TY - JOUR A1 - Hoffmann, Bernd A1 - Feakins, Sarah J. A1 - Bookhagen, Bodo A1 - Olen, Stephanie M. A1 - Adhikari, Danda P. A1 - Mainali, Janardan A1 - Sachse, Dirk T1 - Climatic and geomorphic drivers of plant organic matter transport in the Arun River, E Nepal JF - Earth & planetary science letters KW - plant wax biomarker KW - leaf wax delta D KW - carbon cycle KW - remote sensing KW - erosion Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.07.008 SN - 0012-821X SN - 1385-013X VL - 452 SP - 104 EP - 114 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Meese, Bernd A1 - Bookhagen, Bodo A1 - Olen, Stephanie M. A1 - Barthold, Frauke Katrin A1 - Sachse, Dirk T1 - The effect of Indian Summer Monsoon rainfall on surface water delta D values in the central Himalaya JF - Hydrological processes N2 - Stable isotope proxy records, such as speleothems, plant-wax biomarker records, and ice cores, are suitable archives for the reconstruction of regional palaeohydrologic conditions. But the interpretation of these records in the tropics, especially in the Indian Summer Monsoon (ISM) domain, is difficult due to differing moisture and water sources: precipitation from the ISM and Winter Westerlies, as well as snow- and glacial meltwater. In this study, we use interannual differences in ISM strength (2011-2012) to understand the stable isotopic composition of surface water in the Arun River catchment in eastern Nepal. We sampled main stem and tributary water (n = 204) for stable hydrogen and oxygen isotope analysis in the postmonsoon phase of two subsequent years with significantly distinct ISM intensities. In addition to the 2011/2012 sampling campaigns, we collected a 12-month time series of main stem waters (2012/2013, n = 105) in order to better quantify seasonal effects on the variability of surface water delta O-18/delta D. Furthermore, remotely sensed satellite data of rainfall, snow cover, glacial coverage, and evapotranspiration was evaluated. The comparison of datasets from both years revealed that surface waters of the main stem Arun and its tributaries were D-enriched by similar to 15 parts per thousand when ISM rainfall decreased by 20%. This strong response emphasizes the importance of the ISM for surface water run-off in the central Himalaya. However, further spatio-temporal analysis of remote sensing data in combination with stream water d-excess revealed that most high-altitude tributaries and the Tibetan part of the Arun receive high portions of glacial melt water and likely Winter Westerly Disturbances precipitation. We make the following two implications: First, palaeohydrologic archives found in high-altitude tributaries and on the southern Tibetan Plateau record a mixture of past precipitation delta D values and variable amounts of additional water sources. Second, surface water isotope ratios of lower elevated tributaries strongly reflect the isotopic composition of ISM rainfall implying a suitable region for the analysis of potential delta D value proxy records. KW - Himalaya KW - palaeoclimate records KW - snow melt KW - stream water KW - water isotopes Y1 - 2018 U6 - https://doi.org/10.1002/hyp.13281 SN - 0885-6087 SN - 1099-1085 VL - 32 IS - 24 SP - 3662 EP - 3674 PB - Wiley CY - Hoboken ER - TY - THES A1 - Olen, Stephanie M. T1 - Understanding Himalayan denudation at the catchment and orogen scale T1 - Verständnis von Denudation auf regionalem und orogenem Maßstab im Himalaja N2 - Understanding the rates and processes of denudation is key to unraveling the dynamic processes that shape active orogens. This includes decoding the roles of tectonic and climate-driven processes in the long-term evolution of high- mountain landscapes in regions with pronounced tectonic activity and steep climatic and surface-process gradients. Well-constrained denudation rates can be used to address a wide range of geologic problems. In steady-state landscapes, denudation rates are argued to be proportional to tectonic or isostatic uplift rates and provide valuable insight into the tectonic regimes underlying surface denudation. The use of denudation rates based on terrestrial cosmogenic nuclide (TCN) such as 10Beryllium has become a widely-used method to quantify catchment-mean denudation rates. Because such measurements are averaged over timescales of 102 to 105 years, they are not as susceptible to stochastic changes as shorter-term denudation rate estimates (e.g., from suspended sediment measurements) and are therefore considered more reliable for a comparison to long-term processes that operate on geologic timescales. However, the impact of various climatic, biotic, and surface processes on 10Be concentrations and the resultant denudation rates remains unclear and is subject to ongoing discussion. In this thesis, I explore the interaction of climate, the biosphere, topography, and geology in forcing and modulating denudation rates on catchment to orogen scales. There are many processes in highly dynamic active orogens that may effect 10Be concentrations in modern river sands and therefore impact 10Be-derived denudation rates. The calculation of denudation rates from 10Be concentrations, however, requires a suite of simplifying assumptions that may not be valid or applicable in many orogens. I investigate how these processes affect 10Be concentrations in the Arun Valley of Eastern Nepal using 34 new 10Be measurements from the main stem Arun River and its tributaries. The Arun Valley is characterized by steep gradients in climate and topography, with elevations ranging from <100 m asl in the foreland basin to >8,000 asl in the high sectors to the north. This is coupled with a five-fold increase in mean annual rainfall across strike of the orogen. Denudation rates from tributary samples increase toward the core of the orogen, from <0.2 to >5 mm/yr from the Lesser to Higher Himalaya. Very high denudation rates (>2 mm/yr), however, are likely the result of 10Be TCN dilution by surface and climatic processes, such as large landsliding and glaciation, and thus may not be representative of long-term denudation rates. Mainstem Arun denudation rates increase downstream from ~0.2 mm/yr at the border with Tibet to 0.91 mm/yr at its outlet into the Sapt Kosi. However, the downstream 10Be concentrations may not be representative of the entire upstream catchment. Instead, I document evidence for downstream fining of grains from the Tibetan Plateau, resulting in an order-of-magnitude apparent decrease in the measured 10Be concentration. In the Arun Valley and across the Himalaya, topography, climate, and vegetation are strongly interrelated. The observed increase in denudation rates at the transition from the Lesser to Higher Himalaya corresponds to abrupt increases in elevation, hillslope gradient, and mean annual rainfall. Thus, across strike (N-S), it is difficult to decipher the potential impacts of climate and vegetation cover on denudation rates. To further evaluate these relationships I instead took advantage of an along-strike west-to-east increase of mean annual rainfall and vegetation density in the Himalaya. An analysis of 136 published 10Be denudation rates from along strike of the revealed that median denudation rates do not vary considerably along strike of the Himalaya, ~1500 km E-W. However, the range of denudation rates generally decreases from west to east, with more variable denudation rates in the northwestern regions of the orogen than in the eastern regions. This denudation rate variability decreases as vegetation density increases (R=- 0.90), and increases proportionately to the annual seasonality of vegetation (R=0.99). Moreover, rainfall and vegetation modulate the relationship between topographic steepness and denudation rates such that in the wet, densely vegetated regions of the Himalaya, topography responds more linearly to changes in denudation rates than in dry, sparsely vegetated regions, where the response of topographic steepness to denudation rates is highly nonlinear. Understanding the relationships between denudation rates, topography, and climate is also critical for interpreting sedimentary archives. However, there is a lack of understanding of how terrestrial organic matter is transported out of orogens and into sedimentary archives. Plant wax lipid biomarkers derived from terrestrial and marine sedimentary records are commonly used as paleo- hydrologic proxy to help elucidate these problems. I address the issue of how to interpret the biomarker record by using the plant wax isotopic composition of modern suspended and riverbank organic matter to identify and quantify organic matter source regions in the Arun Valley. Topographic and geomorphic analysis, provided by the 10Be catchment-mean denudation rates, reveals that a combination of topographic steepness (as a proxy for denudation) and vegetation density is required to capture organic matter sourcing in the Arun River. My studies highlight the importance of a rigorous and careful interpretation of denudation rates in tectonically active orogens that are furthermore characterized by strong climatic and biotic gradients. Unambiguous information about these issues is critical for correctly decoding and interpreting the possible tectonic and climatic forces that drive erosion and denudation, and the manifestation of the erosion products in sedimentary archives. N2 - Schlüssel im Verständnis der dynamischen Prozesse in aktiven Orogenen ist die Kenntnis der Abtragungsraten und -prozesse. Eine breite Auswahl geologischer Fragen können mit well-constrained Abtragungsraten erörtert werden. Sind Landschaften im Gleichgewicht so sind die Denudationsraten proportional zu den tektonischen und isostatischen Hebungsraten und geben somit wichtige Hinweise über die tektonischen Eigenschaften der Region. Eine weit verbreitete und etablierte Methode zur Bestimmung mittlerer Denudationsraten eines bestimmten Einzugsgebietes ist Beryllium-10, ein terrestrisches kosmogenes Nuklid (10Be TCN). 10Be TCN Messungen stellen durchschnittliche Abtragungsraten über einen Zeitraum von 10^2 – 10^5 Jahren dar und sind daher weniger verletzlich gegenüber stochastischen Änderungen wie Erosionsraten, die über einen kurzen Zeitraum ermittelt werden z.B. in Suspension. Sie sind daher zuverlässig einsetzbar um langfristige Prozesse zu vergleichen. Allerdings ist unklar welche Einfluss verschiedene klimatische, biologische oder erdoberflächen Prozesse auf die 10Be Konzentration ausüben und somit auch auf die resultierenden Abtragungsraten. In dieser Doktorarbeit, setze ich mich mit dem Zwischenspiel von Klima, Biosphäre, Topographie und Geologie auseinander und dem Einfluss, den sie auf Abtragungsraten ausüben sowohl auf regionalem wie auch auf orogenem Maßstab. In hoch dynamischen aktiven Gebirgen gibt es viele Prozesse, welche die 10Be Konzentration in heutigen Flusssanden beeinflussen und damit auch die, mittels 10Be berechneten, Abtragungsraten. Um diese Raten mittels 10Be Konzentrationen zu berechnen benötigen wir einige vereinfachende Annahmen, die möglicherweise in anderen Regionen keine Gültigkeit haben. Ich untersuche den Einfluss dieser Prozesse auf die 10Be Konzentration. Dazu haben wir im Arun Tal im Osten Nepals 34 neue 10Be Konzentrationen des Arun Flusses und seinen Zuflüssen untersucht. Charakteristisch für das Arun Tal sind die steilen Gradienten im Klima mit einem fünffachen Anstieg des mittleren jährlichen Regenfalls über das Orogens, und in der Topographie mit Höhen von weniger als 100 m über Meer im Vorlandbecken bis über 8000 m über Meer im Gebirge. Die Abtragungsraten der Proben der Zuflüsse nehmen gegen das Zentrum des Gebirges von weniger <0.2 zu mehr als >5 mm/yr zu d.h. ansteigend vom Lesser zum Higher Himalaya. Sehr hohe Denudationsraten (> 2mm/yr) können durch erdoberflächen und klimatische Prozesse verwässert werden z. B. grosse Erdrutsche und Vergletscherungen, und sind daher nicht unbedingt repräsentativ für langzeitliche Abtragungsraten. Im Arun nehmen die Raten des Hauptflusses flussabwärts von 0.2 mm/yr im Bereich der Grenze zu Tibet auf 0.91 mm/yr am Ausfluss in Sapt Kosi zu. Es ist möglich, dass diese 10Be Konzentrationen nicht das vollständige flussauswärtsliegende Einzugsgebiet repräsentieren. Stattdessen lege ich dar wie sich die Korngrösse ab dem tibetischen Plateau verfeinert und dazu führt, dass die 10Be Konzentrationen offenkundig im Bereich einer Grössenordnung abnehmen. Im Arun Tal und sowie über den ganzen Himalaja sind Topographie, Klima und Vegetation sehr stark miteinander verbunden. Das Ansteigen der Denudationsraten im Übergang vom Lesser zum Higher Himalaya stimmt mit dem abrupten Ansteigen der Höhe, des Hangneigungsgradienten und des mittleren jährlichen Regenfalles überein. Es ist schwierig die möglichen Einflüssen von Klima und der Vegetationsdichte auf die Abtragungsraten über das Orogen hinweg (N-S) zu entziffern. Stattdessen, nutzen wir den Vorteil der, von West nach Ost, parallel zum Himalaja verlaufenden, Zunahme des mittleren jährlichen Regenfalles und der Vegetationsdichte. Eine Analyse 136 publizierter 10Be TCN Abtragungsraten entlang des Gebirges, zeigt dass die im Streichen liegenden mittleren Denudationsraten (ca. 1500 km Ost-West) nicht deutlich variieren. Generell sinkt die Wertebereich der Denudationsraten vom Westen gegen Osten, wobei in den nordwestlichen Regionen des Himalajas variablere Abtragungsraten vorherrschen als in den östlichen Regionen. Diese Vielfalt in den Denudationsraten sinkt mit steigender Vegetationsdichte (R=-0.90) und steigt proportional zur (jährlichen) Saisonalität der Vegetation (R=0.99). Vielmehr noch wird das Verhältnis zwischen der topographischen Steilheit und den Abtragungsraten durch Regen und Vegetation beeinflusst z. B. in feuchten Gebieten mit starker Vegetation reagiert die Topographie linearer auf Wechsel in den Abtragungsraten als in trockenen, kaum bewachsenen Regionen, wo die Reaktion der topographischen Steilheit auf die Denudationsraten äusserst nicht-linear ist. Das Verständnis der Beziehung zwischen Erosion, Topographie und Klima ist auch entscheidend für die Interpretation von Sedimentarchiven. Unser Wissen über die Repräsentativität von terrestrisches organisches Material, abgelagert in z.B. Flussdeltas, für die Einzugsgebiete der entsprechenden Flüsse, ist nach wie vor nur vage. Dennoch sind Blattwachse höherer Landpflanzen, extrahiert aus terrestrischen und marinen Sedimenten, ein häufig verwendeter paläohydrologischer Proxy. Im Rahmen dieser Arbeit nutzen wir die Isotopenzusammensetzung von Pflanzenwachsen aus Suspensionsmaterial und aus Flusssedimenten als Herkunftsmarker und zur Quantifizierung des organischen Materials im Arun Tal. Die Analyse von Vegetationsdichte und Regenverteilung in Kombination mit Abtragungsraten des Einzugsgebietes, welche durch die mittleren 10Be-Erosionsraten gestützt werden, zeigen, dass das Vorhandensein dichter Vegetation ein zwar notwendiges, aber nicht hinreichendes Kriterium für hohen OM-Export ist. Vielmehr können wir zeigen, dass nur eine Kombination aus dichter Vegetationsdecke und Erosion zu hohem OM-Export führt. Für die Interpretation entspechender Archive bedeutet das, dass sie im Wesentlichen jene Bereiche des Einzugsgebietes repräsentieren, welche durch hohe Pflanzendichte und starke Erosion charakterisiert sind. Diese Studien belegen wie wichtig es ist die Abtragungsraten in aktiven Gebirgen umfassend zu verstehen. Für die Interpretation kann dieses Verständnis der möglichen tektonischen und klimatischen Gewalten, welche Erosion und Abtragung steuern, und auch das Verständnis der Sedimentarchive aus den Gebirgen stammend, entscheidend sein. KW - geology KW - geomorphology KW - Himalaya KW - Geologie KW - Geomorphologie KW - Himalaja Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-91423 ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo T1 - Mapping Damage-Affected Areas after Natural Hazard Events Using Sentinel-1 Coherence Time Series JF - remote sensing N2 - The emergence of the Sentinel-1A and 1B satellites now offers freely available and widely accessible Synthetic Aperture Radar (SAR) data. Near-global coverage and rapid repeat time (6–12 days) gives Sentinel-1 data the potential to be widely used for monitoring the Earth’s surface. Subtle land-cover and land surface changes can affect the phase and amplitude of the C-band SAR signal, and thus the coherence between two images collected before and after such changes. Analysis of SAR coherence therefore serves as a rapidly deployable and powerful tool to track both seasonal changes and rapid surface disturbances following natural disasters. An advantage of using Sentinel-1 C-band radar data is the ability to easily construct time series of coherence for a region of interest at low cost. In this paper, we propose a new method for Potentially Affected Area (PAA) detection following a natural hazard event. Based on the coherence time series, the proposed method (1) determines the natural variability of coherence within each pixel in the region of interest, accounting for factors such as seasonality and the inherent noise of variable surfaces; and (2) compares pixel-by-pixel syn-event coherence to temporal coherence distributions to determine where statistically significant coherence loss has occurred. The user can determine to what degree the syn-event coherence value (e.g., 1st, 5th percentile of pre-event distribution) constitutes a PAA, and integrate pertinent regional data, such as population density, to rank and prioritise PAAs. We apply the method to two case studies, Sarpol-e, Iran following the 2017 Iran-Iraq earthquake, and a landslide-prone region of NW Argentina, to demonstrate how rapid identification and interpretation of potentially affected areas can be performed shortly following a natural hazard event. KW - Sentinel-1 KW - natural hazards KW - rapid damage mapping KW - coherence KW - potentially affected areas (PAA) Y1 - 2018 U6 - https://doi.org/10.3390/rs10081272 SN - 2072-4292 VL - 10 IS - 8 SP - 1 EP - 19 PB - Molecular Diversity Preservation International (MDPI) CY - Basel ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo T1 - Applications of SAR interferometric coherence time series BT - satiotemporal dynamics of geomorphic transitions in the South-Central Andes JF - Journal of geophysical research : Earth surface N2 - Sediment transport domains in mountain landscapes are characterized by fundamentally different processes and rates depending on several factors, including geology, climate, and biota. Accurately identifying where transitions between transport domains occur is an important step to quantify the past, present, and future contribution of varying erosion and sedimentation processes and enhance our predictive capabilities. We propose a new methodology based on time series of synthetic aperture radar (SAR) interferometric coherence images to map sediment transport regimes across arid and semiarid landscapes. Using 4 years of Sentinel-1 data, we analyze sediment transport regimes for the south-central Andes in northwestern Argentina characterized by steep topographic and climatic gradients. We observe seasonally low coherence during the regional wet season, particularly on hillslopes and in alluvial channels. The spatial distribution of coherence is compared to drainage areas extracted from digital topography to identify two distinct transitions within watersheds: (a) a hillslope-to-fluvial and (b) a fluvial-to-alluvial transition. While transitions within a given basin can be well-constrained, the relative role of each sediment transport domain varies widely over the climatic and topographic gradients. In semiarid regions, we observe larger relative contributions from hillslopes compared to arid regions. Across regional gradients, the range of coherence within basins positively correlates to previously published millennial catchment-wide erosion rates and to topographic metrics used to indicate long-term uplift. Our study suggests that a dense time series of interferometric coherence can be used as a proxy for surface sediment movement and landscape stability in vegetation-free settings at event to decadal timescales. KW - Copernicus KW - SAR KW - critical infrastructure resilience KW - early warning KW - landslides Y1 - 2020 U6 - https://doi.org/10.1029/2019JF005141 SN - 2169-9003 SN - 2169-9011 VL - 125 IS - 3 PB - American Geophysical Union CY - Washington ER - TY - GEN A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo T1 - Mapping Damage-Affected Areas after Natural Hazard Events Using Sentinel-1 Coherence Time Series T2 - remote sensing N2 - The emergence of the Sentinel-1A and 1B satellites now offers freely available and widely accessible Synthetic Aperture Radar (SAR) data. Near-global coverage and rapid repeat time (6–12 days) gives Sentinel-1 data the potential to be widely used for monitoring the Earth’s surface. Subtle land-cover and land surface changes can affect the phase and amplitude of the C-band SAR signal, and thus the coherence between two images collected before and after such changes. Analysis of SAR coherence therefore serves as a rapidly deployable and powerful tool to track both seasonal changes and rapid surface disturbances following natural disasters. An advantage of using Sentinel-1 C-band radar data is the ability to easily construct time series of coherence for a region of interest at low cost. In this paper, we propose a new method for Potentially Affected Area (PAA) detection following a natural hazard event. Based on the coherence time series, the proposed method (1) determines the natural variability of coherence within each pixel in the region of interest, accounting for factors such as seasonality and the inherent noise of variable surfaces; and (2) compares pixel-by-pixel syn-event coherence to temporal coherence distributions to determine where statistically significant coherence loss has occurred. The user can determine to what degree the syn-event coherence value (e.g., 1st, 5th percentile of pre-event distribution) constitutes a PAA, and integrate pertinent regional data, such as population density, to rank and prioritise PAAs. We apply the method to two case studies, Sarpol-e, Iran following the 2017 Iran-Iraq earthquake, and a landslide-prone region of NW Argentina, to demonstrate how rapid identification and interpretation of potentially affected areas can be performed shortly following a natural hazard event. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 471 KW - Sentinel-1 KW - natural hazards KW - rapid damage mapping KW - coherence KW - potentially affected areas (PAA) Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-417766 ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo A1 - Hoffmann, Bernd A1 - Sachse, Dirk A1 - Adhikari, Danda P. A1 - Strecker, Manfred T1 - Understanding erosion rates in the Himalayan orogen: A case study from the Arun Valley JF - Journal of geophysical research : Earth surface N2 - Understanding the rates and pattern of erosion is a key aspect of deciphering the impacts of climate and tectonics on landscape evolution. Denudation rates derived from terrestrial cosmogenic nuclides (TCNs) are commonly used to quantify erosion and bridge tectonic (Myr) and climatic (up to several kiloyears) time scales. However, how the processes of erosion in active orogens are ultimately reflected in Be-10 TCN samples remains a topic of discussion. We investigate this problem in the Arun Valley of eastern Nepal with 34 new Be-10-derived catchment-mean denudation rates. The Arun Valley is characterized by steep north-south gradients in topography and climate. Locally, denudation rates increase northward, from <0.2mmyr(-1) to similar to 1.5mmyr(-1) in tributary samples, while main stem samples appear to increase downstream from similar to 0.2mmyr(-1) at the border with Tibet to 0.91mmyr(-1) in the foreland. Denudation rates most strongly correlate with normalized channel steepness (R-2=0.67), which has been commonly interpreted to indicate tectonic activity. Significant downstream decrease of Be-10 concentration in the main stem Arun suggests that upstream sediment grains are fining to the point that they are operationally excluded from the processed sample. This results in Be-10 concentrations and denudation rates that do not uniformly represent the upstream catchment area. We observe strong impacts on Be-10 concentrations from local, nonfluvial geomorphic processes, such as glaciation and landsliding coinciding with areas of peak rainfall rates, pointing toward climatic modulation of predominantly tectonically driven denudation rates. Y1 - 2015 U6 - https://doi.org/10.1002/2014JF003410 SN - 2169-9003 SN - 2169-9011 VL - 120 IS - 10 SP - 2080 EP - 2102 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo A1 - Strecker, Manfred T1 - Corrigendum to: Olen, Stephanie M.; Bookhagen, Bodo; Strecker, Manfred R. : Role of climate and vegetation density in modulating denudation rates in the Himalaya. - Earth and planetary science letters. - 445 (2016), S. 57 - 67. - doi: https://doi.org/10.1016/j.epsl.2016.03.047 JF - Earth and planetary science letters N2 - Vegetation has long been hypothesized to influence the nature and rates of surface processes. We test the possible impact of vegetation and climate on denudation rates at orogen scale by taking advantage of a pronounced along-strike gradient in rainfall and vegetation density in the Himalaya. We combine 12 new 10Be denudation rates from the Sutlej Valley and 123 published denudation rates from fluvially- dominated catchments in the Himalaya with remotely-sensed measures of vegetation density and rainfall metrics, and with tectonic and lithologic constraints. In addition, we perform topographic analyses to assess the contribution of vegetation and climate in modulating denudation rates along strike. We observe variations in denudation rates and the relationship between denudation and topography along strike that are most strongly controlled by local rainfall amount and vegetation density, and cannot be explained by along-strike differences in tectonics or lithology. A W–E along-strike decrease in denudation rate variability positively correlates with the seasonality of vegetation density (R = 0.95, p < 0.05), and negatively correlates with mean vegetation density (R = −0.84, p < 0.05). Vegetation density modulates the topographic response to changing denudation rates, such that the functional relationship between denudation rate and topographic steepness becomes increasingly linear as vegetation density increases. We suggest that while tectonic processes locally control the pattern of denudation rates across strike of the Himalaya (i.e., S–N), along strike of the orogen (i.e., E–W) climate exerts a measurable influence on how denudation rates scatter around long-term, tectonically-controlled erosion, and on the functional relationship between topography and denudation Y1 - 2020 U6 - https://doi.org/10.1016/j.epsl.2020.116252 SN - 0012-821X SN - 1385-013X VL - 540 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Bookhagen, Bodo A1 - Strecker, Manfred T1 - Role of climate and vegetation density in modulating denudation rates in the Himalaya JF - Earth & planetary science letters N2 - Vegetation has long been hypothesized to influence the nature and rates of surface processes. We test the possible impact of vegetation and climate on denudation rates at orogen scale by taking advantage of a pronounced along-strike gradient in rainfall and vegetation density in the Himalaya. We combine 12 new Be-10 denudation rates from the Sutlej Valley and 123 published denudation rates from fluvially-dominated catchments in the Himalaya with remotely-sensed measures of vegetation density and rainfall metrics, and with tectonic and lithologic constraints. In addition, we perform topographic analyses to assess the contribution of vegetation and climate in modulating denudation rates along strike. We observe variations in denudation rates and the relationship between denudation and topography along strike that are most strongly controlled by local rainfall amount and vegetation density, and cannot be explained by along-strike differences in tectonics or lithology. A W-E along-strike decrease in denudation rate variability positively correlates with the seasonality of vegetation density (R = 0.95, p < 0.05), and negatively correlates with mean vegetation density (R = -0.84, p < 0.05). Vegetation density modulates the topographic response to changing denudation rates, such that the functional relationship between denudation rate and topographic steepness becomes increasingly linear as vegetation density increases. We suggest that while tectonic processes locally control the pattern of denudation rates across strike of the Himalaya (i.e., S-N), along strike of the orogen (i.e., E-W) climate exerts a measurable influence on how denudation rates scatter around long-term, tectonically-controlled erosion, and on the functional relationship between topography and denudation. (C) 2016 Elsevier B.V. All rights reserved. KW - geomorphology KW - erosion KW - vegetation KW - rainfall KW - Himalaya KW - 10-Be terrestrial cosmogenic nuclides Y1 - 2016 U6 - https://doi.org/10.1016/j.epsl.2016.03.047 SN - 0012-821X SN - 1385-013X VL - 445 SP - 57 EP - 67 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Olen, Stephanie M. A1 - Ehlers, Todd A1 - Densmore, Mathew S. T1 - Limits to reconstructing paleotopography from thermochronometer data JF - JOURNAL OF GEOPHYSICAL RESEARCH-EARTH SURFACE N2 - Recent studies suggest that orogens can achieve a topographic steady state whereby equilibrium is reached between tectonics and erosion. However, steady state topography may not be the norm in many orogens experiencing large changes in climate or tectonics, which can produce topographic transients. The quantification of transient topography over geologic timescales requires reconstructing paleotopography, but this has proven difficult in many cases. This study investigates the utility of bedrock thermochronometer data to reconstruct orogen paleotopography over million year timescales. Apatite (U-Th)/He and fission track ages are integrated with a thermokinematic model for a single-parameter inversion of paleotopography. An iterative scheme is used that minimizes the misfit between predicted and observed cooling ages to identify the range of paleotopographies that could produce observed ages within sample uncertainty. Two approaches are considered. First, synthetic 2- D topographies are used to test the robustness of the approach. The following topographic evolution scenarios are considered: (1) lateral ridge migration, (2) topographic relief change, and (3) valley widening and deepening from glaciation. Second, the method is applied in three dimensions to existing data from the Coast Mountains of British Columbia, Canada. Results from both applications of the model suggest that (1) paleotopographic reconstruction will typically underpredict the magnitude of topographic change, especially relief change; (2) paleotopography is most successfully reconstructed after lateral ridge migration in long-wavelength topographies; and (3) reconstructed paleotopography from the Coast Mountains, British Columbia, suggests that glacial erosion may have the potential to remove drainage divides and laterally shift topographic ridges and peaks. Y1 - 2012 U6 - https://doi.org/10.1029/2011JF001985 SN - 0148-0227 VL - 117 PB - AMER GEOPHYSICAL UNION CY - WASHINGTON ER -