Net Horizontal Displacement Research Articles

Squeezing river catchments through tectonics: Shortening and erosion across the Indus Valley, NW Himalaya

Tectonic displacement of drainage divides and the consequent deformation of river networks during crustal shortening have been proposed for a number of mountain ranges, but never tested. In order to preserve crustal strain in surface topography, surface displacements across thrust faults must be retained without being recovered by consequent erosion. Quantification of these competing processes and the implications for catchment topography have not previously been demonstrated. Here, we use structural mapping combined with dating of terrace sediments to measure Quaternary shortening across the Indus River valley in Ladakh, NW Himalaya. We demonstrate ~0.21 m k.y.–1 of horizontal displacement since ca. 45 ka on the Stok thrust in Ladakh, which defines the southwestern margin of the Indus Valley catchment and is the major back thrust to the Tethyan Himalaya in this region. We use normalized river channel gradients of the tributaries that drain into the Indus River to show that the lateral continuation of the Stok thrust was active for at least 70 km along strike. Shortening rates combined with fault geometries yield vertical displacement rates that are compared to time-equivalent erosion rates in the hanging wall derived from published detrital 10Be analyses. The results demonstrate that vertical displacement rates across the Stok thrust were approximately twice that of the time-equivalent erosion rates, implying a net horizontal displacement of the surface topography, and hence narrowing of the Indus Valley at ~0.1 m k.y.–1. A fill terrace records debris-flow emplacement linked to thrust activity, resulting in damming of the valley and extensive lake development. Conglomerates beneath some of the modern alluvial fans indicate a northeastward shift of the Indus River channel since ca. 45 ka to its present course against the opposite side of the valley from the Stok thrust. The integration of structural, topographic, erosional, and sedimentological data provides the first demonstration of the tectonic convergence of drainage divides in a mountain range and yields a model of the surface processes involved.

Experimetal study of a freely falling plate with an inhomogeneous mass distribution

A homogeneous thin plate often flutters while falling through a fluid under gravity. The center of gravity of the plate moves back-and-forth horizontally and the plate tilting angle oscillates symmetrically from the horizontal. Here we show that such a scenario is qualitatively changed for a plate with noncoinciding centers of gravity and buoyancy due to an inhomogeneous mass distribution. Mismatch of the centers causes an external torque that breaks the symmetry of rotational motion, shifts the mean tilting position from the horizontal, and leads to a net horizontal plate displacement. In laboratory experiments with a Reynolds number around 1500, we found that the net horizontal displacement scales linearly with the separation between the centers up to a critical value, beyond which the plate falls vertically in an edge-on configuration with the heavier side downward. Experimental results are compared to predictions of a quasi-steady numerical model. Our work demonstrates that motion of freely moving objects in a fluid depends sensitively on external torques, which potentially can be used as an effective control method.

Experimental study of the particle paths in solitary water waves

We provide experiments that had been conducted to investigate the particle trajectory beneath a solitary water wave. Experimental results show that the surface drift is larger than the bottom drift. Meanwhile, the ratio of the net horizontal displacement to the total height of the trajectory at the free surface and subsurface will decrease with the initial vertical position and increase with the relative wave height.

Swimming ability and behaviour of post-larvae of a temperate marine fish re-entrained in the pelagic environment.

The degree to which behaviour, vertical movement and horizontal transport, in relation to local hydrodynamics, may facilitate secondary dispersal in the water column was studied in post-larval Sillaginodes punctata in Port Phillip Bay, Australia. S. punctata were captured in shallow seagrass beds and released at the surface in three depth zones (1.5, 3 and 7 m) off-shore at each of two sites to mimic the re-entrainment of fish. The behaviour, depth and position of S. punctata were recorded through time. The direction and speed of local currents were described using an S4 current meter and the movement of drogues. Regardless of site, fish immediately oriented toward the bottom, and into the current after release. In shallow water (1.5 m), 86% of fish swam to the bottom within 2 min of release. At one site, the net horizontal displacement of fish was largely unrelated to the speed and direction of local currents; at a second site, fish could not maintain their position against the current, and the net horizontal displacement was related to the speed and direction of currents. In the intermediate depth zone, wide variability in depths of individual fish through time led to an average depth reached by fish that was between the shallow and deep zones. Based on daily increments in the otoliths, however, this variability was not related significantly to the time since entry of fish into Port Phillip Bay. In the deepest depth zone, 81% of fish remained within 1 m of the surface and their horizontal displacement was significantly related to the direction and speed of currents. Secondary dispersal of post-larval fish in the water column may be facilitated by the behaviour and vertical movements of fish, but only if fish reach deeper water, where their displacement (direction and distance) closely resembles local hydrodynamic regimes. In shallow water, fish behaviour and vertical migration actually reduce the potential for secondary dispersal.

Effect of flow velocity and body size on swimming trajectories of sea scallops, Placopecten magellanicus (Gmelin): a comparison of laboratory and field measurements

The effect of flow velocity and body size on swimming trajectories of Placopecten magellanicus (Gmelin) was studied in a 5 m, flow-through laboratory flume and in a shallow (7 m depth) tidal channel in Lunenburg Bay, Nova Scotia, Canada. In the flume, scallops of 4 size classes, 11–20, 21–30, 31–50 and 51–80 mm shell height, (SH) were induced to swim at mean free-stream flow speeds of 0, 5, 9, 14 and 21 cm s −1. Swimming (active) and post-swimming (passive sinking) phases of individual trajectories were quantified in terms of swimming height, net displacement and direction, swimming time and swimming speed. Smaller scallops (≤ 30 mm) were adverted by the flow during both phases while larger scallops (> 30 mm) were advected only during the passive phase. Net horizontal displacement (active and passive stages combined) was positively related to flow speed for all size classes but the proportion of the variance explained by flow speed decreased with increasing scallop size. Most scallops swimming under flow had a downstream net swimming direction (finished their swimming phase downstream of the start point). For small scallops (≤ 30 mm SH), the proportion swimming downstream was independent of flow speed at flows of 0–5 cm s ( p > 0.30), but not independent of the flow speed at higher flows ( p < 0.01). For large scallops (> 30 mm SH), the proportion swimming downstream was independent of flow speed. In the field study, scallops ranging from 17–72 mm were induced to swim at current speeds ranging from 7–55 cm s −1. Model II regression and circular-linear correlation analysis showed a positive relationship between net horizontal displacement and current speed for scallops landing downstream and a negative relationship for scallops landing upstream, indicating the effect of advection. For small scallops that swam at medium (~ 18 cm s −1) current speeds, the distribution of displacement directions was significantly non-random and the mean direction did not differ significantly from the mean current direction. For large scallops that swam at both medium and high (~ 38 cm s −1) current speeds, the distribution of displacement directions was not significantly different from random. However, at high current speeds the mean size of scallops that landed upstream was significantly greater and the mean swimming height was significantly lower than for those that landed downstream. Flume and field measurements of swimming trajectories demonstrated that predictability of dispersion patterns of P. magellanicus released in bottom culture based on near-bed current data will be poor, especially when scallops larger than 30 mm SH are used.

Effects of surface roughness on a sphere sedimenting through a dilute suspension of neutrally buoyant spheres

The influence of microscopic surface roughness on the statistical motion of a heavy sphere falling through a dilute suspension of neutrally buoyant spheres is analyzed for conditions of low Reynolds number and large Péclet number. The presence of roughness on their surfaces allows interacting spheres to come into contact. A stick/rotate model (based on rigid-body motion) and a roll/slip model (based on solid contact friction) are proposed for the motion normal to the line-of-centers of the heavy sphere and a neutrally buoyant sphere when in contact. A trajectory analysis is used to describe pairwise interactions and their contributions to the mean velocity, velocity variance, and hydrodynamic diffusivity of the heavy sphere as it undergoes a fluctuating motion due to interactions with the background spheres. The horizontal component of the hydrodynamic diffusivity becomes nonzero as a direct result of surface roughness and contact, since ideally smooth spheres undergo symmetric pairwise trajectories which result in zero net horizontal displacement. The effects of surface roughness on the vertical components of the diffusivity, mean velocity, and velocity variance are relatively small when the heavy and background spheres are of nearly equal size, but the effects of surface roughness are large for disparate size ratios. The limited experimental data available show better agreement with the roll/slip model than with the stick/rotate model.

Volcanic and structural history of the Hohi volcanic zone, central Kyushu, Japan

More than 5000 km3 of magmatic material was erupted in Pliocene-Pleistocene times in a volcano-tectonic depression, i. e., the Hohi volcanic zone (HVZ) in central Kyushu, Japan. The eruptive deposits consist mainly of andesite lava flows and large-scale pyroclastic-flow deposits. Their eruptions were accompanied by the formation of an EW-oriented graben (70 km × 45 km) under regional NS extensional stress. Pre-Tertiary basement rocks are absent on the surface of the graben but occur at depth, having subsided up to 3 km. Radiometric ages of volcanic rocks on the surface show zoned isochrons from 5 Ma at the margin to 0.3 Ma in the center of the HVZ. The youngest center of age zonation coincides with a 30 mgal negative Bouguer gravity anomaly. Radiometric ages of rocks from drill cores are older toward the bottom of the graben, reaching a maximum of at least 4 Ma. Volcanic activity concentrated over time toward the center of the graben and buried successively erupted material. Areas of active volcanism in the HVZ became smaller and changed in style during the 5-Ma history of activity. Volcanism of the early stage (5-2 Ma) was characterized by voluminous eruptions of andesitic lava flows that formed lava plateaus and were intruded by EW-oriented feeder dikes, perhaps related to fissure eruptions. In contrast, late-stage volcanism (2-0 Ma) resulted primarily in andesitic to dacitic lava domes with features of monogenetic volcanoes produced at low eruption rates. The HVZ shows unimodal volcanism dominated by andesitic and dacitic lavas with a small amount of rhyolite and only traces of basalt; these characteristics differ from those that typify volcanism in most other extensional areas. Erupted material in the HVZ is of the calc-alkali and high-alkali tholeiite series and shows no significant chemical changes over 5 Ma, except for an increase in K2O after 1.6 Ma. The net horizontal displacement along normal faults indicates that the HVZ widened by about 10%–20% across the graben at an average rate of 0.1 cm/yr. I interpret the HVZ to be neither a pull-apart structure of the pre-Tertiary basement nor the result of propagation of the Okinawa Trough, but rather the earliest stage of rifting when vertical subsidence caused by normal faulting is compensated by filling with volcanic material.

Estimate of Displacement in Major Zone of Tear-Thrusting in Fold and Thrust Belt, Southwest Montana: ABSTRACT

The most pronounced deflection of the marginal fold and thrust belt in Montana occurs in the northern Tobacco Root End_Page 986------------------------------ Mountains where a zone of imbricated thrusts follows the southern margin of the eastward-trending Helena embayment of the Belt basin. Movements along major thrusts north and south of this east-trending zone are nearly pure dip-slip. Movements within the zone are demonstrably oblique with nearly equal components of dextral and reverse slip. This suggests that the fault zone may be described as being one of tear-thrusting. Accumulated net slip along the tear-thrust zone may be estimated by summing estimates of net slip along the individual faults which comprise the zone and by examining displaced isopach lines for rocks deposited prior to faulting. Summing net-slip estimates for individual faults along several sections though the fault zone indicates that the horizontal components of net slip is between 15 and 30 km. Right separation of isopach lines for a limestone member of the Kootenai Formation (Cretaceous) indicates a horizontal displacement which is somewhat larger (between 30 and 60 km). Displacements of this magnitude cannot be accounted for by folding and minor thrusting in the rocks north of the tear-thrust zone and strongly suggests one or more zones of detachment within the section above Arc ean basement rocks. Estimates of net horizontal displacement along this fault zone can be very useful in interpreting anomalous isopach trends such as those seen in the Flathead Sandstone (Cambrian) and Maywood Formation (Devonian). End_of_Article - Last_Page 987------------

TESTS OF THE DIAGNOSTIC-CYCLE ROUTINE IN THE INTERPRETATION OF LAYER-CLOUD EVOLUTIONS1

A Routine is described which is a collection of computer-programed techniques designed for the interpretation of meteorological satellite videograph observations. From the inferred evolution of the mass-structure distribution, the Routine diagnoses the horizontal velocity distribution for one or more isentropic surfaces. Using the horizontal velocity distribution as input, the Routine further derives net horizontal and net, vertical, parcel-displacements (in the synoptic range of scale) for specified regions and periods of time. This permits pattern configurations of layer-cloudiness to be remapped to later positions which arc consistent with the mass-motion evolutions. The use of the Routine for interpreting satellite cloud observations is illustrated by the presentation of two case studies. The layer-cloudiness distributions for the initial and terminal times of each case are analyzed primarily from the TIROS operational nephanalysis. The initial distribution of layer-cloudiness is remapped in accordance with the net horizontal displacement field. The cloud evolutions are shown and comparisons are made between the joint 24-hr. cloud displacement and net vertical, parcel-displacement patterns and the verifying 1ayer-cloudiness distributions. A close correspondence is found between the terminal position of the displaced cloudiness and the verifying cloudiness distributions. The patterns evolved in the horizontally displaced cloudiness are realistic reflections of the stages of development associated with vortex cloud patterns. Net vertical, parcel-displacement fields are generated which are consistent with conventional synoptic desiderata and the observed cloudiness. The, results indicate that the major portion of layer-cloudiness distributions in the synoptic range of scale in extratropical latitudes can be accounted for by the time-integrated, horizontal and vertical parcel-displacements. The implications of these results to the objective use of satellite data are discussed.

MEAN-LAYER WIND CHARTS IN TROPICAL ANALYSIS

A discussion of the usefulness of mean-lager winds—defined in terms of the net horizontal displacement of the balloon during the time interval that it ascends through specified layers—in tropical analysis and forecasting is presented. Selected wind soundings in the trade wind regime are used to illustrate the greater representativeness and reliability of the mean winds. Some evidence is presented to support the contention that the wind report in the center of a layer cannot always be trusted to give a reliable picture of the layer as a whole. Other arguments are presented in support of the mean-layer winds for analysis and forecasting purposes, and for computations of derived properties of the field of motion. Some remarks on the analysis of these charts, based on the experience obtained at the National Hurricane Research Project, are included.

THE SOLITARY WAVE: ITS CELERITY, PROFILE, INTERNAL VELOCITIES AND AMPLITUDE ATTENUATION IN A HORIZONTAL SMOOTH CHANNEL

The solitary wave consists of a single elevation of water above the originally undisturbed level as shown in Figure 1. It is translatory, a passing wave causing a definite net horizontal displacement of the liquid. While the characteristics of oscillatory waves depend on wave length as well as wave height and water depth, the solitary wave is apparently described completely by the wave height and water depth so long as attenuation due to friction is unimportant.