Low-relief Terrain Research Articles

Spatio-temporal distribution and evolution of the Tujia traditional settlements in China.

The rapid modernization in China has aggravated the reduction of the traditional settlements and aroused concern about the protection and research. This study aims to examine the spatial-temporal variations Tujia traditional settlements in China and to delineate the driving mechanism of the settlement distribution. Previous studies have focused on the characteristics of settlements in provincial or smaller areas, providing lacked information regarding spatial distribution heterogeneity of Tujia traditional settlements in China. In this study, the spatial heterogeneity and influence factors of the distribution of traditional Tujia settlements were examined using the GIS platform and statistical methods. The results reveal that the spatial distribution of settlements exhibits clustering with the pattern of "scattered distribution in a large region, while concentrated in small areas". The settlements were generally built in low hills, gentle slopes, sunny slopes and low-relief terrain areas, with elevation, relief degree of land surface (RDLS), slope and aspect were the key factors affecting the distribution. In Song, Yuan, Ming and Qing dynasties, settlements showed significant clustering all through, though the location and number of clustering center kept changing. In this process, the history of the Tujia chieftain and the transportation and marketing lines of Sichuan salt had a profound influence on the historical evolution of the settlement.

Multi-decadal changes in river morphology in an urbanizing watershed: Highland Creek, Toronto, Canada

Urban land development causes significant changes to river channel form and function. Outcomes are strongly conditioned by local circumstances although responses such as channel enlargement and incision are common but are highly variable in extent and detectability. Many case studies focus on small watersheds (or short reaches) and before-after conditions, and direct causation and temporal trajectories of change are not well known but often presumed to be a single step change and response. Well-documented examples in fully-urban, larger watersheds are rare, and rarer still are cases covering the full trajectory from pre-urban to fully urban land cover with accompanying data on the direct drivers of change such as discharge and stream power. Highland Creek, Toronto, has a drainage area of 102 km2 and between the early 1950s and 2000s underwent a land cover change from agricultural to completely urban in very low relief terrain with channels in narrow valleys incised locally into glacial sediments. Streamflow monitoring, land cover data and aerial photography over this seven-decade period, along with a calibrated runoff model and digital elevation data, give a complete picture over multiple epochs of the causes and changes in fluvial hydrology and geomorphology. The complete transformation of the flow regime, along with channel straightening and steepening, resulted in increases in average stream power (total and specific) of the order of ten and six times, respectively. The channel is now exceptionally energetic with maximum total and specific stream power for 2-year flood approaching 5000 Wm−1 and 300 Wm−2, respectively. The semi-alluvial and supply-limited character of the channels is also influential. Channel response is variable along the 20–25 km of channel measured and is notably different between the sub-watersheds, related to timing of development and its intersection with engineering intervention, and changing conceptions of the channel over time. In places the channel widened by a factor of four or five and changed from high sinuosity meanders to wide, bar-chute morphology, consistent with regime expectations for gravel-bed channels. In other places the process of urbanization has involved progressive engineering of the channel to convey stormwater (channelized), protect infrastructure and mitigate erosion, so that responses in these reaches are much more restricted and fluvial functions such as bend and bar development have been eliminated. Substantial channel transformation can be seen to have occurred episodically resulting from two major flood events as well as the increases in magnitude and frequency of peak flows, which limit post-flood recovery. Urbanization effects and consequences have developed gradually over a long period, rather than in a single urbanization step change, and they do not match simple models of channel evolution. In many ways urbanization of the river is ongoing, particularly in the form of geomorphically-referenced design of the channels as a response to damage from large floods and overall institutional watershed planning. The ongoing urbanization story of Highland Creek illustrates some extreme effects of urbanization as well as the complexity and contingency of response to the physical and institutional processes influencing the trajectory of urban river evolution.

Accuracy Comparison of 30m Resolution SRTM and ASTER Derived Digital Elevation Models over AL-khamisah Region Using RTK-DGPS Data

Digital elevation models are topographic models of the Earth’s terrain that have had the heights of vegetation, and other cultural landscapes digitally removed. The accuracy and morphologic details of the height models represent the quality. DEMS provide one of the must usefule digital data sets for a wide range of users. This study is aimed at comparing and validating (in terms of elevation accuracy) SRTM and ASTER Global Digital Elevation Model (GDEM) with DGPS Points for AL-Khamisah region. Root-Mean-Square Error (RMSE) is used as the standard measure of accuracy for feature positioning. The results, of this study showed that vertical (RMSE) for ASTER DEM 4.92 m and for SRTM 2.10 m. The objectives of this study are to effectively evaluate the accuracy of ASTER and SRTM DEM datasets and determine which DEM most accurately represents low relief terrain. Findings of this analysis may be used as resources to determine the relevance of a particular DEM dataset in low relief terrain.

Oxia Planum: The Landing Site for the ExoMars "Rosalind Franklin" Rover Mission: Geological Context and Prelanding Interpretation.

The European Space Agency (ESA) and Roscosmos ExoMars mission will launch the “Rosalind Franklin” rover in 2022 for a landing on Mars in 2023.The goals of the mission are to search for signs of past and present life on Mars, investigate the water/geochemical environment as a function of depth in the shallow subsurface, and characterize the surface environment. To meet these scientific objectives while minimizing the risk for landing, a 5-year-long landing site selection process was conducted by ESA, during which eight candidate sites were down selected to one: Oxia Planum. Oxia Planum is a 200 km-wide low-relief terrain characterized by hydrous clay-bearing bedrock units located at the southwest margin of Arabia Terra. This region exhibits Noachian-aged terrains. We show in this study that the selected landing site has recorded at least two distinct aqueous environments, both of which occurred during the Noachian: (1) a first phase that led to the deposition and alteration of ∼100 m of layered clay-rich deposits and (2) a second phase of a fluviodeltaic system that postdates the widespread clay-rich layered unit. Rounded isolated buttes that overlie the clay-bearing unit may also be related to aqueous processes. Our study also details the formation of an unaltered mafic-rich dark resistant unit likely of Amazonian age that caps the other units and possibly originated from volcanism. Oxia Planum shows evidence for intense erosion from morphology (inverted features) and crater statistics. Due to these erosional processes, two types of Noachian sedimentary rocks are currently exposed. We also expect rocks at the surface to have been exposed to cosmic bombardment only recently, minimizing organic matter damage.

Long runout mechanism of the Shenzhen 2015 landslide: insights from a two-phase flow viewpoint

A catastrophic landslide occurred at Hongao dumpsite in Guangming New District of Shenzhen, South China, on December 20, 2015. An estimated total volume of 2.73x10(6) m(3) of construction spoils was mobilized during this event. The landslide traveled a long distance on a low-relief terrain. The affected area was approximately 1100 m in length and 630 m in width. This landslide made 33 buildings destroyed, 73 people died and 4 people lost. Due to the special dumping history and other factors, soil in this landfill is of high initial water content. To identify the major factors that attribute to the long runout character, a two-phase flow model of Iverson and George was used to simulate the dynamics of this landslide. The influence of initial hydraulic permeability, initial dilatancy, and earth pressure coefficient was examined through numerical simulations. We found that pore pressure has the most significant effect on the dynamic characteristics of Shenzhen landslides. Average pore pressure ratio of the whole basal surface was used to evaluate the degree of liquefaction for the sliding material. The evolution and influence factors of this ratio were analyzed based on the computational results. An exponential function was proposed to fit the evolution curve of the average pore pressure ratio, which can be used as a reasonable and simplified evaluation of the pore pressure. This fitting function can be utilized to improve the single-phase flow model.

Multi-Target Risk Assessment of Potentially Toxic Elements in Farmland Soil Based on the Environment-Ecological-Health Effect.

There are potential impacts of Potentially Toxic Elements (PTEs) (e.g., Cd, Cr, Ni, Cu, As, Zn, Hg, and Pb) in soil from the perspective of the ecological environment and human health, and assessing the pollution and risk level of soil will play an important role in formulating policies for soil pollution control. Lingyuan, in the west of Liaoning Province, China, is a typical low-relief terrain of a hilly area. The object of study in this research is the topsoil of farmland in this area, of which 71 soil samples are collected. In this study, research methods, such as the Nemerow Index, Potential Ecological Hazard Index, Ecological Risk Quotient, Environmental Exposure Hazard Analysis, Positive Matrix Factorization Model, and Land Statistical Analysis, are used for systematical assessment of the pollution scale, pollution level, and source of PTEs, as well as the ecological environmental risks and health risks in the study area. The main conclusions are: The average contents of As, Cd, Cr, Cu, Hg, Zn, Ni, and Pb of the soil are 5.32 mg/kg, 0.31 mg/kg, 50.44 mg/kg, 47.05 mg/kg, 0.03 mg/kg, 79.36 mg/kg, 26.01 mg/kg, and 35.65 mg/kg, respectively. The contents of Cd, Cu, Zn, and Pb exceed the background value of local soil; Cd content of some study plots exceeds the National Soil Environmental Quality Standard Value (0.6 mg/kg), and the exceeding standard rate of study plots is 5.63%; the comprehensive potential ecological hazard assessment in the study area indicates that the PTEs are at a slight ecological risk; probabilistic hazard quotient assessment indicates that the influence of PTEs on species caused by Cu is at a slight level (p = 10.93%), and Zn, Pb, and Cd are at an acceptable level. For the ecological process, Zn is at a medium level (p = 25.78%), Cu is at a slight level (19.77%), and the influence of Cd and Pb are acceptable; human health hazard assessment states that the Non-carcinogenic comprehensive health hazard index HI = 0.16 < 1, indicating that PTEs in soil have no significant effect on people’s health through exposure; the PMF model (Positive Matrix Factorization) shows that the contribution rates of agricultural source, industrial source, atmospheric dust source, and natural source are 13.15%, 25.33%, 18.47%, and 43.05%, respectively.

Potential of RADARSAT-2 stereo radargrammetry for the generation of glacier DEMs

ABSTRACTThe study of glaciers and ice caps in remote and cloudy regions remains difficult using current remote sensing tools. Here the potential of stereo radargrammetry (SRG) with RADARSAT-2 Wide Ultra-Fine images is explored for DEM extraction, elevation changes and mass-balance calculations on Barnes Ice Cap (Nunavut, Canada). Over low-relief terrain surrounding Barnes, a vertical precision of ~7 m (1σ confidence level) is measured, as well as an average vertical bias of ~4 m. Moreover, we show that the C-band penetration depth over the ice cap is insignificant at this time of the year (i.e. late ablation season). This is likely due to a wet surface and the presence of superimposed ice that leads to a surface radar response. Comparing the SRG DEMs with other datasets, an historical glacier-wide mass balance of −0.52 ± 0.19 m w.e. a−1is estimated for 1960–2013, whereas it decreases to −1.06 ± 0.84 m w.e. a−1between 2005 and 2013. This clear acceleration of mass loss is in agreement with other recent studies. Given its all-weather functionality and its possible use without ground control points, the RADARSAT-2 SRG technology represents an appropriate alternative for glacier monitoring in cloudy and remote regions.

Modelling landslide liquefaction, mobility bifurcation and the dynamics of the 2014 Oso disaster

Some landslides move slowly or intermittently downslope, but others liquefy during the early stages of motion, leading to runaway acceleration and high-speed runout across low-relief terrain. Mechanisms responsible for this disparate behaviour are represented in a two-phase, depth-integrated, landslide dynamics model that melds principles from soil mechanics, granular mechanics and fluid mechanics. The model assumes that gradually increasing pore-water pressure causes slope failure to nucleate at the weakest point on a basal slip surface in a statically balanced mass. Failure then spreads to adjacent regions as a result of momentum exchange. Liquefaction is contingent on pore-pressure feedback that depends on the initial soil state. The importance of this feedback is illustrated by using the model to study the dynamics of a disastrous landslide that occurred near Oso, Washington, USA, on 22 March 2014. Alternative simulations of the event reveal the pronounced effects of a landslide mobility bifurcation that occurs if the initial void ratio of water-saturated soil equals the lithostatic, critical-state void ratio. They also show that the tendency for bifurcation increases as the soil permeability decreases. The bifurcation implies that it can be difficult to discriminate conditions that favour slow landsliding from those that favour liquefaction and long runout.

The suitability of using ASTER GDEM2 for terrain-based extraction of stream channel networks in a lowland Arctic permafrost catchment

Seasonally inundated areas and water-saturated soils are common features of lowland Arctic and sub-Arctic permafrost environments. With the onset of snow melt, and water percolation down through the snowpack, a principal factor controlling stream channel flow, aside from active layer depth, is topography. This paper investigates stream channel networks derived from the advanced spaceborne thermal emission and reflection radiometer (ASTER) global digital elevation model (GDEM) version 2 in a static terrain-based GIS-model. The suitability of using the ASTER GDEM2 for modelling the drainage network over a low-relief terrain is assessed. The aim is to use GDEM2 for the analysis of the stream channel network and to establish the network’s connectivity to previously observed spring flood patterns over the Yamal peninsula. As such, there are two parts to this study: 1) DEM validation and 2) stream channel network analysis. The results of the DEM validation study show that the root mean square error (RMSE) of the GDEM2 and reference data is approx. 10 m when compared to both reference data sets (RMSE = 12.17 m, N = 86 and RMSE = 9.64, N = 506,877), implying that the GDEM2 is sufficiently accurate for terrain-based modelling. The low connectivity between the stream channel network and seasonal inundation suggests that topographic controls play a less important role compared to the possible overbanking of lakes and basin overflow. However, drainage densities for investigated drainage basins were significantly lower than those expected from typical Arctic basins. Both more sophisticated modelling techniques as well as higher spatial resolution DEMs are needed to extract the stream channel network more accurately and hence establish a more comprehensive link between the drainage network and seasonally inundated areas.

Evaluating Shuttle radar and interpolated DEMs for slope gradient and soil erosion estimation in low relief terrain

The error in slope gradient estimates provided by digital elevation models propagates to spatial modelling of erosion and other environmental attributes, potentially impacting land management prior...

Evaluating Shuttle radar and interpolated DEMs for slope gradient and soil erosion estimation in low relief terrain

The error in slope gradient estimates provided by digital elevation models propagates to spatial modelling of erosion and other environmental attributes, potentially impacting land management priorities. This study compared the slope estimates of Shuttle Radar Topographic Mission (SRTM) DEMs with those generated by interpolation of topographic contours, at two grid cell resolutions. The magnitude and spatial patterns of error in DEM slope, and derived erosion estimates using the Revised Universal Soil Loss Equation (RUSLE), were evaluated at three sites in eastern Australia. The sites have low-relief terrain and slope gradients less than 15%, characteristics which dominate the global land surface by area and are often highly utilised. Relative to a reference DEM resampled to the same resolution (a measure of DEM ‘quality’), the 90 m (3-s) SRTM DEM provided the best estimates of slopes, being within 20% for each 5% slope class outside alluvial floodplains where it over-predicted by up to 220%. Relative to a hillslope scale 10 m reference DEM, the 30 m (1-s) SRTM-derived DEM-S, provided slope gradient estimates slightly less biased towards under-prediction than the 90 m SRTM and significantly less biased on alluvial floodplains. In contrast, the 20 m vertical contour intervals underpinning the interpolated DEMs resulted in under-prediction of slope gradient by more than a factor of 5 over large contiguous areas (>1 km2). The 30 m DEM-S product provided the best estimate of hillslope erosion, being 3–4% better than the 90 m SRTM. The slope errors in the interpolated DEMs translated into generally poorer and less consistent erosion estimates than SRTM. From this study it is concluded that the SRTM DEM products, in particular the 30 m SRTM-derived DEM-S, provide estimates of slope gradient and erosion which are more accurate, and more consistent within and between low relief study sites, than interpolated DEMs.

A Comparison of SRTM V4 and ASTER GDEM for Hydrological Applications in Low Relief Terrain

A Comparison of SRTM V4 and ASTER GDEM for Hydrological Applications in Low Relief Terrain

Controls on large landslide distribution and implications for the geomorphic evolution of the southern interior Columbia River basin

Large landslides (>0.1 km 2 ) are important agents of geomorphic change. While most common in rugged mountain ranges, large landslides can also be widespread in relatively low-relief (several 100 m) terrain, where their distribution has been relatively little studied. A fuller understanding of the role of large landslides in landscape evolution requires addressing this gap, since the distribution of large landslides may affect broad regions through interactions with channel processes, and since the dominant controls on landslide distribution might be expected to vary with tectonic setting. We documented >400 landslides between 0.1 and ∼40 km 2 across ∼140,000 km 2 of eastern Oregon, in the semiarid, southern interior Columbia River basin. The mapped landslides cluster in a NW-SE–trending band that is 50–100 km wide. Landslides predominantly occur where even modest local relief (∼100 m) exists near key contacts between weak sedimentary or volcaniclastic rock and coherent cap rock. Fault density exerts no control on landslide distribution, while ∼10% of mapped landslides cluster within 3–10 km of mapped fold axes. Landslide occurrence is curtailed to the NE by thick packages of coherent basalt and to the SW by limited local relief. Our results suggest that future mass movements will localize in areas stratigraphically preconditioned for landsliding by a geologic history of fluviolacustrine and volcaniclastic sedimentation and episodic capping by coherent lava flows. In such areas, episodic landsliding may persist for hundreds of thousands of years or more, producing valley wall slopes of ∼7°–13° and impacting local channels with an evolving array of mass movement styles.

Holocene tectono-geomorphic evolution of parts of the Upper and Middle Gangetic plains, India

Using multispectral scanning (MSS) images and digital elevation models (DEMs), 26 terrain morphological units were delineated in the study area between the Rapti and Kosi Rivers in the Gangetic plains. Based on the degree of soil development and the infrared stimulated luminescence chronology, these terrain morphological units have been grouped into six members of a morphostratigraphic sequence with ages ≤ 1.65, 1.65–5.3, 5.3–7.5, 7.5–8.5, 8.5–10, and > 10 Ka. Integrated use of geomorphic markers including different drainage patterns identified from MSS images, significant breaks in topographic profiles, terminal fans, and artifact terrain features (e.g., ‘cliffs’ and ‘significant breaks in slopes’) in DEMs/digital terrain models (DTMs) with highly exaggerated vertical dimensions were made to infer and map 20 nascent faults in the region between the Ghaghara and Kosi Rivers in the flat Gangetic plains. The three major tectonic blocks are; the upland Ghaghara–Rapti block of the Upper Gangetic Plain, and the Rapti–Gandak and Gandak–Kosi blocks of the Middle Gangetic Plain, marked by high rates of subsidence and sedimentation. The Ghaghara–Rapti block bounded by the incised Ghaghara and Rapti rivers is an upland region and is primarily overlain by > 10 Ka old soils. Subsequent activity along the NE-SW trending transverse normal faults led to deposition of young terminal fans. Southward tilt of the Ghaghara–Rapti block generated two E–W trending terraces on the left bank of the Ghaghara River. Southwestward tilting of the upper part of the Ghaghara–Rapti block led to development of the widest Old Ghaghara Plain and Rapti Floodplain in the SW direction. Northeastward tilting of the Rapti–Gandak block shifted the Gandak River from west to east over a distance of 80 km during the period from 10 to 8.5 Ka. Further compression from the SW caused development of four extensional normal faults. The activity of three faults between 5.7 and 1.0 Ka generated four terminal alluvial fans on this block. The Gandak–Kosi block is marked by a set of seven thrust splays off the Himalayan Frontal Thrust (HFT) in the footwall. Activity of these thrust splays in the foothill region caused progradation of the gravel piedmont and thus developed the widest piedmont zone (124 km) in the Gangetic plains. This is the first report of gravel piedmont progradation from a modern environment and role of thrust splays in such a progradation. In the southernmost part of this block, the continuous occurrence of terminal fans over a length of 140 km south of the South Muzaffarpur Fault forms a terminal fan piedmont/bajada. Orientation of the faults was used to interpret compression from the SW in the Ghaghara–Rapti Interfluve Plain in the west since ~ 10 Ka and compression from the south in the Gandak–Kosi interfan region in the east after 4.5 Ka. The Rapti–Gandak region in the central part shows the effects of mainly compression from the SW and compression from the south at different times. In addition to terminal fans formed because of low relief terrain features created by the activity of faults by involvement of the entire discharge of small meandering/braided streams, a new type of fan formed by splays from a large river on the downthrown sides of faults, called ‘splay terminal fans’ is observed from the Rapti–Gandak block.

Rock type, precipitation, and the steepness of Himalayan threshold hillslopes

Abstract Studies on the dynamic coupling between tectonics, climate, and erosion at the margins of the Tibetan Plateau entail the notion of widely occurring threshold hillslopes along the southern Himalayan front. Here we show that differences in major lithological units are sufficient to explain trends in topographical relief and mean slope gradients across the eastern Nepal Himalaya. This lithological control is manifest in modal slope gradients that serve as proxies of peak rock-mass strength, and remain strikingly invariant per rock type on both sides of the Main Central Thrust (MCT) despite comparably high amounts of monsoon precipitation. We infer that lithology rather precipitation patterns plays an important though hitherto largely neglected role in modulating threshold hillslope steepness. A nonlinear relationship between mean slope gradients and relief further indicates that significant steepening of threshold hillslopes through relief increases is more readily facilitated in low-relief terrain. Most evidence of large (&gt;10 8 m 3 ) bedrock landslides in the Himalaya clusters where topographical relief &gt;2 km, and slope gradients are above average. This provides the mechanism necessary for rapidly lowering drainage divides and limiting hillslope heights, were the steepness of threshold hillslopes to decline via relief destruction.

Drainage network extraction using LiDAR-derived DEM in volcanic plains

Accurate delineation of drainage networks is critical for many hydrologically related applications. The commonly used methods for drainage network extraction from digital elevation models (DEMs) have limitations in low-relief terrain areas. High-quality DEMs are required for effectively applying these methods in extracting drainage networks in low-relief terrains. Airborne light detection and ranging (LiDAR) offers high-accuracy terrain data. With LiDAR data, high-accuracy and high-resolution DEMs can be generated. The results of drainage network extraction for two sub-catchments on the western Victorian Volcanic Plains (VVP) are reported. Drainage networks and some parameters describing drainage network composition, including the stream orders, the numbers of streams and the stream lengths, were derived from both the LiDAR DEM and the Vicmap DEM. The LiDAR-derived DEM is shown to offer significantly more detail, especially for delineating low-order stream (headwater) segments in sub-catchments of low-relief terrain.

The Effects of Critical Layers on Residual Layer Turbulence

Abstract The authors report results of a study of finescale turbulence structure in the portion of the nocturnal boundary layer known as the residual layer (RL). The study covers two nights during the Cooperative Atmosphere–Surface Exchange Study 1999 (CASES-99) field experiment that exhibit significant differences in turbulence, as indicated by the observed turbulence dissipation rates in the RL. The RL turbulence sometimes reaches intensities comparable to those in the underlying stable boundary layer. The commonly accepted concept of turbulence generation below critical values of the gradient Richardson number (Rig) is scale dependent: Ri values typically decrease with decreasing vertical scale size, so that critical Rig values (≈0.25) occur at vertical scales of only a few tens of meters. The very small scale for the occurrence of subcritical Ri poses problems for incorporating experimentally determined Rig -based methods in model closures in models with poor resolution. There appear to be two distinct turbulence “regimes” in the RL: a very weak but ever-present background turbulence level with minimal temporal and spatial structure and a more intense intermittent regime during which turbulent intensity can approach near-surface nighttime turbulent intensities. It is hypothesized that the locally produced RL turbulence can be related to upward-propagating atmospheric gravity waves generated by flow over the low-relief terrain. The presence of critical layers in the RL, caused by wind turning with height, results in the generation of intermittent turbulence.

Discrimination of fluvial, eolian and neotectonic features in a low hilly landscape: A DEM-based morphotectonic analysis in the Central Pannonian Basin, Hungary

The Gödöllő Hills, a low-relief terrain within the Central Pannonian Basin in Hungary, is characterised by moderate tectonic deformation rates. Although typical tectonic landforms are not clearly recognisable in the study area, this paper succeeded in discriminating between tectonically controlled landforms and features shaped by fluvial erosion or deflation with no tectonic control. DEM-based morphometric parameters including elevation, slope and surface roughness, enabled the delineation of two NW–SE trending spearhead-shaped ridges separated by a wide rectilinear valley of the same strike. Although directional statistics suggested possible tectonic control of NW–SE striking landforms, precise morphometry completed with an analysis of subsurface structures rejected their tectonic preformation. Deflation plays a significant role in shaping the area, and the presence of two large-scale yardangs separated by a wind channel is proposed. In temperate-continental areas of Europe, no deflational landforms of such scale have been described so far, suggesting that Pleistocene wind power in periglacial areas was more significant than it was previously thought. Characteristic drainage patterns and longitudinal valley profiles enabled the recognition of areas probably affected by neotectonic deformation. A good agreement was observed between locations of Quaternary warping predicted by the morphometric study and subsurface structures revealed by the tectonic analysis. Zones of surface uplift and subsidence corresponded to anticlinal and synclinal hinges of fault-related folds. In low-relief and slowly-deforming areas, where exogenous forces may override tectonic deformation, only the integrated application of morphometric and subsurface-structural indications could assure correct interpretation of the origin of various landforms, while a morphometric study alone could have led to misinterpretation of some morphometric indices apparently suggesting tectonic preformation. On the other hand, the described morphological expression of subsurface structures could verify Quaternary age of the deformation.

A Metamorphosed Proterozoic Carbonaceous Shale-Hosted Co-Ni-Cu Deposit at Kalumbila, Kabompo Dome: The Copperbelt Ore Shale in Northwestern Zambia

The Kalumbila Co-Ni-Cu prospect (12°15' S, 25°20' E) is located ~300 km west of the Zambian Copperbelt on the southeastern flank of the Kabompo dome in the Middle Unit of the Lufilian arc. Kalumbila contains a drill-indicated resource of ~3.04 Mt at 0.67 wt percent Ni, 0.2 wt percent Co and 0.11 wt percent Cu using a 0.08 wt percent Co and ~0.3 wt percent Ni cutoff with an average thickness of 12.75 m. Ni-Co-Cu mineralization occurs as strata-bound, disseminated to finely laminated (locally semimassive) to locally discordant chalcopyrite, pyrrhotite, violarite, and siegenite within a finely laminated, highly carbonaceous and pyritic metapelite (300–500 m thick). Surface rock exposure in this low-relief terrain of woodland and seasonal swamp is <1 percent and geophysics (magnetic and electromagnetic surveys) is an essential exploration tool. Detrital zircons in the Kalumbila metasediments (SHRIMP U-Pb ages of 2004–1884 Ma) are derived from the underlying Paleoproterozoic granitic gneiss such as that exposed in the adjacent Kabompo basement dome. The metasedimentary sequence grades upward from siliciclastic rocks (mica schists) to the carbonaceous metapelite, which hosts the Co-Ni-Cu. These units are overlain by dolomitic and Mg-rich schists (possible meta-evaporites) which are, in turn, succeeded by calc-silicate rocks and a deformed diamictite. This sequence is broadly similar to the stratigraphy in the Zambian Copperbelt and suggests that the Kalumbila carbonaceous metapelite may be the chronostratigraphic equivalent of the Katangan Roan Ore Shale, a significant exploration target. Kalumbila occurs within a moderately (40°) north- northwest-dipping band of Wamikumbi Formation carbonaceous metapelite on the flank of a recumbent, south-southeast–verging F1 or F2 back fold. During the Lufilian orogeny, peak metamorphic conditions at F1 were of amphibolite facies grade (~650°C, 13 kbars). Both monazites and rutiles within the Kalumbila metasediments have metamorphic characteristics and late orogenic, Lufilian, SHRIMP U-Pb ages (548.6 ± 7.6 Ma and 531 ± 21 Ma, respectively). Sulfides in the metasediments display metamorphic textures and, therefore, predate the peak of Lufilian tectonism and thermal metamorphism. A suite of spatially associated, apparently late Lufilian gabbros intrude the metasedimentary rocks. These gabbros are unmineralized, but the thermal effects of their emplacement may have modified ore distribution. A genetic model, in which synsedimentary pyrite in a carbonaceous pelite was partially replaced by syndiagenetic or metamorphic Co-Ni-Cu-bearing fluids of unknown origin, is favored.

EVALUATION OF THE ROSGEN STREAM CLASSIFICATION SYSTEM IN CHEQUAMEGON‐NICOLET NATIONAL FOREST, WISCONSIN1

ABSTRACT: Data collected from 121 stream reaches during 1991 to 1993 were evaluated to determine the applicability of the Rosgen Stream Classification System (RSCS) to the low relief terrain within the Chequamegon‐Nicolet National Forest (CNNF) in Wisconsin, USA. All reaches were classified to RSCS Level I and II except that 10.7 percent had sinuosities below the continuum limits and one reach had a predominantly organic substrate. Five of eight possible RSCS Level I types were observed including B, C, D, A, E, and F; 86 percent were C and E types. Seventeen of 94 possible RSCS Level II types were observed. Most reaches were slightly entrenched, had low to moderate width/depth ratios, relatively low sinuosity, low slope, and sand or gravel as the dominant channel material. Discriminant analyses were used to verify the applicability of RSCS for streams within the CNNF; discriminant functions correctly classified 92.5 and 94.7 percent of the Level I and II RSCS types, respectively. When limits for E and F types were modified slightly at Level II by adding an additional category for slopes less than 0.1 percent (a modification we recommend for low relief terrain), discriminant functions correctly classified 99.1 percent of the types. Adding another slope break at 0.3 percent produced similar results. Based on our analyses, RSCS works well within the CNNF and is probably applicable to other areas with low‐relief terrain.