Development Of Alluvial Fans Research Articles

Sedimentary response to thrusting and fold growing on the SE margin of the Ebro basin (Paleogene, NE Spain)

Abstract The Catalan Coastal ranges are the alpine structural unit parallel to the Mediterranean coast in the NE of the Iberian Peninsula. They shape the southeastern margin of the Ebro Foreland basin (the latest stage of the South Pyrenean Foreland trough). The Paleogene sedimentary evolution of this basin margin is closely related to the tectonic evolution of the adjoining Catalan Coastal ranges, a transpressive chain characterized mainly by contractional structures (NNW-verging folds and thrusts). The syntectonic condition of the Paleogene deposits of the Ebro basin is evidenced by facies directly related to the growth of specific structures, thinning, fanning and truncation of the sedimentary units towards the growing structures, as well as to abrupt changes in the composition of the coarse-grained sediments caused by tectonic activity or landslides in the catchment area. A tectonosedimentary evolution of approximately 17 Ma has been deduced: (a) folds and thrusts involving Mesozoic rocks were developed during Ypresian (resulting in the deposition of Mesozoic cover derived breccias); (b) large-scale fold growth mostly from Lutetian to early Bartonian (leading to progressive unconformities, fanning and growth strata); and (c) out-of-sequence basement-involving thrusting during Lutetian and Bartonian (development of large alluvial fans). These events did not take place simultaneously along the 30-km long basin margin studied. There is a clear NE to SW migration of the deformation, as observed along the whole Catalan Coastal ranges and the South Pyrenean Foreland basin.

Little ice age alluvial fan development in langedalen, western norway

This paper reports a preliminary investigation of the sedimentary succession in two alluvial fans in western Norway. Sedimentological information is supplemented by palaeoecological data from pollen analysis and the age of the sequence is constrained by six radiocarbon age estimates on woody fragments and peat. These data suggest that significant accumulation of fan sediments took place after AD 1637–1685. Before this, the fluvial landscape and the adjacent slopes may have been more stable with the development of Betula, Salix and Alnus woodland on the valley floor and sides. Although there is no indication of gradual climatic deterioration in the vegetation record from these sites, the radiocarbon chronology suggests that enhanced fan development was coincident with the climatic change associated with the ‘Little Ice Age’. This was probably a response to glacier expansion and increased discharge and sediment supply to the alluvial fans from outlets of the Jostedalsbreen ice cap on the southern side of Langedalen. Initial response to climate change in this setting was therefore enhanced geomorphic activity and instability of the valley‐side slopes.

Fluvial geomorphology and paleohydrology in Japan

An introduction to fluvial geomorphology and paleohydrology in Japan is provided for researchers who are unfamiliar with these topics. Studies by Japanese geomorphologists are reviewed including those published only in Japanese-language journals. Emphasis is placed upon the following aspects: (1) abundant sediment yields from steep watersheds subjected to frequent heavy rains despite heavily vegetated conditions, (2) extensive sedimentation in mountain piedmonts and coastal fluvial plains especially during the Holocene, (3) catastrophic hydro-geomorphological events associated with earthquakes and volcanic eruptions, and (4) the impacts of the increased heavy rainfall during the Pleistocene–Holocene transition on the post glacial development of hillslopes and alluvial fans. These geomorphological characteristics differ from those in continental regions, such as Europe and North America, indicating that research on Japanese fluvial systems can contribute a great deal to the understanding of the global variety of fluvial geomorphology. Recent work on paleohydrological reconstruction in Japan is also reviewed.

GIS and geostatistics: Essential partners for spatial analysis

Initially, geographical information systems (GIS) concentrated on two issues: automated map making, and facilitating the comparison of data on thematic maps. The first required high quality graphics, vector data models and powerful data bases, the second is based on grid cells that can be manipulated by suites of mathematical operators collectively termed “map algebra”. Both kinds of GIS are widely available and are taught in many universities and technical colleges. After more than 20 years of development, most standard GIS provide both kinds of functionality and good quality graphic display, but until recently they have not included the methods of statistics and geostatistics as tools for spatial analysis. Recently, standard statistical packages have been linked to GIS for both exploratory data analysis and statistical analysis and hypothesis testing. Standard statistical packages include methods for the analysis of random samples of cases or objects that are not necessarily co-located in space—if the results of statistical analysis display a spatial pattern then that is because the underlying data also share that pattern. Geostatistics addresses the need to make predictions of sampled attributes (i.e., maps) at unsampled locations from sparse, often expensive data. To make up for lack of hard data geostatistics has concentrated on the development of powerful methods based on stochastic theory. Though there have been recent moves to incorporate ancillary data in geostatistical analyses, insufficient attention has been paid to using modern methods of data display for the visualization of results. GIS can serve geostatistics by aiding geo-registration of data, facilitating spatial exploratory data analysis, providing a spatial context for interpolation and conditional simulation, as well as providing easy-to-use and effective tools for data display and visualization. The value of geostatistics for GIS lies in the provision of reliable interpolation methods with known errors, methods of upscaling and generalization, and for supplying multiple realizations of spatial patterns that can be used in environmental modeling. These stochastic methods are improving understanding of how errors in models of spatial processes accrue from errors in data or incompleteness in the structure of the models. New developments in GIS, based on ideas taken from map algebra, cellular automata and image analysis are providing high level programming languages for modeling dynamic processes such as erosion or the development of alluvial fans and deltas. Research has demonstrated that these models need stochastic inputs to yield realistic results. Non-stochastic tools such as fuzzy subsets have been shown to be useful for spatial analysis when probabilistic approaches are inappropriate or impossible. The conclusion is that in spite of differences in history and approach, the linkage of GIS, statistics and geostatistics provides a powerful, and complementary suite of tools for spatial analysis in the agricultural, earth and environmental sciences.

Little ice age alluvial fan development in Langedalen, western Norway

Little ice age alluvial fan development in Langedalen, western Norway

Holocene alluvial-fan development in the Macgillycuddyʼs Reeks, southwest Ireland

Holocene alluvial landforms in the Macgillycuddy9s Reeks, southwest Ireland, were investigated to determine the controls and timing of postglacial geomorphic activity. Detailed geomorphologic analysis of three alluvial-fan and debris cones within high-level cirque basins demonstrates evidence of episodic phases of late Holocene surface aggradation and incision. Radiocarbon dates from peat horizons above and below inorganic units show that phases of aggradation cluster into two distinct periods, the first after 230–790 calibrated (cal.) yr A.D. and the second from 1510 cal. yr A.D. to the present. An additional phase of fan aggradation at one site is dated after 1040–1280 cal. yr A.D. All three phases coincide with episodes of enhanced late Holocene valley-floor alluviation and debris-flow activity from upland Britain. Alluvial fans and debris cones have developed primarily as a result of the resedimentation of late Midlandian (Wisconsin) drift and talus slopes, and mobilization of materials involved flooding, transitional-flow, and debris-flow processes. Pollen analysis of peat horizons interbedded with alluvial-fan and debris-cone sediments indicates that land-use changes were an important factor in lowering the threshold for local slope erosion. Phases of aggradation also coincide with well-documented episodes of climate change, and, hence, fan development is probably a function of both anthropogenic and climatic forcing. A sequence of events may have involved initial slope destabilization due to overgrazing and removal of vegetation that was followed by debris mobilization and fan aggradation during intense rainstorms associated with climate change.

Environmental controls on the evolution of alluvial fans in Buena Vista Valley, North Central Nevada, during late Quaternary time

Alluvial fans in Buena Vista Valley, north-central Nevada, formed during at least four time periods during the late Quaternary as evidenced by four temporally and spatially constrained fan deposits: Qf1, Qf2, Qf3, and Qf4, from oldest to youngest. The stratigraphic relation between Qf3 and remnant beach ridge deposits of pluvial Lake Lahontan, the latter of which forms a paleoclimatic proxy for this region, indicate that climate and climatic change are primary controls on the evolution of fans. Qf3 deposition commenced during or immediately following the highstand of Lake Lahontan, between 13.5 and 12.5 ka, and continued as lake levels plummeted to levels below the sill elevation of the Buena Vista subbasin. We interpret Qf3 to be the result of a dynamic interplay between hillslope vegetation, soils, and hydrology as they are conditioned by climate and climatic change. Accelerated pedogenesis, because of aerosolic silts and clays from exposed lake sediments, coupled with decreased density of vegetation reduced infiltration capacity of the hillslope soils in interscrub areas. In contrast to fans in more arid climates, the increased runoff was not associated with increased coarse-grained sediment yield and major fan aggradation. Discharge from sediment-deficient basins entrenched older, proximal fan deposits and transported the sediment downfan to form secondary fans. The process–response of Qf3 to climatic change in north-central Nevada is especially illustrative of the impact of climate on landscapes in that: (1) it results from changes in basin sediment and/or water yield that occur in less than 500 years, and (2) it differs from responses in arid climates to the south and more semiarid climates to the north. The magnitude of vegetation change, including type and density of vegetation and the relative proportion of interscrub area, is particularly critical to water and sediment yield. Unit Qf2, an early late Pleistocene deposit, may also have been deposited during a transition from a wetter to drier climate. The synchronism of aggradation, stability, and entrenchment on all fans along the perimeter of Buena Vista Valley in the late Quaternary is further support for the dominance of climatic control on fan process; on the other hand, the impact of other extrinsic variables on fan process, including tectonism, base level, and basin lithology, all of which vary along the perimeter, is negligible.

Depositional and tectonic evolution of a supradetachment basin: 40Ar/39Ar geochronology of the Nova Formation, Panamint Range, California

The Nova Basin contains an upper Miocene to Pliocene supradetachment sedimentary succession that records the unroofing of the Panamint metamorphic core complex, west of Death Valley, California. Basin stratigraphy reflects the evolution of sedimentation processes from landslide emplacement during basin initiation to the development of alluvial fans composed of reworked, uplifted sections of the basin fill. 40Ar/39Ar geochronology of volcanic units in middle and lower parts of the sequence provide age control on the tectonic and depositional evolution of the basin and, more generally, insights regarding the rate of change of depositional environments in supradetachment basins. Our work, along with earlier research, indicate basin deposition from 11.38 Ma to 3.35 Ma. The data imply sedimentation rates, uncorrected for compaction, of ~100 m Myr−1 in the lower, high‐energy part to ~1000 m Myr−1 in the middle part characterized by debris‐flow fan deposition. The observed variation in sediment flux rate during basin evolution suggests that supradetachment basins have complex depositional histories involving rapid transitions in both the style and rate of sedimentation.

Late Holocene floodplain incision and alluvial fan formation in the central Grampian Highlands, Scotland: chronology, environment and implications

A section cut across an alluvial fan and the underlying floodplain terrace in the central Grampian Highlands provides an unusually complete record of late Holocene events. At ca. 2.7–2.4 cal kyr BP floodplain aggradation was replaced by net floodplain incision. Pollen evidence and charcoal counts provide no evidence for contemporaneous anthropogenic landscape change, and the timing of the transition suggests that it reflects an increase in high-magnitude erosive flood events following overall climatic deterioration. The overlying fan was deposited by torrential hyperconcentrated flows during three brief storm-generated depositional events at ca. 2.2–2.1, 1.9–1.8 and 0.9–0.7 cal kyr BP, separated and succeeded by prolonged periods of stability and peat accumulation. During these three events, a cumulative total of ca. 6750 m3 of sediment was deposited, probably in no more than a few hours over a timescale of two millennia. These findings imply that proposed links between human activity and the development of alluvial fans or debris cones require reassessment, and that different elements of the Holocene alluvial landscape have responded in different ways to the same climatic inputs. Aggregation of dating evidence relating to aggradation or incision of alluvial landforms at different scales therefore may produce misleading results. Copyright © 1999 John Wiley & Sons, Ltd.

Paraglacial and periglacial slope adjustment of a degraded lateral moraine in Glen Torridon

Introduction The importance of paraglacial processes – those which operate immediately following deglaciation–in modifying glacial landforms and sediment associations in mountainous areas has been established for some time ([Ryder 1971 a ][1],[ b ][2]; [Church and Ryder 1972][3]). Of particular importance is the development of large alluvial fans and valley fills, often associated with the redistribution of sediment via large debris flows ([Jackson et al. 1982][4]; [Claque 1986][5]; [Eyles and Kocsis 1988][6]; [Eyles et al 1988][7]; [Owen 1989][8]). On a slightly smaller scale is the development of thick deposits of head due to the reworking of glacial sediments on steep slopes (e.g. [Wright 1983][9]; [Owen 1991][10]; [Harrison 1993][11]; [Ballantyne and Harris 1994][12]; [Benn and Ballantyne 1994][13]). In the Scottish Highlands the significance of periglacial processes and Holocene debris flows in reworking valley side sediments has frequently been described (e.g. [Brazier and Ballantyne 1989][14]; [Ballantyne and Harris 1994][15]). In contrast, paraglacial processes have received relatively little attention, yet these also had the potential to modify the land-form and sediment assemblages in many Highland valleys. Given that recent work on these assemblages has emphasised their complexity (e.g. [Benn 1992][16]; [Bennett and Boulton 1993 a ][17]; [Bennett 1994][18]) the effects and products of paraglacial activity perhaps deserve greater attention within Scotland. This communication records observations made in a road-side cutting, above Loch Torridon (Fig. 1), within a thick, valley-side, sediment accumulation and suggests that this is the product of both paraglacial and periglacial modification of a now indistinct lateral moraine. Geomorphology and sedimentology The section is in a road-side . . . [1]: #ref-20 [2]: #ref-21 [3]: #ref-12 [4]: #ref-17 [5]: #ref-13 [6]: #ref-15 [7]: #ref-14 [8]: #ref-18 [9]: #ref-23 [10]: #ref-19 [11]: #ref-16 [12]: #ref-1 [13]: #ref-5 [14]: #ref-11 [15]: #ref-2 [16]: #ref-3 [17]: #ref-8 [18]: #ref-7

Development of Mountains and Alluvial Fans in Japan, Taiwan, and the Philippines

In Japan, where uplift and denudation have been active during the Quaternary, the growing stage of mountains has been divided into the earliest, early, younger-middle, older-middle, and later substages. In this study, relationships have been discussed quantitatively between the development stage of mountains and alluvial-fan existence and size in tectonically active Japan, Taiwan, and the Philippines. Among relief ratio, drainage-basin area, temperature, and precipitation, relief ratio was determined to be the most important variable for predicting the existence of alluvial fans for rivers with source areas greater than 100 km 2 . As mountains pass through their development stages from earliest to later, their relief ratios increase and the number and size of alluvial fans increase, especially from the older-middle substage. In drainage basins over 100 km 2 , the relief ratio of 30‰ is estimated to be an important threshold for the existence of an alluvial fan. In the older-middle substage almost all rivers have high relief ratios greater than 30‰, while only 63% of the rivers show such high relief ratios in the younger-middle substage. In addition, the size of alluvial fans in drainage basins with relief ratios greater than 60‰ is larger than the size with relief ratios lower than 60‰. The percentage of the rivers with relief ratios over 60‰ in the older-middle substage is markedly higher than that in the younger-middle substage. In this way, the increase in relief ratios (steeper riverbeds) beginning in the older-middle substage provides good conditions for the development and increased size of alluvial fans. Furthermore, the tropical climate in the Philippines, which seems to be disadvantageous for the development of alluvial fans in general, does not necessarily result in smaller alluvial fans when alluvial fans do develop.

Tectonique et évolution géomorphologique : l'exemple du bassin de Korçë (Albanie)/ Tectonics and geomorphological evolution: the example of the Korçë basin (Albania)

Abstract As a part of the Albano-Thessalian furrow, the Korçë basin is an active graben initiated during the Pliocene; its present limits are directly controlled by Quaternary tectonics. There is no system of fluvial terraces and the eastern fault scarps are showing evidence of activity during the Pleistocene (relationships between fault lines and colluvial deposits). Neotectonics combined with the development of the great alluvial fan built up by the Devollit river, accounts for the location of the Maliq lake, a key element in human settlement as early as the Bronze Age. Palynological and archaeological data from the Sovjan site emphasize subtle changes of lacustrine, marshy and alluvial areas which express a complex balance between tectonic, environmental and societal parameters.

Non-linearity and spatial resolution in a cellular automaton model of a small upland basin

Abstract. The continuing development of computational fluid dynamics is allowing the high resolution study of hydraulic and sediment transport processes but, due to computational complexities, these are rarely applied to areas larger than a reach. Existing approaches, based upon linked cross sections, can give a quasi two-dimensional view, effectively simulating sediment transport for a single river reach. However, a basin represents a whole discrete dynamic system within which channel, floodplain and slope processes operate over a wide range of space and time scales. Here, a cellular automaton (CA) approach has been used to overcome some of these difficulties, in which the landscape is represented as a series of fixed size cells. For every model iteration, each cell acts only in relation to the influence of its immediate neighbours in accordance with appropriate rules. The model presented here takes approximations of existing flow and sediment transport equations, and integrates them, together with slope and floodplain approximations, within a cellular automaton framework. This method has been applied to the basin of Cam Gill Beck (4.2 km2 ) above Starbotton, upper Wharfedale, a tributary of the River Wharfe, North Yorkshire, UK. This approach provides, for the first time, a workable model of the whole basin at a 1 m resolution. Preliminary results show the evolution of bars, braids, terraces and alluvial fans which are similar to those observed in the field, and examples of large and small scale non-linear behaviour which may have considerable implications for future models.

Oligo-Miocene Alluvial-Fan Evolution at the Southern Pyrenean Thrust Front, Spain

Oligo-Miocene Alluvial-Fan Evolution at the Southern Pyrenean Thrust Front, Spain

Late quaternary sediment budget in alluvial‐fan–source‐basin systems in Japan

Sediment budgets since the Late-glacial were constructed for five alluvial-fan–source-basin systems in Japan. The Late-glacial and Holocene sediment yield from each source area was estimated based on digital elevation data and the morphometric analyses of geomorphological maps, in which all hillslopes and fluvial surfaces were classified. Late-glacial and Holocene sediment storage in each fan was calculated from stratigraphical data. The results have revealed that the ratio of sediment storage in a fan to sediment supply is between ca. 0.3 and 0.8. Such high ratios of sediment storage over long time periods cast doubt on the previously proposed steady-state theory of alluvial fan development. The storage ratio decreases if fan sediments are removed by neighbouring large rivers. The maximum storage ratio of 0.8 reflects the ratio of washload to total load for Japanese mountain rivers. © 1997 John Wiley & Sons, Ltd.

The development of small-scale sandy alluvial fans at the base of a modern coastal cliff: process, observations and implications

The development of a series of small-scale alluvial fans has been studied at the base of a sandy coastal cliff on the Torre del Loro Beach near Huelva, southwestern Spain. These fans are small enough to permit the experimental modification of flow, sediment load and morphology. Elongate sandy debris flow deposits are also present. The fans are related to sources with perennial discharges and are fed by solitary, shifting distributary channels. The fans have radial morphologies and grow by localized lobe-building at the intersection point, in a mid-fan or fan-toe position, and/or by bulk aggradation due to overflow (sheet flow). Sediment dispersal is by channelized or unconfined water flow, but also involves slugs of “hyperconcentrated” flows and occasionally sandy debris-flows. The radial fans (channelized flow dominated) have surface slopes of up to 20°, their medial segments are often the steepest, and sediment at their toes and lateral flanks can be coarser than in the inner zones. The elongated sandy debris flow deposits are related to sources with ephemeral discharges and are mass flow-dominated. These deposits are smaller and are built chiefly by sandflows (finger-like sandy debris-flows). Their surface slopes are rather uniform, but only up to 6°, and there is no obvious downfan variation in grain size. When regarded as small-scale analogues for larger alluvial fans, these fans deviate from the textbook models, particularly in grain-size distribution, simultaneity of “quiet” and “energetic” processes, and longitudinal gradient profile. Our study indicates that the relationship between fan morphometry and depositional processes still requires a better knowledge.

The role of human activities in the development of alluvial fans

In a study carried out in the Iberian Range, Spain, the characteristics of 293 basins were studied, 165 having developed alluvial fans and 128 without alluvial fans. Different statistical analyses demonstrate that the main factors explaining the presence of alluvial fans are the drainage density and the coefficient of torrentiality. Other important factors are the proportion of abandoned fields and reforestation, that is, the areas most affected by human activities in the past. The basins where the presence of alluvial fans is highest have a large proportion of medium and low gradients, favouring the use of the territory as cultivated fields and pastureland. In contrast, basins without alluvial fans at their mouth are characterized by very steep slopes, generally covered by forest, where agricultural activity was impossible.

Factors affecting the magnitude of post-glacial hillslope incision in Japanese mountains

In Japanese mountains, increased post-glacial rainfall triggered gullying in bedrock and thousands of shallow failures in regolith, resulting in widespread hillslope incision. To identify factors influencing the areal extent of the post-glacial incision, fifteen rugged river basins in central and northeast Japan were surveyed. Topographical and geological properties of hillslopes were measured on geomorphological maps, digital elevation data, and geological maps. Analyses of ca. 3,000 0.5 × 0.5 km morphometric samples have shown that the magnitude of regolith failure depends mainly on slope inclination and geology, and subordinately on local storm intensity. The magnitude of bedrock gullying also depends on these three factors, but with greater dominance of storm intensity. These observations reflect the differential stability of hillslopes with varying inclination, erodibility of bedrock, and sensitivity of regolith and bedrock to change in storm intensity. The three factors also exert control on alluvial-fan development in the lower reaches, because they affect the amount of hillslope sediment supply and in turn the type of fluvial processes.

Reconciling the roles of tectonism and climate in Quaternary alluvial fan evolution

Tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin-fill architecture, yet their roles and relative importance are far from resolved. The Madison Range and Madison River valley, southwestern Montana, were affected during late Quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations; we are thus able to evaluate the impact of tectonism and climate on fan evolution. Two primary fan deposits were correlated along the range front. They were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge. During the present interglacial period, these deposits were entrenched and secondary fans formed on lower fan areas. Temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment. In contrast, stratigraphic relations between fan deposits and surface faults do not support a direct relation, either spatial or temporal, between local faulting and fan deposition. Because tectonism produces and maintains the relief necessary for fans to form, its primary role is long term, controlling the duration over which fan deposition may occur along a mountain front. If Quaternary alluvial fan evolution is representative of ancient alluvial fan evolution, this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences.

Normal and reverse unroofing sequences in syntectonic conglomerates as evidence of progressive basinward deformation

When a new mountain belt is generated by tectonics, the denudation of the mountain front may cause the development of alluvial fans at its base. The retreat of the mountain front by denudation processes and a widening of the drainage network in the source area create adjacent alluvial-fan conglomerates with an inverted vertical clast distribution. This vertical clast distribution represents a normal unroofing sequence. Renewed uplift of a previous inverted vertical clast distribution can produce a reverse unroofing sequence. If continued shortening occurs in the same area, a rejuvenation of the source area and basin margin may produce a new generation of clasts from the source area and a partial or total reworking of previously deposited conglomerates to supply second-generation clasts. If this type of reworking process is repeated as fault uplift steps basinward, several new inverted and stratigraphic vertical clast distributions may arise.