@phdthesis{Munack2014,
  author    = {Munack, Henry},
  title     = {From phantom blocks to denudational noise},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-72629},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xvii, 172},
  year      = {2014},
  abstract  = {Knowing the rates and mechanisms of geomorphic process that shape the Earth's surface is crucial to understand landscape evolution. Modern methods for estimating denudation rates enable us to quantitatively express and compare processes of landscape downwearing that can be traced through time and space—from the seemingly intact, though intensely shattered, phantom blocks of the catastrophically fragmented basal facies of giant rockslides up to denudational noise in orogen-wide data sets averaging over several millennia. This great variety of spatiotemporal scales of denudation rates is both boon and bane of geomorphic process rates. Indeed, processes of landscape downwearing can be traced far back in time, helping us to understand the Earth's evolution. Yet, this benefit may turn into a drawback due to scaling issues if these rates are to be compared across different observation timescales. This thesis investigates the mechanisms, patterns and rates of landscape downwearing across the Himalaya-Tibet orogen. Accounting for the spatiotemporal variability of denudation processes, this thesis addresses landscape downwearing on three distinctly different spatial scales, starting off at the local scale of individual hillslopes where considerable amounts of debris are generated from rock instantaneously: Rocksliding in active mountains is a major impetus of landscape downwearing. Study I provides a systematic overview of the internal sedimentology of giant rockslide deposits and thus meets the challenge of distinguishing them from macroscopically and microscopically similar glacial deposits, tectonic fault-zone breccias, and impact breccias. This distinction is important to avoid erroneous or misleading deduction of paleoclimatic or tectonic implications. -> Grain size analysis shows that rockslide-derived micro-breccia closely resemble those from meteorite impact or tectonic faults. -> Frictionite may occur more frequently that previously assumed. -> M{\"o}ssbauer-spectroscopy derived results indicate basal rock melting in the absence of water, involving short-term temperatures of >1500°C. Zooming out, Study II tracks the fate of these sediments, using the example of the upper Indus River, NW India. There we use river sand samples from the Indus and its tributaries to estimate basin-averaged denudation rates along a ~320-km reach across the Tibetan Plateau margin, to answer the question whether incision into the western Tibetan Plateau margin is currently active or not. -> We find an about one-order-of-magnitude upstream decay—from 110 to 10 mm kyr^-1—of cosmogenic Be-10-derived basin-wide denudation rates across the morphological knickpoint that marks the transition from the Transhimalayan ranges to the Tibetan Plateau. This trend is corroborated by independent bulk petrographic and heavy mineral analysis of the same samples. -> From the observation that tributary-derived basin-wide denudation rates do not increase markedly until ~150-200 km downstream of the topographic plateau margin we conclude that incision into the Tibetan Plateau is inactive. -> Comparing our postglacial Be-10-derived denudation rates to long-term (>10^6 yr) estimates from low-temperature thermochronometry, ranging from 100 to 750 mm kyr^-1, points to an order- of-magnitude decay of rates of landscape downwearing towards present. We infer that denudation rates must have been higher in the Quaternary, probably promoted by the interplay of glacial and interglacial stages. Our investigation of regional denudation patterns in the upper Indus finally is an integral part of Study III that synthesizes denudation of the Himalaya-Tibet orogen. In order to identify general and time-invariant predictors for Be-10-derived denudation rates we analyze tectonic, climatic and topographic metrics from an inventory of 297 drainage basins from various parts of the orogen. Aiming to get insight to the full response distributions of denudation rate to tectonic, climatic and topographic candidate predictors, we apply quantile regression instead of ordinary least squares regression, which has been standard analysis tool in previous studies that looked for denudation rate predictors. -> We use principal component analysis to reduce our set of 26 candidate predictors, ending up with just three out of these: Aridity Index, topographic steepness index, and precipitation of the coldest quarter of the year. -> Topographic steepness index proves to perform best during additive quantile regression. Our consequent prediction of denudation rates on the basin scale involves prediction errors that remain between 5 and 10 mm kyr^-1. -> We conclude that while topographic metrics such as river-channel steepness and slope gradient—being representative on timescales that our cosmogenic Be-10-derived denudation rates integrate over—generally appear to be more suited as predictors than climatic and tectonic metrics based on decadal records.},
  language  = {en}
}