Morphology and emplacement of flows from the Deccan Volcanic Province,India

The present study is probably the first of its kind in the Deccan Volcanic Province (DVP) that deals in detail with the morphology and emplacement of the Deccan Trap flows, and employs modern terminology and concepts of flow emplacement. We describe in detail the two major types of flows that occur in this province. Compound pahoehoe flows, similar to those in Hawaii and the Columbia River Basalts (CRB) constitute the older stratigraphic Formations. These are thick flows, displaying the entire range of pahoehoe morphology including inflated sheets, hummocky flows, and tumuli. In general, they show the same three-part structure associated with pahoehoe flows from other provinces. However, in contrast to the CRB, pahoehoe lobes in the DVP are smaller, and hummocky flows are quite common. 'Simple' flows occur in the younger Formations and form extensive sheets capped by highly vesicular, weathered crusts, or flow-top breccias. These flows have few analogues in other provinces. Although considered to be a'a flows by previous workers, the present study clearly reveals that the simple flows differ considerably from typical a'a flows, especially those of the proximal variety. This is very significant in the context of models of flood basalt emplacement. At the same time, they do not display direct evidence of endogenous growth. Understanding the emplacement of these flows will go a long way in determining whether all extensive flows are indeed inflated flows, as has recently been postulated.Most of the studies relating to the emplacement of Continental Flood Basalt (CFB) lavas have relied on observations of flows from the CRB. Much of the current controversy surrounding the emplacement of CFB flows centers around the comparison of Hawaiian lava flows to those from the CRB. We demonstrate that the DVP displays a variety of lava features that are similar to those from the CRB as well as those from Hawaii. This suggests that there may have been more than one mechanism or style for the emplacement of CFB flows. These need to be taken into account before arriving at any general model for flood basalt emplacement.Editorial responsibility: T. Druitt     

Development of the 1990 Kalapana Flow Field,Kilauea Volcano,Hawaii

The 1990 Kalapana flow field is a complex patchwork of tube-fed pahoehoe flows erupted from the Kupaianaha vent at a low effusion rate (approximately 3.5 m³/s). These flows accumulated over an 11-month period on the coastal plain of Kilauea Volcano, where the pre-eruption slope angle was less than 2°. the composite field thickened by the addition of new flows to its surface, as well as by inflation of these flows and flows emplaced earlier. Two major flow types were identified during the development of the flow field: large primary flows and smaller breakouts that extruded from inflated primary flows. Primary flows advanced more quickly and covered new land at a much higher rate than breakouts. The cumulative area covered by breakouts exceeded that of primary flows, although breakouts frequently covered areas already buried by recent flows. Lava tubes established within primary flows were longer-lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply; tubes within breakouts were never reoccupied once the supply was interrupted. During intervals of steady supply from the vent, the daily areal coverage by lava in Kalapana was constant, whereas the forward advance of the flows was sporadic. This implies that planimetric area, rather than flow length, provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes.     

LONGITUDINAL DISPERSION IN SEDIMENT-LADEN OPEN CHANNEL FLOWS

Laboratory experiments on longitudinal dispersion in clear-water and sediment-laden open channel flows are reported. Data from these experiments and those available from previous studies indicate that the suspended sediment present in the flow affects the longitudinal dispersion process. The observed velocity distributions over the depth of sediment-laden flows indicate that the velocity deviates from the mean velocity more in sediment-laden flows than in clear-water flows. The velocity distributions over the cross section and secondary flow in the channel are also expected to be altereddue to the presence of suspended sediments in the flow. For these reasons, more dispersion is found in sediment-laden flows than in corresponding clear-water flows. A predictor for the dispersion coefficient in sediment-laden flows is proposed.     

Effectiveness of pulse flows in a regulated river for inducing upstream movement of an imperiled stock of Chinook salmon

We assessed the effectiveness of pulse flows in facilitating the upstream migration of an imperiled summer-run Chinook salmon (Oncorhynchus tshawytscha) stock in the Puntledge River, BC, Canada. During July and August, over 3 years, we tracked radio-tagged fish (n = 100) in a reach of the Puntledge River where water is diverted for power generation, resulting in stable low flows that are believed to impede migration. Over the course of  13 pulse flows, we measured migration rate, passage rate at natural barriers that are difficult to pass during low flows, movement away from the turbine outlet pool that creates distracting flows, and locomotor activity. Mean river flow during the peak of the pulses varied from 12.1 to 42.5 m³ s^?1 and was at least 6.1 m³ s^?1 above residual base flows. Typically, the pulse flows lasted 48 h. Migration rate was higher during some pulse flows, but results varied among pulses. Passage at natural barriers was only higher during an abnormal pulse where flows reached twice that of the prescribed flow (i.e., 24+ m³ s^?1). Some fish moved away from the turbine outlet pool during pulse flows. Pulse flows did not affect fish activity levels, as measured by electromyogram telemetry. Although the effect of pulsed flows on the migration of the Puntledge River summer-run Chinook salmon was unclear, no negative impacts, such as hyperactivity or downstream displacement were observed. The use of pulse flows as a management tool still requires further research.     

Analysis of methods to estimate spring flows in a karst aquifer

Hydraulically and statistically based methods were analyzed to identify the most reliable method to predict spring flows in a karst aquifer. Measured water levels at nearby observation wells, measured spring pool altitudes, and the distance between observation wells and the spring pool were the parameters used to match measured spring flows. Measured spring flows at six Upper Floridan aquifer springs in central Florida were used to assess the reliability of these methods to predict spring flows. Hydraulically based methods involved the application of the Theis, Hantush-Jacob, and Darcy-Weisbach equations, whereas the statistically based methods were the multiple linear regressions and the technology of artificial neural networks (ANNs). Root mean square errors between measured and predicted spring flows using the Darcy-Weisbach method ranged between 5% and 15% of the measured flows, lower than the 7% to 27% range for the Theis or Hantush-Jacob methods. Flows at all springs were estimated to be turbulent based on the Reynolds number derived from the Darcy-Weisbach equation for conduit flow. The multiple linear regression and the Darcy-Weisbach methods had similar spring flow prediction capabilities. The ANNs provided the lowest residuals between measured and predicted spring flows, ranging from 1.6% to 5.3% of the measured flows. The model prediction efficiency criteria also indicated that the ANNs were the most accurate method predicting spring flows in a karst aquifer.     

Petrology of the picrite-basalt flows in the Igatpuri area,Nasik district,Maharashtra

In the course of studying the Deccan Trap Hows around Igatpuri (latitudes 19°38′ and 19°45′: longitudes 73°30′ and 73°42′), picrite-basalts, not hitherto reported from this area, have been found occurring associated with basaltic flows. Thirty-eight flows, of a total thickness of 2200 feet, have been delimited. Of these, 8 flows may be termed picrite-basalts with a thickness varying from 25 to 75 feet. A feature of these basic flows is the abundance of olivine phenocrysts, with a complete absence of pyroxene phenocrysts in two of the flows. Two flows may be termed oceanite, two ankaramite, while four flows have phenocrysts of olivine, pyroxene and lelspar of An 65–70 %. In the oceanite flows the olivine phenocrysts constitute 20 to 30 per cent of the rock. They are mostly fresh, but some are altered to iddingsite. As regards the basaltic flows, about half have scanty olivine phenocrysts, the remainder being devoid of olivine. Eight are coarse enough to be termed olivine-dolerites. In the picrite-basalts the pyroxene phenocrysts have an optic axial angle of from 55° to 60°. In the basaltic flows the angle varies from 45° to 52°. The olivine phenocrysts of the picrite-basalts are highly magnesian, whereas those of the basalts are more ferruginous, as determined by optical methods. West’s view that the origin of these picrite-basalts is due to differentiation by crystal settling followed by freezing and extrusion, seems to be supported by this study.     

Morphology of rubbly pahoehoe (simple) flows from the Deccan Volcanic Province: Implications for style of emplacement

Lava flows with preserved bases and brecciated upper crusts constitute a morphological type that differs in character from typical pahoehoe and a'a: such flows have been reported from many provinces around the world. Previous studies had referred to these flows informally as ‘pahoehoe flows with rubbly tops’, ‘broken-top pahoehoe’ and ‘rubbly pahoehoe’. Recent studies have formally applied the latter term to describe parts of the well-studied Laki flow in Iceland as well as flows from the Columbia River Basalt province. Rubbly pahoehoe flows are abundant in the upper stratigraphic formations of the Deccan Volcanic Province (DVP), and are more commonly known as simple flows. This study presents detailed observations of such flows from various parts of the DVP and discusses their implications for understanding flow emplacement. These flows, which appear to be single units at the outcrop-scale, are generally much thicker and significantly more extensive than individual pahoehoe lobes that dominate the lower formations of the Deccan stratigraphy. They are characterised by preserved, gently undulating tachylitic bases but variably disrupted crustal zones that grade into flow-top breccias. The breccias are constituted of highly vesicular and oxidised fragments of varying sizes that appear to have been derived from previously formed pahoehoe crusts. Previous work has indicated that the morphology of these flows might be related to initial inflation, accompanied by rapid volatile exsolution and an increase in effusion rate and/or viscosity with time. This agrees reasonably well with the qualitative and quantitative models of emplacement developed for the Laki flow. The abundance of such flows in the upper formations of the Deccan stratigraphy clearly hints at a significant shift in the nature of the Deccan eruptions; this could be indicative of higher eruption rates during this period. This, in turn, raises the possibility of hazardous impact on the climate during the eruption of these flows, which is also discussed in the paper.     

Comparing the transitional behaviour of kaolinite and bentonite suspension flows

Past research has demonstrated the dramatic effects that variations in suspended clay can have on the properties of flow by producing a range of transitional flows between turbulent and laminar states, depending on clay concentration and fluid shear. Past studies have been restricted to kaolinite flows, a clay mineral that has relatively weak cohesive properties. This paper extends these studies to suspension flows of bentonite, a clay mineral that attains higher viscosities at far lower volumetric concentrations within a flow. The results show that the types of transitional flow behaviour recognized in past studies can also be found in bentonite suspension flows, but at lower suspended sediment concentrations, thus demonstrating an even more dramatic effect on flow properties, and potentially on sediment transport and resulting bed morphology, than kaolinite flows. The paper proposes new stability diagrams for the phase space of bentonite flows and compares these to past work on kaolinite suspension flows. These new data suggest that the transitional‐flow Reynolds number can be used to delineate the types of transitional flow across different clay types and assess modern and ancient clay‐suspension flows. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Remanent magnetism of the Deccan Trap flows around Sagar,Madhya Pradesh,India

The results of remanent magnetic studies on eight of the nine Deccan Trap flows in the vicinity of Sagar (23°56′ N: 78°38′ E) are presented. It is found that the lower four flows in the sequence are of ‘reversed’ magnetic polarity. Of the upper four flows, the top and the bottom ones show ‘intermediate’ directions while the two flows sandwiched between these are ‘normal’. These results suggest a transitional stage between the polarity inversion of the geomagnetic field from ‘reversed’ to ‘normal’ during the eruption of these Deccan Trap flows. The remanent magnetic directions of these ‘reversed’ and ‘normal’ flows show fairly shallow inclinations and are comparable to the remanent magnetic directions of the Pavagarh basalts.     

Emplacement processes of proto-arc basalt in the Izu–Bonin–Mariana arc system

Ascertaining the emplacement mechanism of oceanic basaltic lavas is important in understanding how ocean floor topography is produced and oceanic plates evolve, particularly during the early stages of crustal development of a supra-subduction zone. A detailed study of the volcanic stratigraphy at International Ocean Discovery Program (IODP) Site U1438 in the Amami Sankaku Basin, west of the Kyushu–Palau Ridge, has revealed the development of lava accretion and ridge topography on the Philippine Sea plate at about 49 Ma. Igneous basement rocks penetrated at Site U1438 are the uppermost 150 m of ~6 km-thick oceanic crust, and comprise, in a downhole direction, sheet flows (12.6 m), lobate sheet flows (61.3 m), pillow lavas (50.7 m), and thin sheet flows (25.3 m). The lowermost sheet flows are intercalated with layers of limestone and epiclastic tuff. Lithofacies analysis reveals that the lowermost sheet flows, limestone, and tuff formed on an axial rise, the pillow lavas were emplaced on a ridge slope, and the lobate sheet flows formed off ridge on an abyssal plain. The lithofacies of the basement basalt corresponds to the upper portions of fast-spreading oceanic crust, suggesting that subduction initiation was associated with intermediate to fast rates of seafloor spreading. The surface sheet flows are olivine–clinopyroxene-phyric basalt and differ from the lower basalt flows that contain phenocrysts of olivine and plagioclase, with or without clinopyroxene. The depleted chrome-spinel composition and olivine–clinopyroxene phenocryst assemblage in the surface sheet flows suggests a slight contribution of water for magma generation not present for the lower basalt flows. Considering the lithological difference between the backarc and forearc oceanic crust in the Izu–Bonin–Mariana arc, with sheet flow dominant in the former, seafloor spreading occurred faster in the later stage of subduction initiation.     

Velocity and concentration profiles of particle movement in sheet flows

Sheet flows occur widely in natural free-surface flows including rivers in flood, tidal estuaries and coastal waters in storm conditions when bed shear stress becomes sufficiently high. Particle volumetric concentration in sheet flows normally follows a linear distribution with the Rouse [Rouse H. Modern conceptions of the mechanics of fluid turbulence. Trans ASCE, 1937;102:463–543] distribution applicable in the dilute water column above the sheet-flow layer. However, a well-verified formula for determining particle velocity distribution in sheet flows is still lacking. This paper presents formulas to describe the particle velocity profile in steady or oscillatory sheet flows. They compare well with measured data. In particular, the novel formula for determining the particle velocity at the top of bedload–sediment-dominated sublayer in sheet flows is also well verified with measured data.     

Uncertainty in high and low flows due to model structure and parameter errors

This paper aims to investigate the uncertainty in simulated extreme low and high flows originating from hydrological model structure and parameters. To this end, three different rainfall-runoff models, namely GR4J, HBV and Xinanjiang, are applied to two subbasins of Qiantang River basin, eastern China. The Generalised Likelihood Uncertainty Estimation approach is used for estimating the uncertainty of the three models due to parameter values, henceforth referred as parameter uncertainty. Uncertainty in simulated extreme flows is evaluated by means of the annual maximum discharge and mean annual 7-day minimum discharge. The results show that although the models have good performance for the daily flows, the uncertainty in the extreme flows could not be neglected. The uncertainty originating from parameters is larger than uncertainty due to model structure. The parameter uncertainty of the extreme flows increases with the observed discharge. The parameter uncertainty in both the extreme high flows and the extreme low flows is the largest for the HBV model and the smallest for the Xinanjiang model. It is noted that the extreme low flows are mostly underestimated by all models with optimum parameter sets for both subbasins. The largest underestimation is from Xinanjiang model. Therefore it is not reliable enough to use only one set of the parameters to make the prediction and carrying out the uncertainty study in the extreme discharge simulation could give an overall picture for the planners.     

The influence of debris flows on channels and valley floors in the Oregon Coast Range,U.S.A.

Debris flows are one of the most important processes which influence the morphology of channels and valley floors in the Oregon Coast Range. Debris flows that initiate in bedrock hollows at heads of first-order basins erode the long-accumulated sediment and organic debris from the floors of headwater, first- and second-order channels. This material is deposited on valley floors in the form of fans, levees, and terraces. In channels, deposits of debris flows control the distribution of boulders. The stochastic nature of sediment supply to alluvial channels by debris flows promotes cycling between channel aggradation which results in a gravel-bed morphology, and channel degradation which results in a mixed bedrock- and boulder-bed morphology. Temporal and spatial variability of channel-bed morphology is expected in other landscapes where debris flows are an important process.     

Hyperconcentrated flows on a forested alluvial fan of eastern Canada: geomorphic characteristics,return period,and triggering scenarios

The assessment of the dominant flow type on alluvial fans usually refers to two categories: debris‐flow fans (i.e. sediment gravity flows) and fluvial fans (i.e. fluid gravity flows). Here we report the results of combined morphometric, stratigraphic and sedimentological approaches which suggest that hyperconcentrated flows, a transitional process rheologically distinct from debris flows and floods and sometimes referred to as debris floods, mud floods, or transitional debris flows, are the dominant fan building process in eastern Canada. These flows produce transitional facies between those of debris flows which consist of a cohesive matrix‐supported diamicton, and those of river flows which display more distinct stratification. The size of the blocks in the channels and the abrasion scars at the base of several trees attest to the high transport capacity of these flows. The fan channels are routed according to various obstacles comprised primarily of woody debris that impede sediment transit. However, these conditions of sediment storage are combined with readily available sediment due to the friable nature of the local lithology. Tree‐ring analysis allowed the reconstruction of eight hydrogeomorphic events which are characterized by a return period of 9.25 years for the period 1934–2008, although most of the analyzed events occurred after 1970. Historical weather data analysis indicates that they were related to rare hydrometeorological events at regional and local scales. This evidence led to the elaboration of weather scenarios likely responsible for triggering flows on the fan. According to these scenarios, two distinct hydrologic regimes emerge: the torrential rainfall regime and the nival regime related to snowmelt processes. Hydrogeomorphic processes occurring in a cold‐temperate climate, and particularly on small forested alluvial fans of north‐eastern North America, should receive more attention from land managers given the hazard they represent, as well as because of their sensitivity to various meteorological parameters. Copyright © 2014 John Wiley & Sons, Ltd.     

Transverse structure of subtidal flow in a weakly stratified subtropical tidal inlet

The transverse structure of exchange flows and lateral flows as well as their relationship to the subtidal variability are investigated in a subtropical inlet, Ponce de Leon Inlet, Florida. Two surveys were executed during different phases of the tidal month to determine the spatial structure of subtidal exchange flows. Data from fixed moorings were used to depict the temporal variability of the spatial structure established in the surveys. The data suggested a tidally rectified pattern of net outflow in the channel and inflow over shoals with a negligible influence of streamwise baroclinic pressure gradients on the dynamics and slight modifications due to the wind. Onshore winds strengthened net inflows but weakened net outflows, rarely reversing them, while offshore winds increased net outflows and weakened net inflows. Curvature effects were found to be important in modifying secondary circulations. Slight modifications to the secondary flows were also caused by stream-normal baroclinicity during one survey. Most important, the intensity of the exchange flows was modulated by tides, with the largest exchange flows developing in response to the strongest tidal rectification of spring tides.     

Compound and simple lava flows and flood basalts

Compound lava flows, defined as those lavas which are divisible into flowunits, commonly have a shield-like form and are thought to develop when the rate of extrusion of lava is relatively low.Simple lava flows, defined as those lavas which are not divisible into flow-units, are thought to form when the rate of extrusion of lava is relatively high. A logical definition oflava flow must embrace both simple lava sheets and substantial lava shields (compound lava flows) up to 600 m high. Flood basalt piles include both compound and simple flows, but the most extensive and far-reaching flows are simple and they are believed to form when the rate of extrusion of lava is particularly high.     

Geomorphological characteristics of small debris flows on Junior's Kop,Marion Island,maritime sub ‐ Antarctic

The geomorphological characteristics of small debris flows in a maritime sub‐Antarctic environment are described. The morphological and sedimentological characteristics of the debris flows are comparable to debris flows documented for other parts of the world; their initiation appears closely linked to the unusual environment in which they are found. Sediment supply is generated by diurnal frost heave of loamy sediment associated with Azorella selago. The debris flows are triggered by sediment mobilization upon saturation of the frost‐heaved surface gravel and overland flow over the low‐permeability and frost‐susceptible slope materials. Morphological effects of the flows are short‐lived due to obliteration by subsequent frost heave activity. Copyright © 2000 John Wiley & Sons, Ltd.     

The 1971 and 1973 eruptions of Volcán Fuego,Guatemala, and some socio-economic considerations for the volcanologist

Volcán Fuego erupted ash and ash flows during September 1971 and February–March 1973. The ash flows were restricted to existing drainage channels. Most damage was due to subsequent mud flows and floods. A catastrophe can be expected if the ash flows or mud flows increase in volume and overflow their channels in future eruptions. The only practical remedial measure is temporary evacuation, a formidable social and economic undertaking for an underdeveloped nation. Conscious of this, the geologist at the scene is unsure at what point to recommend evacuation. Probably the volcanologist can make his most useful direct contribution to society by cooperating in studies on the effect of volcanism on agriculture. The lives and wealth saved by even a slight increase in agricultural productivity would vastly outweigh losses due to volcanic disasters.     

Investigating the impact of the Chi‐Chi earthquake on the occurrence of debris flows using artificial neural networks

Debris flows have caused enormous losses of property and human life in Taiwan during the last two decades. An efficient and reliable method for predicting the occurrence of debris flows is required. The major goal of this study is to explore the impact of the Chi‐Chi earthquake on the occurrence of debris flows by applying the artificial neural network (ANN) that takes both hydrological and geomorphologic influences into account. The Chen‐Yu‐Lan River watershed, which is located in central Taiwan, is chosen for evaluating the critical rainfall triggering debris flows. A total of 1151 data sets were collected for calibrating model parameters with two training strategies. Significant differences before and after the earthquake have been found: (1) The size of landslide area is proportioned to the occurrence of debris flows; (2) the amount of critical rainfall required for triggering debris flows has reduced significantly, about half of the original critical rainfall in the study case; and (3) the frequency of the occurrence of debris flows is largely increased. The overall accuracy of model prediction in testing phase has reached 96·5%; moreover, the accuracy of occurrence prediction is largely increased from 24 to 80% as the network trained with data from before the Chi‐Chi earthquake sets and with data from the lumped before and after the earthquake sets. The results demonstrated that the ANN is capable of learning the complex mechanism of debris flows and producing satisfactory predictions. Copyright © 2009 John Wiley & Sons, Ltd.