Browsing by Subject "River profile"
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Item Inferring bedrock uplift in the Klamath Mountains Province from river profile analysis and digital topography(Texas Tech University, 2008-12) Anderson, Timothy Kirt; Yoshinobu, Aaron S.The Klamath Mountains Province (KMP), northern California/Southern Oregon, is situated at the juncture of the Mendocino Triple Junction, the southern boundary of the Cascades Volcanic Arc and the Juan de Fuca-North America convergent margin, and the western boundary of the Basin and Range province. KMP topography extends from sea level to over 2.5 kilometers of elevation. The mean elevation of the central KMP is greater than one kilometer, defining a regional dome of elevated topography. Surface uplift and rock exhumation have been ongoing since the Late Pliocene. A quasi-planar, regionally-extensive erosional surface termed the Klamath Peneplain (KP) is exposed in coastal regions at/near sea level and at elevations in excess of 2 kilometers more than 100 kilometers inland. Pleistocene marine and non-marine deposits have aggraded on the KP, thus preserving the surface. The geometry of the peneplain and the average amount of uplift and erosion may be calculated by interpolating a westward-dipping surface through the basal peneplain exposures. This assumes the peneplain was continuous over the entire western KMP. Time-averaged long-term uplift rates reach a maximum of 0.4mm/yr in the east. The total amount and rate of erosion since formation of the KP may be calculated by subtracting this interpolated surface from modern topography. These time-averaged results indicate that approximately 3850 km3 of material has been removed since the Pliocene at a rate of 0.00077 km3/yr. The maximum long-term erosion rate is 0.29 mm/yr (Salmon River). Our maps suggest that less than sixteen percent of western KMP topography existed before the Pliocene. Paleotopography with elevations greater than a kilometer must have existed in the eastern KMP at the time of maximum peneplanation. Longitudinal river profiles in the central KMP are 2 to 3 times steeper than those in adjacent areas. River profile knickpoints suggest that the central KMP could be experiencing baselevel fall in some locations. Modern surface uplift and rock exhumation in the KMP may be attributed to one or more of the following; 1) northward migration of the Blanco F.Z., 2) recent duplexing of the Franciscan Complex or other accreted terranes beneath the KMP, 3) development of a serpentine wedge beneath the KMP, and 4) climate driven isostatic rebound. This last interpretation seems most favorable given the spatial correlation between uplift and erosion.Item Tectonism and geomorphic response in the Sacramento Mountains, south-central New Mexico(2011-08) Bauman, Joe C.; Yoshinobu, Aaron S.; Leverington, David; Asquith, William H.The Alamogordo Fault bounds the western range-front of the Sacramento Mountains in south-central New Mexico. Previous studies have determined that uplift of the range initiated during Tertiary time and continues to present day. This study utilizes remote-sensing methods to observe relations between geomorphology—the bedrock fluvial network in particular—and tectonism in the Sacramento Mountains. Analysis of longitudinal stream profiles, stream slope-area data, and topographic relief reveal temporal and spatial variations in uplift rates along the Alamogordo Fault and support the hypothesis that the Alamogordo Fault consists of four segments. The geomorphic indices of concavity (Θ) and steepness (ks) are calculated from stream slope-area data. The concavity index is a measure of stream-profile curvature and is a function of channel substrate erosional properties. Concavity indices of the study area exhibit no consistent response to along-stream changes in sedimentary lithology of any type. This suggests that sedimentary bedrock of the Sacramento Mountains—though heterogeneous at small-scales (meters to 10’s of meters)—may be generally uniform at larger-scales. However, concavity indices do suggest that a strong lithologic contrast is apparent at the scale of this study between granitic rocks and the surrounding sedimentary rocks. Concavity index values of stream segments within a granitic pluton are typically low (Θ < 0.40); whereas respective downstream channel segments that flow over sedimentary/tuffaceous rock are typically high (Θ > 1.0). Theoretical considerations of the detachment-limited, shear-stress incision law predict a relation between stream channel steepness (ks) and a response to uplift rates experienced by bedrock channel beds. North-south and west-east trends in normalized steepness indices (ksn, for reference concavity (Θref) of 0.45) are observed. Values of ksn, averaged for each watershed, are lowest (ksn < 60) in watersheds that are coincident to the northernmost, Three Rivers segment of the Alamogordo Fault. Average ksn values increase to maximum values (ksn > 120) along the Deadman fault-segment. This north-south trend of average ksn values mimics the north-south trend of measured, present-day uplift rates. The west-east trend in ksn values is demarcated by knickpoints that separate downstream channel segments with higher steepness (ksn > 120) from upstream channel segments with lower steepness (ksn < 120). It is inferred that these trends reflect spatial variations of relative uplift rates of uplift along the Alamogordo Fault (north-south trend), and relative, temporal variations in uplift rates of the Sacramento Mountains (west-east trend).