Till Zone Research Articles

Evaluating hydroelectric potential in Alaknanda basin, Uttarakhand using the snowmelt runoff model (SRM)

Abstract Hydropower is one of the best renewable energy sources to meet India's rapidly growing energy demand. The Remote Sensing and GIS tools provide reliable information for assessing the available water of the Himalayan rivers. In this study, the basin is divided into 12 elevation zones, and temperature and precipitation were extrapolated within these zones. The MODIS (Terra&Aqua) cloud-free images have been used for mapping the Snow Cover Area and it was found that the SCA will vary from 18–72 % during the simulation period. The model simulation period is divided into calibration (2003–2015) and validation (2016–2019). During the study, it was observed that the model efficiency parameters significantly exceeded the acceptable range. In this study, the snowmelt's contribution increases until zone 8; after this, the snowmelt contribution decreases, and the snow accumulation increases. Also, the Hydro-Electric Power (HEP) generation of the basin is modeled with the help of a power equation for a turbine efficiency of 0.8. The simulation of daily streamflow and generated HEP are compared with the measured values, and both tracked the observed pattern very precisely. The findings of the present study will be implemented on the other ungauged basins and could help us to identify the potential sites for HEP with the help of RS and GIS tools.

Management of scleral tears with concurrent intraocular foreign bodies and factors affecting outcomes.

To report the clinical settings and factors predicting outcomes in scleral tears with concurrent retained intraocular foreign bodies METHODS: All cases with scleral and corneoscleral wounds with retained intraocular foreign bodies (RIOFB) from January 2014 to January 2021 were retrospectively analysed. Favourable anatomic outcome was defined as presence of globe integrity, attached retina, absence of hypotony and active inflammation at last visit. Favourable functional outcome was defined as final visual acuity (VA) > 20/200. Total 139 eyes were included. Mean age was 30.66 ± 13.32 years (median 29 years, IQR 17). Penetrating trauma accounted for 87.1%, rupture for 5.8%, perforation for 7.2%. In 5.8% of the eyes the injury involved zone I extending till Zone II while in 66.9% it involved Zone II and in 27.3% in Zone III. Snellen visual acuity at presentation was logMAR 2.97 ± 1.01 and at last visit was logMAR 2.38 ± 1.45 (p < 0.0001). Time between presentation and repair was 13.93 ± 19.56 h (median 7.6 h, IQR 17.17). Favourable functional outcome was seen in 34.5% eyes and 2/3rd achieved favourable anatomic outcome. Absence of endophthalmitis (OR = 6.25, p = 0.003) and ability to remove the foreign body (OR = 7.05, p = 0.003) were associated with a favourable anatomic outcome. Better presenting Snellen visual acuity (OR = 2.77, p = 0.003), manifest scleral tear (OR = 3.36, p = 0.04), and absence of endophthalmitis (OR = 50, p = 0.0009) were associated with a favourable functional outcome. A third of the cases achieved favourable visual outcome while 2/3rd achieved favourable anatomic outcome. Absence of endophthalmitis is an important factor predicting both.

Clinical Presentations, Management, and Factors Affecting Outcomes in Posterior Segment Open Globe Injuries: An Analysis of 2,360 Eyes

Introduction: The aim of the study was to report the clinical presentations, management, and factors affecting the outcomes of posterior segment open globe injuries in 2,360 consecutive eyes. Methods: This was a retrospective, consecutive, non-comparative interventional case series. All cases with scleral and corneoscleral wounds presenting to these centers from January 2014 to January 2021 were included. The cases were defined according to the Birmingham Eye Traumatology Terminology system (BETTs) classification. The Ocular Trauma Score (OTS) was applied to the dataset. Results: Mean age of presentation was 36.63 ± 19.92 years (median 35 years). Penetrating trauma accounted for 70.92%, rupture for 18.6%, perforation for 4.60%, and IOFB in 5.88% eyes. In 76.60%, the location of injury involved zone 1 extending till zone 2, while in 23.40% it involved zone 2 and/or zone 3. Vision at presentation was logMAR 3.03 ± 0.99 and at the last visit was logMAR 2.47 ± 1.42 (p < 0.0001). Time interval between presentation to the treatment center and globe repair was 13.93 ± 19.56 h (median 7.60 h). Favorable functional outcomes were seen in 29.20% eyes and favorable anatomic outcomes in 66.90%. Decreasing age at presentation, penetrating injury instead of rupture or perforating injury, a higher OTS, absence of corneal involvement, absence of retinal detachment at presentation, and absence of concurrent orbital fracture were associated with a favorable functional outcome (>20/200). Final visual acuity in logMAR correlated with the OTS value calculated at presentation. Conclusions: In the absence of retinal detachment and orbital fracture, posterior open globe injuries typically have a favorable functional outcome. OTS correlated with the final visual acuity.

Abstract 19334: Management and Outcomes of Acute Retrograde Type A Aortic Dissection: Insights From the International Registry of Acute Aortic Dissection

Background: Presentations and outcomes of acute aortic dissection (AD) with an entry tear in the ascending aorta may differ from retrograde dissection with an entry tear in the descending aorta. However, guidelines recommend urgent surgical repair for both entities. Methods and Results: All patients with AD enrolled in the International Registry of Acute Aortic Dissection (IRAD) between 1996 and 2014 were analyzed. We identified 99 patients (67 men; 63.2±14.0 years) with an entry tear in the descending aorta and retrograde extension into the arch or ascending aorta. Overall, independent predictors of retrograde type A AD were increasing age(OR 1.0; 95% CI, 1.0 to 1.0; P=0.004), history of cocaine abuse (OR 4.9; 95% CI, 1.7 to 13.6; P=0.003), back pain at presentation (OR 2.1; 95% CI, 1.3 to 3.3; P=0.002), and non-white race (OR 0.4; 95% CI, 0.2 to 0.6; P&lt;0.001). During initial hospitalization, 44 of these patients were managed medically (MED), 33 with open surgery(SURG) and 22with endovascular therapy (ENDO). Patients in the SURG group presented with larger ascending aortic diameters than MED and ENDO patients (P=0.04). The majority of the MED (72.7%) and ENDO (86.4%) patients had AD extension confined to zone 1 (proximal arch, P&lt;0.001), whereas most of the SURG patients (71.8%) presented with AD extension into zone 0 (proximal to the innominate artery, P&lt;0.001). Early (30-day or in-hospital) mortality rates of the MED, SURG and ENDO groups were 9.1%, 18.2%, and 13.6%, respectively (P=0.51), with 5-year survival of 86.7%, 80.0%, and 90.9%, respectively (mean follow-up, 3.3 years, log rank P=0.67). A trend of favorable early mortality was observed in patients with retrograde extension till zone 1 (8.6%) versus into zone 0 (18.6%, P=0.14).Early mortality of patients with retrograde type A AD (12.9%) was lower than those with type A AD (20.0%, P=0.001), while 5-year survival was similar (86.8% and 89.5%, respectively, mean follow-up, 3.0 years, log rank P=0.96). Conclusion: There is a subset of patients with acute retrograde type A AD who can be managed non-operatively with acceptable short and long-term results. This implies that a selective approach may be reasonable, particularly among those with proximal extension limited to the arch distal to the innominate artery.

Inferring Heterogeneity in Aquitards Using High‐Resolution δD and δ18O Profiles

Vertical depth profiles of pore water isotopes (deltaD and delta18O) in clay-rich aquitards have been used to show that solute transport is dominated by molecular diffusion, to define the timing of geologic events, and to estimate vertical hydraulic conductivity. The interpretation of the isotopic profiles in these studies was based on pore water samples collected from piezometers installed in nests (typically 4 to 15 piezometers) over depths of 10 to 80 m. Data from piezometer nests generally have poor vertical resolution (meters), raising questions about their capacity to reveal the impact of finer scale heterogeneities such as permeable sand bodies or fractured till zones on solute transport. Here, we used high-resolution (30-cm) depth profiles of deltaD and delta18O from two continuously cored boreholes in a till aquitard to provide new insights into the effects of sand bodies on solute transport. High-resolution core-derived profiles indicate that such heterogeneities can cause major deviations from one-dimensional diffusion profiles. Further, comparison of piezometer-measured values with best-fit diffusion trends shows subtle deviations, suggesting the presence of heterogeneities that should not be ignored. High-resolution profiles also more clearly defined the contact between the highly fractured oxidized zone and the underlying unoxidized zone than the piezometers.

Characterizing the hydrogeology of a complex clay-rich aquitard system using detailed vertical profiles of the stable isotopes of water

High-resolution 1D profiles of the stable isotopes of porewater (δ2H and δ18O) obtained by direct porewater-equilibration of core samples were used to identify hydrogeologic zones in a thick, complex, till aquitard system in Saskatchewan, Canada. Detailed 1D isotope profiles revealed the presence of three distinct hydrogeological zones: an upper (5–10 m), an intermediate (10–30 m), and a lower (30–62.5 m) till zone. The upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity (K). The lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers. The curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion. We show that high-resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost-effective and invaluable hydrogeologic information on groundwater flow in aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles (i.e. δ2H and δ18O analyses of water samples and K determinations). Further, the direct equilibration approach overcomes the problem of piezometer leakage in low K aquitards.

Characterizing the hydrogeology of a complex clay-rich aquitard system using detailed vertical profiles of the stable isotopes of water

High-resolution 1D profiles of the stable isotopes of porewater (δ 2H and δ 18O) obtained by direct porewater-equilibration of core samples were used to identify hydrogeologic zones in a thick, complex, till aquitard system in Saskatchewan, Canada. Detailed 1D isotope profiles revealed the presence of three distinct hydrogeological zones: an upper (5–10 m), an intermediate (10–30 m), and a lower (30–62.5 m) till zone. The upper hydrogeological zone was controlled by a sand layer having a high hydraulic conductivity ( K). The lack of vertical variability in the stable isotope data in the intermediate zone suggested groundwater flow and solute transport was controlled by a system of interconnected vertical fractures and lateral sand layers. The curved shape of the isotope profile in the lower till zone suggested that solute transport in this zone was controlled mainly by molecular diffusion. We show that high-resolution vertical stable isotope profiles of porewater obtained from core samples and direct equilibration yield cost-effective and invaluable hydrogeologic information on groundwater flow in aquitard systems that cannot be realistically obtained by construction of costly conventional piezometer bundles (i.e. δ 2H and δ 18O analyses of water samples and K determinations). Further, the direct equilibration approach overcomes the problem of piezometer leakage in low K aquitards.

Chloride‐bromide‐δ11B systematics of a thick clay‐rich aquitard system

Boron, Cl−, and Br− concentrations and boron isotopic compositions (δ11B) were used to provide insight into the sources and water‐sediment interactions of fossil water in a thick nonfractured aquitard system in Saskatchewan, Canada. The aquitard system consists of 80 m of late Pleistocene clay‐rich till disconformably overlying 77 m of late Cretaceous marine clay. The clay is underlain by a regional sand aquifer. Variations in Cl− and Br− confirmed the presence of well‐defined conservative mixing relationships between four types of fluids present in the aquitard system: (1) low‐Cl− water from the base of the fractured and oxidized till zone at 4 m depth; (2) water characterized by an elevated Cl− peak (190 mg/L) at about 12 m; (3) glacial meltwater present between 20 and 60 m depth; and (4) more saline water (Cl− up to 1000 mg/L) from the underlying Cretaceous clay and sand aquifer. Glacial meltwater has low Cl−, δ11B (∼20‰), and Cl−/Br− ratios (50). The low Cl−/Br− ratio of the glacial meltwater is similar to that of modern inland precipitation, which suggests that the Br− budget in the atmosphere 20–30 ka B.P. was similar to that of today and that Br− enrichment in the atmosphere may be a natural process. The relatively low Cl−/Br− ratio (∼150) and δ11B values of the saline water in the sand aquifer (35 and 39‰, respectively) and pore water in the Cretaceous clay (25.6 and 32.6‰, respectively) are not consistent with simple dilution of seawater but suggest dilution and modification of fifteenfold evaporated seawater with a low Cl−/Br− and a high δ11B value (&gt;39‰). This evaporitic seawater may have been entrapped in the Cretaceous clay upon or after its deposition and subsequently flushed from the clay by fresher water. We suggest that the refreshening process modified the original brine into Na‐HCO3 water type and extracted boron with δ11B &lt; 39‰ from the adsorbed sites. In contrast, increase of Cl− in the upper section of the till (the 12 m peak) resulted in apparent depletion of dissolved boron and relative 11B enrichment, which can be explained by adsorption processes. The B‐δ11B relationships can thus be used to trace water‐clay interactions in aquitard systems.

Distribution and Biogeochemical Importance of Bacterial Populations in a Thick Clay-Rich Aquitard System.

To investigate the distribution of microbial biomass, populations and activities within a clay-rich, low hydraulic conductivity (10-11 to 10-12 m s-1) aquitard complex, cores were aseptically obtained from a series of overlying clayey deposits; a fractured till, unfractured till (20-30 ka BP), a disturbed interfacial zone (20-30 ka BP), and a Cretaceous clay aquitard (71-72 Ma BP). The results of confocal microscopy studies, culture methods, molecular approaches, and extractive fatty acid analyses all indicated low bacterial numbers that were non-homogeneously distributed within the sediments. Various primers for catabolic genes were used to amplify extracted DNA. Results indicated the presence of eubacterial 23S rDNA, and the narH gene for nitrate reductase and ribulose-1,5-biphosphate carboxylase (RuBP carboxylase). Although there was no evidence of limitation by electron acceptors or donors, sulfate-reducing bacteria were not detected below the fractured till zone, using PCR, enrichment, or culture techniques. Denaturing gradient gel electrophoresis (DGGE) analyses indicated differences in community composition and abundance between the various geologic units. Results of FAME analyses of sediments yielded detectable extractable fatty acids throughout the aquitard complex. Bacterial activities were demonstrated by measuring mineralization of (14C) glucose. Porewater chemistry and stable isotope data were in keeping with an environment in which extremely slow growing, low populations of bacteria exert little impact. The observations also support the contention that in low permeability sediments bacteria may survive for geologic time periods.

Isotopic Constraints on Off‐Site Migration of Landfill CH4

AbstractOccurrences of CH4 in residential areas in the vicinity of the Beare Road landfill, Toronto, Canada, have raised public concern about potential off‐site migration of CH4 from the landfill site. Carbon isotopic analysis of dissolved and gas phase CH4 at the Beare Road site, however, indicates that CH4 in the ground water systems in the vicinity of the landfill is related to naturally occurring microbial methanogenesis within these geologic units, rather than to contamination by landfill CH4. CH4 gas in the landfill and landfill cover has δ13C values (−60.2 ± 0.9%e) typical of microbially produced gas. Concentrations of CH4 (508 to 693 uM) found in deep ground water in the Scarborough, Don, and Whitby Formations underlying the landfill are isotopically distinct from the landfill gases. They are isotopically and compositionally similar, however, to naturally occurring microbial CH4 identified in organic‐rich glacial deposits throughout Ontario. The lack of any significant CH4 concentrations or concentration gradients in the upper till zone between the landfill and the deep ground water aquifer is further evidence that no transport between the landfill and deep ground water is occurring.

Organic carbon isotope geochemistry of clayey deposits and their associated porewaters, southern Alberta

The organic carbon cycle of slowly permeable, clayey glacial till deposits in the Western Interior Great Plains, southern Alberta, was investigated by examining the relationship between solid organic matter (SOM) in the till sediments and dissolved organic carbon (DOC) in the till porewaters. Geochemically, the tills can be divided into two distinct zones: an upper oxidized (low SOM) till zone, and a lower unoxidized (high SOM) till zone. Till porewaters in both zones are characterized by high DOC contents. Radiocarbon dating and comparison of SOM and DOC fractions suggest DOC in the deep unoxidized zone originated during deglaciation, and is probably representative of groundwater ages in this till zone. In the oxidized zone, DOC originates from variable mixtures of soluble organic matter emplaced during deglaciation, and Cretaceous age coal fragments in this till zone. SOM in the upper till zone was mainly oxidized to CO 2 gas during lowered water table conditions of the Altithermal climatic period. The subsurface production of fossil CO 2 gas has serious implications for using the conventional dissolved inorganic carbon (DIC) 14C groundwater dating method in these clayey till porewaters.

Hydrogeology of Clay Till in a Prairie Region of Canada

ABSTRACTHydrogeologic and isotopic investigations were conducted on thick profiles of clayey glacial till at three study areas in the Interior Plains Region of southern Alberta, Canada. The till consists of an upper weathered zone (9 to 18 m thick) and a lower nonweathered zone (10 to 30 m thick). The presence of tritiated ground water at depths of up to 5 m below the water table in the weathered zones shows that the upper part of the weathered zone is hydrogeologically active. Interpretation of hydraulic head and hydraulic conductivity data, indicates that vertical seepage velocities in the nonweathered till zones range from 2 to 6 m per 1000 years. Calculated lateral ground‐water velocities in the till zones are only about 9 m per 1000 years, and it is concluded that most of the ground water recharging the weathered till zone is returned to the atmosphere by evapotranspiration. Oxygen‐18 and deuterium analyses of ground‐water samples for the weathered till zones support this conclusion.

Origin and Distribution of Sulfate in a Fractured Till in Southern Alberta, Canada

Glacial till in a 22‐km2 area of the Interior Plains Region of southern Alberta, Canada consists of an upper brown gypsiferous weathered zone (up to 20 m thick) and a lower discontinuous grey nonweathered zone (up to 25 m thick). Although the total sulfur content of the two till zones is the same (0.34%), the mean total sulfate content of the weathered till (4.0 mg g−1) exceeds that of the nonweathered till (0.8 mg g−1). Similarities suggest that all SO42− in the nonweathered till and 20% of the sulfate in the weathered till was derived from sulfate‐rich bedrock fragments incorporated in the till during deposition. Laboratory experiments and δ18O and δ34S analyses of total SO42− and the sulfur forms in the two zones show that the majority of the sulfate in the weathered till was derived from the oxidation of organic S at some time after the till was deposited. Mass balance and flux calculations indicate that this oxidation occurred under partially saturated conditions. Groundwater flow simulations suggest that the water table was much lower and that a thick partially saturated zone was possible during the drier Altithermal period (11,000 to 3000 years B.P.). The following chemical processes account for the major ions that are found in the groundwater but were generated when the partially saturated zone existed. The oxidation of reduced S produced SO42− and H+. The H+ reacted with carbonate minerals under elevated PCO2, with Ca2+ loss by exchange for Na+ and gypsum precipitation. Volume shrinkage in the weathered till resulting from these geochemical processes may have enhanced the development of fractures and caused the associated increased hydraulic conductivity.

Soft zones in the glacial till in downtown Edmonton: Discussion

The note by Thomson et al. is a valuable contribution likely to be much greater through the anomalous zones to the case history of Canadian glacial tills. It points out than elsewhere. A comment from the authors on this some important facts about foundation design in so-called point would be appreciated. competent glacial tills. Although their note refers to the On a recent project in Metropolitan Toronto, the Edmonton site, similar anomalous conditions have been writer has discovered anomalous till zones similar to reported by others (Adams 1960; Coates and McRostie those reported by the authors for the Edmonton tills. The 1960; Eden 1976) for other parts of Canada. Adams anomaly occurs within the Leaside till (Karrow 1967) in (1960) reported that, at a site 32 km west of Cornwall, the Borough of Scarborough at a site adjoining the the N values in the softer zones ranged between 5 and 20 Scarborough Civic Centre in the vicinity of Highway blows per 300mm in a till generally exhibiting blow 401 and McCowan Road. The till is a silty sand with counts of 50 or more. On removal from the sampling some gravel and is nonplastic. tubes, the material was reported to be . . quite soft and During a preliminary site investigation in 1977, two in many cases it slumped. The moisture content of the low N values (5-10 blows per 300 mm) in two of six softer till was reported to be high. It would be extremely boreholes were passed off as being caused by soil interesting to discover if the authors found a similar disruption7' due to drilling and sampling. In a follow-up correlation between N values and moisture content for investigation in June 1981 for the building site, anomathe 107 Street site. lously low N values were encountered in three of six In their paper, the authors predict settlements of the boreholes. Subsequently, in October-November, 1981, order of 1 10 mm for a bearing capacity of 240 kPa, a detailed investigation of the site was carried out (Mirza based on the in-situ pressuremeter testing results of the 1982) to find the extent of the anomalous zone. The softer till zones. However, earlier observations of actual additional work costing under $15 000.00, resulted in building settlements in the Edmonton area reported by savings of over $250 000.00 in projected additional DeJong and Harris (1971) indicate the field modulus of costs for piling, caisson, or raft foundations. deformation values to be significantly higher than those Because of the noncohesive nature of the till, extreme predicted by them from laboratory tests, or those care was exercised during drilling and sampling to reported later for in-situ pressuremeter tests by Eisenprevent unbalanced hydrostatic heads. Below the groundstein and Morrison (1973). Therefore, the uncorrected water level, all borings were advanced by casing and use of the in-situ pressuremeter modulus values to washboring techniques, the casing being kept full of predict the 110-mm settlement may be on the conservawater during sampling. Upon recovery, the samples of tive side. This is especially so if one postulates that the weaker silty sand till zone appeared limp, unlike the ground disturbance around the pressuremeter probe is stiff samples from the competent zones which could be lifted out in one solid cyclindrical mass from the ' ~ o t e by S. Thomson, R. L. Martin, and Z. Eisenstein. split-barrel sampler body. 1982. Canadian Geotechnical Journal, 19, pp. 175-180. Samples from both the competent and incompetent

A case study of a chemical spill: Polychlorinated biphenyls (PCBs): 2. Hydrogeological conditions and contaminant migration

The purpose of the second paper in this pair is to describe the hydrogeology and to account for the observed patterns of PCB contamination at the Federal Pioneer site in Regina, Canada. Six major hydrostratigraphic units were identified from detailed test drilling and sampling. From the surface downward these are a thin surface fill, the Regina clay, the Condie silt, the till zone, the interglacial silt, and the Regina aquifer system. This latter unit is an important source of potable groundwater. At present the nearest wells are hundreds of meters from the site. The permanent water table is situated below the Condie silt in sandy glacial till. An active perched groundwater system has developed within the thin fill layer beneath the floor of the plant. The extensive lateral flow of groundwater in this zone has contributed significantly to the spreading of PCBs at the site. The PCBs have also moved downward through fractures in the Regina clay and in the upper part of the Condie silt. It can be expected that capillary forces will halt the downward movement of Inerteen 70‐30® as fractures narrow or stop. However, the possible existence of fractures connecting the contaminated zone to the Regina aquifer system or the potential for transport as a dissolved phase in the groundwaters may permit PCBs migrate downward to the aquifer or to flow laterally off‐site. The most significant hazard represented by the spill is the potential for contamination of future water supply wells that may be placed near the site or aquifer contamination that could result if future drilling provides pathways for contaminants through poorly sealed wells or test holes.

Source and Distribution of Sodium in Solonetzic Soils in Illinois

Possible sources of extractable Na (water-soluble plus exchangeable) considered for Illinois solonetzic soils were: Pennsylvanian bedrock, Illinoian till, Farmdale and Peorian loess, and ocean spray salts from rain. Extractable Na in Illinois sononetzic soils originated chiefly from the weathering in situ of Na-rich feldspars of the parent loess. Members of the albite series (namely, albite and oligoclase) and the Na-rich microcline, anorthoclase, aggregate 70 to 80% of the silt-sized Na-bearing minerals which comprise 75 to 90% of the total mineral Na in these soils. Sufficient Na has weathered from the 50 to 5µ silt fraction in solonetzic soils to account for accumulations of extractable Na currently present in their B horizons. Little evidence of local variability in loess or differential weathering between solonetzic and associated soils suggests that differential redistribution of soluble products of weathering is responsible for extractable Na accumulations in Illinois solonetzic soils. It is believed that the local distribution of solonetzic soils is correlated with more permeable till zones of the highly impervious, underlying Illinoian till paleosol. Based on this assumption, a redistribution mechanism involving aqueous movement and differential segregation of soluble products of weathering is presented.

Glacial geology of Grand Coulee Dam, Washington

Research Article| May 01, 1939 Glacial geology of Grand Coulee Dam, Washington RICHARD FOSTER FLINT; RICHARD FOSTER FLINT Search for other works by this author on: GSW Google Scholar WILLIAM H. IRWIN WILLIAM H. IRWIN Search for other works by this author on: GSW Google Scholar Author and Article Information RICHARD FOSTER FLINT WILLIAM H. IRWIN Publisher: Geological Society of America Received: 23 Dec 1938 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1939 Geological Society of America GSA Bulletin (1939) 50 (5): 661–680. https://doi.org/10.1130/GSAB-50-661 Article history Received: 23 Dec 1938 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation RICHARD FOSTER FLINT, WILLIAM H. IRWIN; Glacial geology of Grand Coulee Dam, Washington. GSA Bulletin 1939;; 50 (5): 661–680. doi: https://doi.org/10.1130/GSAB-50-661 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Sections of the fill in Columbia canyon near Grand Coulee Dam, together with the stratigraphy and morphology of related features downstream, record the expansion and later shrinkage of the Okanogan glacier lobe during the last glaciation. Three stratigraphic zones are recognized: (1) A Basal Sequence of lacustrine fines inter-bedded with fluvial sediments, recording oscillatory ponding of the Columbia River as the glacier dammed it downstream. At first the lake was shallow and drained west around the ice margin. Later it was more effectively dammed, deepened, and forced to discharge south through Grand Coulee. (2) A Till Zone, recording the arrival of ice, with fluctuations, at Grand Coulee Dam during the glacial climax. (3) Later deposits stratigraphically (but not everywhere vertically) overlying the Till Zone, recording oscillatory deglaciation accompanied by transition from lacustrine to fluvial conditions.The San Poil glacier lobe entered the lake-filled Columbia canyon at Keller Ferry, 15 miles upstream from Grand Coulee Dam, and contributed sediment to the lake. The maximum of this lobe appears to have been approximately contemporaneous with the maximum of the neighboring Okanogan lobe.While residual ice was still present locally in Columbia canyon downstream, drain-age abandoned Grand Coulee and resumed its former (and present) course. Thereafter, grading of the long profile of Columbia River proceeded both by erosion of the lake fill and by deposition in depressions partly of ice-block origin and was marked by at least one delay recorded by a particularly conspicuous stream terrace. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.