Statistics and Data Analysis in Geology

[1] Arctic amplification (AA) – the observed enhanced warming in high northern latitudes relative to the northern hemisphere – is evident in lower-tropospheric temperatures and in 1000-to-500 hPa thicknesses. Daily fields of 500 hPa heights from the National Centers for Environmental Prediction Reanalysis are analyzed over N. America and the N. Atlantic to assess changes in north-south (Rossby) wave characteristics associated with AA and the relaxation of poleward thickness gradients. Two effects are identified that each contribute to a slower eastward progression of Rossby waves in the upper-level flow: 1) weakened zonal winds, and 2) increased wave amplitude. These effects are particularly evident in autumn and winter consistent with sea-ice loss, but are also apparent in summer, possibly related to earlier snow melt on high-latitude land. Slower progression of upper-level waves would cause associated weather patterns in mid-latitudes to be more persistent, which may lead to an increased probability of extreme weather events that result from prolonged conditions, such as drought, flooding, cold spells, and heat waves.

Toward a complete Himalayan hydrological budget: Spatiotemporal distribution of snowmelt and rainfall and their impact on river discharge

Empirical observations from fl uvial systems across the globe reveal a consistent power-law scaling between channel slope and contributing drainage area. Theoretical arguments for both detachmentand transport-limited erosion regimes suggest that rock uplift rate should exert fi rst-order control on this scaling. Here we describe in detail a method for exploiting this relationship, in which topographic indices of longitudinal profi le shape and character are derived from digital topographic data. The stream profi le data can then be used to delineate breaks in scaling that may be associated with tectonic boundaries. The description of the method is followed by three case studies from varied tectonic settings. The case studies illustrate the power of stream profi le analysis in delineating spatial patterns of, and in some cases, temporal changes in, rock uplift rate. Owing to an incomplete understanding of river response to rock uplift, the method remains primarily a qualitative tool for neotectonic investigations; we conclude with a discussion of research needs that must be met before we can extract quantitative information about tectonics directly from topography.

Tectonics from topography: Procedures, promise, and pitfalls

■ Abstract Bedrock rivers set much of the relief structure of active orogens and dictate rates and patterns of denudation. Quantitative understanding of the role of climate-driven denudation in the evolution of unglaciated orogens depends first and foremost on knowledge of fluvial erosion processes and the factors that control incision rate. The results of intense research in the past decade are reviewed here, with the aim of highlighting remaining unknowns and suggesting fruitful avenues for further research. This review considers in turn (a) the occurrence and morphology of bedrock channels and their relation to tectonic setting; ( b) the physical processes of fluvial incision into rock; and (c) models of river incision, their implications, and the field and laboratory data needed to test, refine, and extend them.

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Bedrock rivers and the geomorphology of active orogens

The USGS Place Based Studies Program for San Francisco Bay investigates this sensitive estuarine system to aid in resource management. As part of the inter-disciplinary research program, the USGS collected side-scan sonar data and bed-sediment samples from north San Francisco Bay to characterize bed-sediment texture and investigate temporal trends in sedimentation. The study area is located in central California and consists of Suisun Bay, and Grizzly and Honker Bays, sub-embayments of Suisun Bay. During the study (1998-2002), the USGS collected three side-scan sonar data sets and approximately 300 sediment samples. The side-scan data revealed predominantly fine-grained material on the bayfloor. We also mapped five different bottom types from the data set, categorized as featureless, furrows, sand waves, machine-made, and miscellaneous. We performed detailed grain-size and statistical analyses on the sediment samples. Overall, we found that grain size ranged from clay to fine sand, with the coarsest material in the channels and finer material located in the shallow bays. Grain-size analyses revealed high spatial variability in size distributions in the channel areas. In contrast, the shallow regions exhibited low spatial variability and consistent sediment size over time. Introduction The San Francisco Bay estuary begins at the confluence of the Sacramento and San Joaquin Rivers in central California. Since the discovery of gold in 1848, the region has undergone immense environmental changes. Hydraulic mining activity during the late 1800’s in the Sierra Nevada resulted in the influx of large quantities of sediment to the San Francisco Bay estuary (Gilbert, 1917; Cappiella et al., 1999). At the same time, increased development has resulted in the loss of wetlands, re-routing of rivers, and species decline. The USGS Place Based Studies Program is an inter-disciplinary program aimed at understanding the San Francisco Bay estuary system, its response to modern stresses, and disseminating information to aid in resource management of the area. As part of the San Francisco Place Based Studies Program, the USGS began research in northern San Francisco Bay to characterize bed-sediment texture and investigate temporal trends in sedimentation. The study area comprises approximately 170 km and consists of Suisun Bay, and Grizzly and Honker Bays, sub-embayments of Suisun Bay (Fig. 1). At present, the region is characterized by three channels. The primary navigation channel is situated on the south side of Honker Bay into Suisun Bay, where it passes south of Ryer Island. A smaller channel runs between Roe Island and Ryer Island. The third channel flows through Suisun Cutoff, north of Ryer Island, on the south side of Grizzly Bay, and through the Reserve Fleet Channel on the western side of Suisun Bay. All three channels join at Carquinez Strait where they continue through the southern section of San Pablo Bay and into the Central Bay. The channels and shallows range in depth from 10 to 22 m and 1 to 2 m, respectively. During the years 1998 through 2002, the USGS collected bed-sediment samples, and performed three side-scan sonar surveys of the region. We completed grain-size and statistical analyses on the sediment samples, which were compiled in a spreadsheet and are included with this report as Tables 2 and 3. The side-scan sonar data (Plate 1) from one survey was digitally mosaiced and interpreted to reveal bed morphology and composition. Methods The following section describes sample collection, sediment grain-size analyses, and side-scan sonar data collection. Sediment Sample Collection Sediment sampling took place between December 1998 and January 2002 using two USGS research vessels, the RV David Johnston and the RV Polaris. Table 1 summarizes the details regarding each cruise such as the research vessel, cruise ID, cruise dates, the number of samples collected, and whether side-scan sonar data was collected. Additional information on these cruises can be found at the link provided in Table 1. The goal of the sampling scheme with the RV Johnston was to collect samples before and after the rainy season to investigate possible seasonal changes in bed texture (Table 1). The sample locations using this vessel are displayed on Figures 2-5 with symbols colored to represent percent sand-sized material. Percent sand is emphasized in this report as a means of characterizing the bimodal distribution of grain sizes in the samples. The sediment sampling locations ranged from Montezuma and Suisun Sloughs to the north, Honker Bay to the east, and Carquinez Strait to the west. Sampling was largely concentrated in the channel area known as Garnet Sill (Fig. 1; Plate 1) due to its location as an important area of estuarine mixing adjacent to the large shallow-water habitat of Grizzly Bay (Schoellhamer, 2001). Sampling depths ranged from 1.17 m to 15.63 m. Table 1: Sediment sample and side-scan data collection Vessel Cruise ID/Information Cruise Date Number of Samples SideScan Sonar RV David Johnston J-5-98-SF http://walrus.wr.usgs.gov/infobank/j/j598sf/html/j5-98-sf.fmeta.outline.html December 1-2, 1998 28 Yes RV David Johnston J-2-99-SF http://walrus.wr.usgs.gov/infobank/j/j299sf/html/j2-99-sf.fmeta.outline.html March 48, 1999 56 Yes RV David Johnston J-3-99-SF http://walrus.wr.usgs.gov/infobank/j/j399sf/html/j3-99-sf.fmeta.outline.html November 15-18, 1999 85 Yes RV David Johnston J-1-00-SF http://walrus.wr.usgs.gov/infobank/j/j100sf/html/j1-00-sf.fmeta.outline.html March 1315, 2000 64 No RV Polaris P-1-00-SF http://walrus.wr.usgs.gov/infobank/p/p100sf/html/p1-00-sf.fmeta.outline.html August 89, 2000 11 No RV Polaris P-2-00-SF http://walrus.wr.usgs.gov/infobank/p/p200sf/html/p2-00-sf.fmeta.outline.html November 7-8, 2000 12 No RV Polaris P-1-01-SF http://walrus.wr.usgs.gov/infobank/p/p101sf/html/p1-01-sf.fmeta.outline.html February 6-7, 2001 7 No RV Polaris P-2-01-SF http://walrus.wr.usgs.gov/infobank/p/p201sf/html/p2-01-sf.fmeta.outline.html February 26-27, 2001 12 No RV Polaris P-3-01-SF http://walrus.wr.usgs.gov/infobank/p/p301sf/html/p3-01-sf.fmeta.outline.html June 1920, 2001 12 No RV Polaris P-4-01-SF http://walrus.wr.usgs.gov/infobank/p/p401sf/html/p4-01-sf.fmeta.outline.html October 16-17, 2001 12 No RV Polaris P-1-02-SF http://walrus.wr.usgs.gov/infobank/p/p102sf/html/p1-02-sf.fmeta.outline.html January 22-23, 2002 12 No The RV Polaris was used for seven sampling cruises from 2000 to 2002 as indicated on Table 1. Unlike the Johnston cruises, samples were collected at 12 specific sites (Fig. 6) at variable intervals throughout the year. These locations are part of a network of long-term monitoring sites used by the USGS (see http://sfbay.wr.usgs.gov/access/wqdata/ for more information). Sampling depths ranged from 1.5 m at locations 415, 416, and 417, to 17.4 m at location 8.1 (Fig. 6). The shallow regions in the sloughs and Grizzly Bay were sampled using a smaller boat transported aboard the RV Polaris. We used two types of equipment for the sampling: a Van Veen grab sampler, and box cores. The grab sampler has a clam-like scoop, and can penetrate about 20 cm deep. Sampling involved careful selection of the surface layer of sediment (top ~1 cm) into two sample bags, one for archive and one for analysis. The majority of the RV Johnston samples and all of the RV Polaris samples were collected using this instrument. A few samples on the RV Johnston cruise were collected by scraping the fine surface sediment from the top of a box core. Occasionally, samples were taken from various intervals below the surface in the grab or core. The specific equipment and interval used for each sample is indicated on Tables 2 and 3. After collection, samples were stored in a refrigerator on board the boat, and then transferred to a refrigerator in Menlo Park where they were stored at 3.8 C. Sediment Grain-Size Analysis Grain-size analysis typically lasted about one week for a batch of 30 samples. All instrumentation used for the analysis is located on the USGS Menlo Park campus. The following sections describe the various instruments used and a detailed account of the laboratory procedures. Differing Grain-Size-Analysis Methodologies Comparisons between the RV Johnston datasets are hampered by the changing methodologies used for the grain-size analysis. We used three different methods of analysis on the RV Johnston samples during the course of the project. The oldest samples of the data set (J-5-98-SF) were processed using the Rapid Sediment Analyzer (RSA) for the intermediates, and the Micromeritics 5100 Sedigraph for the fine material. 10 samples from the J-2-99-SF cruise were analyzed using the RSA for the intermediates, and the Coulter LS100Q laser particle-size analyzer for the fines. The remaining RV Johnston samples and all of the RV Polaris samples were processed utilizing only the laser particle-size analyzer for both size fractions. It is important to note that the RV Polaris samples were processed by the same individual and used a consistent analysis method, facilitating comparisons between samples throughout the study period. The techniques used to analyze the samples from the RV Johnston and the RV Polaris are indicated on Tables 2 and 3, respectively. The changing methodologies were due to the limitations of the Sedigraph in processing the finest fraction (<0.0005 mm) of material. As a result, the data for the J-5-98-SF cruise show an increase in this size fraction as seen on Figures 7A and B. The laser particle-size analyzer was ultimately chosen as the best laboratory technique because of its ability to analyze a large range of grain sizes (0.0003 mm to 1.0 mm, 11.5 phi to 0 phi,), resulting in the use of only one instrument. In order to facilitate comparisons between the samples, we omitted the coarsest material (>1 mm) from the RV Johnston samples for the computer analysis. We made this change for two reasons: 1) this size 

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Bed-sediment grain-size and morphologic data from Suisun, Grizzly, and Honker Bays, CA, 1998-2002

Modeling stochastic floods and erosion thresholds in bedrock rivers: Field data from northern California

A comparison of land-use and glacial controls on erosion in the northeastern united states

All culinary water in Castle Valley is from wells. Increased residential development using individual waste-water-disposal systems has raised concerns for the long-term quality of ground water in the valley-fill aquifer. In this study, ground-water recharge and discharge areas, potentiometric surface elevation, and specific conductance were mapped to serve as tools for protecting ground-water quality and managing potential contaminant sources in Castle Valley. Castle Valley is one of several northwest-trending salt anticline valleys on the Colorado Plateau in southeastern Utah. The unconsolidated valley fill is the principal aquifer in the valley and consists of coarse alluvial-fan deposits and stream alluvium, with minor clay. Some recharge to the valley-fill aquifer comes from underflow from bedrock aquifers, but most is from La Sal Mountains runoff via Castle Creek and Placer Creek. Because of the absence of protective, low-permeability confining layers, the valley-fill aquifer is unconfined, and most of the valley is classified as primary recharge area. The only discharge area is along lower Castle Creek. Water quality in the valley-fill aquifer is generally high in upper Castle Valley, but declines in the lower valley, perhaps due to recharge from saline ground water in bedrock aquifers in contact with Paradox Formation evaporites. Wells tapping the Cutler Formation aquifer beneath the valley fill also yield poor-quality water. The coarse-grained, unconfined valley-fill aquifer is highly susceptible to contamination from surface recharge.

Noah P. Snyder

Papers

Bed-sediment grain-size and morphologic data from Suisun, Grizzly, and Honker Bays, CA, 1998-2002

Modeling stochastic floods and erosion thresholds in bedrock rivers: Field data from northern California

A comparison of land-use and glacial controls on erosion in the northeastern united states

Recharge Area and Water Quality of the Valley-Fill Aquifer, Castle Valley, Grand County, Utah

Impacts of beneficial use of sediment placements on water biogeochemistry in a back-barrier new jersey salt marsh