classified according to their plan‐view morphology as either river‐dominated, tide‐dominated or wave‐dominated. However, most deltas form under the mixed influence of these processes, commonly with laterally varying process regimes. It has also become clear that there is a mismatch between the plan‐view morphology and internal facies composition in some deltas. Combined outcrop and subsurface data from the Eocene Battfjellet Formation, Spitsbergen, provide an example of ancient shelf deltas that formed under mixed influence. Internally, these shelf deltas are characterized by wave‐dominated facies that are normally associated with strike‐extensive, nearly linear shoreline sandstones. However, the formation comprises partially overlapping sandstone bodies of limited lateral extent (<20 km in any direction). This stacking pattern is attributed to frequent autogenic lobe switching that caused localized and rapid transgressions. Such processes typify fluvial‐dominated deltas and occur less commonly in wave‐dominated ones. Thus, there is an apparent mismatch between inferred plan‐view morphology and internal facies composition. It is argued that the Battfjellet deltas were flood‐dominated and prograded mainly during periods of high fluvial discharge. However, reworking of the fluvial‐flood facies by fair‐weather and storm waves, as well as longshore currents, resulted in a wave‐dominated facies character. Delta lobes undergoing auto‐retreat were particularly prone to reworking by basinal processes, including tidal currents. It is suggested that repeated delta progradation from inner shelf settings towards the outer shelf and shelf edge was aided by high sediment supply rather than relative falls in sea‐level as previously suggested. This interpretation is supported by: (i) the lack of major facies dislocations and extensive sub‐aerial unconformities; and (ii) an overall relative rise in sea‐level as evidenced by an overall low‐angle (0·8 to 1·2°) ascending shoreline trajectory. The latter results from the combined effect of basin subsidence, eustatic highstand and sediment compaction.     

87Sr/86Sr ratio: a natural tracer to monitor groundwater flow paths during artificial recharge in the Bangkok area, Thailand

The aquifer system in the Thon Buri sedimentary basin below the deltaic flood plain of the Chao Phraya River, central Thailand, has been exploited for public water supply for the capital Bangkok since the early 1920s. Groundwater withdrawal, currently 1.4 million m³/d, has resulted in a maximum decline in hydraulic head of up to 40 m. This has induced land subsidence of as much as 1.7 m (1940–1992) in the eastern suburbs of the metropolis. Artificial injection of purified water within an area-wide network of recharge wells could constitute a remedy to slow the water level depression within the sedimentary basin, and thus the subsidence. This requires a prior shutdown of water withdrawal. The flow paths of the injected water can be traced by changes in the ⁸⁷Sr/⁸⁶Sr ratio of the groundwater and injected water mixture within the three main aquifers in the basin that are used for public supply. The ratios, monitored at five monitoring stations within the cone of depression, have been constant over 3 years. Injection of the calculated cone volume of 5.2?×?10⁹ m³ would take at least 10 years, depending on the injection pressure and the number and position of wells.     

Equilibrium resurfacing of Venus: Results from new Monte Carlo modeling and implications for Venus surface histories

Venus’ impact crater population imposes two observational constraints that must be met by possible model surface histories: (1) near random spatial distribution of ～975 craters, and (2) few obviously modified impact craters. Catastrophic resurfacing obviously meets these constraints, but equilibrium resurfacing histories require a balance between crater distribution and modification to be viable. Equilibrium resurfacing scenarios with small incremental resurfacing areas meet constraint 1 but not 2, whereas those with large incremental resurfacing areas meet constraint 2 but not 1. Results of Monte Carlo modeling of equilibrium resurfacing (Strom et al., 1994) is widely cited as support for catastrophic resurfacing hypotheses and as evidence against hypotheses of equilibrium resurfacing. However, the Monte Carlo models did not consider intermediate-size incremental resurfacing areas, nor did they consider histories in which the era of impact crater formation outlasts an era of equilibrium resurfacing. We construct three suites of Monte Carlo experiments that examine incremental resurfacing areas not previously considered (5%, 1%, 0.7%, and 0.1%), and that vary the duration of resurfacing relative to impact crater formation time (1:1 [suite A], 5:6 [suite B], and 2:3 [suite C]). We test the model results against the two impact crater constraints.Several experiments met both constraints. The shorter the time period of equilibrium resurfacing, or the longer the time of crater formation following the cessation of equilibrium resurfacing, the larger the possible areas of incremental resurfacing that satisfy both constraints. Equilibrium resurfacing is statistically viable for suite A at 0.1%, suite B at 0.1%, and suite C for 1%, 0.7%, and 0.1% areas of incremental resurfacing.     

The 1888 shoreline landslide and tsunami in Trondheimsfjorden,central Norway

Marine Geophysical Research - The 1888 landslide and tsunami along the shore of the bay of Trondheim, central Norway, killed one person and caused major damage to port facilities. Recent...