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Branney and Kokelaar (1992) emphasized that many features of pyroclastic flow deposits largely record the last processes involved in their formation, so Wolff and Turbeville's glib reminder of this philosophy at the end of their comment is quite unnecessary. Many structures in high-grade ignimbrites record non-particulate flow that occurred some considerable time after particulate aggradation ceased. This is not in question, and we pointed this out in our paper. It is the earlier deposition and deformation history of rheomorphic ignimbrites that is at issue. This is the aspect that bears more widely on the nature of pyroclastic flows and related eruptive phenomena. In another paper (Branney and Kokelaar 1994) we have documented evidence for hotstate remobilization and deformation of some stationary rheomorphic ignimbrites by post-emplacement disturbance (caldera collapse). However, in Branney and Kokelaar (1992) we provided evidence that shows that for most rheomorphic ignimbrites it is inappropriate to assume a twofold flow history (of hot remobilization after an initial flow came to rest). Progressive aggradation and agglutination provide the most straightforward explanation for many of the markedly irregular vertical variations in welding intensity characteristic of high-grade ignimbrites, just as progressive aggradation best accounts for vertical variations in sedimentary lithofacies and/or in chemical composition in other ignimbrites.

The El Tigre archaeological site (39°46′49″ S; 62°22′32″ W) is located in the south of Provincia de Buenos Aires, Argentina, on an ancient delta of the Rio Colorado. Its sedimentary sequence shows periods of landscape stability and soil formation processes during the period ca. 1,000–400 years bp. The aim of this paper is to investigate the evolutionary history of the vegetation in order to understand palaeoenvironmental changes during the late Holocene. The study of microremains, mainly phytoliths, from the sedimentary sequence indicates that cold and dry conditions predominated at 2,700–2,200 cal bp, from deposition of non-pedogenetic, aggradational sediments in arid or semi-arid environments and/or sparse vegetation cover. Then the climate became much warmer at ca. 2,200–1,200 cal bp, with greater availability of moisture and the presence of xerophytic shrubs and halophytic grasslands, and also extra-regional trees and shrubs. The records indicate that for ca. 1,500–300 cal bp the climate conditions changed to temperate with periods of greater water availability and the presence of a saline steppe and a greater abundance of Monte-Caldenal scrub vegetation elements. This climatic trend is also in agreement with the soil formation processes defined in the archaeological site sequence. The upper layers of the El Tigre site show lower temperatures in the last 300 years, accompanied by variations in the availability of moisture, with alluvial processes characterized by the presence of saline grasslands with xerophytic shrubs and an increase in Asteraceae and Poaceae, continued by the recent top samples with ruderal communities and sandy grasslands.

Explosive eruptions can severely alter the boundary conditions of fluvial systems around volcanoes by depositing large volumes of erodible fragmental material, increasing erosion rate and drainage mass flux (water and sediment) in the affected basin. In this paper, the environmental response to the 13 ka Croscat Violent Strombolian eruption in the Garrotxa Volcanic Field (NE Spain) has been investigated using a stratigraphic approach. Volcaniclastic material was mainly delivered at headwater tributaries (Les Tries plain in the Ser river basin) of the Fluvia River, one of the main drainage systems of NE Spain. Deposits in the Les Tries valley was initially reworked by hyperconcentrated-flows to braided stream-flows and by debris-flows involving mixed terrains (volcaniclastic materials and sands–gravels of the Eocene sedimentary basement) as registered in the stratigraphic record. The erosive pattern observed at the Les Tries valley reflects the erosion model of well-sorted and coarse-grained deposits (as the tephra deposited during the Violent Strombolian phase of the Croscat eruption), in which deep gullying and downstream aggradation are typically retarded where coarse tephra deposits remained highly permeable. Moreover, the Croscat eruption occurred soon after the Last Glacial Maximum, implying the shift from dry to wet conditions during the remobilization of the Croscat tephra. In this framework, the semiarid conditions retarded soil stabilization, driving the development of hyperconcentrated-flow-dominated alluvial fans, whereas the more humid environmental conditions favoured the partial stabilization of loose pyroclastic material, until it is periodically remobilization by mass-wasting processes as debris-flow-dominated lahars.

Due to the periodic rising and falling of the reservoir water level, the rock–soil body of bank slope is constantly changing between the saturated and unsaturated status, which changes the limit equilibrium condition of the slope body, resulting in a large number of dormant landslide reactivation and new landslide generation after water impounding operation of the three gorges reservoir. Based on the long-term monitoring data of pore-water pressure, water content, reservoir water level, rainfall and landslide deformation, the deformation response regularity of Liujiaba landslide under the fluctuating reservoir level combined scenario is studied in this paper. The results show that the landslide deformation is mainly in the lower section affected by the fluctuation of the reservoir water. The slide deformation appears in the mid-early stage of the water level declining and during the running of 175 m water level. The deformation is gradually increasing from a slowly to rapidly stage, then slows down and gradually reduces to a relative stopped state. Considering that the variation of the saturation line in the landslide will be influenced by the water level fluctuation rate, the SEEP and SLOPE modules are used with Geo-studio software for the fluctuant reservoir level and response pattern of landslide deformation analysis. The study can be provided as a reference for landslides study of debris aggradational landslide.

Based on high-resolution seismic and well datasets, this paper examines the evolution and drowning history of a Paleocene–Eocene carbonate platform in the Offshore Indus Basin of Pakistan. This study uses the internal seismic architecture, well log data as well as the microfauna to reconstruct factors that governed the carbonate platform growth and demise. Carbonates dominated by larger benthic foraminifera assemblages permit constraining the ages of the major evolutionary steps and show that the depositional environment was tropical within oligotrophic conditions. With the aid of seismic stratigraphy, the carbonate platform edifice is resolved into seven seismic units which in turn are grouped into three packages that reflect its evolution from platform initiation, aggradation with escarpment formation and platform drowning. The carbonate factory initiated as mounds and patches on a Cretaceous–Paleocene volcanic complex. Further, the growth history of the platform includes distinct phases of intraplatform progradation, aggradation, backstepping and partial drownings. The youngest succession as late-stage buildup records a shift from benthic to pelagic deposition and marks the final drowning in the Early Eocene. The depositional trend of the platform, controlled by the continuing thermal subsidence associated with the cooling of volcanic margin lithosphere, was the major contributor of the accommodation space which supported the vertical accumulation of shallow water carbonate succession. Other factors such as eustatic changes and changes in the carbonate producers as a response to the Paleogene climatic perturbations played secondary roles in the development and drowning of these buildups.

Garhwal Himalaya has witnessed extreme climatic conditions in the form of incessant rainfall during June 15–17, 2013, generating numerous primary as well as secondary landslide hazards due to flooding event in the Bhagirathi River. This was probably the second highest flood after the 1978 flood in the area. The paper documents the spatial distribution of landslides and its consequences in the lower reaches of the Bhagirathi Valley between Bhatwari and Uttarkashi. It has been observed that within a stretch of 28 km in the study area, the river gradient is highly variable ranging from 3.6 to 66.6 m/km and is marked by three major knick points. These knick points are well correlated with the disposition of thrusts and a fault present in the area. An inventory of 23 active landslides has been prepared. Based on these knick points, the entire area has been divided into four zones. The area between Bhatwari and Ganeshpur is marked by the zone of transportation and between Ganeshpur and Uttarkashi, the zone of deposition of river sediments. It has been estimated that there is an average aggradation of about 0.5 m/year in the Bhagirathi River around Uttarkashi. Further, the huge volume of material deposited in the river around Uttarkashi township is posing serious threat to the slope stability on either banks of river. This calls for an urgent need for the formulation of policy for dredging the material from riverbed in order to maintain the continuous and uninterrupted flow of water during high discharge, in order to mitigate the problems of slope stability along the course of the river.

Rivers change through time in response to upstream and downstream controls and may change over very short time periods (i.e., few years), in particular when human impact affects fluvial systems. In the Lighvan River catchment, a semi-arid mountainous area in northwestern Iran, remarkable changes in the fluvial environment and channel morphology have taken place over the last few years. The aim of this paper is to explain driving factors of channel changes along the Lighvan River, in a 16-km-long reach, over the period 2000–2012. Data and methods used include maps and field survey to quantify channel changes; analysis of hydrological data (precipitation and discharges); Landsat images for land-use classification and then evaluation of possible changes in flood peak discharge by SCS method; and calculation of unit stream power changes. In general, the channel underwent incision (up to 1 m) and narrowing (up to 18 m), although aggradation occurred in few cross sections in the upstream part of the study reach and widening in few cross sections in the downstream part. Investigation of causes of these changes showed that magnitude of annual peak discharges increased over the period 1991–2012, and it can be suggested that such increase is related to natural causes (i.e., increase of precipitation) and human impact so that both human and natural factors had a role in the recent evolution of the Lighvan River. Channelization and increase of peak discharges (due to an increase of precipitation and land-use changes) have been the main drivers of channel evolution.

Statigraphic exposures, fluvial archives and borehole data have been allowed to reconstruct the alluvial history of Late Pleistocene to Early Holocene and climate changes in the monsoonal wet–dry region of lower Damodar Basin (West Bengal, India). The facies architectures and climate proxies suggest that five to six climate changes occurred in between ∼14 and 6 kiloannum (ka). Supporting evidence from the floodplain of Damodar River demonstrates that the successive phases of aggradation and incision were linked to the south-west monsoonal variability of Late Quaternary period. The onset of semi-arid climate was associated with caliches, pond and backswamp deposits of waning low-energy floods. The relatively warm-humid climate was associated with sandy bedforms, valley fills, slack water deposits and ferruginous nodules. This paper presents a synthesis of the available palaeoclimatic records from the lower Ganga Basin and the rivers of western and central India for the palaeoenvironmental significance of Late Quaternary deposits and discusses the influence of palaeoclimatic controls on the fluvial architectures and archives that developed below the floodplain of Damodar River. We have taken some representative studies from the region to reveal the spatial variability in fluvial successions in response to climate changes during this period.

The paper presents the results of studies of fault zones carried out in the Upper Silesian Coal Basin. Three types of changes of the coal were distinguished: degradative changes connected with a deterioration in the quality of the coal; aggradational changes connected with an increase in the quality of coal; and the type of coal which shows no significant change in the values of its parameters.

The quantity of suspended sediment in an estuary is regulated either by transport, where energy or time needed to suspend sediment is limiting, or by supply, where the quantity of erodible sediment is limiting. This paper presents a hypothesis that suspended-sediment concentration (SSC) in estuaries can suddenly decrease when the threshold from transport to supply regulation is crossed as an erodible sediment pool is depleted. This study was motivated by a statistically significant 36% step decrease in SSC in San Francisco Bay from water years 1991–1998 to 1999–2007. A quantitative conceptual model of an estuary with an erodible sediment pool and transport or supply regulation of sediment transport is developed. Model results confirm that, if the regulation threshold was crossed in 1999, SSC would decrease rapidly after water year 1999 as observed. Estuaries with a similar history of a depositional sediment pulse followed by erosion may experience sudden clearing.

A new archaeological excavation on the northern slope of Vesuvius has provided invaluable information on the eruptive activity and post-eruptive resedimentation events between the late Roman Empire and 1631. A huge Roman villa, thought to belong to the Emperor Augustus, survived the effects of the 79 A.D. Plinian eruption, but was mainly engulfed in volcaniclastic materials eroded and redeposited immediately after a subsequent eruption or during repose periods. Primary pyroclastic deposits of the 472 A. D. eruption are only few centimeters thick but are overlain by reworked volcaniclastic deposits up to 5 m thick. The resedimented volcaniclastic succession shows distinct sedimentary facies that are interpreted as debris flow deposits, hyperconcentrated flow deposits, and channel-fill deposits. This paper has determined that the aggradation above the roman level is about 9 m in 1,200 years, leading an impressive average rate of 0.75 cm/year.

In the geological evolution of the Tarim Basin, many transgressions and relictions happened. So there have been plentiful sources of salt. Moreover, because of uttermost drought, a lot of salt has been deposited. It is possible to find potash salt in this area. In our fieldwork, we have found salt and brine in western Tarim Basin. Based on a geological survey and the characteristics of sedimentary facies and paleogeography, this paper deals with the geochemical parameters and discusses the possibility of formation of potash salt in terms of the chemical analyses of samples collected from western Tarim Basin. Results of brine analysis lead to some conclusions: most of these salt brines have eluviated from very thick halite beds, mainly chloride-type salt and this kind of halite does not reach the stage of potash deposition in all aspects; WK-SL (Wukeshalu) occupies a noticeable place, and we should attach importance to this district because there have been some indicators of the occurrence of potash deposits as viewed from the contents of Br and K. Finally, low Br contents are recognized in the Tarim Basin as a result of salt aggradation, and this point of view has been proved by the results of this experiment and the data available. It cannot depend upon the index of Br to judge the evolution stage of halite. We must look for other facies of potash except marine facies.

Modern and Holocene muddy strata were studied along the shoreline adjacent to the Amazon river mouth using sedimentological, radiochemical, physical, and seismic methods. The present paper is a synthesis of the results, collected during the AmasSeds project, that is used to outline a regional shoreline sediment budget. Erosion of relict Amazon muds in southern Amapa supplies 106 tons yr−1 to the Amazon advective mud stream. Local rivers are sediment-poor (total suspended discharge ~ 1 × 106 tons yr−1), but form depositional sandflats on the shoreface downdrift of the river mouths. Mudflat accumulation in northern Amapa sequesters 106–107 tons yr−1 by tidal-flat aggradation, alongshore mudcape accretion, and sediment trapping by mangroves. The processes temporarily store 1.5 × 108 tons of Amazon mud in January–June.

In recent years the frequency of abnormal floods in Bangladesh has increased substantially, causing serious damage to lives and property. The most crucial questions that need to be addressed are: what really causes the havoc-creating floods and is there any solution to the problem? The heavy monsoon downpour and synchronization of flood-peaks of the major rivers are generally considered to be the main causes of the floods. Some underlying factors also deserve serious consideration as possible contributors to the recent floods: change in the base level of the rivers due to local sea level rise and subsidence, inadequate sediment accumulation on flood plains, a possible increase in the watershed area due to seismic and neotectonic activities in the region, river bed aggradation due to siltation and damming of rivers, soil erosion due to unwise tilling practices, deforestation in the upstream region, and excessive development and population growth. Without regional cooperation among the co-riparian nations any major interbasin flood control activity is considered to be almost impossible. However, among other proposals in this paper, extensive annual dredging of the rivers, channels and creeks, and reoccupation of the abandoned channels in Bangladesh through re-excavations could still increase the water carrying capacity of the rivers. Land elevations could be increased if the dredged or excavated materials are dispersed on the flood plains, which would in turn reduce the severity of floods. Language: en

The paper discusses the tin mining industry in Malaysia and legislations promulgated to prevent environmental degradation due to mining activities. Soil erosion and sediment contribution from mining areas were studied by examining inflow and outflow sediment loads and stormflow sediment transport characteristics at two sediment sampling stations in the Kelang River Basin. It was observed that despite the cessation of mining activities, rivers draining mining areas still carry high sediment loads. It was found that sediment yield increases by three to six times after the river passes through mining land. Low-flow sediment transport is more significant in the mining area compared to non-mining areas. Clockwise hytheretical loops observed at the two sampling stations indicate that sediment sources are located near the river and within the channel system itself.

A longitudinal profile of a river under static equilibrium shows no degradation or aggradation and can be ideally described as a straight line on a semi-logarithmic graph. This type of profile is called a ”Hack profile”. If a river runs across uprising active structure systems, its Hack profile becomes convex. Accumulated tectonic strain varies positively with the intensity of the up warping in Hack-profile convexity. In this paper, we compare curvature changes in Hack profiles of a series of rivers running through faults in the central and southwestern Foothills of Taiwan. Longitudinal profiles of these rivers were derived from two versions of topographic maps (1904 and 1985) and recent DTM data (2000). Prior to comparisons, we calibrated the 1904 topographic map, named ”Taiwan Bautu”, by ”offsetting” horizontal coordinates north and westward approximately 440 m and then ”linear transforming” the elevation values. The Tungtzchiau fault of the central Foothills has remained inactive since 1935. Here relatively high uplift activity near the Wu River is indicated by significantly convex Hack profiles. This strain accumulation can be attributed to a lack of small magnitude earthquakes along the fault over the past 70 years. In the southwestern Foothills, relatively high uplift activity of similar intensity to the central Foothills is indicted near the Neocho River. Significant profiles with concave segments below the ideal graded profiles, at the lower reaches of rivers where continuous small magnitude strain release events have occurred, can only be found along the Sandieh, Neocho and Bazhang rivers in the southwestern Foothills. All these findings indicate that fault systems in the central Foothills tend to be locked and these faults could yield large earthquakes similar to the Chi-Chi event.

Study of Landsat MSS imagery and aerial photographs along with selected field checks in Sabi river basin area has thrown some light on the plausible reasons of floods in parts of Rajasthan, Haryana and Delhi regions. It is noticed that the course of river Sabi, a tributary to Yamuna river flowing through the sandy tracks is being controlled by the prominent linears, most of them are faults within the Delhi rocks. But, as the river approaches near Haryana, that controlled course is lost and it develops a very wide river bed, full of sands and have abrupt decrease in its gradient to as low as 2° to 3°. This may be attributed to the migration and aggradational alluvial plains developed thereof, on the western side of Yamuna river. All these factors have been discussed in the paper which shall reflect some points as remedial measures of floods of the Sabi River.