Hillslope Colluvium Research Articles

Quaternary geomorphological dynamics of colluvial deposits from silicophytoliths and soil micromorphology, Araripe plateau, northeast of Brazil

Quaternary geomorphological dynamics in the lowland tropics of South America can be described from the stratigraphy of hillslope colluvium and alluvial deposits. The analysis of sediments through the identification of depositional microfeatures and biomineralized microfossils, combined with their absolute dating by optically stimulated luminescence (OSL), allow the reconstruction of paleoenvironmental conditions. The objective of this work was to investigate the dynamics of depositional processes leading to colluvial deposition in the Araripe Plateau, Northeastern Brazil, from the analysis of stratigraphic sections, using phytoliths as indicators of paleovegetation and sediment micromorphology in the identification of depositional processes. The correlation of sediments ages, ranging from the OS3 to the OS2 (Last Glacial Maximum) with phytophysiognomy indices indicated the contribution and deposition of phytoliths from an arboreal/shrubby vegetation, replaced on the surface by grass vegetation. Periods of drier climates were correlated with LGM ages, with more open vegetation composed of grasses, in synchronously with less intense geomorphological events. The micromorphological analysis revealed that the characteristics of the deposits reflect more the action of depositional processes than pedogenetic ones. The correlation of phytolithic indices with micromorphology corroborated the environmental and geomorphological dynamics of the periods dated in the stratigraphic sections.

Paleoseismic investigation of the Teton fault at Leigh Lake, Grand Teton National Park, Wyoming

To improve knowledge of the Teton fault’s ground-rupturing earthquake history, we excavated trenches across two fault scarps near the southwest shore of Leigh Lake. Detailed stratigraphic and sedimentologic analyses allow preliminary inferences regarding the fault history. The trenches exposed faulted glacial sediments and overlying hillslope colluvium sediments, documenting at least two fault ruptures since deglaciation of the range front at ~15 ka. Samples are currently being analyzed using radiocarbon and luminescence dating techniques to determine the ages of the sediments and constrain the timing of fault rupture.
 
 Featured photo from Figure 3 in report.

Holocene earthquakes and right-lateral slip on the left-lateral Darrington–Devils Mountain fault zone, northern Puget Sound, Washington

Sources of seismic hazard in the Puget Sound region of northwestern Washington include deep earthquakes associated with the Cascadia subduction zone, and shallow earthquakes associated with some of the numerous crustal (upper-plate) faults that crisscross the region. Our paleoseismic investigations on one of the more prominent crustal faults, the Darrington–Devils Mountain fault zone, included trenching of fault scarps developed on latest Pleistocene glacial sediments and analysis of cores from an adjacent wetland near Lake Creek, 14 km southeast of Mount Vernon, Washington. Trench excavations revealed evidence of a single earthquake, radiocarbon dated to ca. 2 ka, but extensive burrowing and root mixing of sediments within 50–100 cm of the ground surface may have destroyed evidence of other earthquakes. Cores in a small wetland adjacent to our trench site provided stratigraphic evidence (formation of a laterally extensive, prograding wedge of hillslope colluvium) of an earthquake ca. 2 ka, which we interpret to be the same earthquake documented in the trenches. A similar colluvial wedge lower in the wetland section provides possible evidence for a second earthquake dated to ca. 8 ka. Three-dimensional trenching techniques revealed evidence for 2.2 ± 1.1 m of right-lateral offset of a glacial outwash channel margin, and 45–70 cm of north-side-up vertical separation across the fault zone. These offsets indicate a net slip vector of 2.3 ± 1.1 m, plunging 14° west on a 286°-striking, 90°-dipping fault plane. The dominant right-lateral sense of slip is supported by the presence of numerous Riedel R shears preserved in two of our trenches, and probable right-lateral offset of a distinctive bedrock fault zone in a third trench. Holocene north-side-up, right-lateral oblique slip is opposite the south-side-up, left-lateral oblique sense of slip inferred from geologic mapping of Eocene and older rocks along the fault zone. The cause of this slip reversal is unknown but may be related to clockwise rotation of the Darrington–Devils Mountain fault zone into a position more favorable to right-lateral slip in the modern N-S compressional stress field.

Earliest Dates and Implications of Microlithic Industries of Late Pleistocene from Mahadebbera and Kana, Purulia District, West Bengal

Microlithic industries, a technology associated with modern humans, as defined by the production of microblades have been found in different parts of the Indian subcontinent with the earliest date being 48 ka. The present communication reports on recent archaeological excavations of these industries from a colluvial context located in the pediment surface of Precambrian hills in Purulia, West Bengal. These are dated to 34-25 ka by optically stimulated luminescence dating and are the earliest dates for microlithic industries in eastern India. To our knowledge such dating does not exist for any prehistoric site in Bengal. The context of the sites - hill-slope colluvium - is also unique and a rarity in the subcontinent. These findings add additional inputs to the knowledge of these industries, providing supporting evidence to their antiquity.

A nonlocal theory of sediment transport on hillslopes

Hillslopes are typically shaped by varied processes which have a wide range of event‐based downslope transport distances, some of the order of the hillslope length itself. We hypothesize that this can lead to a heavy‐tailed distribution of displacement lengths for sediment particles. Here, we propose that such a behavior calls for a nonlocal computation of the sediment flux, where the sediment flux at a point is not strictly a function (linear or nonlinear) of the gradient at that point only but is an integral flux taking into account the upslope topography (convolution Fickian flux). We encapsulate this nonlocal behavior in a simple fractional diffusive model which involves fractional derivatives, with the order of differentiation (1 < α ≤ 2) dictating the degree of nonlocality (α = 2 corresponds to linear diffusion and strictly local dependence on slope). The model predicts an equilibrium hillslope profile which is parabolic close to the ridgetop and transits, at a short downslope distance, to a power law with an exponent equal to the parameter α of the fractional transport model. Hillslope profiles reported in previously studied sites support this prediction. Furthermore, we show that the nonlocal transport model gives rise to a nonlinear dependency on local slope and that variable upslope topography leads to widely varying rates of sediment flux for a given local hillslope gradient. Both of these results are consistent with available field data and suggest that nonlinearity in hillslope flux relationships may arise in part from nonlocal transport effects in which displacement lengths increase with hillslope gradient. The proposed hypothesis of nonlocal transport implies that field studies and models of sediment fluxes should consider the size and displacement lengths of disturbance events that mobilize hillslope colluvium.

Relative-age dating of transported regolith and application to study of landform evolution in the Appalachians

Surficial deposits in the Appalachians generally are thin, discontinuous, and difficult to date. In the absence of numerical dates, particularly for older deposits, relative-age indices based on degree of weathering and soil development have been used to distinguish and correlate deposits of different ages. A favorite locale of relative-age studies has been stream terraces, where chronosequences have been developed to shed light on the relationship between time and weathering/soil development. The lack of applicable numerical dating techniques has led some researchers to establish “relative” chronosequences in which height of stream or fan terraces above modern river level (ARL) serves as a proxy for time. Approximate incision rates can then be used to estimate numerical ages of the deposits. Relative-age correlations between the weathering indices on the terraces and comparable indices on dated deposits on the Coastal Plain and in nearby glaciated regions suggest that ages so estimated are the right order of magnitude. Relative-age indices show correlations with height ARL that are as high as those with time, perhaps because more data sets are available for relative chronosequences than for true chronosequences. Analogous relative-age sequences can be established for alluvial fans and even for hillslope colluvium. Many weathering indices have been employed, but weathering-rind thickness on mafic-to-intermediate clasts has proved to be a particularly consistent and useful parameter. In addition to showing how weathering and soil development progress over time, relative-age dating has shed light on the manner in which landforms evolve. Along some rivers, for example, the areal extent of old, highly weathered alluvium far exceeds that of younger alluvium, suggesting that formerly floodplains and low terraces were much more extensive than at present. In addition, the manner in which weathering indices on some river terrace sequences vary with height ARL suggests that incision rate has changed through time. Relative-age mapping of alluvial fans produces a map pattern of older and younger fan surfaces that allows the sequence of fan development to be inferred, in one case suggesting a scenario different from those previously described for fans. Mapping also shows that the relative abundance of young, intermediate, and old fan surfaces varies greatly from one area to another. Several studies have demonstrated clustering of relative-age values into a small number of groups, suggesting temporal grouping and thus episodic deposition on fans. Regression of weathering-rind thickness against height above modern drainageways of remnant fan surfaces in two areas suggests that fans are being incised more rapidly in one area than in another. Relative age of hillslope colluvium also aids geomorphic interpretation. Young brown colluvium is much more common than old red colluvium near the glacier border, where red colluvium rarely occurs at the surface but typically is covered by brown colluvium probably mobilized during the late Pleistocene. Distant from the ice margin, however, red colluvium is extensively exposed on interfluves. Relatively stable hillslopes can also be distinguished from active ones in this manner. For example, colluvium on hillslope noses is somewhat more weathered than that on hollow floors and sideslopes.

The impact of recent climate change on flooding and sediment supply within a Mediterranean mountain catchment, southwestern Crete, Greece

AbstractThis paper presents work from a geomorphological investigation carried out in the Aradena Gorge, southwestern Crete, Greece. The gorge is typical of many steepland fluvial systems in the Mediterranean, with steep relief, coarse‐gravel sediments and high rates of sedimentation generated during intense winter storm events. Hillslope deposits and coarse‐gravel flood units within a 5 km section of the gorge have been mapped, dated (using lichenometry and dendrochronology), and their sedimentological characteristics recorded to establish a c. 200‐year record of flood frequency/magnitude and hillslope/channel sediment supply variability. This record has been compared with instrumented and previously published records of climate change from Crete and the Mediterranean region and used to establish the major controls on flooding and sediment dynamics within the Aradena Gorge.Rates of colluviation and sediment delivery to the channel appear to have been greater than the present sometime before c. AD 1800 and may be related to cooler climates with a more seasonal precipitation regime during the Little Ice Age (c. AD 1450 to 1850). In gorge sections where the present rate of sediment supply from hillslope colluvium is very low, the channel has incised into older alluvial and colluvial deposits. Conversely, in the few sections where sediment supply is currently very high, the channel is aggrading with a braided pattern. Major rock‐fall deposits at certain locations in the gorge have restricted any major downstream sediment transfer.Twelve periods of increased flooding during the last 150 years have been identified and these correlate quite well with negative or declining phases of the North Atlantic Oscillation (NAO). Analysis of daily precipitation data from Crete suggests negative phases of the winter NAO are characterized by an increase in the number of long‐duration, high‐intensity storms. These storms, particularly those with five‐day and greater duration, appear to be significant in triggering major floods in the Aradena Gorge. During the last 40 years the NAO index has been increasing and become locked into a positive phase. As a consequence of this, major flooding appears to have declined during the same period. Copyright © 2002 John Wiley & Sons, Ltd.

Using 10Be and 26Al to determine sediment generation rates and identify sediment source areas in an arid region drainage basin

We measured 10Be and 26Al in 64 sediment and bedrock samples collected throughout the arid, 187 km 2 Yuma Wash drainage basin, southwestern Arizona. From the measurements, we determine long-term, time-integrated rates of upland sediment generation (81±5 g m −2 year −1) and bedrock equivalent lowering (30±2 m Ma −1) consistent with other estimates for regions of similar climate, lithology, and topography. In a small (∼8 km 2), upland sub-basin, differences in nuclide concentrations between bedrock outcrops and hillslope colluvium suggest weathering of bedrock beneath a colluvial cover is a more significant source of sediment (40×10 4 kg year −1) than weathering of exposed bedrock surfaces (10×10 4 kg year −1). Mixing models constructed from nuclide concentrations of sediment reservoirs identify important sediment source areas. Hillslope colluvium is the dominant sediment source to the upper reaches of the sub-basin channel; channel cutting of alluvial terraces is the dominant source in the lower reaches. Similarities in nuclide concentrations of various sediment reservoirs indicate short sediment storage times (<10 3 years). Nuclide concentrations, measured in channel sediment from tributaries of Yuma Wash and in samples collected along the length of the Wash, were used to construct mixing models and determine sediment sources to the main stem channel. We find an exponential decrease in the channel nuclide concentrations with distance downstream, suggesting that as much as 40% of sediment discharged from Yuma Wash has been recycled from storage within basin fill alluvium. Sediment generation and denudation rates determined from the main stem are greater (25%) than rates determined from upland sub-basins suggesting that, currently, sediment may be exported from the basin more quickly than it is being generated in the uplands. Independence of nuclide concentration and sediment grain size indicates that channels transport sediment in discrete pulses before rapidly depositing poorly sorted material, suggesting that differences in transport times for different size materials are minimal.

Sediment yield exceeds sediment production in arid region drainage basins

Research Article| November 01, 2000 Sediment yield exceeds sediment production in arid region drainage basins Erik M. Clapp; Erik M. Clapp 1School of Natural Resources and Department of Geology, University of Vermont, Burlington, Vermont 05401, USA Search for other works by this author on: GSW Google Scholar Paul R. Bierman; Paul R. Bierman 1School of Natural Resources and Department of Geology, University of Vermont, Burlington, Vermont 05401, USA Search for other works by this author on: GSW Google Scholar Asher P. Schick; Asher P. Schick 2Department of Geography, Hebrew University of Jerusalem, Jerusalem, Israel Search for other works by this author on: GSW Google Scholar Judith Lekach; Judith Lekach 2Department of Geography, Hebrew University of Jerusalem, Jerusalem, Israel Search for other works by this author on: GSW Google Scholar Yehouda Enzel; Yehouda Enzel 2Department of Geography, Hebrew University of Jerusalem, Jerusalem, Israel Search for other works by this author on: GSW Google Scholar Marc Caffee Marc Caffee 3Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94551, USA Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (11): 995–998. https://doi.org/10.1130/0091-7613(2000)28<995:SYESPI>2.0.CO;2 Article history received: 31 Mar 2000 rev-recd: 26 Jul 2000 accepted: 07 Aug 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Erik M. Clapp, Paul R. Bierman, Asher P. Schick, Judith Lekach, Yehouda Enzel, Marc Caffee; Sediment yield exceeds sediment production in arid region drainage basins. Geology 2000;; 28 (11): 995–998. doi: https://doi.org/10.1130/0091-7613(2000)28<995:SYESPI>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We use 10Be and 26Al to determine long-term sediment generation rates, identify significant sediment sources, and test for landscape steady state in Nahal Yael, an extensively studied, hyperarid drainage basin in southern Israel. Comparing a 33 yr sediment budget with 33 paired 10Be and 26Al analyses indicates that short-term sediment yield (113–138 t · km−2 · yr−1) exceeds long-term sediment production (74 ± 16 t · km−2 · yr−1) by 53%–86%. The difference suggests that the basin is not in steady state, but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield. Nuclide data indicate that (1) sediment leaving the basin is derived primarily from hillslope colluvium, (2) bedrock weathers more rapidly beneath a cover of colluvium than when exposed, and (3) long-term erosion rates of granite, schist, and amphibolite are similar. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Multiple Large Earthquakes in the Past 1500 Years on a Fault in Metropolitan Manila, the Philippines

The first 14 C-based paleoseismic study of an active fault in the Philippines shows that a right-lateral fault on the northeast edge of metropolitan Manila poses a greater seismic hazard than previously thought. Faulted hillslope colluvium, stream-channel alluvium, and debris-flow deposits exposed in trenches across the northern part of the west Marikina Valley fault record two or three surface-faulting events. Three eroded, clay-rich soil B horizons suggest thousands of years between surface faulting events, whereas 14 C ages on detrital charcoal constrain the entire stratigraphic sequence to the past 1300–1700 years. We rely on the 14 C ages to infer faulting recurrence of hundreds rather than thousands of years. Minimal soil development and modern 14 C ages from colluvium overlying a faulted debris-flow deposit in a nearby stream exposure point to a historic age for a probable third or fourth (most recent) faulting event.

Volumetric analysis and hydrologic characterization of a modern debris flow near Yucca Mountain, Nevada

On July 21 or 22, 1984, debris flows triggered by rainfall occurred on the southern hillslope of Jake Ridge, about 6 km east of the crest of Yucca Mountain, Nevada. Rain gages near Jake Ridge recorded 65 mm and 69 mm on July 21, and 20 mm and 17 mm on July 22. Rates of rainfall intensity ranged up to 73 mm/h on the twenty-first, and 15 mm/h on the twenty-second. Digital elevation models with 2.0 m grid-node spacing, measured from pre-storm and post-storm aerial stereo-photographs, were used to map hillslope erosion and the downslope distribution of debris. Volumetric calculations indicate that about 7040 m 3 of debris was redistributed on the 49,132 m 2 hillslope study area during the two-day storm period. About 4580 m 3 (65%) of the eroded sediment was deposited within the study area and the remaining 35% was deposited outside the study area in a short tributary to Fortymile Wash and in the wash itself. The maximum and mean depths of erosion in the study area were about 1.8 m and 5 cm, respectively. The mean depths of erosion on the upper and middle hillslope were 27 cm and 4 cm, respectively. The mean depth of deposition on the lower hillslope was 16 cm. Analysis of the values of cumulative precipitation in the context of the precipitation-frequency atlas of the National Oceanic and Atmospheric Administration indicates that precipitation from the main storm on July 21 was more than double that expected, on average, once during a 100-year-period. The relations of precipitation intensity/duration, developed from data recorded at a nearby precipitation gage, indicate a storm interval of 500 years or greater. The amount of erosion caused by such a storm is primarily dependent on three variables; storm intensity, development of the drainage network on the hillslope, and the amount of available colluvium. Additionally, the erosive ability of successive storms of equal intensity will decrease because such storms would tend to progressively isolate and reduce the amount of colluvium available. The preservation of Pleistocene deposits on hillslopes of Yucca Mountain, in general, indicates that erosional events that strip 5% of the available hillslope colluvium must be quite rare. We conclude that the recurrence interval of an erosional event comparable to the July, 1984 event is probably much longer than 500 years.

Sackungen at the Aspen Highlands Ski Area, Pitkin County, Colorado

Numerous linear geomorphic features of suspected gravitational spreading origin, collectively termed sackungen, occur at elevations of 3,475–3,775 m at the head of the Aspen Highlands Ski Area near Aspen, Colorado. Features include double-crested ridges, upslope-facing scarps, linear troughs, and downslope-facing scarps. Most features are aligned with the prominent joint set (strike N25°–45°E, dip 80°–90° NW) that parallels the flanking, 1,150-m deep U-shaped glacial valleys of Castle and Maroon creeks. A backhoe trench 6 m long and 2 m deep was excavated across an upslope-facing scarp and adjacent trough to reveal the style and age of surface deformation. Sandstone bedrock of the Maroon Formation was extensively fractured under the scarp face, with abundant dilational voids. Hillslope colluvium was truncated at the main sackung fault plane, and was overlain by up to 1.2 m of fine-grained sag pond sediments. Seven buried soils were present in the trough fill, composed of A, and E or Bw horizons; A horizons at 35 cm, 84 cm, and 98 cm below the surface yield uncorrected 14 C ages of 3060+150, 6290+70, and 7910+80 14 C yrs B.P., respectively. Extrapolation of deposition rates to the base of the fill indicates that the trough formed ca. 11–11.5 ka, several thousand years after glacial ice had melted from the flanking glacial valleys. Trench stratigraphy suggests that slow vertical offset across the trough has continued since 11 ka, at rates of 0.14–0.75 mm/yr, perhaps accompanied by horizontal spreading at 0.43 mm/yr in the past 3 ka. This rate of spreading is slower than the 1–5 mm/yr measured by Varnes and others (1990) across sackungen in the Sawatch Range to the east, but still constitutes a constraint on foundation design for buildings and lift towers.

Applications of in Situ Cosmogenic Nuclides in the Geologic Site Characterization of Yucca Mountain, Nevada

AbstractThe gradual buildup of rare isotopes from interactions between cosmic rays and atoms in an exposed rock provides a new method of directly determining the exposure age of rock surfaces. The cosmogenic nuclide method can also provide constraints on erosion rates and the length of time surface exposure was interrupted by burial. Numerous successful applications of the technique have been imperative to the complete surface geologic characterization of Yucca Mountain, Nevada, a potential high level nuclear waste repository. The 10Be exposure age of Black Cone lava, within a ten mile radius of the proposed repository site, is 840 ± 210 kyr (in agreement with previous K/Ar dates of 1.0 ± 0.1 Ma). Rates of erosion of the tuff bedrock (&lt; 0.4 cm/kyr from 7 10Be measurements) and of hillslope colluvium (∼ 0.5 cm/kyr from 10Be dates on boulder deposits) preclude denudation of the mountain as a concern. Neotectonic concerns (rate of slip and timing of last significant movement along faults) are also being addressed with in situ 14C and 10Be measurements on scarp surfaces and on fault-dissected landforms where no surficial expression of the fault is preserved.

Quaternary deposits and landscape evolution in northeast Southland, New Zealand

Three kinds of Quaternary sediments are present in northeast Southland: aeolian deposits, terrace gravels, and hill slope colluvium. The aim of this paper is to review and describe the Quaternary sediments and erosion pattern of northeast Southland and reconstruct the likely climate under which sedimentation and erosion occurred. Aeolian deposition occurred intermittently from 250,000 yr B.P. but stratigraphic studies indicate widespread erosion of loess in the period 80,000–25,000 yr B.P. before a final period of loess accumulation in the late Otiran (δ 18O stage 2). Terrace gravels are attributable to two sources. A younger suite of three terraces is attributed to aggradation phases of the Mataura River. An older suite of three more weathered terraces is attributed to aggradation by a river flowing eastwards through the Waimea Plains from Lumsden to Gore. The river is named the Lumsden River. At about 180,000 yr B.P. this river ceased flowing through the Waimea Plains. Colluvium on hill slopes is regionally stratified into two layers. The lower deposits are identified as weathered sand and gravel sized colluvium derived from argillite and siltstone screes, dated as being formed before 29,000 yr B.P., and attributed to δ 18O stage 4. The upper, stonier deposits are attributed to δ 18O stage 2. The erosion and deposition pattern of aeolian deposits, terrace gravels and slope colluvium cannot be explained by a temperature drop of c. 5°C calculated for the last glacial period. We conclude that on lowlands vegetation cover was periodically limited by extreme droughts and cold windy conditions, causing erosion of previously-deposited loess and encouraging scree formation on slopes. During these periods the severe climate of northeast Southland approximated to that of a cold desert.

Clast-Fabric Strength in Hillslope Colluvium as a Function of Slope Angle

Clast fabric was measured in the upper 20 cm of soil at 16 sites on forested hillslopes in Giles County, Virginia, U.S.A. Slope angles ranged from 9° to 42°. Despite an abundance of roots in the soil, most sites displayed a significant fabric, with long axes parallel to slope and imbricated uphill. There was a significant correlation (r=0.771) between slope angle and fabric strength as measured by the eigenvalue technique. Elevation, slope aspect, andsoil texture appeared to have little effect on fabric strength. Soil creep probably produces the fabric.

Clast-Fabric Strength in Hillslope Colluvium as a Function of Slope Angle

Clast-Fabric Strength in Hillslope Colluvium as a Function of Slope Angle