- Email: [email protected]
Erosion of Grand Canyon tributary basins at multiple spatial and temporal scales
Abstracts / Quaternary International 279-280 (2012) 346–461
suggestions that the beetle and pollen records are in conflict, in particular over the extent, distribution and character of forest vegetation that survived this period and contend that most divergences can be easily reconciled. The beetle evidence, rather than being in conflict, actually are strongly supportive of the vegetation patterns indicated by pollen and plant macrofossils. Together these show widespread survival of forest and shrubland with non-forest communities becoming increasingly dominant towards the south, the east and with increasing elevation. We further consider the possible climatic factors underlying these vegetation patterns as well as significant changes that occurred during the course of the LGM. INVENTORY OF QUATERNARY GEOLOGY AND THE EVOLUTION OF THE OGUTA LAKE, SOUTHEASTERN NIGERIA
351
Grand Canyon are lower than in the eastern Grand Canyon. The 10Be concentrations of mainstem sand increase systematically from the eastern to the western Grand Canyon consistent with slower eroding basins in the western Grand Canyon. If the contemporary sediment yields are extrapolated for the entirety of the Holocene, then the cosmogenic data suggest much lower average sediment yields prior to the Pleistocene-Holocene transition suggesting a change in process during the effective range of cosmogenic 10Be. If correct, these data suggest increased sediment yields at the Pleistocene-Holocene has had a significant impact on the sediment budget of the Grand Canyon and probably the Colorado River basin. A SEMI-QUANTITATIVE REGIONAL PRECIPITATION DATA SET FOR NINETEENTH-CENTURY AFRICA Sharon Nicholson. Florida State University, United States
Bruno Ndiocho Nfor. Department of Geology, Anambra State University, Nigeria
E-mail address: [email protected]
E-mail address: [email protected]
A wealth of information on climate and weather in Africa during the nineteenth century is available from documentary sources. Unfortunately long-term time series from a single observer at a single location are uncommon. This paper deals with a methodology that allows such sources to be utilized and combined with gauge data and natural proxies, such as information on lake levels. This approach reduces the problems of calibration and observer bias and allows for fragmentary information from many locations to be optimally utilized. The resultant data set has seven classes that represent anomalous conditions of rainfall, ranging from extreme drought to extremely wet. Resolution is annual and information is available for some 90 regions on the continent, beginning in the 1820s. The data set can be evaluated with standard climatological methods, including principal component analysis, linear correlation, and spectral analysis. Time series can be extended to the present time by converting modern data to the seven-class system. In this talk, the data set and the results of various statistical analysis are presented. A comparison is made with results for the twentieth century. The relationship to factors governing interannual variability, such as sea-surface temperatures, is also explored.
Individual and/or combined contributions of globally accepted processes of natural lake formation were investigated and used in consonance with field observations to propose a geologic setting for the genesis and evolution of the Oguta Lake. Results suggest that combined structural and fluvio/hydrodynamic forces initiated its formation during the Wurm-Wisconsin (10,000 YBP) eustatic low sea level that affected the Guinea Coast. The resultant base level erosion/incision of the Niger and Njaba Rivers and subsequent aggradations of thick sandy alluvium during eustatic Flandrian transgression, would have been such that, the Njaba R. eroded its valley into a ‘U’ shape around the Oguta area. The valley was further aggravated by instability, resulting from subsurface growth faults common within the Niger Delta. At their mature stage around Oguta, both Rivers could have deposited enough sediments to choke their passage, resulting in meandering, braiding and ox-bow/ slough lakes. In such a floodplain, the depressions formed by natural levees and the outer margins of the floodplains were filled by water and the coalescence of a number of ox-bow lakes from the wailing Niger and Orashi Rivers resulted in the Oguta Lake. Additionally, the Awbuna and Utu Rivers (tributaries to the Njaba R.) could have built deposits across the Njaba R. valley to pond it or the latter could have aggravated its valley flow more rapidly than its two tributaries and ended up being ponded. Furthermore, hydrodynamics between sedimentation and erosion under varying climatic conditions broke the empoundment at the western end into an outflow route, which eventually was captured by a larger Orashi R., giving birth to a hydrodynamically natural, fresh water open Oguta Lake System.
EROSION OF GRAND CANYON TRIBUTARY BASINS AT MULTIPLE SPATIAL AND TEMPORAL SCALES Kyle Nichols. Skidmore College, United States E-mail address: [email protected]
Dams on the Colorado River regulate and store water for irrigation and domestic use, but flow regulation has had major impacts on hydrological processes within the watershed. Intrinsic to understanding these impacts requires a quantitative knowledge of sediment yields. Unfortunately, little is known about the long-term sediment yields or sediment transport and contemporary data are either estimated or measured over only a few decades and only at only a few locations. Therefore, the data may not reflect the longer cycles of erosion, aggradation, and transport within the mainstem Colorado River or within the tributary basins. Here, we present data that compares contemporary sediment yield derived from models of ungaged tributaries in the Grand Canyon (Webb et al., 2000) with millennial-scale sediment yield data derived from cosmogenic 10Be to highlight the sediment delivery processes over the past several thousand years. We also use 10Be to trace mainstem bedload in order to understand transport processes. Preliminary results show that contemporary sediment yield models are up to several times higher than the long-term averages estimated using 10Be, and that average basin-wide erosion rates in the western
LINKING TROPICAL GLACIER MASS BALANCE TO REGIONAL CLIMATE DRIVERS, LEWIS GLACIER, MT KENYA Lindsey Nicholson. University of Innsbruck, Austria E-mail address: [email protected]
Uniquely in the tropics, Lewis Glacier (Kenya, 0 090 S; 37 180 E) has an 18 year historical annual mass balance record, spanning 1979-1996. This offers an opportunity to investigate the glacier-climate interactions at w4800m a.s.l. in the equatorial zone, which in turn allows investigation of the possible tropical mid-tropospheric conditions that must have prevailed in order to permit formerly larger glacier extents on the mountain. In this work we use ERA-40 reanalysis data at annual and sub-annual scales to understand the climate drivers dictating variability in the 18 year glacier mass balance record. No single season emerges as a driving season, but combined precipitation amount from the two rainy seasons explains the majority of the inter-annual variability. There is a complex link between summit precipitation and Indian Ocean sea surface temperatures and the strength of local mountain convection conditions. At times in the record the mass balance is less strongly linked to the annual wet season precipitation conditions, and these years are associated with annual temperature anomalies in the 500mb temperature field, which are in turn associated with regional wind fields. Using the assumption that significant downvalley moraines were constructed during periods of glacier terminus still-stand, this analysis allows an assessment of possible climate conditions over the late 19th century that correspond to these quasi stable glacier extents. HUMAN IMPACT ON LANDSCAPES BY LAND USE CHANGES IN LOWER LUSATIA (SOUTHERN BRANDENBURG, EAST GERMANY) – PEDOLOGICAL AND GEOMORPHOLOGICAL APPROACHES Alexander Nicolay. Brandenburg University of Technology Cottbus, Germany E-mail address: [email protected]
suggestions that the beetle and pollen records are in conflict, in particular over the extent, distribution and character of forest vegetation that survived this period and contend that most divergences can be easily reconciled. The beetle evidence, rather than being in conflict, actually are strongly supportive of the vegetation patterns indicated by pollen and plant macrofossils. Together these show widespread survival of forest and shrubland with non-forest communities becoming increasingly dominant towards the south, the east and with increasing elevation. We further consider the possible climatic factors underlying these vegetation patterns as well as significant changes that occurred during the course of the LGM. INVENTORY OF QUATERNARY GEOLOGY AND THE EVOLUTION OF THE OGUTA LAKE, SOUTHEASTERN NIGERIA
351
Grand Canyon are lower than in the eastern Grand Canyon. The 10Be concentrations of mainstem sand increase systematically from the eastern to the western Grand Canyon consistent with slower eroding basins in the western Grand Canyon. If the contemporary sediment yields are extrapolated for the entirety of the Holocene, then the cosmogenic data suggest much lower average sediment yields prior to the Pleistocene-Holocene transition suggesting a change in process during the effective range of cosmogenic 10Be. If correct, these data suggest increased sediment yields at the Pleistocene-Holocene has had a significant impact on the sediment budget of the Grand Canyon and probably the Colorado River basin. A SEMI-QUANTITATIVE REGIONAL PRECIPITATION DATA SET FOR NINETEENTH-CENTURY AFRICA Sharon Nicholson. Florida State University, United States
Bruno Ndiocho Nfor. Department of Geology, Anambra State University, Nigeria
E-mail address: [email protected]
E-mail address: [email protected]
A wealth of information on climate and weather in Africa during the nineteenth century is available from documentary sources. Unfortunately long-term time series from a single observer at a single location are uncommon. This paper deals with a methodology that allows such sources to be utilized and combined with gauge data and natural proxies, such as information on lake levels. This approach reduces the problems of calibration and observer bias and allows for fragmentary information from many locations to be optimally utilized. The resultant data set has seven classes that represent anomalous conditions of rainfall, ranging from extreme drought to extremely wet. Resolution is annual and information is available for some 90 regions on the continent, beginning in the 1820s. The data set can be evaluated with standard climatological methods, including principal component analysis, linear correlation, and spectral analysis. Time series can be extended to the present time by converting modern data to the seven-class system. In this talk, the data set and the results of various statistical analysis are presented. A comparison is made with results for the twentieth century. The relationship to factors governing interannual variability, such as sea-surface temperatures, is also explored.
Individual and/or combined contributions of globally accepted processes of natural lake formation were investigated and used in consonance with field observations to propose a geologic setting for the genesis and evolution of the Oguta Lake. Results suggest that combined structural and fluvio/hydrodynamic forces initiated its formation during the Wurm-Wisconsin (10,000 YBP) eustatic low sea level that affected the Guinea Coast. The resultant base level erosion/incision of the Niger and Njaba Rivers and subsequent aggradations of thick sandy alluvium during eustatic Flandrian transgression, would have been such that, the Njaba R. eroded its valley into a ‘U’ shape around the Oguta area. The valley was further aggravated by instability, resulting from subsurface growth faults common within the Niger Delta. At their mature stage around Oguta, both Rivers could have deposited enough sediments to choke their passage, resulting in meandering, braiding and ox-bow/ slough lakes. In such a floodplain, the depressions formed by natural levees and the outer margins of the floodplains were filled by water and the coalescence of a number of ox-bow lakes from the wailing Niger and Orashi Rivers resulted in the Oguta Lake. Additionally, the Awbuna and Utu Rivers (tributaries to the Njaba R.) could have built deposits across the Njaba R. valley to pond it or the latter could have aggravated its valley flow more rapidly than its two tributaries and ended up being ponded. Furthermore, hydrodynamics between sedimentation and erosion under varying climatic conditions broke the empoundment at the western end into an outflow route, which eventually was captured by a larger Orashi R., giving birth to a hydrodynamically natural, fresh water open Oguta Lake System.
EROSION OF GRAND CANYON TRIBUTARY BASINS AT MULTIPLE SPATIAL AND TEMPORAL SCALES Kyle Nichols. Skidmore College, United States E-mail address: [email protected]
Dams on the Colorado River regulate and store water for irrigation and domestic use, but flow regulation has had major impacts on hydrological processes within the watershed. Intrinsic to understanding these impacts requires a quantitative knowledge of sediment yields. Unfortunately, little is known about the long-term sediment yields or sediment transport and contemporary data are either estimated or measured over only a few decades and only at only a few locations. Therefore, the data may not reflect the longer cycles of erosion, aggradation, and transport within the mainstem Colorado River or within the tributary basins. Here, we present data that compares contemporary sediment yield derived from models of ungaged tributaries in the Grand Canyon (Webb et al., 2000) with millennial-scale sediment yield data derived from cosmogenic 10Be to highlight the sediment delivery processes over the past several thousand years. We also use 10Be to trace mainstem bedload in order to understand transport processes. Preliminary results show that contemporary sediment yield models are up to several times higher than the long-term averages estimated using 10Be, and that average basin-wide erosion rates in the western
LINKING TROPICAL GLACIER MASS BALANCE TO REGIONAL CLIMATE DRIVERS, LEWIS GLACIER, MT KENYA Lindsey Nicholson. University of Innsbruck, Austria E-mail address: [email protected]
Uniquely in the tropics, Lewis Glacier (Kenya, 0 090 S; 37 180 E) has an 18 year historical annual mass balance record, spanning 1979-1996. This offers an opportunity to investigate the glacier-climate interactions at w4800m a.s.l. in the equatorial zone, which in turn allows investigation of the possible tropical mid-tropospheric conditions that must have prevailed in order to permit formerly larger glacier extents on the mountain. In this work we use ERA-40 reanalysis data at annual and sub-annual scales to understand the climate drivers dictating variability in the 18 year glacier mass balance record. No single season emerges as a driving season, but combined precipitation amount from the two rainy seasons explains the majority of the inter-annual variability. There is a complex link between summit precipitation and Indian Ocean sea surface temperatures and the strength of local mountain convection conditions. At times in the record the mass balance is less strongly linked to the annual wet season precipitation conditions, and these years are associated with annual temperature anomalies in the 500mb temperature field, which are in turn associated with regional wind fields. Using the assumption that significant downvalley moraines were constructed during periods of glacier terminus still-stand, this analysis allows an assessment of possible climate conditions over the late 19th century that correspond to these quasi stable glacier extents. HUMAN IMPACT ON LANDSCAPES BY LAND USE CHANGES IN LOWER LUSATIA (SOUTHERN BRANDENBURG, EAST GERMANY) – PEDOLOGICAL AND GEOMORPHOLOGICAL APPROACHES Alexander Nicolay. Brandenburg University of Technology Cottbus, Germany E-mail address: [email protected]