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Pictured Rocks National Lakeshore is located in the Upper Peninsula of Michigan along the southern shore of Lake Superior. The park spans approximately 300 km2 and is almost fully incorporated within the ten 7.5-minute quadrangles presented in this new, detailed surficial geology map. The western quadrangles are mainly characterized by thin accumulations of undifferentiated Quaternary sediment above shallow bedrock while the eastern quadrangles mostly show thick accumulations of various glacial outwash units. This map was produced by integrating field data with a high-resolution LiDAR digital elevation model and associated hillshade, aerial imagery, and passive seismic data. The high-resolution elevation information was essential to differentiate between outwash units, post-glacial sand accumulations, and interpreting subtle glacial features that would have otherwise remained unrecognized. This new map provides fundamental information to help decipher the glacial history of this region to enhance our understanding of how this popular landscape developed.

Exhumed Paleozoic glacial deposits and landforms of the North Gondwana are reported here for the first time from the South Eastern Desert (SED) of Egypt. Using field observations and remote sensing...

Mega-streamlined landforms on Earth and Mars have been attributed to aeolian, glaciogenic, fluvial, and tectonic processes. Identifying the forces that shaped these landforms is paramount for understanding landscape evolution and constraining paleo-climate models and ice sheet reconstructions. In Arabia, east-northeast, kilometer-scale streamlined landforms were interpreted to have been formed by Quaternary aeolian erosion. We provide field and satellite-based evidence for a Late Ordovician glacial origin for these streamlined landforms, which were exhumed during the Red Sea–related uplift. Then we use Late Ordovician paleo-topographic data to reconstruct the Late Ordovician ice sheet using identified and previously reported glacial deposits and landforms. Our reconstruction suggests these glacial features are part of a major, topographically controlled, marine-terminating ice stream, twice the length of the largest known terrestrial ice streams. Our results support models that advocate for a single, major, and highly dynamic ice sheet and provide new morphological-based constraints for Late Ordovician climate models.

The last-glacial megaflood Kankakee Torrent streamlined hills and the remarkably straight backslope of the Kalamazoo moraine (Lake Michigan lobe of the Laurentide ice sheet) in southwestern Michigan. Flooding ensued as proglacial Lake Dowagiac overflowed across remnants of the Lake Michigan lobe at the position of the inner margin of the Kalamazoo moraine as glacial debris and ablating ice were pinned against Portage Prairie. Proglacial Lake Dowagiac developed in the Dowagiac River valley as the lobe retreated to form the Valparaiso moraine. A minimum age of the Kankakee Torrent (18.7 ± 0.6 k.y. B.P) is indicated by the weighted mean value of six optically stimulated luminescence ages determined from quartz sand in glaciofluvial sediment on the Kalamazoo moraine (Lake Michigan and Saginaw lobes). This value is consistent with tighter age control based on radiocarbon ages of tundra plants within silty sediment forming ice-walled lake plains and in a torrent-scoured lake basin (Oswego channel) in Illinois. Crosscutting relationships of well-dated moraines indicate the Kankakee Torrent occurred sometime between 19.7 and 18.9 calibrated (cal.) k.y. B.P. as it skirted the south margin of the Valparaiso Morainic System.

Water resources, depending on quality, potential, and location, are vital for sustainable development in many countries of the world, including Egypt. The Eastern El-Minia area, where limestone (cavernous and fractured) constitutes an important aquifer, also included in the development plans of the Egyptian government. Therefore, the region was chosen to be the subject of extensive study. This study aims to assess the reservoir and determine its thickness, water quality and recharging sources. Geoelectrical investigations in combination with groundwater chemistry and stable isotope measurements were applied to achieve the study objectives. The aquifer in the study area is mainly hosted within the irregular distribution of cavernous limestone of the Samalout and El-Minia formations, which are characterized by great thickness with an average value of about 100 m and average resistivity value of about 60 Ωm reflecting good water quality between fresh to brackish conditions. River Nile water contributes 16–80% of aquifer recharge , and the remaining recharge comes from precipitation. Thus, the cavernous carbonate aquifer in the East El-Minia region is classified as a highly potential aquifer that is ideal for many uses and development projects.

This study utilized several isotopic tracers and geochemical parameters to characterize the source and hydrogeochemical setting of elevated ammonium (NH 4 + ) concentrations (>2 mg/L) in a confined glacial drift aquifer in Ottawa County, Michigan. Results from this investigation indicate that NH 4 + is attributed to degrading in situ organic matter and not from surficial anthropogenic sources. Tritium, δ 18 O, and δ 2 H values suggest that primary recharge in the confined aquifer occurred during the middle to late Holocene and before the mid-1900's. Geochemical constituents, including redox parameters and a suite of common ions, demonstrate a compositional difference between the confined and unconfined aquifers in the study area and therefore further support the isolation of the confined aquifer from a significant amount of recent recharge (post 1950's). Insignificant δ 15 N- NH 4 + fractionation (+0.81‰ to +1.38‰) implies that NH 4 + in the confined aquifer originated from degrading in situ organic matter. A complete Rotosonic glacial sediment core, collected to characterize the physical setting of the NH 4 + -rich aquifer, confirmed the presence of in situ organic matter in the confined aquifer. A limited set of δ 15 N-NO 3 and δ 18 O-NO 3 values suggest that the application of manure to row crops may be contributing nitrate (up to 10 mg/L) to nearby shallow residential wells. As implemented in this study, the use of multiple geochemical and isotopic parameters, including δ 15 N-NH 4 , can be applied to evaluate the potential source of NH 4 + in an aquifer.

Wadi Qena basin represents one of the most promising regions for future development in Egypt. Fresh water supplies are crucial for such plans. We provide an integrated remote sensing (Landsat, ASTER DEM, Geoeye-1), geophysical (aeromagnetic), isotopic (δ 18 O, δ 2 H), field (stratigraphic and structural interpretation) and geochemical (major dissolved ions) approach to delineate zones of potential groundwater resources in Wadi Qena basin. Four water-bearing horizons were sampled: fractured crystalline aquifer, Nubian Aquifer System (NAS), Post Nubian Aquifer System (PNAS) and the Quaternary aquifer. Findings include: (1) spatial analysis of remote sensing data in a GIS environment indicates extensive structural deformation by dextral faults trending NE-SW (i.e. Qena-Safaga shear zone [QS]) and sinistral faults trending NW-SE (i.e. Najd shear zone) and sufficient surface water supply from the east through Wadi Fattera sub-basin; (2) analysis of geophysical data indicates that these faults control the water-bearing horizons in the subsurface; (3) isotopic analysis reveals four isotopic groups including two end members, one mixed group and one mixed and evaporated group: group (I) highly depleted fossil Nubian waters (range: δ 18 O from − 6.39 to − 6.74‰ and δ 2 H from − 48.21 to − 52.46‰); group (II) modern waters in fractured basement (range: δ 18 O from − 1.41 to − 1.51‰ and δ 2 H from 5.46 to − 6.04‰); group (III) a mixed cluster between NAS and modern waters (range: δ 18 O from − 4.82 to − 5.05‰ and δ 2 H from − 33.28 to − 38.54‰); and group (IV) samples which have both mixing between the Nubian and meteoric waters and also have a considerable deviation from the Global Meteoric Water Line (GMWL) (range: δ 18 O from − 0.58 to − 4.69‰ and δ 2 H from − 19.59 to − 38.68‰), (4) samples with a mixed isotopic signature (in group III), which tap the NAS and are located along the main channel of Wadi Fattera (area 3600 km 2 ) provide evidence for modern recharge along surface exposures of the NAS and enhanced infiltration along deep-seated faults; (5) samples with a mixed isotopic signature (in group IV), which tap the Quaternary and PNAS aquifers and are located along deep-seated faults provide evidence of artesian upward leakage from the deep NAS into the shallower Quaternary and PNAS aquifers. The present study improves our understanding of the role of structural control and modern recharge in exploration for aquifer potential in arid environments.

The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; 'Quaternary Glaciations - Extent and Chronology, Part II' [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km(2), which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world's largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval. (C) 2020 Elsevier Ltd. All rights reserved.

International audience; The Yellow River (YR) is one of the longest and most sediment-laden rivers in the world. However, the timing and mechanism of the integration of upstream and downstream reaches of the YR is still debated, with estimates ranging from >34 Ma to ~0.15 Ma. Here we address this debate by studying the detrital-zircon age spectra from three boreholes that penetrate late Miocene sediment in the lower YR floodplain. Our results show a significant provenance change between 1.6 and 1.5 Ma marking the input of new materials from the Middle Reach and/or the Upper Reach, suggesting the upstream and downstream parts of the YR were connected between 1.6 and 1.5 Ma. This late establishment of the YR is not consistent with the timing of uplift of the northeastern Tibetan Plateau and surrounding mountain ranges and thus precludes a tectonic control; however, it follows the Plio-Pleistocene onset of large-amplitude sea level changes, associated with a worldwide increase of fluvial incision. We propose that Plio-Pleistocene base level fluctuations likely triggered fluvial erosion propagating upstream from the YR lower reach and were thus the main driving force for river integration.

The Middle Eocene carbonate aquifer constitutes the major source of groundwater for the expansion of reclamation projects outside the Nile Valley southeast of Beni-Suef, Egypt. In the past few decades, groundwater abstraction from the Middle Eocene carbonate aquifer has increased, leading to the deterioration of groundwater quality. The current study combines geochemical methods and multivariate statistical analysis to assess the factors controlling the deterioration of groundwater quality in this aquifer. The results show that the total dissolved solids (TDS) varies between 263.7 and 4214 mg/l. The groundwater is dominantly of Na–Ca–Cl SO4 type. Various plots were used to assess processes such as carbonate and evaporite dissolution, silicates weathering and/or cation exchange controlling groundwater quality. Geochemical modelling with NETPATH indicates that recharge sources and mixing of groundwater within the aquifer result from occasional storms over the eastern watershed. These rainfall events account for ~32% of aquifer recharge, along with infiltration of Nile water in the west, which contributes ~36% of the recharge. The groundwater salinity is controlled by precipitation of calcite, dissolution of dolomite, gypsum and halite and ion exchange along the groundwater flow path. Multivariate statistical analysis highlights that the Ca, Na, Cl and SO4 ions control groundwater salinity within the aquifer through water-rock reactions and mixing of Nile water from the western side of the study area with subsurface recharge from mountainous areas in the eastern portion of the watershed. Integration of hydro-geochemical data and multivariate statistical analysis leads to better understanding of geochemical processes controlling regional groundwater quality in the Middle Eocene carbonate aquifer near Beni-Suef, Egypt and in areas with comparable conditions.

Sixteen groundwater samples collected from production wells tapping Lower Cretaceous Nubian Sandstone and fractured basement aquifers in Sinai were analyzed for their stable isotopic compositions, dissolved noble gas concentrations (recharge temperatures), tritium activities, and 14C abundances. Results define two groups of samples: Group I has older ages, lower recharge temperatures, and depleted isotopic compositions (adjusted 14C model age: 24,000–31,000 yr BP; δ18O: − 9.59‰ to − 6.53‰; δ2H: − 72.9‰ to − 42.9‰; < 1 TU; and recharge T: 17.5–22.0°C) compared to Group II (adjusted 14C model age: 700–4700 yr BP; δ18O: − 5.89‰ to − 4.84‰; δ2H: − 34.5‰ to − 24.1‰; < 1 to 2.78 TU; and recharge T: 20.6–26.2°C). Group II samples have isotopic compositions similar to those of average modern rainfall, with larger d-excess values than Group I waters, and locally measurable tritium activity (up to 2.8 TU). These observations are consistent with (1) the Nubian Aquifer being largely recharged prior to and/or during the Last Glacial Maximum (represented by Group I), possibly through the intensification of paleowesterlies; and (2) continued sporadic recharge during the relatively dry and warmer interglacial period (represented by Group II) under conditions similar to those of the present.

Tunnel valleys are common throughout the terrain of the Saginaw Lobe of the Laurentide Ice Sheet in southern Michigan. The set of valleys described in this paper is regularly spaced in a radial pattern behind the Kalamazoo Moraine, an ice-marginal position formed during retreat from the Last Glacial Maximum. These valleys are divided into proximal and distal groups lying north and south, respectively, of a major river valley that cross-cuts the tunnel valleys at right angles. Based on a series of rotasonic borings and core analysis, the proximal valleys are shallow, contain minimal sediment fill, and overlie fine-grained diamicton and glaciolacustrine sediment, whereas the distal valleys are deeply incised into the substrate and are partially filled with coarse sediment. The distal valleys terminate within a broad zone of high-relief, hummocky topography representing stagnation and collapse behind the Kalamazoo ice margin. The proximal valleys occur within a more subdued landscape located farther from the ice margin. Although some elements of existing genetic models are consistent with these valleys, none appears to be completely compatible with their stratigraphy and morphology. Initial incision of the valleys could have involved short-lived moderate- to high-discharge flows, followed by deposition during or after the events. The deep incision and thick, coarse sediment in distal valleys in the stagnant marginal zone probably involved supraglacial meltwater draining to the bed as the margin downwasted. Fining-upward eskers inset into the valleys were formed by flows of declining energy in small late-stage conduits.

The surficial terrain of the Saginaw Lobe in southern Michigan is divided into 4 landsystems, numbered sequentially from southwest to northeast, containing related assemblages of sediments and landforms, two of which appear to have a genetic relationship with the bedrock units over which they lie. Landsystem 1 consists of the Sturgis Moraine, a terminal/recessional moraine, and an adjacent drumlin field. The moraine is a high-relief ridge with hummocky topography and ice-walled lake plains at its crest, and thick, coarse outwash fans on its distal margin. The drumlin field extends up-glacier from the Sturgis Moraine across the subcrop of the Mississippian Coldwater Shale to the subcrop of the overlying Marshall Sandstone. The low permeability of the shale may have increased basal pore pressures into a range in which deformation of basal sediment into drumlins occurred. Landsystem 2 overlies the subcrop of the Marshall Sandstone. Stagnation of the lobe behind a discontinuous moraine in this area is indicated by high relief, collapse topography, composed of kames, eskers, and ice-walled lake plains. A system of tunnel valleys terminates and merges in this landsystem with large outwash fans and plains sloping away from the margin. High basal drainage into the sandstone may have facilitated stagnation across a broad area to form this landsystem. Landsystem 3 may have also developed during stagnation of the lobe, but it differs from landsystem 2 by its more subdued relief. It contains a network of evenly spaced, southwest-trending open tunnel valleys that contain discontinuous esker segments. Landsystem 4 consists of till plains and low recessional moraines formed as the Saginaw Lobe retreated downslope into Saginaw Bay of the Lake Huron Basin. Tunnel valleys are absent in this area.

The isotopic composition of modern precipitation collected monthly from the International Atomic Energy Agency (IAEA) stations over North Africa is enriched (average δD: Morocco: -25.8‰; Algeria: -21.3‰; Tunisia: -20.6‰; Libya: -17.7‰; Egypt: -11.7‰) compared to fossil groundwater across North Africa, which shows progressive west-to-east depletion; this indicates that precipitation from paleowind regimes was different from those prevailing in the present day (late Holocene). However, a few monthly records (March 1982, December 1987, December 1991, March 2002, and April 2002) collected from IAEA stations (Sidi Barrani, Cairo, Rafah, and El-Arish) showed isotopic depletions (δD = –56‰ to –43.7‰) approaching those of the fossil groundwater in Egypt. For each of the five events, we investigated the direction of cloud propagation in relation to the isotopic composition of precipitation as it travels over the African continent and surroundings. Cloud propagation directions and air parcel flow paths were extracted from temporal (every 30 min) Meteosat image products: (1) Infra-red EUMETSAT, (2) Cloud Motion Winds (CMW), and (3) Back Trajectory Models (BTM). The inferred wind regimes for each of these events were then compared to those for the remaining Egyptian records (160) that produced precipitation with enriched to intermediate isotopic compositions (δD: –39.7‰ to + 34.6‰). The extracted cloud propagation directions and the observed spatial variation in the isotopic compositions of the precipitating rain support a model that attributes previous wet climatic periods over North Africa to the intensification of palaeowesterlies during glacial periods.

High iron concentrations create water quality problems for municipal use in glacial drift aquifer units. The chemical evolution of oxic groundwater in shallow aquifer units to anoxic groundwater in deeper aquifer units, in which soluble Fe(II) is stable, is attributed to coupled reduction of Fe(III) on aquifer solids with oxidation of organic carbon. The objective of this study was to characterize the distribution of organic carbon in aquifer and aquitard sediments to determine the availability of potential electron donors to drive these reactions. To do this, four complete rotasonic cores in a glacial aquifer/aquitard system were sampled at close intervals for analyses of grain-size distribution and organic carbon content. The results indicate significantly higher organic carbon concentrations in diamicton (till) units that function as aquitards, relative to coarse-grained aquifer units. In addition, readily reducible iron content in the diamicton units and lower aquifer unit materials is sufficient to produce far more dissolved iron than is present in the aquifer. Groundwater evolves to the level of iron reduction as a terminal electron-accepting process as it moves downward through aquitard units along flow paths from upland recharge areas to downgradient discharge areas. Deeper aquifer units are therefore unlikely to contain groundwater with low iron concentration.

Concentration trends of monitor wells utilized in monitored natural attenuation at petroleum underground storage tank sites can be used to predict achievement of regulatory standards if the data approximate a first-order decline trend. However, declining concentration trends often display seasonal and other fluctuations that complicate trend interpretation. Seasonal correlations between concentration and water-level elevation, including in-phase and inverse relationships, constitute one of the most common types of variation. The in-phase fluctuations are most common for monitor wells located in or near the source area of the release. This relationship may be the result of increased contact with the smear zone in the source area during periods of high water table. Conversely, inverse trends of water-level elevation and concentration are most common in downgradient wells beyond the limit of the source area. In a year long study of short-term fluctuations in BTEX and other parameters in a downgradient monitor well, the data suggest that the winter/spring recharge event significantly controls the concentration trends of BTEX as well as inorganic compounds in the well. Recharge and associated water table rise began in late fall and were soon followed by a slug of inorganic ions strongly influenced by road salt application. This slug of recharge diluted the concentrations of petroleum compounds and alkalinity (bicarbonate). Electron acceptors including oxygen, nitrate, and sulfate, which is a component of road salt, are also contributed to the water table during recharge. Oxygen and nitrate were not detected in the monitor well samples and were most likely consumed quickly in biodegradation reactions at the top of the contaminant plume. Sulfate peaked during winter/spring recharge and then slowly declined during the summer and fall, along with redox potential. Alkalinity (bicarbonate) increased during this period, which may represent the coupled oxidation of organic carbon to CO2 with sulfate as the electron acceptor. BTEX concentrations peaked in the fall probably due to the lack of diluting recharge. The slow changes in concentration over the summer and fall months, interpreted to be caused by biodegradation, contrast with the rapid changes associated with dilution during the recharge event.

The Wadi Isla drainage basin, a narrow steep bedrock canyon and its tributaries, rises near the highest elevations of the Precambrian Sinai massif on the eastern margin of the tectonically active Gulf of Suez rift. The basin area upstream from the mountain front is 191 km 2 and downstream the wadi crosses a broad alluvial plain to the Red Sea. Stream-transported boulders within the lower canyon (up to 5 m in diameter) and in a fan downstream indicate extremely high competence. In one reach, a 60-m-long boulder berm, ranging in height from 3 to 4 m, lies along the southern wall of the canyon and contains boulders 2–3 m in diameter. Boulder deposits beyond the mouth of the canyon generally appear to be less than several metres thick and are composed of imbricated, well-sorted boulders. The last flood that deposited these boulders is believed to have been a debris torrent with a low content of fines. Mean intermediate diameter decreases from about 1.5 m just beyond the mouth of the canyon, where the channel width expands to 300 m, to about 0.5 m downstream to the point at which the valley is no longer confined on its south side. Using the empirical formula of Costa (1983) , these clasts represent velocities decreasing from about 6.5 m s − 1 to 3.7 m s − 1 . Flood velocity and discharge were also calculated within the canyon, using Costa's (1983) method and by the Manning equation. Parameters for the calculation include a channel width of 65 m, flow depth of 3.5 m (average height of the boulder berm), an average slope of 0.038 and a roughness coefficient of 0.06. The resulting values include a velocity range between 6.8 m s − 1 and 7.3 m s 1 and a corresponding discharge range of ∼ 1550 m 3 s − 1 to 1660 m 3 s − 1 . A lower limiting discharge of 1320 m 3 s − 1 was obtained with an assumption of critical flow conditions. The boulder fan is much coarser than the older alluvial plain sediment, suggesting an increase in flood magnitudes in more recent times — perhaps in response to renewed uplift of the mountain front and/or climate change. A calibrated rainfall–runoff model was developed using SWAT to estimate modern flood discharges in Wadi Isla. The magnitude of discharge from 1998–2006 did not exceed 500 m 3 s − 1 . Artificial precipitation amounts (90 and 150 mm) were used to extrapolate from recent rainfall amounts to the amount of rainfall needed to produce a discharge range of 1320 m 3 s − 1 to 1660 m 3 s − 1 . Results show that rainfall must range between ∼ 102 mm and 125 mm to produce this discharge.

Gaussian quadrature, a numerical integration technique through fixed points, is applied to improve accuracy and efficiency in the cross-section balance modeling of a slope subjected to progressive displacements. This integration is employed to compute geometrical areas of individual stratigraphic units that have participated in the deformation. Given the initial and final states of a natural slope in which progressive failure has been carefully monitored for 7 years, the internal geometry of four stratigraphic layers that were displaced in a manner that characterizes the displacement kinematics of the entire slope has been analyzed. The area differences between the initial and final sections for three of the layers are zero. A fourth, basal, layer shows a unit area reduction of 13 percent, which can be accounted for by toe erosion. This implies that the total internal geometric area is found to be preserved during the course of the progressive deformation, a fact that is evident in repeated ground surveys conducted during the 7-year history of displacement. Also, factors of safety computed for the basal surface of slip at the initial and final stages of displacement monitoring demonstrate that the slope became less stable over a period of 7 years as a result of the progressive failure. Such a reduction in stability would be difficult to quantify without the application of numerical integration that allows the accurate construction of area-balanced geometrical models in a digital format amenable to validation and stability analysis.

Cross sections of slopes subjected to progressive displacements can be constructed from arrays of deeply embedded survey poles aligned in the directions of slip. Changes in the spacing and plunge angles of the poles can be used to construct vertical sections that show positions of slip surfaces and the changing shapes and/or positions of stratigraphic boundaries by applying the principles of cross-section balancing. Balanced models of such progressive failures can be used as the basis for determining field locations, data needs, and mitigation strategies associated with more rigorous geotechnical investigations. A slow debris slide in the coastal bluffs of Lake Michigan has been monitored bi-weekly to tri-weekly beginning in 1996 with balanced cross sections constructed annually. When the debris slide was drilled in 47 different places in 2003 as part of a bluff de-watering study, surfaces of rupture and stratigraphic contacts observed in drill cores matched with strong correlation the predicted depth positions of slip surfaces from balanced section models. Without access to the balanced geometric models of the debris slide as guides to drilling sites and geotechnical analyses of soils, the drilling program would not have produced the level of knowledge necessary for a well planned mitigation strategy.

The dynamics of the late Wisconsin Lake Michigan Lobe of the Laurentide Ice Sheet, as interpreted by sediment–landform assemblages along its southeastern margin, are consistent with fast flow driven by high subglacial pore pressures. A major advance of the Lake Michigan Lobe terminated at the Kalamazoo Moraine, where proglacial glaciotectonic activity, marginal stagnation, and release of subglacial meltwater marked the extent of the advance. A large portion of the Valparaiso “Moraine”, west of the Kalamazoo Moraine, is actually a drumlinized, till-capped upland plain rather than an ice–marginal landform assemblage. Lacustrine sediment, underlying the surficial diamicton in the Valparaiso upland, is glaciotectonically deformed to a depth of 10 m. The deformed interval consists of folded sandy and silty lacustrine sediment, which is in places sharply truncated by the overlying diamicton. Decoupling of the glacier from its bed is suggested by a discontinous thin bed of sand at the base of the diamicton, and by the sharp truncation of deformed lacustrine sediment. The association of drumlins, proglacial and subglacial deformation, marginal stagnation, and major ice-marginal outwash-fan deposition are indicative of fast flow, perhaps in a surge. These characteristics are consistent with a terrestrial ice-stream model for the Lake Michigan Lobe.

Geomorphic evidence and stratigraphic information from boreholes suggest that the oversized Central Kalamazoo River Valley (CKRV) in southwest Michigan resulted from a catastrophic outburst flood emanating from subglacial channels under the Saginaw lobe of the Laurentide Ice Sheet. The CKRV occurs as a deeply incised trench over 2 km wide and in excess of 50 m deep situated in a reentrant formed by the Lake Michigan, Saginaw and Huron-Erie lobes. The course of the CKRV follows an irregular flow path that bisects the Kalamazoo Moraine of the Lake Michigan lobe. Erosional terraces near the mouth of the channel indicate that Lake Michigan lobe meltwater drained eastward prior to the westward Saginaw outburst. Prior to valley formation the Lake Michigan lobe had retreated westward to at least the Lake Border Moraine. With the Lake Michigan lobe absent to impede flow, drainage from the CKRV proceeded southwesterly until draining into glacial Lake Chicago near St. Joseph, Michigan. The outburst originated from a system of Saginaw tunnel channels that display convex-up flow profiles and contain eskers. Meltwater drainage transitioned from subglacial-to-ice marginal and proglacial environments. During the interval represented by the outburst, the Saginaw Lobe appears to have been in a relatively stationary position.

Herbicide and herbicide degradate compounds were measured in tile drains, monitoring wells, domestic wells, and in the receiving stream at a farm in south-central Michigan, in which corn, soybeans, and livestock are the major products. Immunoassay screens of two herbicide groups (triazines and alachlor) in 2000 showed a decrease in the number of detections from June to September, after the well-known spring flush, of 48% to 26% for alachlor and 62% to 22% for the triazines. Gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry analyses of 2001 samples documented a fall flush as well, mobilizing relatively high levels of both parent and degradate compounds to the tile drain system. The compounds included both metolachlor and atrazine, which were applied on the farm earlier that year, as well as the degradates of alachlor, which had not been applied on the farm for several years. In four tile drain samples, metolachlor was detected at concentrations ranging from 18 to 25 μg/L, whereas atrazine ranged from nondetect to 2.25 μg/L. Contrary to previous studies, metolachlor concentrations were higher than metolachlor ethane sulfonic acid, by a factor of 3 to 7. The high soil permeability, high water table, and shallow screened intervals of monitoring wells directly below the point of application may explain the lesser degree of breakdown at the point of sampling. Although most detections were below maximum contaminant level or health advisory levels, the unknown effects of degradates and the aggregate levels of compounds measured in many samples may pose higher health risks than for individual compounds.

AQUIPRO, a PC-based method, was used to assess aquifer vulnerability using digital water well logs. The AQUIPRO model is a parameter/factor weighting system for rating the pollution potential of an aquifer. This method uses the well depth, as well as the clay and partial clay thickness in a well, to generate pollution potential scores. In this model, aquifer protection increases as the AQUIPRO vulnerability scores increase and ground water pollution potential decreases. Computerized water well records of 2435 domestic wells with partial chemistry data were used to determine the ground water pollution potential of Kalamazoo County, Michigan. Theoretically, low AQUIPRO pollution potential scores should have more frequent occurrences of ground water contamination events than areas with high AQUIPRO scores with similar land-use, well construction, and well densities. The relative AQUIPRO scores were compared with the frequency of occurrences of nitrate-N in ground water wells. The average nitrate-N concentrations within each relative AQUIPRO vulnerability scores category were also compared. The results indicate that domestic wells containing 5 mg/L or more nitrate-N showed a positive correlation between the frequency of occurrences of nitrate-N and relative decrease of AQUIPRO (r2 = 0.99) vulnerability scores. In other words, as the ground water pollution potential increases, the occurrence frequency of nitrate-N also increases. Furthermore, the results show that as the relative AQUIPRO (r2 = 0.96) vulnerability scores decrease, the mean nitrate-N concentrations also increase.

For the monitoring of incremental slope displacements, electronic instruments are very sensitive to movements, but are expensive and can be disabled because of vandalism, catastrophic events, or power failures. Repeated surveys are time-consuming and detect only finite movements. Positioning of slip planes often requires boreholes or excavations. The kinematics of incremental failure can be readily and inexpensively determined using a rugged extensometer-inclinometer system consisting of ordinary building supplies. Calibrated steel cables are anchored at the tops of slopes, strung through eyebolts at the tops of deeply driven fence poles, and drawn tightly by free-hanging weights at the bases of slopes. Cable plunge angles, pole positions and heights, and pole plunge angles are recorded at regular intervals and entered into a spreadsheet that contains necessary trigonometric and sag corrections. Periodic surveys show pole position errors representing less than six percent of total displacements. Positions and plunge angles of poles are surface expressions of displacements that can be modeled at depth by construction of balanced cross-sections. Slope failure studies over a three-year period along the Lake Michigan shoreline clearly demonstrate the utility of this inexpensive monitoring system and the usefulness of numerous balanced cross-sections to produce a "motion picture" of slope displacements. Cross-section details are verified by boring, by projecting accurately the locations where slip planes eventually appeared on the surface and poles rotated above curved slip surfaces, and by reproduction of the slip surfaces using limit equilibrium digital models. (A)

During retreat from the lateWisconsinan maximum advance in the Great Lakes region of North America, the Laurentide ice sheet margin became distinctly lobate. The Lake Michigan, Saginaw, and Huron—Erie lobes converged in southern Michigan and Indiana, U.S.A. to form a complex interlobate region. Some time after the glacial maximum, the Lake Michigan lobe advanced over landscapes previously formed by the Saginaw lobe. This can be explained by an asynchronous advance of the Lake Michigan lobe during a Saginaw lobe retreat or by an increase in size of the Lake Michigan lobe relative to the Saginaw lobe during a synchronous readvance.Cross-cutting relationships in southwestern Michigan, including palimpsest tunnel valleys, document the overriding of Saginaw lobe terrain. Deep, generally straight trenches parallel to glacial flow lines with hummocky, irregular sides and bottoms are interpreted as tunnel valleys. Saginaw lobe tunnel valleys trend northeast—southwest and Lake Michigan lobe tunnel valleys generally trend east—west.At some time after a Saginaw lobe retreat in southern Michigan, the drumlinized landscape was overridden by an advance of the Lake Michigan lobe to an ice-marginal position at the Tekonsha moraine. Saginaw lobe tunnel valleys in the overridden area were completely filled with ice and debris from the Saginaw lobe retreat at the time of the Lake Michigan lobe advance. Supraglacial and proglacial sediments were deposited over the buried valleys by the Lake Michigan lobe, sometimes by meltwater streams that flowed at high angles to the trends of the valleys. After entrenchment of the Kalamazoo River valley, probably by a subglacial outburst flood, short tributaries were cut nearly at right angles across and through the debris and ice within several buried Saginaw lobe tunnel valleys. After the retreat of the Lake Michigan lobe, subsequent melting of ice in the palimpsest tunnel valleys exhumed the valleys, creating the cross-cutting relationships with the Lake Michigan lobe deposits.

In the glacial topography of southwestern Michigan, the water table does not always conform exactly to the land surface and flow-through wetlands, those with both ground water recharge and discharge, are common. The W-l wetland in Cass County, Michigan, a flow-through system, shows a distinct contrast between upgradient and downgradient ground water quality. Ground water discharging into the wetland is oxic, has up to 40 mg/L NO3-N derived from fertilizer and hog manure application to corn fields, and has major ion concentrations typical of the shallow unconfined aquifer in the area. In contrast, shallow ground water that originates as recharge from the wetland forms a plume extending downgradient that can be identified by isotopic enrichment in 18O and deuterium resulting from evaporation in the wetland prior to recharge and by distinct chemical characteristics similar to the wetland surface water (low conductivity and alkalinity, low concentrations of sulfate, nitrate and dissolved oxygen and high concentrations of ammonia, and DOC). As the wetland surface water infiltrates into the unconfined aquifer, conductivity and alkalinity increase due to carbonate mineral dissolution and iron concentrations increase as ferric iron in the aquifer solids serves as an electron acceptor in microbially mediated reactions. The other chemical characteristics, including the lack of nitrate, persist in the flow system for significant distances downgradient from the wetland. The chemical and isotopic composition of shallow ground water around wetlands can be used to spatially delineate areas of ground-water discharge to the wetland and ground water recharge from the wetland, thereby providing a supplemental method to the use of sometimes inconclusive hydraulic head data in the determination of wetland recharge-discharge function. In this study, the chemical and isotopic data confirm that the water table does not replicate surface topography around closed depressions in the landscape.

The Prairie Ronde fan, a discrete glaciofluvial deposit in southwestern Michigan, contains a productive but highly vulnerable unconfined aquifer used for irrigation, municipal, and domestic supply. A comprehensive hydrogeological study of the aquifer delineated shallow, local flow systems that interact with ponds and wetlands on the fan surface, overlying a deeper intermediate/regional flow system extending to the base of the glacial drift. Ground water within the shallow flow systems contains tritium concentrations indicative of a post-bomb age and is heavily impacted by nonpoint source contamination. Nitrate commonly exceeds drinking water standards in the shallow flow system. Although no continuous physical barrier separates the two flow systems, the deeper flow system is generally lacking in tritium as well as nonpoint source contaminants derived from surface land uses. High capacity pumping from the deeper flow system, however, will likely draw contaminants downward from the shallow flow system. Background-water quality in the aquifer is controlled by equilibrium with calcite and slight undersaturation with respect to dolomite. No spatial trends in major ions were observed, suggesting that carbonate mineral equilibrium is achieved rapidly in the vadose zone and further chemical evolution along ground-water flow paths is minimal. Iron concentrations are highly variable in the aquifer and not correlated with depth. Recharge from lakes and wetlands is a significant cause of elevated iron concentrations in the shallow flow systems.

In the Great Lakes region, bluff recession is a major cause of residential, commercial, municipal, and federal property loss. The average rate of recession in Allegan County, Michigan, ranged from 1 to 2 ft per year, from 1831 to 1958, or a total of 130 to 258 ft over 127 years (Powers 1958). From 1938 to 1996, a 0.1 to 1.7 ft per year recession rate was measured, for a total land loss of 5 to 100 ft over 58 years (Montgomery 1998). Reports show that recession rates are not uniform along the shoreline, nor are they similar during two different time periods at a given site (Chamberlin 1877; Powers 1958; Seibel 1972; Montgomery 1998; Chase et al. 2000). It is difficult to predict future rates of recession. Also, it is evident that recession has not slowed with the introduction of modern stabilization structures. The purpose of this research is to investigate the natural factors that influence lake-bluff instability and to demonstrate an innovative approach (i.e., dewatering the bluff) for deterring or slowing the recession rate. Three geologically distinct sites along the Lake Michigan coast in Allegan County were chosen. In 2004, measurement instrumentation was installed at each of the sites. Part of each site was dewatered using submersible pumps or gravity drains, while another part of each site was not. A total of 76 in-place inclinometers (IPIs) and 28 vibrating wire piezometers (VWPs) among 26 monitoring wells, 45 dewatering wells, and two weather stations were installed.

Although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago, the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate. The most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin; time-transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge, probably catastrophically; and rapid erosion during widespread, catastrophic basal sheetflood events. Recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages. In addition, new advances in understanding of subglacial hydrology, both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds. This work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed, but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation. Both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed. Because of the inability of groundwater flow to account for all the meltwater produced by basal melting, other drainage mechanisms involving both non-channelized and channelized meltwater flow have been proposed. The notion of catastrophic drainage of impounded basal meltwater is still favored by many, and the discovery of hundreds of subglacial lakes beneath the Antarctic Ice Sheet and the likelihood of similar lakes beneath Pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys. Proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them. Tunnel valleys produced by the Scandinavian Ice Sheet have been described and mapped on land as well as on the sea bed. Valleys and networks of valleys, some of which are totally buried, have been linked to 3 or more glaciations. Tunnel valley networks from the last (Weichselian) glaciation in Denmark can be related to specific ice margins developed during ice retreat. In North America, most research has focused on tunnel valleys associated with ice margins formed by the last (Wisconsin) glaciation along the southern margin of the Laurentide Ice Sheet.

The Watrous spillway was rapidly incised during a short-lived outburst from glacial Lake Elstow. In its outlet area, the bed of Lake Elstow was composed of stagnant ice. The 40 km long spillway is incised across a divide, and terminates in the glacial Last Mountain Lake basin, where a coarse-grained fan, herein named the Little Manitou fan, was deposited. Clast sizes fine systematically from the mouth of the spillway across the surface of the fan, from boulders with a maximum mean intermediate diameter of 1.26 m to cobbles, over a distance of 7 km on the south lobe of the fan. Large clasts are concentrated on the surface, and probably represent deposition at peak discharge. The proximal margin of the south lobe of the fan is hummocky, suggesting that deposition of sediment at its apex was on stagnant ice with subsequent collapse. Paleovelocity, paleodischarge, and other parameters were estimated for the outburst flood using a critical shear stress approach. These approaches yielded paleodischarge estimates lower than those deduced from previous analyses of floods in channels of similar size in the region, and lower than values given by empirical equations relating shear stress to particle size. Due to the lack of high-water marks along the channel, the progressive flood erosion of the spillway floor, and the possible presence of stagnant ice in at least the headwater reach of the spillway during the flood, slope is the most difficult parameter to estimate for the flood.

The routing of runoff from the retreating Laurentide Ice Sheet was controlled by a combination of ice-marginal position and topography; isostatic depression also played an important role in the evolution of the ice-marginal landscape. A major redirection of drainage occurred after ice retreated north of the Missouri Escarpment about 12 ka BP. Runoff that had previously flowed south to the Missouri River could then be routed eastward to Lake Agassiz, which in turn drained to the upper Mississippi River valley. Changes in drainage routing in the region west of glacial Lake Agassiz typically were abrupt, as new and lower paths along the retreating ice margin became available. Each new basin was larger than its predecessor and its headwaters extended farther west. Four distinct, sequential phases of ice-marginal drainage occurred between 12 and 10.7 ka BP: the James, Sheyenne, Souris-Pembina and Qu'Appelle-Assiniboine. Starting with the Qu'Appelle-Assiniboine phase about 11.2 ka BP, Lake Agassiz collected runoff from as far west as the Rocky Mountains. By about 10.7 ka BP, ice had retreated north of the lower reaches of the Saskatchewan River, allowing meltwater to by-pass the Qu'Appelle-Assiniboine basin. At about the same time, the eastern outlets of Lake Agassiz opened, initiating drainage to the North Atlantic Ocean from this vast region. Drainage routes evolved by a common sequence of events, beginning with the impoundment of proglacial lakes along the ice margin. Most of these lakes drained catastrophically, resulting in the formation of spillways with distincitve geomorphic features that include broad, scoured and streamlined subupland channels along with subsequently incised narrow, deep inner channels. Characteristic deposits of these outbursts include boulder mantles on subupland channel floors, boulder-gravel bars within the inner channels, and large, primarily subaqueous fans in lake basins that received the flood bursts. These outbursts progressed from basin to basin, causing the drainage of other proglacial lakes, until they reached Lake Agassiz. Spillways associated with the next younger drainage phase were commonly incised across the abandoned lake floors.

Geomorphic and sedimentologic evidence in the Grand Valley, which drained the retreating Saginaw Lobe of the Laurentide Ice Sheet and later acted as a spillway between lakes in the Huron and Erie basins and in the Michigan basin, suggests that at least one drainage event from glacial Lake Saginaw to glacial Lake Chicago was a catastrophic outburst that deeply incised the valley. Analysis of shoreline and outlet geomorphology at the Chicago outlet supports J H Bretz's hypothesis of episodic incision and lake-level change. Shoreline features of each lake level converge to separate outlet sills that decrease in elevation from the oldest to youngest lake phases. This evidence, coupled with the presence of boulder lags and other features consistent with outburst origin, suggests that the outlets were deepened by catastrophic outbursts at least twice. The first incision event is correlated with a linked series of floods that progressed from Huron and Erie basin lakes to glacial Lake Saginaw to glacial Lake Chicago and then to the Mississippi. The second downcutting event occurred after the Two Rivers Advance of the Lake Michigan Lobe. Outbursts from the eastern outlets of glacial Lake Agassiz to glacial Lake Algonquin are a possible cause for this period of downcutting at the Chicago outlets.

Groundwater samples from 288 domestic wells in Barry County, Michigan, were analyzed for 33 inorganic chemical parameters. Variations in chemical composition were investigated by considering the possible effects of human impact, aquifer type (bedrock vs glacial drift), chemical evolution along groundwater flow paths, and glacial landform type (moraine vs outwash). Approximately 25 percent of the glacial drift wells were classified as degraded by human impact and were excluded from further analysis of chemical variation. Two-sample tests comparing individual concentrations from drift and bedrock aquifers suggest that groundwater in the Marshall Sandstone aquifer is derived from local recharge through the glacial drift. This conclusion is supported by generalized groundwater flow patterns recognized for the two aquifers.