No description available.

Tübingen, Univ., Diss., 2008.

No description available.

Abstract Resent studies have demonstrated that rivers in the western Pacific islands can be very important in affecting global riverine material flux. The Kaoping River is a typical tropical, island-type river with the largest drainage area in Southern Taiwan. Material outputs from the Kaoping River are expected to play a major role in affecting the local coastal environment. Therefore, this study aims at understanding processes and mechanisms for generation, transport and transformation of terrigenous materials in the Kaoping drainage basin. The temporal and spatial distributions of hydrochemical parameters, total suspended matter (TSM), major ions, nutrients, and particulate and dissolved species of C, N and P (DOC, DIN, DIP, DON, DOP, POC and PON) were measured in the Kaoping River from August 1999 to August 2000. The collected data are used to elucidate sources and the influence of external forcing on fluxes of sediment, carbon and nutrients form the Kaoping drainage basin. Based on the fluxes of TSM and total dissolved solid (TDS) observed in the Kaoping River, the total, physical and chemical weathering rates were estimated about 7,368, 5985 and 1,383 g/m2/yr, respectively. The significant correlation between TSM-load and water discharge suggested that the sediment flux was primarily controlled by the runoff in the drainage basin. The generation of total carbon (DIC¡ÏDOC¡ÏPIC¡ÏPOC) in the Kaoping drainage basin was about 191g C/m2/yr. The yields of DIC, DOC, PIC and POC were 110 (60%), 2.27 (1.7%), 35.6 (17%) and 42.6 (21%) g C/m2/yr, respectively. These values of carbon yield from the Kaoping drainage basin were very high in comparison with ones obtained from the Lanyang River and the other major rivers in the world. The annual fluxes of riverine DIC, DOC, PIC, POC and TC from the Kaoping River were about 34.5, 0.705, 11.0, 13.2 and 63.2 x 1010 g C, respectively. Regarding the nutrient results, the riverine fluxes of dissolved and particulate nitrogen were 2.298 x 109 mole/yr and 1.55 x 108 mole/yr, respectively. By taking out the natural input of total dissolved nitrogen, anthropogenic input of total dissolved nitrogen in the Kaoping River was about 5-6 x 104 kg/day that is similar to the one (56,779 kg/day) reported by the EPA. The fluxes of total dissolved phosphate and silicate were 3.378 x 107 and 1.285 x 109 mole/yr, respectively. The high riverine flux of silicate also reflects the high weathering rate in the Kaoping drainage basin. The flux of anthropogenic phosphate from the Kaoping River was about 4 - 8 x 103 kg/day which was similar to that estimated from the Tanshui River. Taking the nutrient content in the Kaoping upstream as background level, the natural fluxes of total nitrogen and phosphate in the Kaoping River were estimated to be 8 x 103 and 4 x 103 kg/day which were equivalent to 16% and 57% of the anthropogenic inputs, respectively. Anthropogenic input appears to be the major source of riverine nutrients in the Kaoping River. Overall, human activities play a major role on affecting the generation, transport and transformation of terrigenous materials in the Kaoping drainage basin. This study also confirms that rivers in Taiwan may be very important in affecting the local and/or the global fluxes of terrestrial materials.

No description available.

Located beyond the southern limit of glaciation in Britain, the upland granitic terrain of Dartmoor, south-west England, has been exposed to long intervals of intense periglacial activity during the Pleistocene. This region has been significant in debates about appropriate models of long-term landscape change, most notably two-phase versus single-phase models of landform evolution, and the development of tors. However, given the previous lack of quantitative techniques capable of constraining denudation and specific process rates, and thereby testing developmental models for these features, there remains much uncertainty in the interpretation of the classic landforms of the region. This study measures concentrations of the cosmogenic nuclide 10Be produced in-situ in quartz within the upper few metres of the Earth surface. These reflect the history of near-surface exposure to cosmic radiation of sampled material, and allow for the interpretation of exposure age and/or erosion rates of the land surface. This research utilises these cosmogenic nuclide values to evaluate geomorphological processes and investigate key aspects of landform development. These include the formation of tors in non-glaciated regions, the development of regolith and boulderfields under periglacial conditions, and the derivation of catchment-averaged denudation rates. This study provides the first quantitative measurement of erosion on tor surfaces in Dartmoor, with typical rates of 14-45 mm ka-1. These are relatively high and comparable to other components of the landscape. In addition, there is no clear relationship of cosmogenic nuclide concentration to tor dimensions. It is shown that the tors are dynamic landforms and simple, two-stage development is an inappropriate model. Catchment-averaged denudation rates are derived and these long-term rates of 20-94 mm ka-1 are significantly higher than modern, short-term values. Finally, downslope transport in a palaeo-periglacial blockslope is investigated using 10Be concentrations. This variety of landforms and scale of investigation facilitates an integrated approach to the understanding of catchment-scale erosional dynamics. In addition, the complex nature of landform development that is evident in the area provides challenges to the application of in-situ cosmogenic nuclides and highlights both the potential and limitations of the technique.

Understanding how mountain landscapes respond to variations in tectonic forcing over a range of temporal scales in active mountain belts remains as a prominent challenge in tectonic and geomorphological studies. Although a number of empirical and numerical studies have examined this problem, many of them were complicated by issues of scale and climatic variability. More specifically, the relative efficiencies of fluvial and glacial erosion, which are presumably controlled by climate, are difficult to unravel. The Teton Range in Wyoming, which results from motion on the crustal-scale Teton fault, is an ideal natural laboratory for addressing this challenge as the tectonic uplift boundary condition and the variation of uplift along strike is well-documented by previous studies and due to its relatively small size, climate can be reasonably expected to vary consistently along strike. Here, we present the results from a study that examines how the Teton landscape responds across the longest (106-7 yrs) and shortest (102-4 yrs) temporal scales. Long-term canyon incision rates determined from apatite (U-Th)/He (AHe) analysis of major drainages are highest (0.24 mm yr-1) where measured uplift rates and duration are highest (near Mount Moran), leading us to propose that tectonic forcing operates as the first order control on long-term Teton erosion. Short-term denudation rates, which are derived by determining sediment volumes in Moran Bay that are deposited in catchments generated during the most recent glacial interval (Pinedale, ~15.5 ka), are 0.00303 – 0.4672 mm yr-1. We compare these rates to previous work, which found that high rock fall rates (1.13-1.14 mm yr-1) deposit large talus volumes in Avalanche and Moran Canyons. Despite their magnitude, such high rates of mass wasting are not sustained over long periods of time, as measured lake sediment volumes (0.007 km3) are. We conclude that the Tetons are transport limited during the interglacial and large volumes of canyon sediment generated during this time cannot be moved absent the advance of valley glaciers. That is, fluvial systems in small mountain systems are substantially less effective than glaciers in denuding mountain topography.

The relative importance of infrequent, episodic geomorphic events (e.g. floods, landslides, debris flows, earthquakes, tsunamis, etc.) in the evolution of the landscape has been a long-discussed question in the geomorphology community. These events are large in magnitude, but low in frequency, posing the complex question of how effective these events are at shaping the landscape. Unfortunately, the frequencies of these events are so low that it is extremely difficult to observe these events over human time scales. Also, the dangerous nature of these events makes them extremely difficult to observe and measure. However, the last few decades have brought new technology and techniques that provide a way to measure and calculate the magnitudes of these events more accurately and completely. In the present study, we use Next-Generation-Radar (NEXRAD) precipitation products, LiDAR tools, and multiple denudation-rate techniques to approach the magnitude and frequency of episodic events in different ways. Using NEXRAD precipitation products in conjunction with flow-routing algorithms, we were able to improve upon the traditional flood-envelope curves used to estimate the largest possible flood for a given basin area within a region. Improvements included adding frequency and uncertainty information to curves for the Upper and Lower Colorado River Basin, which in turn makes these curves more informative for flood hazard and policy applications. This study allowed us to improve upon a known flood-analysis method for identifying the distribution of the maximum floods with basin area. Both airborne and terrestrial LiDAR methods were used to measure the magnitude and time scale of the post-wildfire erosional response in two watersheds after the Las Conchas fire of 2011 in the Valles Caldera, NM. We found that sediment yield (measured by differencing LiDAR-derived DEMs) decreased exponentially with time in one watershed, while sediment yield in the other watershed decreased in a more complex way with time. Both watersheds had a recovery time (i.e. time interval over which sediment yields recovered to pre-wildfire levels) of one year. LiDAR was also used to understand the complex response of, and the processes on, the piedmonts adjacent to the watersheds. Overall, LiDAR proved to be extremely useful in measuring the magnitude and time scale of post-wildfire geomorphic response and observing the piedmont dynamics associated with elevated sediment yield. To understand the effects of wildfire on the long-term evolution of the landscape, techniques ranging from the relatively simple, traditional techniques (i.e. suspended-sediment-load sampling and paleosurface and modern surface differencing) to more complex and new techniques (i.e. ¹⁰Be and LiDAR) were used to measure the volumes and rates of denudation over multiple time scales in the Valles Caldera, NM. Long-term denudation rates were higher than short-term, non-wildfire-affected denudation rates, but lower than short-term, wildfire-affected denudation rates. Wildfire-affected denudation rates occurring at previously predicted frequencies (occurring<3% of the time interval) were found to account for the majority of long-term denudation, attesting to the importance of these episodic and extreme events in the evolution of the landscape.

The magnitude of global sediment flux from streams to the oceans over the last 5 Ma is poorly quantified, yet important for predicting future fluxes and deciphering the relative control of tectonic uplift, climate change, vegetation, and related feedback mechanisms on landscape evolution. Despite numerous proxy studies on global sediment delivery to the oceans, it remains uncertain whether bulk sedimentation increased, decreased, or remained approximately constant across one of the most significant global climate changes: the Plio-Pleistocene transition. New developments and strategies in the application of cosmic-ray-produced isotopes, in part developed by this thesis, provide records of pre-historic denudation of confined fluvial catchments in Texas and Yukon. Non-glaciated, tectonically passive regions were targeted in contrast to other studies on modern sedimentation rates in order to isolate the climate influence from glacial and tectonic controls. The results suggest that average catchment temperature, and surficial processes and other factors such as vegetation cover associated with temperature, are the primary controls on the variation in landscape denudation in regions lacking tectonics and direct glacial cover. Specifically, warmer temperatures yield higher denudation rates, both at the scale of glacial-interglacial climate change and over the Plio-Pleistocene transition. The implication is that stream sediment flux to the ocean from tropical and temperate regions was higher during the Pliocene than in the Quaternary. However, this may have been balanced by an increase in sediment flux from regions covered by warm-based glaciers during glacial periods, or by increased temporary continental storage during interglacial periods.

No description available.