Multiple Terraces Research Articles

An Online Planning Tool forDesigning Terrace Layouts

<abstract><title><italic>Abstract. </italic></title> A web-based conservation planning tool, WebTERLOC (web-based TERrace LOCation program), was developed to provide multiple terrace layout options using digital elevation model (DEM) and geographic information systems (GIS). Development of a terrace system is complicated by the time-intensive manual layout process, which can take up to 50% of the total design time. The objective was to develop a web-based conservation planning tool for designing terrace layouts. The use of WebTERLOC enables automation of the terrace layout procedure, potentially saving time and money. Functionality of the program was enhanced by integration with an online ArcGIS interface. Multiple help menus and automated drawing and uploading tools increased input efficiency and ease of program use. Based on an earlier version of TERLOC, existing design procedures were modified to enhance layout results for fields with irregular boundaries, topography, and orientation. Program design modifications included variable terrace spacing, channel grade adjustments to meet non-erosive velocities, and the option for multiple key terraces. These new features provide means of selecting layout designs based on conservation, overall terrace length, and farmability. Analysis of WebTERLOC and its output was performed by comparing the program layout results for five fields with manually located terraces using standard NRCS procedures. Program results were comparable to the manual terrace layout results, with fields having large drainage areas most similar. Terrace number, shape, and length were the features with the most similarities. Terrace spacing was found to be most variable, with the program spacing typically larger than the manual result, particularly for smaller, more uniform fields. For example, fields less than 10 ha resulted in program spacings 25% to 67% greater than manual layouts, while larger fields were 4% to 22% greater. Depending on location of the uppermost terrace in larger fields, total field terrace numbers were equal or within one or two of the constructed layout. Excluding these uppermost or lowest terraces additional terraces, total field terrace lengths were within 1% to 3% of the constructed lengths. In general, the WebTERLOC program successfully demonstrated its use as an efficient terrace layout planning tool.

Highly Adaptable Two-Dimensional Metal–Organic Coordination Networks on Metal Surfaces

The formation of extended two-dimensional metal-organic coordination networks (2D-MOCNs) showing high adaptability to surface step edges and structural defects is revealed by scanning tunneling microscopy. Rod-like 4,4'-di-(1,4-buta-1,3-diynyl)-benzoic acid (BDBA) and iron atoms assemble into extended 2D-MOCNs on Au(111) and Ag(100) surfaces. Independent from the chosen substrate and its surface symmetry the MOCN grows continuously over multiple surface terraces through mutual in-phase structure adaptation of network domains at step edges as well as on terraces. The adaptability of the MOCNs is mainly ascribed to the high degree of conformational flexibility of the butadiynyl functionality of the ligand. Despite their flexibility, the MOCNs exhibit considerable robustness against annealing at high temperatures. The findings show that mesoscale self-assembled functional architectures with a high degree of substrate error tolerance can be realized with metal coordination networks.

Paleovalley morphology and fluvial system evolution of Eocene-Oligocene sediments ("auriferous gravels"), northern Sierra Nevada, California: Implications for climate, tectonics, and topography

Research Article| September 01, 2011 Paleovalley morphology and fluvial system evolution of Eocene–Oligocene sediments (“auriferous gravels”), northern Sierra Nevada, California: Implications for climate, tectonics, and topography Elizabeth J. Cassel; Elizabeth J. Cassel † 1Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania 17604, USA †E-mail: ejcassel@gmail.com Search for other works by this author on: GSW Google Scholar Stephan A. Graham Stephan A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Elizabeth J. Cassel † 1Department of Earth and Environment, Franklin and Marshall College, Lancaster, Pennsylvania 17604, USA Stephan A. Graham 2Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305, USA †E-mail: ejcassel@gmail.com Publisher: Geological Society of America Received: 21 Jun 2010 Revision Received: 03 Oct 2010 Accepted: 09 Nov 2010 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2011 Geological Society of America GSA Bulletin (2011) 123 (9-10): 1699–1719. https://doi.org/10.1130/B30356.1 Article history Received: 21 Jun 2010 Revision Received: 03 Oct 2010 Accepted: 09 Nov 2010 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Elizabeth J. Cassel, Stephan A. Graham; Paleovalley morphology and fluvial system evolution of Eocene–Oligocene sediments (“auriferous gravels”), northern Sierra Nevada, California: Implications for climate, tectonics, and topography. GSA Bulletin 2011;; 123 (9-10): 1699–1719. doi: https://doi.org/10.1130/B30356.1 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 SocietyGSA Bulletin Search Advanced Search Abstract In the northern Sierra Nevada, California, Eocene–Oligocene fluvial sediments (the “auriferous gravels”) rest unconformably in well-defined basement-incised paleovalleys, providing a record of paleolandscape geomorphology and drainage system evolution. Paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad, terraced paleovalley segments, which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition. High-gradient, high-energy deposits are present near the edges of these areas, suggesting that tributaries and outlets resided in steeper, narrow paleovalleys. Multiple strath terraces are common in broad paleovalleys, indicating that incision events occurred both before deposition and during paleovalley widening, followed by periods of aggradation. Broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system. Multiple upward-fining cycles, bounded by erosional surfaces, are composed of alternating coarse-grained channel-belt and fine-grained floodplain packages. An overall upward-fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys.Paleochannel slope estimates of 0.004–0.055 were obtained based on average grain sizes of coarse channel fills. Anomalously thick (up to 11 m), laterally continuous (1–3 km) floodplain units, containing kaolinite-rich clay and Oxisol intervals, record high fine-grained sediment supply, driven by high rates of chemical weathering in the warm Eocene climate. Based on sedimentary characteristics, combined with floral and detrital zircon data, braided stream deposition within the basin occurred from the late early Eocene through late Eocene, and aggradation primarily occurred in broad, lower-gradient reaches behind a major bedrock knickpoint, created in the late Mesozoic–early Cenozoic, possibly due to asymmetric batholith unroofing. The diachronous, localized nature of paleovalley incision and braided stream aggradation within the northern Sierra Nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients. Both internal and external drivers influenced the evolution of the fluvial system through (1) the pattern of basin filling, as the locus of deposition migrated east to west, (2) the warm Eocene climate, which increased chemical weathering and contributed a high sediment supply, and (3) changes in base level due to eustasy and/or Laramide tectonism. This record of Laramide tectonics in the Sierra Nevada and Basin and Range is important for the timing of Sierra Nevada uplift, for tectonic reconstructions of western North America, and for studies of landscape evolution in tectonically active orogens. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The use of high-resolution elevation histograms for mapping submerged terraces: Tests from the Eastern Tyrrhenian Sea and the Eastern Atlantic Ocean

Histogram plots can be used as a cost- and time-efficient tool to detect horizontal or gently dipping geomorphic surfaces within a background regional topography. One of the main classes of these surfaces is typified by terraces formed during marine still-stands. This contribution uses elevation histogram plots as morphometric indicators for detecting the possible existence of concealed terrace orders in Digital Elevation Models (DEMs) derived by the processing of bathymetric data. The approach is particularly useful when dealing with submerged terraces and platforms, because of the obvious difficulties in mapping those surfaces. The advantage of using this indicator consists in the rapid identification of DEM recurrent bathymetric values. This tool is most powerful when dealing with shortly developed terraces and/or multiple terrace orders, whose detection could have been missed by direct observation. Two case studies characterized by the presence of a single terracing event are tested: the southern slope of the Ischia Island and the top of the Palinuro Seamount, both located in the Eastern Tyrrhenian Sea Margin. Elevation histograms are used for terrace order computation in a more complex setting, the Gorringe Bank, located offshore SW Portugal in the Eastern Atlantic Ocean. The results show that a joint use of elevation histogram computation and geomorphologic analysis can be particularly efficient in the study of planar surfaces.

Geoarchaeological Investigations in the Upper North Fork River Valley in Southern Missouri

The first geoarchaeological investigations in the upper North Fork River valley in 1993 and 1994 revealed the presence of multiple terraces and associated sediment assemblages that contain archaeological deposits. Most of the field work, however, focused on the two lowest and youngest sediment assemblages. These include an aggrading flood plain (F-1) and a low terrace (T-1). The flood plain sediment assemblage is late Holocene in age, probably less than 2,000 years old. Although not common, Late Woodland and Mississippian artifacts are deeply buried in this unit. The T-1 appears to be late Pleistocene in age. Artifacts dating from Late Paleoindian to Mississippian times are very common on T-1 landforms, but they appear to be restricted to the upper 1 m of the sediment assemblage. Alluvial deposits similar to the F-1 sediment assemblage appear to be widespread in the Ozarks, whereas chronological and sedimentological discrepancies exist between the T-1 sediment assemblage in the North Fork River valley and those located elsewhere in the Ozarks, especially north of the Ozarks Divide.

African Video Film Arts Festival, Obafemi Awolowo University, Ile-Ife, Nigeria

October 28-31, 2007 I was invited to be a discussant at this two-day conference held at Nigeria's Obafemi Awolowo University, the 140-acre campus near the brownroofed, medieval town of Ile-Ife. All screenings and panels took place in the spacious, cool auditorium of Oduduwa Hall, a beautiful, gargantuan building of black and white architecture, built in 1960 with round holes cut into large flat walls set amidst floating, wide, cement staircases and multiple terraces. This conference was targeted to be the first in an annual series, focused on African video and film arts. Though work from other countries on the continent was screened, from the outset opinions clustered around the muchmaligned, much-adored Nigerian video industry, also known as Though twenty years old, the Nigerian video industry is a frontier world and poses remarkable possibilities around economies, national identity, and a new renaissance of the film industry working with today's destructions, reconstructions, and technologies. The conference looked beyond Nollywood. It called up an examination of consciousness with open questions about identity, art forms, and colonial impact. Younger people vocally challenged the idea of a precolonial character that could be found intact. The welcome address by conference organizer, Dr. Foluke Ogunleye, set a practical, enthusiastic tone. She encouraged a new perspective of this video industry, currently Africa's largest-as a foundation on which to rejuvenate cinema. The Nigerian video world is very profitable, very multiple in its sources, production values and quality, and is very international, exporting around the world. It is an in-house national product, which finances its own pictures and recycles its profits quickly. Its major backers are scrap-metal businessmen, so its economy is hands-on and financially canny. Ogunleye pointed out that art already exists in these popular videos as well as messages of Africanness and that, easy as it is to dismiss the videos as shallow and poorly made, they nevertheless hold the seeds of a future African, specifically Nigerian, cinema, one both lucrative and artistically successful. The indigenous structures of identity and prosperity are there: many of these videos are in languages (Yoruba and Hausa), many are built on traditional folktales or on the young men's fiction of the 1950s Onitsha market literature, and the industry itself arose from the illustrious Yoruba theater, whose players needed work when the economy (and the theater) collapsed in the 1980s and so turned to video acting. It also owes much to the Mexican and Brazilian soaps that have engrossed television viewers for decades. This makes the Nigerian video industry a special mishmash of global culture, oral and epic folk culture, routine culture, television culture, and new culture. Many contemporary features and documentaries from Senegal, Kenya, Ghana, and Uganda as well as classic Nigerian videos, such as Tunde Kelani's Thunderbolt (2001) were screened. The students loved the torrid Ghanaian youth soap opera Caravans of Dreads, made by twentysomething director, Sam Atsu Akbo, as both amusing and hip, and, equally loved and hip, the gentle Mee (2006), a spiritual documentary on finding one's self, by Ugandan nun, Sister Dominica Dipio. Ogunleye wanted students to see films on a large screen and in a large audience as few had experienced this. In most countries, movie houses are almost nonexistent, often too difficult or dangerous to get to, too costly and not worth the hassle of leaving home when a TV screen will do. This important detail allowed the phenomenon of film history and its reliance on the big screen to hover in the conference. In every approach to a revived film industry were debates about identity per se, about identity as the basis for new cinema, about Yoruba, Hausa, or Igbo traditions as the crux of a Nigerian film culture, and about the future of celluloid versus digital or video. …

Terrace staircases of the River Euphrates in southeast Turkey, northern Syria and western Iraq: evidence for regional surface uplift

We present the first overall synthesis of the terrace deposits of the River Euphrates in SE Turkey, northern Syria, and western Iraq, combining new observations with summaries of data sets from different reaches that had previously been independently studied on a piecemeal basis. The largest number of terraces observed in any reach of the Euphrates is 11, in western Iraq, where this river leaves the uplands of the Arabian Platform. In many other localities not more than 5 or 6 terraces have previously been identified, although we infer that some of these are resolvable into multiple terraces. These terraces are typically formed of gravel, principally consisting of Neotethyan ophiolite and metamorphic lithologies transported from Anatolia. Although older gravels are also evident, most of the Euphrates terrace deposits appear, given the chronologies that have been established for different parts of the study region, to date from the late Early Pleistocene onwards, the cold stages most often represented being interpreted as marine Oxygen Isotope Stages 22, 16, 12, 8, 6 and/or 4, and 2. The formation of this terrace staircase reflects regional uplift of the Arabian Platform. Estimated amounts of uplift since the Middle Pliocene decrease southeastward from almost 300m in SE Turkey to ∼150m in western Iraq. Uplift rates increased in the late Early Pleistocene, the uplift estimated since then decreasing from ∼110m in SE Turkey to a minimum of ∼50m in the Syria–Iraq border region, then increasing further downstream across western Iraq to ∼70m. Numerical modelling of this uplift indicates a relatively thin mobile lower-crustal layer, consistent with the low surface heat flow in the Arabian Platform.

Reassessing landslide deformation in Ganges Chasma, Mars

High‐resolution images of landslide aprons in Ganges Chasma show extensive scarps, rock chutes, and talus accumulations on the canyon rim. Below these exists a topographic bench formed of multiple terraces, ridges and scarps. The terrace slopes are talus covered similar to the canyon rim. Small volume lobes and sheets originate from talus accumulations and extend downslope. While previously determined to be the result of large volume catastrophic landslides, the characteristics and dimensions of the terraces forming the topographic bench can be explained by deep‐seated gravitational creep of the ancient rock mass. Gravity driven movements over millions of years can also account for the morphology and dimensions of talus lobes thus offering an alternative to catastrophic long‐runout landslide mechanisms. The movement of lobes is suggested to be analogous to terrestrial periglacial rock glaciers.

Drowned carbonate platforms in the Huon Gulf, Papua New Guinea

The western Huon Gulf, Papua New Guinea, is an actively subsiding foreland basin dominated by drowned carbonate platforms. We investigated these platforms using new high‐resolution multibeam, side‐scan sonar and seismic data, combined with submersible observations and previously published radiometric and sedimentary facies data. The data reveal 14 distinct drowned carbonate platforms and numerous pinnacles/banks that increase in age (∼20–450 kyr) and depth (0.1–2.5 km) NE toward the Ramu‐Markham Trench. Superimposed on this overall downward flexing of the platforms toward the trench is a systematic tilting of the deep platforms 15 m/km toward the NW and the shallow platforms 2 m/km toward the SE. This may reflect the encroaching thrust load from the NW (Finisterre Range) and spatial variations in the flexural rigidity of the underlying basement. The drowned platforms form a complex system of promontories and reentrants, with abundant pinnacles and banks preserved at similar depths seaward of the main platforms. This configuration closely mimics the present‐day Huon coastline and its seaward islands fringed by modern coral reefs. The platforms retain structural, morphologic, and sedimentary facies evidence of primary platform growth, drowning, and subsequent backstepping, despite some lateral erosion of the platform margins (&lt;100 m slope defacement) by mass wasting. Both platforms and pinnacles are composite features containing multiple terrace levels and notches, corresponding to multiple phases of growth, emergence, and drowning in response to rapid climatic and sea level changes during the evolution of each structure. On the basis of all observational and numerical modeling data, we propose a chronology for the initiation, growth, and drowning of the 14 platforms. Over shorter timescales (≤100 kyr) the rate and amplitude of eustatic sea level changes are critical in controlling initiation, growth, drowning or subaerial exposure, subsequent reinitiation, and final drowning of the platforms. However, continued tectonic subsidence and basement substrate morphology influence the overall backstepping geometry and subsequent tilting of the platforms over longer timescales (≥100–500 kyr).

Multiple terraces within the deep incised Zaire Valley (ZaïAngo Project): are they confined levees?

Abstract Terraces have been frequently observed and described along turbidite valleys. Many interpretations have been aimed at determining the origin of these structures, including a tectonic origin, succession of infilling and incision processes, channel-wall slumps, or inner levee aggradation. The Zaire submarine valley presents a complex structure with multiple terraces bordering a deep incised meandering thalweg. The detailed analysis of the morphology, the seismic structure and the recent sedimentation (in cores) along the Zaire upper-fan valley show that terraces are inner levees confined within the incised valley. Many terraces correspond to the infilling of abandoned meanders, and aggrade by deposition of turbidite sequences due to current overflows. The major process affecting the initiation and the development of terraces inside the valley is the vertical incision of the thalweg, simultaneously with meander migration.

Autogenic response of fluvial deltas to steady sea-level fall: Implications from flume-tank experiments

Flume-tank experiments on fluvial deltas, conducted with constant fall of relative sea level (rate A < 0), constant sediment discharge ( q S), and constant water discharge ( q W), reveal a built-in geomorphic process that inevitably causes valley incision (“autoincision”) after the beginning of the sea-level fall and forms paired stream terraces on the abandoned alluvial slope. Despite steady sea-level fall, deltas aggrade without major incision until the autoincision threshold is attained, at which time the aggradational regime is replaced by a degradational one. Results of the experiments imply that multiple valley incision and terrace formation can occur as an autogenic response of the depositional system to steady forcing by constant sea-level fall. Changes of A , q S, and q W, or changes in river energy, are not required to account for these geomorphic events. The understanding of the autogenic response, when combined with the theory of shoreline autoretreat, provides an alternative view of the geomorphic development of fluviodeltaic systems during base-level fall.

Long-term changes to river regimes prior to late Holocene coseismic faulting, Canterbury, New Zealand

Two sites are described from range front faults along the foothills of the Southern Alps of New Zealand, where apparently a period of 200–300 years of accelerated river incision preceded late Holocene coseismic ruptures, each probably in excess of M w 7.5. They relate to separate fault segments and seismic events on a transpressive system associated with fault-driven folding, but both show similar evidence of off-plane aseismic deformation during the downcutting phase. The incision history is documented by the ages, relative elevations and profiles of degradation terraces. The surface dating is largely based on the weathering rind technique of McSaveney (McSaveney, M.J., 1992. A Manual for Weathering-rind Dating of Grey Sandstones of the Torlesse Supergroup, New Zealand. 92/4, Institute of Geological and Nuclear Sciences), supported by some consistent radiocarbon ages. On the Porters Pass Fault, drainage from Red Lakes has incised up to 12 m into late Pleistocene recessional outwash, but the oldest degradation terrace surface T I is dated at only 690±50 years BP. The upper terraces T I and T II converge uniformly downstream right across the fault trace, but by T III the terrace has a reversed gradient upstream. T II and T III break into multiple small terraces on the hanging wall only, close to the fault trace. Continued backtilting during incision caused T IV to diverge downstream relative to the older surfaces. Coseismic faulting displaced T V and all the older terraces by a metre high reverse scarp and an uncertain right lateral component. This event cannot be younger than a nearby ca. 500 year old rock avalanche covering the trace. The second site in the middle reaches of the Waipara River valley involves the interaction of four faults associated with the Doctors Anticline. The main river and tributaries have incised steeply into a 2000 year old mid-Holocene, broad, degradation surface downcutting as much as 55 m. Beginning approximately 600 years ago accelerating incision eventually attained rates in excess of 100 mm/year in those reaches closely associated with the Doctors Anticline and related thrust and transfer faults. All four faults ruptured, either synchronously or sequentially, between 250 and 400 years ago when the river was close to 8 m above its present bed. Better cross-method checks on dating would eliminate some uncertainties, but the apparent similarities suggest a pattern of precursor events initiated by a period of base level drop extending for several kilometres across the structure, presumably in response to general uplift. Over time, deformation is concentrated close to the fault zone causing tilting of degradation terraces, and demonstrably in the Waipara case at least, coseismic rupture is preceded by marked acceleration of the downcutting rate. Overall base level drop is an order of magnitude greater than the throw on the eventual fault scarp. The Ostler Fault (Van Dissen et al., 1993) demonstrates that current deformation is taking place on similar thrust–fault driven folding in the Southern Alps. Regular re-levelling since 1966 has shown uplift rates of 1.0–1.5 mm/year at the crest of a 1–2 km half wave length anticline, but this case also illustrates the general problem of interpreting the significance of rates derived from geophysical monitoring relative to the long term seismic cycle. If the geomorphic signals described can be shown to hold for other examples, then criteria for targeting faults approaching the end of the seismic cycle in some tectonic settings may be possible.

Artifacts in helium atom surface scattering time-of-flight spectra

Artifacts have long been reported in the scattering of helium atoms from surfaces, particularly in the time-of-flight spectra used to study lattice dynamics. They are caused by elastic scattering of atoms in the low-intensity tails of the incident helium beam wave-vector distribution, which simulate inelastic scattering events. These ``deceptons'' have only been observed near the Bragg diffraction peaks. In this paper, modulation of the coherent elastic helium-atom signal, due to interference effects caused by surface scattering from multiple terraces and possibly other surface defects, is shown to give rise to additional artifacts in helium-atom time-of-flight spectra. Experiments on rutile ${\mathrm{TiO}}_{2}(110)$ illustrating the occurrence of these modulated deceptons (or m deceptons) in time-of-flight spectra of the specular reflected beam are reported and discussed. Additional discussion is presented to show that these modulations can also influence the intensities of the previously described deceptons around the Bragg diffraction peaks.

Novel Surface Structure of Microporous Faujasitic-like Zincophosphate Crystals Grown via Reverse Micelles

The surface morphologies of microporous zincophosphate crystals obtained by the conventional hydrothermal synthesis method and the reverse micelle method are compared. The particular zincophosphate under examination is of faujasite topology and is referred to as ZnPO-X (analogy to zeolite X). The crystal growth process is about an order of magnitude slower in the reverse micelle method, as compared to the hydrothermal method. The topologies of crystals prepared by both methods are similar and of octahedral shape, as expected for faujasitic structure. However, the surface of the hydrothermal crystals was found to have multiple layers and terraces, whereas the crystals obtained from the reverse micelle method were atomically smooth, except for a few triangular terraces/indentations. On the basis of the literature of microporous materials, the terraces are expected and arise because nucleation dynamics on the crystal surfaces is comparable to growth of terraces along the crystal surfaces. We propose that the striking surface structural difference of the reverse micelle grown crystals arises because the water layer surrounding the crystal lowers the supersaturation of the nutrient species and primarily serves as a reservoir of growth units.

Middle–late Holocene river terraces in the Erhjen River Basin, southwestern Taiwan—implications of river response to climate change and active tectonic uplift

We reconstruct the Holocene river history of the Erhjen River (area: 140 km 2) by correlating river terraces aided by 28 radiocarbon dates. Multiple terraces developed in the lower Erhjen River since the middle Holocene; they converge downstream to the Coastal Plain. The rates of channel incision into bedrock calculated from these terraces at Yuehshihchieh are 7–8 mm/year during ca. 5.7–2.5 ka, 5 cm/year during 1.5–1.3 ka, and 1 cm/year since 1 ka; the last is close to the average incision rate since middle Holocene. Meanwhile, only a single but wide middle–late Holocene paleo-floodplain was developed in the upper Erhjen River; it was completely abandoned only after 0.8 ka, likely following an episode of base-level fall starting from the Coastal Plain. Based on the apparent downstream and upstream convergence of these dated terraces, we identify a doming structure or anticline within the basin, which results in a tilt rate of 10 −6 to 10 −7 per year in the lower Erhjen River valley. The major terraces here had different initial long profiles, which implies that a critical (graded) long profile may not be a prerequisite for formation of a wide erosional terrace surface. Instead, we propose that these terraces were initiated by a series of catastrophic rainfall events, probably climatic-related, which brought a large amount of bedload from hillslopes to prevent the channel from incising when valley widening was facilitated by high-discharge runoff. We find that not only terrace-surface formation but also channel incision can be strongly controlled by climatic-driven discharge and bedload conditions, as suggested by the contrast of bedrock incision rates we observe at Yuehshihchieh. Apparently, the climate and its effects on the landscape cannot be regarded as constant during the Holocene even in a humid tropical area like Taiwan. However, such a fluctuation of climate could only be recorded in a setting where rivers have a high tendency to incise so that multiple terraces can be created. The lower Erhjen River that is characterized by active tectonic tilting is an example of this setting.

Is magmatic underplating the cause of post-rift uplift and erosion within the Cabora Bassa Basin, Zambezi Rift, Zimbabwe?

The Cabora Bassa Basin in northern Zimbabwe is an Upper Paleozoic karoo basin trending almost east-west. It has clearly recognisable gravity and magnetic signatures from which its dimensions are estimated to be approximately 150 km long and at least 62 km wide. Its southern boundary is marked by a north dipping, listric, master fault of possibly a ramp-flat-ramp geometry. Within the basin there is erosional truncation of over 2 km of sediment at the top of the stratigraphy and an absence of a post-rift thermal subsidence phase. Modern and major river channels are characteristically narrow, deep and without considerable amounts of silt on the river beds, whilst their valley sides are marked by multiple terraces. These ongoing erosional processes are evidence for sustained and possibly episodic uplift of the basin since the end of rifting in the Late Cretaceous/Early Tertiary. An evaluation of possible uplift mechanisms for the basin and its surroundings lends support to lithospheric thickening as the most likely mechanism. Compression and magmatic underplating and/or intrusion are two common ways of thickening the lithosphere. The absence of major compressional structures within the basin suggests that magmatic underplating and intrusion may have played a major role in lithospheric thickening. Major element data for the mantle-derived Jerama basalts indicate substantial hidden cumulates, which possibly thickened the lithospheric column. Modelling of gravity data, constrained by both seismic reflection results, and the densities of the surface rocks, show that the crustal thickness beneath the basin is in the range 19–23 km. The stretching factors from seismic and gravity models range from 1.6 to 1.9. There is up to 5 km difference between the expected and modelled crustal thicknesses beneath the basin, which could be explained by magmatic underplating.

Laboratory experiment and digital simulation of multiple fill-cut terrace formation

The formation mechanism of multiple erosional terraces which develop in the dissection process of sedimentary valley fills was investigated by laboratory experiments and computer simulations. Sequences of unpaired terraces were produced on experimental fan-like deposits under conditions of constant water discharge, no base-level change, and no sediment supply. The terraces developed as a result of the repetition of lateral shifting and stillstand of the stream channel at each cross-section during continuous downcutting. This mode of channel migration was caused by meander growth during which amplitude and wavelength increased with time. The terrace formation process was well-reproduced by computer simulations using a meander model having a similar wave mode.

Morphology and orientational disorder of C70 single crystals

C70 single crystals, free from solvent contamination, were grown via vapor phase transport technique. The (0001) face of the C70 crystal was imaged with Atomic Force Microscopy (AFM) under ambient atmosphere. Low-resolution images of a freshly prepared crystal revealed well-ordered faceted regions with multiple terraces extending over a region of several hundred square nanometers. The terraced structure in the images indicates that the crystals formed as a layer growth. In the high-resolution images, C70 molecules were resolved in a hexagonal close packed (hcp) structure with an average center-to-center distance of 10.5±0.5 A. After one month's exposure to the ambient atmosphere, the molecules rearranged into a mixed structure consisting of hcp and face centered cubic (fcc) regions.

Scanning Tunneling Microscopy of Carbon Blacks

Abstract Three kinds of carbon black, HAF (high abrasion furnace, N330), MT (medium thermal, N990), and graphitized MT were observed with the scanning tunneling microscope (STM), the transmission electron microscope (TEM), and the scanning electron microscope (SEM) All the STM images are formed from measurements of the x, t, and z position of points on the surface of the particle. The STM images of carbon blacks were compared to transmission electron microscope (TEM) photographs. Pitted and stepped bumps were observed on the surface of HAF carbon black. The surface of MT carbon black was more rough and disorganized At the atomic scale, ordered structure was found on the surface of HAF carbon-black particles Graphitized MT carbon-black particles were faceted polyhedra. Some facets were smooth while others had multiple terraces. The surface of graphitized MT carbon black was so well ordered that a lattice of carbon atoms similar to HOPG (highly ordered pyrolytic graphite) was observed on the smooth facets.

Soil and geomorphic evolution within the rolling red plains using pleistocene volcanic ash deposits

Pleistocene volcanic ash deposits are found within alluvium from the Arkansas river south to the Brazos river. This drainage area includes tributaries originating in the High Plains, the Raton volcanic field and the Rocky Mountain Front Range within the states of Colorado, New Mexico, Kansas, Texas, and Oklahoma. Thirteen ash deposits are dated from within the High Plains of Kansas and Texas eastward into central Oklahoma to understand the geomorphic history and improve soil and geologic mapping. Within the study area unsolidated Tertiary and Quaternary sediments deposited in a west to east direction overlie Triassic, Permian, and Pennsylvanian bedrock. Volcanic ash deposits are predominantly Early to Middle Pleistocene age. Volcanic ash deposits were dated by the fission track method on shards. The ash deposits are contained within four land resource regions, the Southern and Central High Plains, the High Plains Breaks, the Rolling Red Plains, and the Reddish Prairies. Extensive Middle Pleistocene constructional stream terrace surfaces occur within the Rolling Red Plains. Multiple stream terrace surfaces were recognized across the study area with the highest level being dated Early Pleistocene to Pliocene and the lowest bordering the Holocene floodplains. Topographic cross-sections (100 km long at 1:24,000 scale) transecting dated ash deposits and perpendicular to major river systems were used to distinguish terrace levels. Constructional terrace surfaces dated by ash deposits range from 21 to 100 m above and 1 to 16 km distance from present river channels. Soil orders formed in Quaternary alluvium are Entisols, Inceptisols, Mollisols, Alfisols and Vertisols. Ustic and udic soil moisture regimes and a thermic (15 to 22°C mean annual temperature) soil temperature regime dominate the study area. The same soil series is often mapped on terrace surfaces spanning Early to Middle Pleistocene age because current classification does not recognize differences in deeply weathered soils (greater than 2 m) and lacks recognition of loess. Soil great groups found on Early and Middle Pleistocene surfaces were Paleustolls and Argiustolls.