Bluff Face Research Articles

Geologic Controls on Erosion Mechanism on the Alaska Beaufort Coast

Two prominent arctic coastal erosion mechanisms affect the coastal bluffs along the North Slope of Alaska. These include the niche erosion/block collapse mechanism and the bluff face thaw/slump mechanism. The niche erosion/block collapse erosion mechanism is dominant where there are few coarse sediments in the coastal bluffs, the elevation of the beach below the bluff is low, and there is frequent contact between the sea and the base of the bluff. In contrast, the bluff face thaw/slump mechanism is dominant where significant amounts of coarse sediment are present, the elevation of the beach is high, and contact between the sea and the bluff is infrequent. We show that a single geologic parameter, coarse sediment areal density, is predictive of the dominant erosion mechanism and is somewhat predictive of coastal erosion rates. The coarse sediment areal density is the dry mass (g) of coarse sediment (sand and gravel) per horizontal area (cm2) in the coastal bluff. It accounts for bluff height and the density of coarse material in the bluff. When the areal density exceeds 120 g cm−2, the bluff face thaw/slump mechanism is dominant. When the areal density is below 80 g cm−2, niche erosion/block collapse is dominant. Coarse sediment areal density also controls the coastal erosion rate to some extent. For the sites studied and using erosion rates for the 1980–2000 period, when the sediment areal density exceeds 120 g cm−2, the average erosion rate is low or 0.34 ± 0.92 m/yr. For sediment areal density values less than 80 g cm−2, the average erosion rate is higher or 2.1 ± 1.5 m/yr.

Characterization of a Disjunct Population of Eastern Hemlock (Tsuga canadensis) and Surrounding Plant Communities in the North Carolina Piedmont after 65 Years of Forest Change

Hemlock Bluffs Nature Preserve is a 57-ha preserve in the piedmont of North Carolina. A small disjunct Tsuga canadensis (Eastern Hemlock) population exists in the preserve, primarily within a microclimate on a north-facing bluff. A study published in 1956 included a 1952–1953 inventory of the hemlock population as well as records of the local flora and climate. We re-inventoried the Eastern Hemlock population, conducted a new floristic survey, and recorded new climate data in the preserve in 2018–2019. Our new data reveal a notable change in both the Eastern Hemlock population and preserve-wide stand structure. Only 2% average light transmittance through the canopy was recorded in the preserve in the 2019 growing season, compared to 11% in the 1953 growing season (P = 0.02). At least 7 plant taxa underwent notable shifts in distribution, mostly moving down-slope on the bluff face. Average ambient air temperatures on the bluff were 1.62 °C higher in 2018–2019 than in 1952–1953. Canopy closure, inbreeding depression, increased temperatures, erosion, and browsing by Odocoileus virginianus (White-tailed Deer) all likely contribute to low Eastern Hemlock seed germination and high seedling mortality within the preserve. These factors may also partially account for observed shifts in floristic distribution. In addition to mortality caused by Adelges tsugae (Hemlock Woolly Adelgid), these environmental changes endanger the future viability of this Eastern Hemlock population.

Seasonality in cold coast bluff erosion processes

High water levels in the Laurentian Great Lakes are causing widespread erosion of unlithified coastal bluffs and damaging infrastructure. Measurements of bluff recession along Wisconsin's Lake Michigan coast are mostly limited to estimates generated from comparisons of historical orthophotos with little information about the short-term scales (months to years) that affect many management and hazard-based decisions. Here we investigate the physical factors driving coastal bluff response to toe erosion at seasonal timescales using a multi-method case study of a mixed lithology bluff in Southeastern Wisconsin, an area that undergoes annual freezing. Five drone photogrammetry surveys were conducted from the winter of 2018 through the winter of 2020, and time lapse photography was collected from March 2019 through February 2020. The bluff face volumetric erosion rate between December 2018 and June 2019 was 3800 m3 a−1, which is 300% larger than the erosion rate between June 2019 and November 2019. Statistical analysis of the time lapse photography indicates that high magnitude erosion events are significantly correlated with environmental factors, including freeze-thaw events. These observations suggest that bluff erosion occurs episodically and is dominated by freeze-thaw related mass wasting events during the winter and spring. To investigate the physical processes driving this pattern, we model transient pore pressure response to a frozen bluff face as an input to a 3-D moment-balance slope stability model. Results show that increases in pore pressures up to one meter are possible at the face of the bluff over 5 days, which corresponds to 4–7% reduction in slope stability, indicating that observed increases in upslope bluff erosion during the winter and spring are a result of increased pore pressures, in combination with sediment strength reduction and high vadose zone saturation. As elevated lake levels continue to steepen bluff toes, upslope impacts will likely be temporally clustered during times of freeze-thaw. To accurately predict the seasonality of bluff recession on cold coasts, landscape change models must incorporate transient conditions caused by freeze-thaw events as they appear to be a dominant process.

Assessing patterns of annual change to permafrost bluffs along the North Slope coast of Alaska using high-resolution imagery and elevation models

Coastal permafrost bluffs at Barter Island, on the North Slope, Beaufort Sea Coast of Alaska are among the most rapidly eroding along Alaska's coast, having retreated up to 132 m between 1955 and 2015. Here we quantify rates and patterns of change over a single year using very-high resolution orthophotomosaics and co-registered surface elevation models derived from a survey-grade form of structure-from-motion photogrammetry from a fixed-wing, manned aircraft. The resulting elevation models were validated with over 10,000 ground check points and found that 95% agreed to within 20 cm, before accounting for real differences in the ground surface due to seasonality, vegetation, and checkpoint acquisition errors. This data set provides the most detailed and accurate measurements of coastal change to date along the Alaskan coast and the method is scalable to more extensive coastlines. Between July 2014 and July 2015, the bluffs retreated an average of 1.3 m, and a maximum of 8.1 m, with an associated net volume loss of 38,100 ± 300 m3 (1.3 m3/m). This average retreat over this single year was slightly less than the 60-year mean rate of change of −1.5 ± 0.1 m/yr, suggesting the 2014–2015 year represented relatively typical to slightly below average conditions. Most of the bluff material (70%) was lost during the 3 summer months (July to Sept) of 2014 and the remaining 30% between the late-summer and following winter-spring. The pattern of change was predominantly landward retreat of the top of the bluffs, removal of the debris apron and subsequent niching at the base of the bluffs during mid to late summer (July to Sept) followed by erosion of the bluff face and deposition of debris at the base of the bluff through the remainder of the year (Sept to the following July). Drivers of the observed change are likely a combination of thermal erosion on the bluff face throughout the summer and episodic thermo-mechanical removal of material, niching, and undercutting of the base associated with high-water levels driven by low-pressure storms and westerly winds. These patterns and high rates of change are believed to be broadly representative of coastal permafrost bluffs found along many high-latitude coastlines worldwide.

High Resolution Monitoring of River Bluff Erosion Reveals Failure Mechanisms and Geomorphically Effective Flows

Using a combination of Structure from Motion and time lapse photogrammetry, we document rapid river bluff erosion occurring in the Greater Blue Earth River (GBER) basin, a muddy tributary to the sediment-impaired Minnesota River in south central Minnesota. Our datasets elucidated dominant bluff failure mechanisms and rates of bluff retreat in a transient system responding to ongoing streamflow increases and glacial legacy impacts. Specifically, we document the importance of fluvial scour, freeze–thaw, as well as other drivers of bluff erosion. We find that even small flows, a mere 30% of the two-year recurrence interval flow, are capable of causing bluff erosion. During our study period (2014–2017), the most erosion was associated with two large flood events with 13- and 25-year return periods. However, based on the frequency of floods and magnitude of bluff face erosion associated with floods over the last 78 years, the 1.2-year return interval flood has likely accomplished the most cumulative erosion, and is thus more geomorphically effective than larger magnitude floods. Flows in the GBER basin are nonstationary, increasing across the full range of return intervals. We find that management implications differ considerably depending on whether the bluff erosion-runoff power law exponent, γ, is greater than, equal to, or less than 1. Previous research has recommended installation of water retention sites in tributaries to the Minnesota River in order to reduce flows and sediment loading from river bluffs. Our findings support the notion that water retention would be an effective practice to reduce sediment loading and highlight the importance of managing for both runoff frequency and magnitude.

Analysis of a sudden bluff failure along the southwest Lake Michigan shoreline

Elevated lake levels in the Lake Michigan-Huron basin have resulted in erosion at the bases of coastal bluffs composed of unconsolidated glacial deposits. Base erosion leads to a general steepening of the bluff face that can cause the bluffs to suddenly fail, transporting sediment into the nearshore hydrodynamic system. Sudden bluff failure impacts infrastructure built near the bluffs and the sediment budget of the coastal region. A better understanding of the mechanics that govern bluff failure will improve predictions of bluff retreat and sediment budgets. Here we present findings collected from a set of newly developed in-situ monitoring devices that record and measure several properties of the bluff leading up to and during a sudden failure. The devices are capable of accurately measuring, amongst other properties, displacement of the failing bluff at the millisecond sampling rate needed to capture sudden changes. A bluff failure was recorded on December 13, 2016, which prior to failure underwent an elevated creep rate for approximately 1.5 days and a highly-accelerated creep rate for the final 2.5 h. A creep to failure technique was used to analyze the displacement record and substantiated that the bluff failure was likely caused by the formation of segregation ice within the bluff as temperatures dropped from − 1 to − 12 °C over a 40-hour period prior to failure. Finally, a time to failure prediction estimate provided an upper bound for the time until ultimate failure from any one instance of time depending on the instantaneous creep rate.

Analysis of a Deep-Seated Landslide in Permafrost, Richardson Highway, South-Central Alaska

A portion of the Richardson Highway near Glennallen, Alaska, is threatened by slope movement in an area where the highway travels along a bluff overlooking the Copper River. Analysis of aerial photographs indicates that portions of the bluff have experienced an average of 1.5 m of retreat per year since 1979, and gully erosion has completely obliterated portions of the pre-1965 highway alignment. The subsurface consists of a 1.5-m-thick surficial silt layer underlain by frozen, ice-rich clayey soils with an average annual temperature of −0.56°C. At 16 m below the ground surface, the soils become ice-poor and coarser grained. In situ measurements, soil creep tests, and slope stability analysis indicate that the ice-rich clayey soils are experiencing movement, with creep velocities of up to 2.5 cm per year. This deep-seated creep results in fracturing of the near-surface soil layer that is manifested at the surface by cracks, scarps, and back-tilted blocks. Groundwater perched above the permafrost table and seeping toward the bluff face facilitates the rapid retreat of the bluff edge through the formation of gullies.

Decade-scale coastal bluff retreat from LiDAR data: Lake Erie coast of NW Pennsylvania, USA

Bluff retreat is an ongoing problem on the southern Great Lakes coast of the United States where Pleistocene unconsolidated sediments overlie Devonian bedrock. This retreat results in loss of sediment from the coastal zone and a decrease in coastal water quality, and is of concern because evaluating landslide hazards and developing regulations on coastal construction setbacks must account for spatial variability in coastal retreat. The goal of this pilot study is to explain and quantify short to medium term spatial variability in bluff-retreat patterns, magnitudes, and rates along a 6 km littoral cell on the Pennsylvania coast of Lake Erie. High-resolution LiDAR data covering a one-decade time frame (1998–2007) permit mapping of the bluff-crest position on two comparable, high-quality data sets. The rates of bluff retreat range from unresolvable (~20% of coast) to 2.2 m/year, averaging 0.22 ± 0.1 m/year. Average-annual change rates and 9-year net movement values show an along-coast periodicity, with a spatial wavelength of ~1 km and an amplitude of 0.2 m/year. Observed variability is inferred to occur because variations in surface watershed size and groundwater recharge area, topographic shielding of the bluff from overland flow, and groundwater-table topography, cause groundwater discharge and overland flow to the bluff face to vary along the coast. In addition, short ravines (<300 m in length) fed by groundwater seepage distort groundwater equipotential lines and cause locally enhanced bluff retreat. While other factors likely influence bluff retreat spatially along this coast, their roles are relatively minor at the scale of this study.

High‐resolution pollen analysis of tundra polygons from the North Slope of Alaska

Modern and fossil pollen analyses have established the local vegetation succession and landscape evolution along the Meade River near Atqasuk, Alaska. Three data sets were analyzed: (1) a 142‐cm‐long peat deposit on the exposed river bluff face, (2) a short, 13‐cm peat monolith from the near‐surface sediment, and (3) a modern data set of surface samples collected along a transect representative of a geomorphic gradient of low‐center, transitional, and high‐center polygons. Pollen‐microfossil assemblages changed significantly along this gradient. Detailed analysis of the short pollen profile shows successional vegetation changes over the last 250 years. The long profile, a 9400‐year record of past vegetation, indicates that initially, the site was covered by shallow lakes. Eolian activity had a substantial effect on sediment deposition, but a period of rapid peat growth from 8500 to 5000 14C year B.P. is coincident with increased vegetation cover of mixed grass‐shrub tundra. Following this period, peat growth slowed, and shrub vegetation was replaced by tussock‐forming sedge vegetation.

Role of Soil Joints in Causing Bluff Erosion Along the Lake Erie Shoreline, Northeast Ohio

Bluff erosion along the Lake Erie shoreline in Ohio is a major environmental problem causing extensive damage to homes, agricultural land, and lakeshore roads. The most extensive erosion takes place in areas where the bluffs are made of well-jointed, overeonsolidated, glacial till material (CL; ML-CL) that is overlain by lacustrine silts (ML) or silty clays (CL). In order to investigate the effect of soil joints on bluff erosion, four sites, all characterized by the presence of well-developed joints, were selected between Painesville, Ohio, and the Ohio-Pennsylvania border. The detailed line survey technique was used to measure orientations and other aspects (continuity, spacing, surface features, aperture, nature of infilling material, presence or absence of water) of the joints at the four sites. Erosion rates were monitored on a bi-weekly basis for a period of one year, using equally spaced pegs on the bluff face. Photographs were taken frequently to aid in monitoring of bluff erosion. Results indicate that bluff erosion in the study area is greatly influenced by the presence of joints in the glacial till. The joints enhance erosion by providing pathways for water movement in both horizontal and vertical directions which, in turn, leads to widening of the joint openings and piping of the overlying silty material. The buildup of pore pressure along the joints, after a prolonged rainfall or a sudden snowmelt, also contributes to bluff instability. In the toe area, wave attack results in the formation of notches, cavities, and concave zones. Erosion at the bluff toe, accelerated by soil joints, initiates block falls and planar slides along the pre-existing joint surfaces above the toe area. The slump and flow type failures that occur in the overlying lacustrine material are a consequence of the joint-promoted failures in the underlying till. Thus, any remedial measures that are undertaken to minimize bluff erosion along Lake Erie must take into account the effect of soil joints.

Buried Soils in a Perched Dunefield as Indicators of Late Holocene Lake-Level Change in the Lake Superior Basin

A stratigraphic analysis of buried soils within the Grand Sable Dunes, a dune field perched 90 m above the southern shore of Lake Superior, reveals a history of eolian activity apparently linked with lake-level fluctuations over the last 5500 yr. A relative rise in the water plane of the Nipissing Great Lakes initially destabilized the lakeward bluff face of the Grand Sable plateau between 5400 and 4600 14C yr B.P. This led to the burial of the Sable Creek soil by eolian sediments derived from the bluff face. Subsequent episodes of eolian activity appear to be tied to similar destabilizing events; high lake levels may have initiated at least four and perhaps eleven episodes of dune building as expressed by soil burials within the dunes. Intervening low lake levels probably correlate with soil profile development, which varies from the well-developed Sable Creek Spodosol catena to thin organic layers containing in-place stumps and tree trunks. Paleoecological reconstructions available for the area do not imply enough climatic change to account for the episodic dune activity. Burial of soils by fine-fraction sediments links dune-building episodes with destabilization of the lower lake-facing bluff, which is rich in fines.

Toe erosion of glacial till bluffs: Lake Erie south shore

Toe erosion and rates of recession of the toe were measured at four sites along a 3.5 km long stretch of shoreline on the south shore of Lake Erie from April to December 1986. The shoreline consists of bluffs ranging from 5 to 12 m in height and developed in overconsolidated till. Toe erosion was measured at peg lines consisting of pins driven horizontally into the face of the bluff at 0.25 m intervals to a height of 1.75 m above the beach, and steel rods driven vertically into the beach with a spacing of 1.5 m. At each site three lines were established and monitored at 1–2 week intervals. Because of record high lake levels, beaches in front of the bluffs were generally &lt;5 m wide, and some erosion was measured on all but three occasions. Recession of the toe during any measurement period was generally 2–6 cm, with the maximum recorded being about 12 cm. Wave action during high-magnitude storms resulted in erosion occurring much higher up the bluff face than for low-magnitude events, but the actual recession of the toe was not substantially greater. A multiple regression model shows that there is a significant relationship between toe recession and several variables that indirectly control wave energy at the bluff toe. However, factors such as beach width and thickness of beach sediment did not have a significant influence on recession rates in this study, likely because the high lake levels resulted in very narrow beaches at all four sites throughout the study period.

Wind Erosion and Sand Dune Formation on High Lake Superior Bluffs

The Grand Sable Dunes and the Sleeping Bear Sand Dunes are the largest fields of active sand dunes in the Great Lakes. Both are situated along the crests of high bluffs which rise 40–90 m above the lakes and are composed of sandy glacial deposits. Annual rates of wind erosion of sand from the Grand Sable bluff face have been estimated from sand deposits interbedded with leaf litter on the forest floor adjacent to the dune field. Annual wind erosion increases linearly with slope height, reaching a maximum of almost 1 m3 per m of distance along the strike of the bluff for a 90 m slope, and is concentrated in a belt along the brow of the slope. Despite the strength added to the slope by ground frost, most sand is eroded in winter. Sand, freed from the bluff by sublimation of ice, is transported into the dune field sometimes with snow sometimes without, depending on weather conditions. Groundfrost increases with distance up-slope, reaching a depth of several m at the crestslope. Frost depth is controlled by the rate of conductive heat transfer above the footslope where the ground is warmed by groundwater seepage. The annual flux of sand into the dune field for the period 1973–83 is estimated to be 6300 m3/yr. This rate of nourishment, however, varies with fluctuations in lake levels as they influence wave erosion, slumping and devegetation of the bluff.

Short-Term Climate Changes and Coastal Erosion, Barrow, Alaska

Records of shoreline and bluff positions in the vicinity of Barrow, Alaska, have been obtained from aerial photographs and taped measurements for intervals between 1948 and 1969. Although the source material in the bluffs is frozen and masses of pure ice are present, temperature and rainfall data fail to show any marked correlation with the retreat of the bluff face or with the retreat of the fronting or downdrift beaches. Removal of beach material for construction and frequency of storms from the west do show a relationship. Recorded retreats of the bluffs up to 3 m per year and of the beaches up to 4 m per year have resulted where there has been excessive beach borrow or where a series of severe storms have attacked the coast.

INLAID MODERN SEDIMENTS IN PLEISTOCENE TERRACE ALLUVIUM, SOUTHERN ILLINOIS

Research Article| August 01, 1967 INLAID MODERN SEDIMENTS IN PLEISTOCENE TERRACE ALLUVIUM, SOUTHERN ILLINOIS C. S ALEXANDER; C. S ALEXANDER DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 Search for other works by this author on: GSW Google Scholar L. W PRICE; L. W PRICE DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 Search for other works by this author on: GSW Google Scholar M. M VUK M. M VUK DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 Search for other works by this author on: GSW Google Scholar Author and Article Information C. S ALEXANDER DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 L. W PRICE DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 M. M VUK DEPT. GEOGRAPHY, UNIVERSITY OF ILLINOIS, URBANA, ILLINOIS 61803 Publisher: Geological Society of America Received: 22 Apr 1966 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1967, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1967) 78 (8): 1037–1038. https://doi.org/10.1130/0016-7606(1967)78[1037:IMSIPT]2.0.CO;2 Article history Received: 22 Apr 1966 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 C. S ALEXANDER, L. W PRICE, M. M VUK; INLAID MODERN SEDIMENTS IN PLEISTOCENE TERRACE ALLUVIUM, SOUTHERN ILLINOIS. GSA Bulletin 1967;; 78 (8): 1037–1038. doi: https://doi.org/10.1130/0016-7606(1967)78[1037:IMSIPT]2.0.CO;2 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 Inlaid modern sediments occur in the base of the bluffs above the Ohio flood plain west of Joppa, Illinois. These are thought to have been deposited in reentrants or notches cut and eroded by wave action during unusually high river floods. Along the bottom edge of the notches debris dams provide small catchment basins for silt washed by rain from the bluff. Once the notches are filled or partly filled, the retreating bluff removes the debris dams, leaving the silt as an inlaid deposit in the bluff face. 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.