The following is a summary of the geomorphic setting, pit bathymetry and sediment particle data a... more The following is a summary of the geomorphic setting, pit bathymetry and sediment particle data and analysis for the 10 specified mine sites examined along the Yakima River floodplain (Figure 1). Included is a description of the methods used for analysis, the general geomorphic and stratigraphic setting, pit bathymetry, sample locations, sediment in terms of the Unified Soil Classification System, grain size distribution, explanation of sediment deposition patterns with respect to flow regimes of the Yakima River, and recommendations for best management practices for floodplain sand and gravel mines of the Yakima River basin with respect to geologic and geomorphic conditions.
Journal Of Geophysical Research: Planets, May 1, 2022
Mars' surface exhibits abundant topographic expressions of large thrust fault‐related folds t... more Mars' surface exhibits abundant topographic expressions of large thrust fault‐related folds that have been attributed to global planetary contraction. Morphometric analyses of such structures provide insight into their growth history. With global THEMIS imagery and HRSC–MOLA topographic data, 49 thrusts with lengths between 35 and 544 km were mapped across Mars' surface. Assuming planar fault geometries with dips of 30°, the average maximum displacement‐length ratio (Dmax/L) of these structures is 6.1 × 10−3 ± 1.4 × 10−3, with smaller ratios observed for faults within the northern lowlands (2.9 × 10−3 ± 0.9 × 10−3) compared to the southern highlands (9.2 × 10−3 ± 1.9 × 10−3). However, these differences may be accounted for if mechanical layering in the northern lowland crust promotes either a shallowing of the fault dip angle relative to the southern highlands or the development of ramp‐flat geometries such that the topographic scarp height may under‐estimate the total fault displacement or a combination of these two scenarios together. Alternatively, these Dmax/L patterns may reflect hemispheric differences in the brittle‐ductile transition (BDT) depth; however, the observed pattern is stratigraphically inconsistent with the Martian crustal dichotomy, whereby the northern lowlands have thinner (or denser) crust and therefore presumably a deeper BDT than the southern highlands. Fault displacement‐length profiles are commonly asymmetric, with multiple local minima observed along their lengths. Spectral analysis of these profiles, using Fourier‐ and S‐Transforms, indicates power at a range of spatial frequencies, reflecting complex growth and linkage histories, with peak spectral frequency, or number of segments, being negatively correlated with the Dmax/L ratios.
Earth Surface Processes and Landforms, Oct 26, 2022
European‐American settlement of the south‐eastern United States introduced agricultural practices... more European‐American settlement of the south‐eastern United States introduced agricultural practices that included extensive clearing of forested hillslopes to support food and cash‐crop agriculture. This land disturbance has long‐term effects on stream morphology by displacing channel heads down‐valley, impacting downstream sediment and nutrient supply as channel heads migrate back up‐valley towards their pre‐disturbance locations. This study investigates 40 stream channels in William B. Umstead State Park in the Piedmont of North Carolina using relationships between local slope and contributing drainage areas to predict channel head locations and compare these to their observed positions. Further, expected eroded sediment and nutrient contributions are quantified using migration distances and sampled soils near channel heads. Of the 40 investigated channel heads, 23 are located down‐valley from their predicted location by an average of 174.4 m ± 109.6 (1 − σ). Using this distance and average channel cross‐sectional area, 1.6 ± 1.4 m2 (1 − σ), the expected future erosion per channel is 282.6 ± 177.6 m3 (1 − σ). Drainage density was used to extrapolate volumes to the 23 km2 park using a conservative estimate that 50% of the first‐order channel heads will migrate up‐valley, implying an additional 90.4 ± 56.8 × 103 m3 (1 − σ) of sediment is expected to erode from the study area. Finally, scaling these volume estimates to sampled soil nutrient values indicates that approximately 1053 ± 662 t (68% confidence) of carbon, 51 ± 32 t of total nitrogen, and 15 ± 9 t of phosphorus are anticipated to enter the fluvial system in response to channel head migration from within the confines of this state park, representing only 1% of the land area in Wake County. These findings suggest that regional water quality challenges posed by suspended sediments and nutrients will persist for hundreds to perhaps thousands of years from non‐point sources as first‐order channels continue to erode headward towards their equilibrium landscape positions.
The timing of surface uplift of the Altai Mountains in northern Central Asia—and the climatic con... more The timing of surface uplift of the Altai Mountains in northern Central Asia—and the climatic consequences—remains controversial. Today, the Altai Mountains cast a substantial rain shadow, effectively separating the western Gobi Desert and steppe from the Siberian Taiga. We take advantage of this stark climatic gradient to trace the interaction of climate and topography in the lee of the Altai. First, we present new water stable isotope data that demonstrate that—along with this climatic gradient—the Altai modify the δ18O of precipitation via rainout on the leeward side of the range. Second, we present a new paleosol carbonate clumped isotope (Δ47) record that spans much of the Neogene from the immediate lee of the Altai in western Mongolia to address how surface temperatures may have responded to potential uplift during the Neogene. We find that Δ47-derived temperatures have, overall, declined by approximately 7 °C over the course of the Neogene, though the precise timing of this decrease remains uncertain. Third, we pair our Δ47 record with previously published stable isotope data to demonstrate that the timing of decreasing temperatures corresponds with long-term stability in paleosol carbonate δ13C values. In contrast, increases in paleosol carbonate δ13C values—linked to declining vegetation productivity—are correlated with intervals of increasing temperatures. We speculate that declines in vegetation biomass and leaf area changed the partitioning of latent and sensible heat, resulting in rising surface temperatures during Altai uplift. In contrast, long-term Neogene cooling drove the overall decline in surface temperatures. Reconstructed soil water δ18O values (based on carbonate δ18O and Δ47 values) remain surprisingly stable over our Neogene record, differing from our expectation of decreasing δ18O values due to progressive uplift of the Altai Mountains and Neogene cooling. We demonstrate that the shift in precipitation seasonality that likely accompanied Altai uplift obscured any change in lee-side precipitation δ18O that would be expected from surface elevation change alone.
Geological Society of America Bulletin, Mar 20, 2019
Lake Crescent, a 180-m-deep, glacially carved lake located on the Olympic Peninsula in western Wa... more Lake Crescent, a 180-m-deep, glacially carved lake located on the Olympic Peninsula in western Washington, USA, overlies the Lake Creek-Boundary Creek fault zone, a system of structures with at least 56 km of late Pleistocene to Holocene surface rupture. Investigation of the lake’s sediment, including a reflection seismic survey and analysis of piston cores, reveals evidence that the fault beneath the lake has ruptured four times in the past ∼7200 years, producing unusually thick deposits termed megaturbidites. The earthquakes triggered rockslides that entered the lake and caused displacement waves (lake tsunamis) and seiches, most recently ca. 3.1 ka. Seismic reflection results from beneath the depth of core penetration reveal at least two older post-glacial ruptures that are likely to have similarly affected the lake. The stratigraphy of Lake Crescent provides insight into the behavior of a fault system that partially accommodates regional clockwise rotation and contraction of the northern Cascadia forearc through oblique dextral shear, and highlights the potential for disruption to critical infrastructure, transportation corridors, and industry on the North Olympic Peninsula during future surface-rupturing earthquakes. Our results illustrate the potential synergism between lacustrine paleoseismology and fault-scarp trench investigations. More precise dating of strong earthquake shaking afforded by continuous accumulation of lake sediment improves earthquake histories based on trenched fault scarp exposures, which are commonly poorly dated.
Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinaul... more Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinault, Washington, reveal an ~4000-year flood-dominated depositional record. Individual flood event layers are identified by combining core stratigraphy, sedimentology, and the ratio of incoherent to coherently scattered x-ray radiation (inc/coh) from µXRF (x-ray fluorescence) core scans. The inc/coh time series is used as a proxy for sediment grain size and, in combination with radiocarbon-anchored core age-depth models, enables the reconstruction of late-Holocene hydrologic variability for the Quinault River catchment. Decadal to centennial variability in inc/coh is interpreted to reflect trends in ocean-atmosphere teleconnections favorable for the formation of land-falling atmospheric rivers along the Pacific Ocean flank of the Olympic Mountains. Such processes likely modulate the rate of flooding and may explain notable increases in the frequency of flood event layers observed during the periods 2350-2450 cal. yr BP and the most recent century (AD 1910-2010). Understanding past hydrologic variability has important implications for the landscape and ecosystem response of Olympic Mountain catchments to future climate warming.
Investigation of Lake Quinault in western Washington, including a reflection seismic survey, anal... more Investigation of Lake Quinault in western Washington, including a reflection seismic survey, analysis of piston cores, and preliminary mapping in the steep, landslide-prone Quinault River catchment upstream of the lake, reveals evidence for three episodes of earthquake disturbance in the past 3000 yr. These earthquakes triggered failures on the lake’s underwater slopes and delta front, as well as subaerial landsliding, partial channel blockage, and forced fluvial sediment aggradation. The ages of the three Lake Quinault disturbance events overlap with those of coseismically subsided, coastal marsh soils nearby in southwest Washington that are interpreted to record ruptures of the Cascadia megathrust. Absent from Lake Quinault, however, are signals of obvious disturbance from five additional subduction earthquakes inferred to have occurred during the period of record. The lack of evidence for these events may reflect the limitations of the data set derived from the detrital, river-dominated lake stratigraphy but may also have bearing on debates about segmentation and the distribution of slip along the Cascadia subduction zone during prior earthquakes.
The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision ... more The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision is debated, especially in non-glaciated regions. Here we present paleo-denudation rates and geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvial-fan sequences on Crete, Greece. We report seven optically stimulated luminescence (OSL), ten radiocarbon ages, and eight 10Be and eight 36Cl denudation rates from modern and terrace sediments. For five samples, 10Be and 36Cl were measured on the same sample by measuring 10Be on cherts and 36Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicate a link with shifts in climate. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occur...
The following is a summary of the geomorphic setting, pit bathymetry and sediment particle data a... more The following is a summary of the geomorphic setting, pit bathymetry and sediment particle data and analysis for the 10 specified mine sites examined along the Yakima River floodplain (Figure 1). Included is a description of the methods used for analysis, the general geomorphic and stratigraphic setting, pit bathymetry, sample locations, sediment in terms of the Unified Soil Classification System, grain size distribution, explanation of sediment deposition patterns with respect to flow regimes of the Yakima River, and recommendations for best management practices for floodplain sand and gravel mines of the Yakima River basin with respect to geologic and geomorphic conditions.
Journal Of Geophysical Research: Planets, May 1, 2022
Mars' surface exhibits abundant topographic expressions of large thrust fault‐related folds t... more Mars' surface exhibits abundant topographic expressions of large thrust fault‐related folds that have been attributed to global planetary contraction. Morphometric analyses of such structures provide insight into their growth history. With global THEMIS imagery and HRSC–MOLA topographic data, 49 thrusts with lengths between 35 and 544 km were mapped across Mars' surface. Assuming planar fault geometries with dips of 30°, the average maximum displacement‐length ratio (Dmax/L) of these structures is 6.1 × 10−3 ± 1.4 × 10−3, with smaller ratios observed for faults within the northern lowlands (2.9 × 10−3 ± 0.9 × 10−3) compared to the southern highlands (9.2 × 10−3 ± 1.9 × 10−3). However, these differences may be accounted for if mechanical layering in the northern lowland crust promotes either a shallowing of the fault dip angle relative to the southern highlands or the development of ramp‐flat geometries such that the topographic scarp height may under‐estimate the total fault displacement or a combination of these two scenarios together. Alternatively, these Dmax/L patterns may reflect hemispheric differences in the brittle‐ductile transition (BDT) depth; however, the observed pattern is stratigraphically inconsistent with the Martian crustal dichotomy, whereby the northern lowlands have thinner (or denser) crust and therefore presumably a deeper BDT than the southern highlands. Fault displacement‐length profiles are commonly asymmetric, with multiple local minima observed along their lengths. Spectral analysis of these profiles, using Fourier‐ and S‐Transforms, indicates power at a range of spatial frequencies, reflecting complex growth and linkage histories, with peak spectral frequency, or number of segments, being negatively correlated with the Dmax/L ratios.
Earth Surface Processes and Landforms, Oct 26, 2022
European‐American settlement of the south‐eastern United States introduced agricultural practices... more European‐American settlement of the south‐eastern United States introduced agricultural practices that included extensive clearing of forested hillslopes to support food and cash‐crop agriculture. This land disturbance has long‐term effects on stream morphology by displacing channel heads down‐valley, impacting downstream sediment and nutrient supply as channel heads migrate back up‐valley towards their pre‐disturbance locations. This study investigates 40 stream channels in William B. Umstead State Park in the Piedmont of North Carolina using relationships between local slope and contributing drainage areas to predict channel head locations and compare these to their observed positions. Further, expected eroded sediment and nutrient contributions are quantified using migration distances and sampled soils near channel heads. Of the 40 investigated channel heads, 23 are located down‐valley from their predicted location by an average of 174.4 m ± 109.6 (1 − σ). Using this distance and average channel cross‐sectional area, 1.6 ± 1.4 m2 (1 − σ), the expected future erosion per channel is 282.6 ± 177.6 m3 (1 − σ). Drainage density was used to extrapolate volumes to the 23 km2 park using a conservative estimate that 50% of the first‐order channel heads will migrate up‐valley, implying an additional 90.4 ± 56.8 × 103 m3 (1 − σ) of sediment is expected to erode from the study area. Finally, scaling these volume estimates to sampled soil nutrient values indicates that approximately 1053 ± 662 t (68% confidence) of carbon, 51 ± 32 t of total nitrogen, and 15 ± 9 t of phosphorus are anticipated to enter the fluvial system in response to channel head migration from within the confines of this state park, representing only 1% of the land area in Wake County. These findings suggest that regional water quality challenges posed by suspended sediments and nutrients will persist for hundreds to perhaps thousands of years from non‐point sources as first‐order channels continue to erode headward towards their equilibrium landscape positions.
The timing of surface uplift of the Altai Mountains in northern Central Asia—and the climatic con... more The timing of surface uplift of the Altai Mountains in northern Central Asia—and the climatic consequences—remains controversial. Today, the Altai Mountains cast a substantial rain shadow, effectively separating the western Gobi Desert and steppe from the Siberian Taiga. We take advantage of this stark climatic gradient to trace the interaction of climate and topography in the lee of the Altai. First, we present new water stable isotope data that demonstrate that—along with this climatic gradient—the Altai modify the δ18O of precipitation via rainout on the leeward side of the range. Second, we present a new paleosol carbonate clumped isotope (Δ47) record that spans much of the Neogene from the immediate lee of the Altai in western Mongolia to address how surface temperatures may have responded to potential uplift during the Neogene. We find that Δ47-derived temperatures have, overall, declined by approximately 7 °C over the course of the Neogene, though the precise timing of this decrease remains uncertain. Third, we pair our Δ47 record with previously published stable isotope data to demonstrate that the timing of decreasing temperatures corresponds with long-term stability in paleosol carbonate δ13C values. In contrast, increases in paleosol carbonate δ13C values—linked to declining vegetation productivity—are correlated with intervals of increasing temperatures. We speculate that declines in vegetation biomass and leaf area changed the partitioning of latent and sensible heat, resulting in rising surface temperatures during Altai uplift. In contrast, long-term Neogene cooling drove the overall decline in surface temperatures. Reconstructed soil water δ18O values (based on carbonate δ18O and Δ47 values) remain surprisingly stable over our Neogene record, differing from our expectation of decreasing δ18O values due to progressive uplift of the Altai Mountains and Neogene cooling. We demonstrate that the shift in precipitation seasonality that likely accompanied Altai uplift obscured any change in lee-side precipitation δ18O that would be expected from surface elevation change alone.
Geological Society of America Bulletin, Mar 20, 2019
Lake Crescent, a 180-m-deep, glacially carved lake located on the Olympic Peninsula in western Wa... more Lake Crescent, a 180-m-deep, glacially carved lake located on the Olympic Peninsula in western Washington, USA, overlies the Lake Creek-Boundary Creek fault zone, a system of structures with at least 56 km of late Pleistocene to Holocene surface rupture. Investigation of the lake’s sediment, including a reflection seismic survey and analysis of piston cores, reveals evidence that the fault beneath the lake has ruptured four times in the past ∼7200 years, producing unusually thick deposits termed megaturbidites. The earthquakes triggered rockslides that entered the lake and caused displacement waves (lake tsunamis) and seiches, most recently ca. 3.1 ka. Seismic reflection results from beneath the depth of core penetration reveal at least two older post-glacial ruptures that are likely to have similarly affected the lake. The stratigraphy of Lake Crescent provides insight into the behavior of a fault system that partially accommodates regional clockwise rotation and contraction of the northern Cascadia forearc through oblique dextral shear, and highlights the potential for disruption to critical infrastructure, transportation corridors, and industry on the North Olympic Peninsula during future surface-rupturing earthquakes. Our results illustrate the potential synergism between lacustrine paleoseismology and fault-scarp trench investigations. More precise dating of strong earthquake shaking afforded by continuous accumulation of lake sediment improves earthquake histories based on trenched fault scarp exposures, which are commonly poorly dated.
Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinaul... more Sedimentological and geochemical analyses of gravity and piston cores retrieved from Lake Quinault, Washington, reveal an ~4000-year flood-dominated depositional record. Individual flood event layers are identified by combining core stratigraphy, sedimentology, and the ratio of incoherent to coherently scattered x-ray radiation (inc/coh) from µXRF (x-ray fluorescence) core scans. The inc/coh time series is used as a proxy for sediment grain size and, in combination with radiocarbon-anchored core age-depth models, enables the reconstruction of late-Holocene hydrologic variability for the Quinault River catchment. Decadal to centennial variability in inc/coh is interpreted to reflect trends in ocean-atmosphere teleconnections favorable for the formation of land-falling atmospheric rivers along the Pacific Ocean flank of the Olympic Mountains. Such processes likely modulate the rate of flooding and may explain notable increases in the frequency of flood event layers observed during the periods 2350-2450 cal. yr BP and the most recent century (AD 1910-2010). Understanding past hydrologic variability has important implications for the landscape and ecosystem response of Olympic Mountain catchments to future climate warming.
Investigation of Lake Quinault in western Washington, including a reflection seismic survey, anal... more Investigation of Lake Quinault in western Washington, including a reflection seismic survey, analysis of piston cores, and preliminary mapping in the steep, landslide-prone Quinault River catchment upstream of the lake, reveals evidence for three episodes of earthquake disturbance in the past 3000 yr. These earthquakes triggered failures on the lake’s underwater slopes and delta front, as well as subaerial landsliding, partial channel blockage, and forced fluvial sediment aggradation. The ages of the three Lake Quinault disturbance events overlap with those of coseismically subsided, coastal marsh soils nearby in southwest Washington that are interpreted to record ruptures of the Cascadia megathrust. Absent from Lake Quinault, however, are signals of obvious disturbance from five additional subduction earthquakes inferred to have occurred during the period of record. The lack of evidence for these events may reflect the limitations of the data set derived from the detrital, river-dominated lake stratigraphy but may also have bearing on debates about segmentation and the distribution of slip along the Cascadia subduction zone during prior earthquakes.
The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision ... more The impact of Quaternary climate cycles on denudation rates and fluvial aggradation and incision is debated, especially in non-glaciated regions. Here we present paleo-denudation rates and geochronological constraints on aggradation and incision from the Sfakia and Elafonisi alluvial-fan sequences on Crete, Greece. We report seven optically stimulated luminescence (OSL), ten radiocarbon ages, and eight 10Be and eight 36Cl denudation rates from modern and terrace sediments. For five samples, 10Be and 36Cl were measured on the same sample by measuring 10Be on cherts and 36Cl on calcite. Results indicate relatively steady denudation rates throughout the past 80kyr, but the aggradation and incision history indicate a link with shifts in climate. At the Elafonisi fan, we identify four periods of aggradation coinciding with Marine Isotope Stages (MIS) 2, 4, 5a/b, and likely 6, and three periods of incision coinciding with MIS 1, 3, and likely 5e. At the Sfakia fan, rapid aggradation occur...
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