Outwash Deposits Research Articles

Precariously Balanced Rocks in Northern New York and Vermont, U.S.A.: Ground-Motion Constraints and Implications for Fault Sources

ABSTRACT Precariously balanced rocks (PBRs) and other fragile geologic features have the potential to constrain the maximum intensity of earthquake ground shaking over millennia. Such constraints may be particularly useful in the eastern United States (U.S.), where few earthquake-source faults are reliably identified, and moderate earthquakes can be felt at great distances due to low seismic attenuation. We describe five PBRs in northern New York and Vermont—a region of elevated seismic hazard associated with historical seismicity. These boulders appear to be among the most fragile PBRs in the region, based on reports from hobbyists. The PBRs are glacial erratics, best evidenced by glacial striations on bedrock pedestals. The pedestals themselves are locally high knobs, often situated on regionally high topography; this setting limits soil development and indicates that any outwash deposits were likely ephemeral. As a result, PBR ages can be reliably established by the retreat of the last continental ice sheet, ∼15–13 ka. To quantify the fragility of the PBRs, we surveyed them with ground-based light detection and ranging and calculated geometric parameters from the point clouds, field observations, and seismic responses. Preliminary validation of the 2023 time-independent U.S. National Seismic Hazard Model (NSHM) shows that the existence of PBRs is generally consistent with the median site-specific hazard curves. Only the Blue Ridge Road site suggests a modest reduction in hazard. To visualize the ensemble of data, we mapped the minimum permissible distance to potential source faults around each PBR site as a function of source magnitude by using the ground-motion models from the 2023 NSHM. Viewed in this manner, our data are consistent with potential M∼6.5 earthquake-source faults in many parts of the Lake Champlain Valley and northern Adirondack Mountains. Our work illustrates a potential pathway for better constraining earthquake-source faults in regions of cryptic faults.

The Temporal and Spatial Dynamics of Succession in a Glacial Foreland in Southern Iceland: The Effects of Landscape Heterogeneity

One of the more visible consequences of anthropogenic climate change is the ongoing retreat of glaciers worldwide. Rates of primary succession in the resulting glacial forelands are commonly calculated from a single measurement set using a single set of measurements across a landscape of varying age, but repeated measurements over decadal scales may be a more effective means of examining the rates and trends of colonization and community development. Repeated measurements of vegetation groups in a glacial foreland in southern Iceland demonstrate that successional changes are measurable, as shown by the calculation of the dissimilarity index at sites over a 15 year interval. Inter-site dissimilarity validates the essential paradigm of primary succession, where vegetative coverage increases in the glacial foreland as a function of time and supports earlier interpretations saying that species richness decreases on older surfaces, even as the total vegetation cover increases. However, successional processes are subject to major abiotic factors, such as aspect, which is controlled by landscape topography, and the substrate composition. The glacial moraines and outwash plain are underlain by different substrates which produce separate successional trajectories. Succession on the moraines ultimately produces a birch-shrub-heath community, while the outwash deposits promote development of a moss-heath community.

Albedo on a glacial foreland at ground level and landscape scale driven by vegetation-substrate patterns

Recent anthropogenic climate change has caused both glacial retreat and increased vegetative growth on Arctic and subarctic tundra landscapes resulting in changing albedo and energy budgets. Glacial forelands are topographically and ecologically heterogeneous landscapes comprising ice-contact and outwash deposits subject to primary succession. The most recent moraines on the foreland of the Skaftafellsjökull in southern Iceland are mostly unvegetated, but vegetation cover increases with the age in a general sense. Vegetated outwash channel terraces occur between the moraines, and a broad vegetated outwash plain occurs distal to the oldest moraine. Variations in albedo were measured at ground level to determine the specific role of vegetation types and varying substrates. Albedo and coverage by major plant groups were measured along transects established on moraines ranging in age from 20 to 130 years and the terrace of one outwash channel and three locations on the outwash plain. Total vegetation cover and coverage by mosses increases on the glacial moraines largely as a function of time but is subject to strong aspect effects. Total vegetation cover and moss cover are highest on outwash deposits, possibly due to a sheltered aspect and greater uniformity of the outwash surface. Measured albedo exhibits a modest positive correlation with total vegetation cover and a modest negative correlation with rock and soil exposure. The strongest positive correlation was found between albedo and moss cover. The differences in brightness between moraines and outwash deposits are evident visually at the landscape scale on satellite photographs and quantifiable by image-processing software.

Long-term glacial and fluvial system coupling in southern Greece and evidence for glaciation during Marine Isotope Stage 16

Pleistocene glacial activity was a major influence on runoff and sediment supply in many river systems across the Mediterranean. The geomorphological impacts of changes in sediment supply between glaciated headwater terrains and downstream depocentres spanning several glacial cycles are, however, poorly understood. By applying uranium-series and optically stimulated luminescence dating to fluvial and glacial sediments preserved on Mount Chelmos (2355 m a.s.l.) in southern Greece, we show how changes in the long-term coupling between glacial and fluvial systems are preserved within a major glaciofluvial outwash fan system that functioned during multiple cold stages. We also present evidence in the form of a cemented till unit, stratigraphically below younger Middle Pleistocene glacial deposits, yielding a U-series age close to the limit of the technique, indicating glaciation during Marine Isotope Stage (MIS) 16 - one of the most severe cold stages recorded in the Mediterranean. This is the first time such early glaciation has been directly recorded in Greece and the wider Balkans and is defined here as the Valvousian Stage based on glacial deposits on Mount Chelmos. Geomorphological and geochronological data point to the formation of a more extensive plateau ice field over Chelmos during MIS 12, another severe glacial period in the Balkans that corresponds with the Skamnellian Stage glaciation of Northern Greece. During this phase, very strong coupling of glacial and fluvial systems led to meltwater flood events transferring large volumes of sediment to lower valley zones culminating in the formation of an extensive glaciofluvial outwash fan complex and glaciofluvial terraces. A smaller plateau ice field during MIS 6 and localised valley glaciers between MIS 5d to 5c correlate with the Vlasian and early Tymphian Stage glaciations in Greece, respectively. The delivery of much less meltwater and sediment through a single valley during MIS 6 and MIS 5b to MIS 4 signalled the transition to progressively weaker glacial and fluvial system coupling. After MIS 4 the uncoupling of depositional zones from sediment sources in glaciated catchments led to fluvial incision of glaciofluvial outwash deposits in several valleys. Despite this incision, the glaciofluvial outwash fans preserve a record of glacial and fluvial system interactions during the Middle Pleistocene and early stages of the Late Pleistocene.

Last Glacial Maximum glacier fluctuations on the northern Alpine foreland: Geomorphological and chronological reconstructions from the Rhine and Reuss glacier systems

Fresh glacial landforms of the Alpine forelands evidence the presence and extent of large piedmont glaciers during the Last Glacial Maximum (LGM) and yield valuable insights into LGM glacier dynamics. This study assesses widespread ice marginal landforms preserved within the limit of the former LGM Rhine glacier and the eastern lobes of the LGM Reuss glacier system by means of geomorphological mapping. Timing of formation of the studied ice margins in Rhine and Reuss systems are chronologically framed by new 10Be and 36Cl surface exposure ages, as well as new radiocarbon dates. This includes redating of radiocarbon samples first determined in the 1980s. Results of this and an earlier study focussing on outwash deposits downstream of the outer LGM ice margin, suggest that the Rhine glacier advanced to and reached its LGM maximum between ca. 26–22 ka, thereby forming a broad >100 km wide foreland piedmont lobe and constructing prominent and largely continuous chains of frontal moraines (outer Schaffhausen moraines). The eastern lobes of the Reuss glacier likely advanced to their LGM maximum position by 25/24 ± 2 ka as indicated by published luminescence dates. Stabilization of the corresponding Untertannwald ice margin and the slightly internal yet more prominent Mellingen moraines (Reuss glacier system) occurred no later than 22 ± 1 ka and 21 ± 1 ka, respectively. Glacier oscillations following the LGM maximum position are evidenced in both Rhine and Reuss systems but show varying degrees of preservation. Largely contemporaneous, late LGM readvances of Rhine (Stein am Rhein stadial) and Reuss (Bremgarten stadial) glaciers occurred after 20.6 ± 1.7 ka and 20.8 ± 1.3 ka, respectively. Absence of upstream moraines suggests rapid ice decay without marked stabilization, thereafter. Despite clear differences in the size and nature of their foreland lobes, with Rhein glacier as a broad piedmont lobe and narrow valley glacier like lobes characterising the eastern Reuss system, a remarkable similarity in timing is shown between the two.

The Last Glacial Maximum and Deglacial History of the Seno Skyring Ice Lobe (52°S), Southern Patagonia

There are still many uncertainties about the climatic forcing that drove the glacier fluctuations of the Patagonian Ice Sheet (PIS, 38–55°S) during the last glacial period. A key source of uncertainty is the asynchrony of ice lobe fluctuations between the northern, central, and southern PIS. To fully understand the regional trends requires careful mapping and extensive geochronological studies. This paper presents geomorphological and geochronological reconstructions of the glacial and deglacial landforms formed during the last glacial period at the Seno Skyring lobe, southernmost Patagonia (52°S, 71°W). We present a detailed geomorphological map, where we identify two moraine systems. The outer and older is named Laguna Blanca (LB) and the inner Río Verde (RV). The LB moraines were built subaerially, whereas parts of the RV were deposited subaqueously under the palaeo lake Laguna Blanca, which developed during deglaciation. We conducted surface exposure 10Be dating methods on boulder samples collected from LB and RV glacial margins. The moraine LB III and LB IV formed at 26.3 ± 2.3 ka (n = 5) and 24.3 ± 0.9 ka (n = 3), respectively. For the inner RV moraine, we obtained an age of 18.7 ± 1.5 ka (n = 6). For the palaeo Laguna Blanca evolution, we performed 10Be exposure ages on shoreline berms and optically stimulated luminesce dating to constrain the lake levels, and 10Be depth profile dating on an outwash deposit formed by a partial lake drainage event, which occurred at 22 ± 3 ka. For the RV moraine deglaciation, we performed radiocarbon dating of basal sediments in a peat bog, which indicates that the glacier retreated from the terminal RV moraine by at least c. 16.4 cal kyr BP. Our moraine geochronology shows an asynchrony in the maximum extents and a different pattern of ice advances between neighbouring lobes in southern Patagonia. We speculate that this may be due, at least in part, to the interaction between topography and the precipitation carried by the southern westerly wind belt. However, we found broad synchrony of glacial readvances contemporaneous with the RV moraine.

Sediment fill of Baffin Island fjords: Architecture and rates

This Review quantitatively and qualitatively describes 10 representative Baffin Island fjords chosen to explore the nature of a glaciation in delivering sediment to a fjord, with focus on deglacial (within 13–6.7 kyr BP) and postglacial conditions (within 8.2–0 kyr BP). Fjords are compared using observed sediment thicknesses (49–175 m, averaged) and volumes (0.7–14.6 km3), and modeled sediment yields: (1) deglacial 140–1060 t/m2/yr; (2) paraglacial 45–350 t/m2/yr; (3) neoglacial 30–150 t/m2/yr; (4) Little Ice Age 70–440 t/m2/yr; and (5) Anthropocene 60–290 t/m2/yr. Modeled sediment loads, when converted to deposit volumes, compare favorably to observations from geophysical surveys and terrestrial mapping, or separately to sediment accumulation rates (SAR) determined from marine sediment cores. Fjord-averaged SAR during deglaciation range from 4.6 to 25 mm/yr, and 0.6–3.1 mm/yr for the postglacial interval. Fjords directly impacted by the Laurentide Ice Sheet (central and northern Baffin Island) are 2–3 times larger in dimensions than southern Baffin Island fjords, with ∼4.5x deglacial and ∼5x postglacial larger deposits, including well-defined ice-proximal outwash deposits. To the south, Penny Ice Cap associated fjords with no withholding sills, lose 30–40% of their incoming fjord sediment to Broughton Trough that dissects the continental shelf. Sunneshine is the only sampled fjord that was neither directly nor indirectly impacted by the Wisconsin continental ice sheet; Sunneshine responded instead to local maritime conditions and an alpine glaciation.

Investigating hydrologic controls on 26 Precambrian shield catchments using landscape, isotope tracer and flow metrics

AbstractAlthough many studies focus on catchment classification, hydrologists are challenged to find the most important variables for a meaningful catchment classification, especially in the heterogeneous environment of the Precambrian Shield. This study investigates landscape controls on hydrologic response by conducting a catchment classification of 26 catchments located within two Precambrian Shield watersheds (Sturgeon–French–Nipissing [SNF] and Muskoka) in central and Northeastern Ontario, Canada, using combinations of landscape characteristics (e.g. topography, geology, landcover), hydrometric variables, and stable isotopes of δ18O and δ2H in river flow. Weekly to monthly surveys of δ18O and δ2H in river flow were collected between 2013 and 2019. Flow metrics (e.g. Pardé coefficient and coefficient of variation of streamflow) were generated for 14 of the 26 rivers between 2008 and 2018. Principal component analyses (PCA) and Hierarchical Clustering on Principal Components (HCPC) analyses were used to identify variables controlling catchment clustering according to their similarities for four different scenarios. Despite their similar location along the southern edge of the Precambrian Shield, the 26 catchments generally clustered by watershed (SNF and Muskoka) with some exceptions. Differences in wetland and lake area (%), mean slope, and % area covered by glacialacustrine and glaciofluvial outwash deposits were the most influential variables in catchment classification. A positive correlation between % wetland area and streamflow stable isotope damping ratios suggests greater % wetland area (with shallow and potentially seasonally variable surface areas and/or hydrologic connection) observed in the SNF catchments increases variability in the influence of evaporative enrichment in SNF catchments. The catchment classification analyses in combination with stable isotopes of δ18O and δ2H were functional tools to investigate the combined influences of diverse types of catchment characteristics that lead to differences in hydrometric response. These results could support future studies focusing on generating hydrologic models and representing wetlands connectivity in the region.

Landscape mapping using ground-penetrating radar, electrical resistivity tomography survey and landscape profiling

<abstract> <p>This work aims to verify and correct the boundary between two landscapes—moraine and outwash plain—delineated earlier by the classical landscape approach. The initial interpretation of the boundary caused controversy due to the appearance of the thermokarst depression in the outwash landscape. The lithological structure is one of the main factors of landscape differentiation. The classical approach includes drilling to obtain the lithological and sedimentary data. However, the boreholes are usually shallow, while geophysical methods allow to look deeper into the subsurface and improve our knowledge about lithological structure and stratigraphy. In this study, we use ground-penetrating radar with a peak frequency of 250 and 50 MHz and detailed electrical resistivity tomography (with 1 m electrode spacing) in addition to the landscape mapping and drilling to correct the landscape boundary position. We conclude that it is primarily defined by the subsurface boundary between lithological complexes of clayish moraine deposits and sandy outwash deposits located at 7 m depth. Moving the boundary to the northeast by 70–100 m from the current position removes inconsistencies and clarifies the history of the area's formation in the Quaternary.</p> </abstract>

Geological Oceanography of the Pliocene Warm Period: A Review with Predictions on the Future of Global Warming

Atmospheric carbon dioxide reached a record concentration of 419 parts per million in May 2021, 50% higher than preindustrial levels at 280 parts per million. The rise of CO2 as a heat-trapping gas is the principal barometer tracking global warming attributed to a global average increase of 1.2 °C over the last 250 years. Ongoing global warming is expected to perturb extreme weather events such as tropical cyclones (hurricanes/typhoons), strengthened by elevated sea-surface temperatures. The melting of polar ice caps in Antarctica and Greenland also is expected to result in rising sea levels through the rest of this century. Various proxies for the estimate of long-term change in sea-surface temperatures (SSTs) are available through geological oceanography, which relies on the recovery of deep-sea cores for the study of sediments enriched in temperature-sensitive planktonic foraminifera and other algal residues. The Pliocene Warm Period occurred between ~4.5 and 3.0 million years ago, when sea level and average global temperatures were higher than today, and it is widely regarded as a predictive analog to the future impact of climate change. This work reviews some of the extensive literature on the geological oceanography of the Pliocene Warm Period together with a summary of land-based studies in paleotempestology focused on coastal boulder deposits (CBDs) and coastal outwash deposits (CODs) from the margin of the Pacific basin and parts of the North Atlantic basin. Ranging in age from the Pliocene through the Holocene, the values of such deposits serve as fixed geophysical markers, against which the micro-fossil record for the Pliocene Warm Period may be compared, as a registry of storm events from Pliocene and post-Pliocene times.

Luminescence dating of sand wedges constrains the Late Wisconsin (MIS 2) permafrost interval in the upper Midwest, USA

Large parts of the upper Midwest, USA were impacted by permafrost during the Last Glacial Maximum (LGM). Even though permafrost persisted as the Laurentide Ice Sheet began to recede, direct age control of this interval is largely lacking. To better temporally constrain the permafrost interval in western Wisconsin, we identified two sites, outside the Late Wisconsin (MIS 2) glacial limit, that contain relict, ice‐wedge pseudomorphs, initially interpreted to be sand wedges, hosted within well‐drained outwash deposits. The pre‐Wisconsin (>MIS 5) host material commonly displays up‐turned bedding near the contact with the wedges, indicative of well‐formed features. The wedges are filled with well‐sorted, gravel‐free, medium and fine sands, and lack evidence of post‐formational disturbance, pointing to an aeolian sand infill and confirming them as sand wedges. Ventifacts on nearby uplands attest to windy conditions here in the past. Optically stimulated luminescence (OSL) ages on five sand wedges indicate that they filled with sand between c. 19.3 and 18.3 ka at the southerly site and between c. 15.1 and 14.7 ka at the northerly site, which is closer to the LGM margin. Sand wedges at the latter site were wider and had more complex morphologies, possibly suggesting a longer interval of formation and/or more intense permafrost. We also examined a site along a ridge crest, between the two wedge sites, which displayed interbedded loess and sand, dated by OSL to 12.7 ka. Together, these results point to dry, cold, windy conditions in west‐central Wisconsin, within 100 km of the LGM limit. At this time, aeolian sands were being transported across a landscape with (at least scattered) permafrost. The OSL results suggest multiple phases, or perhaps time‐transgressive, sand‐wedge formation, associated with permafrost between c. 19 and 15 ka, with dry, windy (and likely, cold) conditions persisting until at least 12.7 ka.

Study on the mechanical properties of outwash deposits with random structure method

Abstract Outwash deposit is one of the major threats to the safety and stability of railway transit engineering in the Sichuan–Tibet area. In this paper, different samples of outwash deposits were prepared based on the random structure method, and a series of large-scale direct shear tests were carried out under different normal stresses. The influence of stone content and the spatial distribution of stone blocks on the physical and mechanical properties of outwash deposits were studied. The results show that with the increase of stone content, the shear stress-displacement curve changs from strain softening to strain hardening. The shear zone is larger, and its shape is more tortuous due to the movement and rotation of stone blocks. The internal frictional angle increases linearly while the cohesion diseases with the increase of stone content. The main influence of the spatial distribution of stone blocks on the mechanical properties of outwash deposits is the peak stress. The shear zone is mainly determined by the distribution of the stone blocks near the shear zone.

Clonal variation in coppiced and uncoppiced growth, root sprout stem formation, and biomass partitioning in Salix interior on two highly disturbed site types

Salix interior Rowlee (INT) is a wide-ranging North American willow from the small taxonomic group Salix section Longifoliae, notable for its ability to form multi-stemmed vegetative stem colonies arising via root sprouts (RS) from a shallow horizontal root network. This study quantifies biomass production for both 1-year-old coppiced plants and the original 4-year-old plants established from dormant, unrooted stem cuttings, as well as for the RS stems associated with each ortet (original mother plant) using eight selected INT clones established on two distinct site types. Significantly greater coppiced and uncoppiced ortet stem dry mass was recorded on coarse-textured, shale rock overburden (SO); possibly due to significantly greater fertility, compared to adjacent gravel outwash deposits (GD), which had greater RS stem mass. The total stem dry mass (ortet + associated RS) was comparable across the two different site types for both the 1-year-old coppiced plants and the 4-year-old uncoppiced plants, showing rapid recovery of biomass growth and yield in the year following coppicing. Significant clonal differences, as well as site type × clone interactions, were found for ortet stem dry mass, especially on SO sites, indicating that clonal selection might be useful to increase biomass production on different site types. When expressed as a fraction of total stem dry mass produced on 2 m × 2 m biomass plots, the RS component represented a significant 57% of total stem dry mass per plot (ortet + associated RS) on GD sites and only 18% on SO sites. The use of colony-forming willows such as INT minimizes the need for periodic replanting, providing a cost advantage over conventional short-rotation, coppice-based woody biomass plantations using species that do not have the ability to produce new stems via root sprouting. This root-sprouting trait enables INT to rapidly colonize and spread on difficult-to-manage sites, making it suitable for use in land reclamation.

Transport Direction and Scandinavian Source Regions of the Saalian Glacial and Glaciofluvial Deposits in a Case Study of Łubienica-Superunki (Central Poland)

The article contains detailed petrographic studies, which covered a coarse and medium-grain gravel fraction of two layers of glacial till (units ŁS II and ŁS IV) and two layers of sand-gravelly outwash deposits (units ŁS I and ŁS III) related to the Odranian Glaciation (MIS6, Saalian) in Łubienica-Superunki, North Mazovian Lowland, central Poland. Additionally, the indicator erratics were identified to indicate their Scandinavian source areas and the directions of the ice sheet transgressions. This case study is discussed against the background of similar sediments and forms from the same age but from other places in the Polish Lowlands. Regardless of the facies types and fractions, crystalline rocks dominated over all other petrographic groups in all samples. The most common were the indicator erratics derived from the Åland Islands, followed by those from the south-eastern area of Sweden (Småland) and from Dalarna in central Sweden. Amongst the erratics of limited indicative significance, the most common were Lower Palaeozoic limestones and the Jotnian red sandstones. The complex petrographic analyses point to the dipartite nature of the studied profile. This separateness was confirmed by the TBC: 59.1–59.2° N and 18.0–18.2° E for the lower units and 58.8–59.4° N and 17.3–17.9° E for the upper ones.

Quaternary landscape evolution of patagonia at the Chilean Triple Junction: Climate and tectonic forcings

Glacial and fluvial landforms record the recent history of the Earth surface and have the potential to provide information about uplift and climate changes during Quaternary times. Patagonia hosts uniquely well-preserved moraine deposits, along with outwash and fluvial terraces. This offers the possibility of determining the timing of glacier advances since the Great Patagonian Glaciation (ca. 1.2 Ma) and allows us to investigate landscape response to climate and tectonic forcing.In this study, we present twenty-eight new in situ 10Be exposure ages for glacial deposits, outwash sediments, and fluvial terraces at the latitude of the Chile Triple Junction (∼46°30′S). We combine this database with a detailed mapping and a morphological analysis of the Deseado River terrace system. The glacial and outwash deposits document at least five major glacial advances in the Lago Buenos Aires valley before the deposition of the Moreno system during Marine Isotope Stage (MIS) 8. Key advances occurred during MIS 12 and MIS 16. Further ice expansions that resulted in Telken V and VI/VII outwash surfaces date to 780 ka and ca. 1.2 Ma respectively. Overall, our data show the difficulty of dating pre-LGM glacial deposits using surface exposure methods and reinforce the idea that outwash surfaces are better targets to determine the age of glacial sequences in the region.The Deseado River terrace system yields stratigraphically consistent ages that range from 1167 to 447 ka, which indicate that these terraces formed during Pleistocene times. Our analysis suggests that terraces T3, T7 and T8 may have been formed during cold stages, close to the glacial-interglacial transitions. We also calculated incision rates that reveal a strong initial pulse, from ca. 1200 to 900 ka, which was followed by significantly weaker river incision pulses.Finally, our geomorphological analysis confirms that the oldest fluvial terraces of the Deseado River system exhibit a NE-SW tilting through a broad area, next to the Atlantic Ocean. This was previously interpreted as the surface response to a long-wavelength dynamic uplift, a phenomenon that should be reassigned to the early Pleistocene.

Quaternary Geology of the Indiana Portion of the Eastern Extent of the South Bend 30- x 60-Minute Quadrangle

The Quaternary Geology of the eastern South Bend 30- x 60-Minute Quadrangle in Indiana represents landforms and near-surface sediments deposited during the Wisconsin Episode, Late Pleistocene. Sediments and landforms reflect the interplay between the Saginaw and Michigan Lobes of the Laurentide Ice Sheet. A relatively shallow, buried pre-Wisconsin and mid-Wisconsin morphology has been overridden by advances leading to the Last Glacial Maximum (LGM), ca. 24 ka. Between 24 and 17 ka, retreating ice fronts from the Michigan Lobe left a succession of ice-contact sediment ramps and associated pitted and collapsed fan-moraine complexes throughout the south and west of the map area. A sequence of stacked diamicton and sand and gravel fan heads appears at the hinged interlobate area north and northeast of South Bend. Ice margin positions are marked by distinct features like fans, kames and ice-walled lake plains, which are well developed on Michigan Lobe margins. The thicker glaciofluvial sand and gravel packages appear mostly interbedded with diamicton beds along fan heads, with relatively minor deposits in valley train units. Lowlands are mostly occupied by post-LGM (ca. 18 ka) valley-train outwash deposits, with interpreted flow toward the south and west, derived from an ice margin retreating first from south to north, near Mishawaka, then from southeast to northwest across the Kankakee valley. Sand and gravel colluvial and alluvial fans developed in a short span after ice retreated, along with incision of the ice-sculpted morphology. Late-glacial aeolian sand dunes sealed the landscape. Relatively minor modification of the landscape during the Holocene is indicated by alluvial and palustrine deposits.

Shallow seismic reflection imaging of the Alpine Fault through late Quaternary sedimentary units at Whataroa, New Zealand

ABSTRACT The glacio-fluvial sediments of the Whataroa Valley on the west coast of New Zealand’s South Island contain a record of environmental change since the Last Glacial Maximum. The valley is cut by the Australia–Pacific plate-bounding Alpine Fault, the position of which is obscured by recent glacio-fluvial outwash deposits. Five seismic profiles collected across the inferred surface trace of the Alpine Fault between 2011 and 2018, using a variety of source types, are presented here; these profiles provide constraints on the fault’s location in the upper few hundred metres of the near surface. The sedimentary strata in the Whataroa Valley have been classified into seismic facies based on their reflectivity characteristics. Two reflective seismic facies, recognisable in all profiles, have been interpreted to correspond to recent fluvial outwash gravels (seismic facies 1) and older post-glacial glaciofluvial or marine sediments (seismic facies 2). These reflective packages are cut by Alpine Fault rupture surfaces with reverse motion dips of 60° to 80° and total throw of up to 50 m. Faults imaged in three of the profiles are interpreted to correspond to the most recent surface rupture of the Alpine Fault, due to their close proximity to a recently trenched surface scarp.

Development of the Truckee River terraces on the northeastern flank of the Sierra Nevada

The distribution and elevation of the abandoned strath terraces along the Truckee River in the Carson Range on the eastern flank of the Sierra Nevada are mapped and quantified with measurements from Lidar accompanied by field survey. Each mapped strath terrace is formed by incision into the Hunter Creek Sandstone and deposition of fluvial gravel by the Truckee River. The gravel contains granitic boulders sourced from the glaciated headwaters of the Truckee >20 km upstream from the terraces and display boulders ranging from 4 to 12 m in dimension, in comparison to the <1 m dimension of boulders observed in the bedload of the modern Truckee River. Be-10 terrestrial cosmogenic nuclide (TCN) surface exposure dating places limits on the age distribution of the strath terraces. The terrace sediments are suggested to be glacial outwash deposits, temporally linked with glacial cycles, and to record an average of ~0.3 mm/a tectonic uplift with respect to the Reno Basin over the last ~350 ka. Building upon earlier studies, the observations collected here increase the number of terrace levels previously mapped along the Truckee, provide initial quantitative bounds on the age of their formation, and further point to tectonic uplift as an important component in preserving this most extensive suite of strath terraces along the eastern flank of the Sierra Nevada.

Distribution and properties of sandy soils in the conterminous USA – A conceptual thickness model, and taxonomic analysis

Sandy soils, as a group of soils, are unique soils. They have a specific set of physical and chemical soil properties that include rapid infiltration and conductivity, susceptibility to drought and erosion by wind, and low ability to hold water and nutrients. Sandy soils have a sandy or loamy sand texture in the fine-earth (<2 mm) fraction. They occur extensively in Florida, Nebraska, Michigan, Texas, Georgia, Wisconsin, and Minnesota. We present a conceptual thickness model for sandy soils with four depth classes: 1. soils that are sandy throughout the upper 100 cm, 2. soils that contain a sandy layer that is 50 cm or more thick over a finer-textured layer, 3. soils that have a fine-textured layer 50 cm or less over a sandy layer, and 4. soils that are sandy throughout but that are underlain by bedrock at a depth of 50 cm or less. These four classes include 2054 soil series covering nearly 600,000 km2 or 8% of the conterminous USA. There is a wide range of parent materials, but most sandy soils are formed in aeolian, marine, and outwash deposits and sandy soils occur mainly in dunes and coastal and outwash plains. Nearly three-quarters of the sandy soil area are over 100 cm deep. Sandy soils are contained primarily in the Entisol order (48% of soils on area basis), followed by Spodosols (15%) and Ultisols (13%). Nearly two-thirds of sandy soils occur in nine great groups, including Ustipsamments (12%), Torripsamments (10%), Udipsamments (7%), Quartzipsamments (7%), Haplorthods (6%), Alaquods (6%), Paleudults (5%), Kandiudults (4%), and Psammaquents (3%). As nearly half are Entisols, only 24% of the sandy soils have a diagnostic subsurface horizon. Argillic and spodic horizons occur in 18% and 13% of the soils, respectively. There is concern regarding climate change and erosion of beaches, particularly in Florida and California, the influence of sand mining on flooding in Texas, and the impact of sand mining on dunes in Michigan.

Reply to Carlson (2020) comment on “Deglaciation of the Greenland and Laurentide ice sheets interrupted by glacier advance during abrupt coolings”

This Review quantitatively and qualitatively describes 10 representative Baffin Island fjords chosen to explore the nature of a glaciation in delivering sediment to a fjord, with focus on deglacial (within 13–6.7 kyr BP) and postglacial conditions (within 8.2–0 kyr BP). Fjords are compared using observed sediment thicknesses (49–175 m, averaged) and volumes (0.7–14.6 km3), and modeled sediment yields: (1) deglacial 140–1060 t/m2/yr; (2) paraglacial 45–350 t/m2/yr; (3) neoglacial 30–150 t/m2/yr; (4) Little Ice Age 70–440 t/m2/yr; and (5) Anthropocene 60–290 t/m2/yr. Modeled sediment loads, when converted to deposit volumes, compare favorably to observations from geophysical surveys and terrestrial mapping, or separately to sediment accumulation rates (SAR) determined from marine sediment cores. Fjord-averaged SAR during deglaciation range from 4.6 to 25 mm/yr, and 0.6–3.1 mm/yr for the postglacial interval. Fjords directly impacted by the Laurentide Ice Sheet (central and northern Baffin Island) are 2–3 times larger in dimensions than southern Baffin Island fjords, with ∼4.5x deglacial and ∼5x postglacial larger deposits, including well-defined ice-proximal outwash deposits. To the south, Penny Ice Cap associated fjords with no withholding sills, lose 30–40% of their incoming fjord sediment to Broughton Trough that dissects the continental shelf. Sunneshine is the only sampled fjord that was neither directly nor indirectly impacted by the Wisconsin continental ice sheet; Sunneshine responded instead to local maritime conditions and an alpine glaciation.