Sherman Island Research Articles

An age scale for new climate records from Sherman Island, West Antarctica

Abstract. Few ice cores from the Amundsen Sea and Bellingshausen Sea sectors of the West Antarctic Ice Sheet (WAIS) extend back in time further than a few hundred years. The WAIS is believed to be susceptible to collapse as a result of anthropogenic climate change and may have at least partially collapsed during the Last Interglacial (LIG) period. Understanding the stability of the WAIS during warm periods such as the LIG and Holocene is important. As part of the WACSWAIN (WArm Climate Stability of the West Antarctic ice sheet in the last INterglacial) project, the British Antarctic Survey's (BAS) Rapid Access Isotope Drill (RAID) was deployed in 2020 on Sherman Island in the Abbot Ice Shelf, West Antarctica. We drilled a 323 m deep borehole, with discrete samples of ice chippings collected that cover the entire depth range of the drilled ice. The samples were analysed for stable water isotope composition and major ion content at BAS from 2020–2022. Using annual layer counting of chemical records, volcanic horizon identification and ice modelling, an age scale for the record of 1724 discrete samples is presented. The Sherman Island ice record extends back to greater than 1240 years, providing the oldest, continuous ice-derived palaeoclimate records in the coastal Amundsen and Bellingshausen Sea sectors to date. We demonstrate the potential for recovery of a complete Holocene climate record from Sherman Island in the future and confidence in the ability of RAID samples to contain sufficiently resolved records for meaningful climatic interpretation.

Ice drilling on Skytrain Ice Rise and Sherman Island, Antarctica

AbstractTo understand the long-term climate and glaciological evolution of the ice sheet in the region bordering the Weddell Sea, the British Antarctic Survey has undertaken a series of successful ice core projects drilling to bedrock on Berkner Island, James Ross Island and the Fletcher Promontory. A new project, WACSWAIN, seeks to increase this knowledge by further drilling to bedrock on two further ice rises in this region. In a single-season project, an ice core was recovered to bedrock at 651 m on Skytrain Ice Rise using an ice core drill in a fluid-filled borehole. In a second season, a rapid access drill was used to recover ice chips to 323 m on Sherman Island in a dry borehole, though failing to reach the bedrock which was at an estimated depth of 428 m.

Monitoring of subsidence with UAVSAR on Sherman Island in California's Sacramento–San Joaquin Delta

Sherman Island, the westernmost island in the Sacramento–San Joaquin Delta in California, plays a crucial role in maintaining the water flux between saline ocean water from the San Francisco Bay to its west and the rest of the Delta to its east. Land elevation below mean sea level and continuous subsidence over the past century has made this island a high priority area for investigations of subsidence and restoration in the Delta. This study reports the results of successful application of Interferometric Synthetic Aperture Radar (InSAR) data and technique to measure subsidence in the Delta, which is a coherence-challenged non-urban area. We carried out a time-series interferometric analysis of Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) L-band (23.8 cm) data, collected from July 2009–August 2014, to assess both the spatial and temporal variation of subsidence on Sherman Island. We report both large-scale (island-wide) subsidence trends and small-scale (levee/farm scale) subsidence features in Sherman Island. Assuming the subsidence is linear during the five years of UAVSAR data acquisition, subsidence rates across the island range from 0–5 cm/yr, with an average of 1.3 ± 0.2 cm/yr. We estimate our systematic uncertainty to be 0.3 cm/yr. Overall, the central region in the island has subsided at a faster rate than the rest of the island. We find our results to be consistent with previous measurements of subsidence rates at electric transmission line towers scattered throughout the island. The results of this study provide insights into several factors influencing subsidence, including soil type, water table depth, land use, land elevation and the location and time of levee repairs. Subsidence monitoring on Sherman Island is essential for maintaining a reliable water supply for the state of California and for protecting the Delta ecosystem.

Three-dimensional levee and floodwall underseepage

Levee and floodwall seepage models based on two-dimensional (2D) conditions can underpredict landside vertical hydraulic gradients and uplift pressures due to excavations and convex bends. The Sherman Island levee system is used to calibrate a three-dimensional (3D) seepage model to evaluate the effect of finite landside excavations and convex levee bends on landside seepage. The model shows that a 3D analysis is required for a landside excavation with an aspect ratio (length to width) less than 1L:1.5W. For drainage canals and ditches that parallel a levee or floodwall and are wider than 15 m, gradients at the excavation center are essentially equal to 2D vertical gradients but greater than 2D gradients near the excavation sidewalls. The Sherman Island calibrated seepage model also confirms concave bends diverge seepage and yield lower vertical gradients than 2D models. Varying the degree of levee curvature (ω = 45°–100°) indicates that sharper convex bends (ω = 100°; axisymmetric radius, 150 m) cause vertical gradients that can be about 150% greater than 2D analyses.

Dynamic Response of a Model Levee on Sherman Island Peat: A Curated Data Set

A model levee resting atop soft compressible peaty organic soil in the Sacramento/San Joaquin Delta was shaken by forced vibration to study the seismic deformation potential of the underlying peat and measure dynamic levee–peat interaction. Forced vibration testing occurred over a frequency range of 0 Hz to 5 Hz and produced force amplitudes applied to the embankment crest that induced elastic to nonlinear levee-foundation responses. Available data include acceleration records from sensors mounted on the model levee and on the ground surface near the model levee, and acceleration and pore pressure measurements from sensors embedded in the underlying peat. A remote data acquisition system measured settlements and pore pressures over a span of more than a year, encompassing time before and after the dynamic testing. Small pore pressures were generated in the peat during testing although embankment settlements from cyclic loading were small.

Method to Account for Human Intervention in Calculating the Probability of Failure

AbstractAlthough human and organizational factors play a major role in the performance of civil infrastructure, risk assessment does not often explicitly account for them. Although these factors can cause failures, they can also significantly improve a system’s reliability, provided that appropriate procedures are in place to be performed by individuals and the organization as a whole. It is therefore important that engineers, operators, and planners incorporate human and organizational factors into the overall risk-management paradigm. This paper builds on previous risk-assessment methods to develop a framework for quantifying the contribution of human intervention to the overall probability of failure of a system. The six steps of the approach are (1) system definition, (2) conceptual model, (3) event tree, (4) task structure map, (5) quality-management assessment system, and, ultimately, (6) the probability-of-failure computation. The Sherman Island flood-protection system in the Sacramento–San Joaquin...

Glaciomarine sedimentation dynamics of the Abbot glacial trough of the Amundsen Sea Embayment shelf, West Antarctica

Abstract Sedimentary sequences of the continental shelf of the eastern Amundsen Sea Embayment in West Antarctica represent records of past outlet glaciers and ice streams. The former flow of ice streams was channelled through glacial troughs, which now form large bathymetric depressions. We therefore selected one of the largest troughs, the Abbot glacial trough in the outer shelf, to analyse its glacial depositional and erosional history, based on horizon-stratigraphy derived from seismic data. Several basement highs channellized the delivery of sediment and controlled the grounded ice sheet in early glacial periods. Both pre-glacial and full glacial seismic facies were identified. Glacially transported and deposited sediments extended the shelf break by 75 km from the pre-glacial shelf-edge. The main Abbot glacial trough contains sediment from confluent ice flows of the Pine Island/Thwaites, Cosgrove and Abbot Glacier systems, as well as smaller contributions from local ice streams emanating from Thurston Island. Sherman Island of Peacock Sound played an important role in the dynamics of the Abbot Glacier by dividing the ice flow into two ice streams, which interfered with the main glacial sediment transport paths from the south. This study contributes to an understanding of the formation of the Amundsen Sea shelf and the extent of past ice sheet advances.

Sustaining Sherman Island: A Water Management and Agricultural Diversification System

The Sacramento-San Joaquin River Delta isthe main water resource for California’s urbanand agricultural development. Sherman Islandsits on the western edge of Delta system and isone of the key geographic features in balancingthe flux of saltwater into the Delta. Flooding,saltwater intrusion, and ongoing subsidence arecurrent threats to Sherman Island. The integrationof components of aquaculture, hydroponics, anda levee enclosed flood storage area create a system that can actively protect against flooding disastersby reversing subsidence and stabilizing levees, hasthe ability to sequester carbon and restore habits,and the capacity to produce economic yields. Theenvironmental, technical, and economic attributesof the system are examined through failuresimulations, economic analysis, and environmentdiscussion to determine if the proposed system isa feasible, sustainable and profitable solution forSherman Island and the Delta.Sustaining Sherman Island: A Water Management andAgricultural Diversification System

Historic, Recent, and Future Subsidence, Sacramento-San Joaquin Delta, California, USA

To estimate and understand recent subsidence, we collected elevation and soils data on Bacon and Sherman islands in 2006 at locations of previous elevation measurements. Measured subsidence rates on Sherman Island from 1988 to 2006 averaged 1.23 cm/year (0.5 in/yr) and ranged from 0.7 to 1.7 cm/year (0.3 to 0.7 in/year). Subsidence rates on Bacon Island from 1978 to 2006 averaged 2.2 cm/year (0.9 in/yr) and ranged from 1.5 to 3.7 cm/year (0.6 to 1.5 in/yr). Changing land-management practices and decreasing soil organic matter content have resulted in decreasing subsidence rates. On Sherman Island, rates from 1988 to 2006 were about 35% of 1910 to 1988 rates. For Bacon Island, rates from 1978 to 2006 were about 40% less than the 1926-1958 rates. To help understand causes and estimate future subsidence, we developed a subsidence model, SUBCALC, that simulates oxidation and carbon losses, consolidation, wind erosion, and burning and changing soil organic matter content. SUBCALC results agreed well with measured land-surface elevation changes. We predicted elevation decreases from 2007 to 2050 will range from a few centimeters to over 1.3 m (4.3 ft). The largest elevation declines will occur in the central Sacramento-San Joaquin Delta. From 2007 to 2050, the most probable estimated increase in volume below sea level is 349,956,000 million cubic meters (281,300 acre-feet). Consequences of this continuing subsidence include increased drainage loads of water quality constituents of concern, seepage onto islands, and decreased arability.

Dynamic Properties of Sherman Island Peat

The dynamic properties of peat have been identified as a major source of uncertainty in the evaluation of seismic hazards throughout the Sacramento-San Joaquin Delta in northern California. This paper summarizes the results of a laboratory study of the dynamic properties of a layer of peaty organic soil underlying the south levee on Sherman Island near the western side of the delta. Conventional Shelby tube sampling procedures were able to obtain high-quality samples because of the compactness of this peat layer, located between depths of 9 and 16 m. The samples tested were very fibrous and had ash contents of 35--56%. Staged cyclic triaxial loading was used to measure the stress-strain behavior of several specimens under cyclic shear strains ranging from about 0.0005% to 10%. Other tests included piezo-ceramic bender element tests to measure the shear wave velocity of specimens within the triaxial device, and undrained monotonic triaxial compression and extension tests. The effects of loading frequency, cyclic degradation, consolidation stress history, and structural anisotropy are evaluated. The resulting modulus reduction and damping relationships for the Sherman Island peat are compared with published results for other peats, solid waste materials, and mineral soils.

Threatened levees on Sherman Island : Foott, R; Sisson, R; Bell, R Proc Conference Stability and Performance of Slopes and Embankments II, Berkeley, 29– June–1 July 1992V1, P756–774. Publ New York: ASCE, 1992 (ASCE Special Geotechnical Publication No 31)

Threatened levees on Sherman Island : Foott, R; Sisson, R; Bell, R Proc Conference Stability and Performance of Slopes and Embankments II, Berkeley, 29– June–1 July 1992V1, P756–774. Publ New York: ASCE, 1992 (ASCE Special Geotechnical Publication No 31)

Subsurface Structure in the Montezuma Hills, Southwestern Sacramento Basin

Abstract The Montezuma Hills, in the southwestern corner of the Sacramento Basin, are underlain by a deep, asymmetric, south-plunging graben that is bounded on the east by the Midland Fault System and on the west by the Kirby Hills Fault System. The thickest and most complete Paleogene stratigraphic section in northern California is preserved within this graben, and the base of the Tertiary lies below 11,000 ft along the graben axis. Commonly refered to as the “delta depocenter”, the graben is herein termed the Rio Vista Basin. Both west-dipping and east-dipping normal faults of the Midland Fault System are present along and east of the eastern boundary of the Montezuma Hills. These faults form a complex network of north-to-northwest striking faults. Paleocene strata are offset by as much as 500 ft, but these faults die out upward and do not offset Neogene strata. West of the Midland system, the Sherman Island Fault System forms a wide, arcuate zone of east-dipping normal faults that dissects the gently-dipping eastern flank of the basin. Mapped vertical offsets on faults of this system range from less than 100 to over 400 ft on Paleocene horizons. Activity in this system progressed from east to west as older faults died out and new faults developed farther west. In the northwestern corner of the Montezuma Hills, the Sherman Island system converges toward several slightly older faults that dip in the opposite direction, forming a horst block that is partially responsible for the Denverton Creek gas field. These faults trend nearly north-south and offset Paleocene strata by as much as 300 ft, but they die out upward near the base of the Eocene section. West of the Rio Vista Basin axis, Paleogene strata dip to the east and are offset by several east-dipping normal faults along the western edge of the Montezuma Hills. These faults strike north-south and offset Paleocene strata by as much as 1000 ft. At least one west-dipping reverse fault is also present in this area, and offsets Eocene strata by approximately 100 ft. These faults are herein termed the Montezuma Fault System.

Interannual variability of middle atmosphere and Indian summer monsoon

The interannual variability of the mean zonal wind and the mean temperature, obtained from the rocketsonde data for January (symbolizing winter), of the middle atmosphere over the Northern Hemisphere for the 6-year period, 1970–1972 and 1974–1976 has been investigated. The stations considered for the study are Thule, Poker Flat, Fort Churchill, Wallops Island, Cape Kennedy, Fort Sherman, Kwajalein and Ascension Island. The study has shown marked interannual variation in the zonal wind northward of 35–40°N. In the stratosphere (25–45 km), the westerly zonal wind reached its maximum during 1970, 1971 and 1975 near 35–40°N whereas it reached its maximum during 1972, 1974 and 1976 near 60°N, where the polar night jet is located. At stratopause level (50 km), the temperature gradient between equator-middle latitude and the polar region showed interannual variability. The gradient was stronger during 1970, 1971 and 1975 than during 1972, 1974 and 1976.

Sherman Island Dam and Power-House

This paper describes the design and construction of the Sherman Island Dam and Power-House on the Hudson River, about 8½ miles west of Glens Falls, N. Y. The development, built in 1921-23, is an hydro-electric plant with an ultimate capacity of 50 000 h.p. under a normal head of 66 ft. There are four 10 000-h.p. generating units now in operation; when additional regulation of the river is provided, the fifth unit will be installed.

Closure to “Parsons on Sherman Island dam and Power-House”

Closure to “Parsons on Sherman Island dam and Power-House”

Discussion of “Halmos on Sherman Island Dam and Power-House”

Discussion of “Halmos on Sherman Island Dam and Power-House”