No description available.

Earth’s climate can exist in many stable states that are vastly different from the modern climate state. Understanding modern and future climate requires a thorough understanding of the full range of possible climate states and the processes that trigger transitions between states. Quantitative reconstructions of past climate variables provide constrains on the magnitude, mechanisms and feedbacks involved in producing stable climate states. As such, they provide insights into past climate states unobservable today. This thesis focuses on quantifying three metrics of past climate systems: (a) quantitative rainfall amount, which provides means for assessing how the spatial distribution of rainfall changed in the past, (b) the isotopic composition of past rainwater (δP ), which provides means for understand- ing how atmospheric circulation changed in the past, and (c) relative humidity, which provides estimates of evaporative processes and hydrospheric fluxes. The regions studied are in the two far reaches of the Asian continent. In eastern Asia, changes in rainfall amount and δP over the past 125 ka were studied using geomorphological evidence from a closed basin lake in Inner Mongolia, China and compound-specific δDwax and δ13Cwax from organic molecules in lake sediments. In western Asia, the research focused on processes that govern modern δP and modern δDwax and δ13Cwax in soils. In addition the hydrological regime of the Eastern Mediterranean and the Levant during the Last Glacial Maximum were studied using evidence from speleothem δ18Oc and foraminifera δ18O. These records provide empirical and quantitative information about rainfall amount, δP and relative humidity at singular locations, and as such provide the building blocks for producing coherent large-scale reconstruction of the migration of rain-belts in the past.

Rivers sourced in the Himalayan mountains support more than 10% of the global population, where the majority of these people live downstream of the mountain front on the alluvial Indo-Gangetic Plain. Many of these rivers however, are also the source of devastating floods. The tendency of these rivers to flood is directly related to their large-scale morphology. In general, rivers that drain the east Indo-Gangetic Plain have channels that are perched at a higher elevation relative to their floodplain, leading to more frequent channel avulsion and flooding. In contrast, those further west have channels that are incised into the floodplain and are historically less prone to flooding. Understanding the controls on these contrasting river forms is fundamental to determining the sensitivity of these systems to projected climate change and the growing water resource demands across the Plain. This thesis examines controls on river morphology across the central portion of the Indo-Gangetic Plain drained by the Ganga River (the Ganga Plain). Specifically, the relative roles of basin subsidence, sediment grain size and sediment flux have been explored in the context of large-scale alluvial river morphology over a range of timescales. Furthermore, this thesis has developed and tested techniques that can be utilised to help quantify these variables at catchment-wide scales. This analysis has been achieved through combining new sediment grain size, pebble lithology and cosmogenic radionuclide data with quantitative topographic and sedimentological analysis of the Ganga Plain. In the first part of this thesis, I examine the contrast in channel morphology between the east and west Ganga Plain. Using topographic analysis, basin subsidence rates and sediment grain size data, I propose that higher subsidence rates in the east Ganga Plain are responsible for a deeper basin, with perched low-gradient rivers systems that are relatively insensitive to climatically driven changes in base-level. In contrast, lower basin subsidence rates in the west are associated with a shallower basin with entrenched river systems that are capable of recording climatically induced lowering of river base-level during the Holocene. Through an analysis of fan geometry, sediment grain size and lithology, I then demonstrate that gravel flux from rivers draining the central Himalaya with contributing areas spanning three orders of magnitude is approximately constant. I show that the abrasion of gravel during fluvial transport can explain this observation, where gravel sourced from more than 100 km upstream is converted into sand by the time it reaches the Plain. I attribute the over-representation of quartzitic pebble lithologies in the Plain (relative to the proportion of the upstream catchment area likely to contribute quartzite pebbles) to the selective abrasion of weaker lithologies during transport in the mountainous catchment. This process places an upper limit on the amount of coarse sediment exported into the Indo-Gangetic Plain. Finally, I consider the use of cosmogenic 10Be derived erosion rates as a method to generate sediment flux estimates over timescales of 102-104 years. Cosmogenic radionuclide samples from modern channel and independently dated Holocene terrace and flood deposits in the Ganga River reveal a degree of natural variability in 10Be concentrations close to the mountain front. This is explored using a numerical analysis of processes which are likely to drive variability in catchment-averaged 10Be concentrations. I propose that the observed variability is explained by the nature of stochastic inputs of sediment (e.g. the dominant erosional process, surface production rates, depth of landsliding, degree of mixing), and secondly, by the evacuation timescales of individual sediment deposits which buffers their impact on catchment-averaged concentrations. In landscapes dominated by high topographic relief, spatially variable climate and multiple geomorphic process domains, the use of 10Be concentrations to generate sediment flux estimates may not be truly representative. The analysis presented here suggests that comparable mean catchment-averaged 10Be concentrations can be derived through different erosional processes. For a given 10Be concentration, volumetric sediment flux estimates may therefore differ.

No description available.

Here I develop a cross-correlation approach to estimating heights of shoreline features, and apply the new method to paleo-shorelines of Pleistocene Lake Bonneville. I calculate 1st-derivative (slope) and 2nd-derivative (curvature) profiles from Digital Elevation Model (DEM) or Global Positioning System Real-Time Kinematic (GPS-RTK) measurements of elevation. I then cross-correlate pairs of profiles that have been shifted by various "lags," or shifts in elevation. The correlation coefficient (a normalized dot-product measure of similarity) is calculated as a function of lag within small (~40 m) windows centered at various elevations. The elevation and lag with the greatest correlation coefficient indicates the shoreline elevation at the reference profile and the change in shoreline height for the profile pair. I evaluate several different algorithms for deriving slope and curvature by examining closure of elevation lags across profile triples. I then model isostatic response to Lake Bonneville loading and unloading. I first model lakeshore uplift response to lake load removal assuming an elastic layer over an inviscid half-space. I obtain a best-fit comparison of predicted to observed shoreline heights for the Bonneville level with an elastic layer thickness, Te, of 25±2 km (at 95% confidence) when using only previously published shoreline elevation estimates. The best-fit for the Bonneville level when using these estimates plus 44 new estimates suggests a Te of 26±2 km. The best-fit model for the Provo level suggests Te of 17±3 km. For the Gilbert level, the response is insensitive to the assumed Te. I next model isostatic response to Bonneville loading and unloading assuming an elastic layer over a viscoelastic halfspace. This approach assumes constant parameters for the entire loading history, and yields a best-fit model with Te =70±5 km and viscosity ç=~2x1018 Pa s with 95% confidence ranging from ~1x1018 to ~5x1019 Pa s when only the previously published data are used. With the newer data added, the best-fit model has Te =58±2 km and ç ranging from ~1x1018 to ~1x1019 Pa s with 95% confidence. The 12-15 m weighted root-mean-square misfit to the best-fitting model is dominated by tectonic signals related to Basin-and-Range tectonics particularly seismic offsets of the Wasatch fault, and closely mimics the geological timescale pattern of basin-subsidence and range-uplift.

No description available.

Thesis (M.S.)--Ohio State University, 2006. / Includes bibliographical references (leaves 76-83). Available online via OhioLINK's ETD Center.

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 76-82). Also available on the World Wide Web.

Thesis (M.A.Geo.)--Texas State University--San Marcos, 2009. / Vita. Reproduction permission applies to print copy: Blanket permission granted per author to reproduce. Includes bibliographical references (leaves 44-47).

Σκοπός της εργασίας είναι η αναγνώριση και καταγραφή των φυσικογεωγραφικών, γεωλογικών και γεωμορφικών στοιχείων της περιοχής μελέτης (Πηνειού ποταμού). Για το αυτό έγιναν, παρατηρήσεις και ερμηνείες από τοπογραφικούς χάρτες της ΓΥΣ κλίμακας 1:50.000, από το Google Earth και ολοκληρώθηκαν με την εργασία πεδίου. / --