Coastal Bluffs Research Articles

Small Heat Shock Protein Responses of a Closely Related Pair of Desert and CoastalEncelia

Evolutionary variation for accumulation of small heat shock protein (sHsp) may contribute to thermal niche differentiation between species. Here we examine temperature and time‐course‐dependent variation for sHsp accumulation in a recently diverged pair of Encelia raised in a common environment: Encelia farinosa, common in the Mojave desert, and Encelia californica, which is found along the cool coastal bluffs of southern North America. Both species exhibit peak sHsp accumulation at 42°C. Encelia californica accumulated greater levels of sHsp at temperatures below 42°C, while E. farinosa had greater levels above 42°C. Encelia farinosa accumulates sHsp at temperatures up to 45°C, while E. californica does not synthesize sHsp above 44°C. Both species accumulated significant levels of sHsp while maintaining photosynthetic electron transport (Fv/Fm), but above the temperatures that elicited peak sHsp expression, levels of sHsp and Fv/Fm declined in parallel to zero. Encelia californica accumulated greater levels of sHsp more rapidly than E. farinosa following a 15 min, 42°C heat treatment; however, E. farinosa maintained greater Fv/Fm at all time points. Our results indicate that there are significant differences between Encelia species for sHsp accumulation but that these results depend on the duration, magnitude, and recovery time following temperature stress.

The Last Interglacial to Glacial Transition, Togiak Bay, Southwestern Alaska

An 18-m-high coastal bluff at Togiak Bay (northwestern Bristol Bay, southwestern Alaska) exposes marine, lacustrine, fluvial, glacial, volcanic, and organic deposits that record the ∼50,000-year-long transition from the peak of the last interglaciation to the early Wisconsin glaciation. The base of the section is dominated by stratified sand and silt extending up to 4.3 m above sea level; marine diatoms are present, and pollen assemblages are characterized by relatively high percentages of Picea, Alnus, and Betula and low percentages of Poaceae and Cyperaceae. The marine sediment was probably deposited during the peak of marine oxygen-isotope stage (OIS) 5e. An infrared stimulated luminescence (IRSL) age of 151,000±13,000 yr from near the base of the exposure is permissive of this correlation. The marine sand and silt are overlain by 0.8 m of peaty silt with diatoms that record a transition from marine to lacustrine conditions. During this interval, Poaceae and Cyperaceae dominate the pollen assemblages, and Picea and shrubs are nearly absent, suggesting that herb tundra occupied the landscape. This interval probably encompasses OIS 5d on the basis of the herb tundra and an IRSL age of 119,000±10,000 yr from 60 cm below the marine/lacustrine transition. The organic mud is overlain by 3.1 m of stratified sand and organic silt that apparently record shallowing of the lake; reappearance of spruce and shrubs (=OIS 5c?); and subsequent deepening of the lake (=OIS 5b?); followed by aggradation of a floodplain (=OIS 5a?), which was dry at the time basaltic lava buried the site. Thermoluminescence analyses on lava-baked sediment indicate that the eruption occurred 70,000±10,000 yr ago. Sometime thereafter, but prior to 53,600 14C yr B.P. an outlet of the Ahklun Mountains ice cap advanced over the site and deposited ∼7 m of bouldery ice-contact drift. The sedimentary sequence contains at least four tephra beds. Major- and trace-element chemistry provide a basis for correlating two of the tephras with tephra beds at nearby sites. The tephras, luminescence ages, and correlations with marine isotope stages provide the geochronological control to place the Togiak Bay section into a global context. The site serves as an important new reference section for late Pleistocene paleoenvironmental change in eastern Beringia.

Geological Causes of Local Variation in Coastal Bluff Recession Rates, Northeast Ohio Shoreline of Lake Erie

The Lake Erie shoreline at Painesville-on-the-Lake has receded 180 m since 1876, yet during the past decade rates have varied locally by 0–5 m/yr. The study area is a portion (0.5 km in length) of a continuous section of coastal bluffs 17 m tall. The section was selected to minimize variation in physical parameters, including shoreline orientation and exposure, offshore bathymetry and sediment, beach width, minimal shoreline protection structures, and generally homogeneous bluff materials. In spite of these similarities, some portions of the bluff recede episodically by block-fall and other portions continuously by slumping.

Paleogeographic and paleoclimatic significance of diatoms from middle Pleistocene marine and glaciomarine deposits on Baldwin Peninsula, northwestern Alaska

A newly revised diatom biostratigraphic scheme for the North Pacific Ocean based on studies of the diatom flora of the Cape Blossom and Hotham Inlet Formations of Baldwin Peninsula, northwestern Alaska provides new information on the paleoceanography of Kotzebue Sound, Alaska, during middle Pleistocene time. Sediments exposed along coastal bluffs of Baldwin Peninsula contain subarctic North Pacific zonal-index species, including extinct Proboscia barboi, Pr. curvirostris, Actinocyclus ochotensis var. fossilis, Thalassiosira nidulus var. nidulus, Th. jouseae, Th. gravida var. fossilis, and Stephanopyxis dimorpha, which are correlated with the middle part of the Proboscia barboi Zone (0.43–0.36 Ma). Based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages (e.g., warm- vs. cold-water assemblages), we conclude that the marine deposits of the Cape Blossom Formation and lower Baldwin Silt member of the Hotham Inlet Formation formed under relatively warm, high sea-level conditions associated with the marine oxygen isotope stage (OIS) 11 transgression. Glaciomarine sedimentation (middle and upper Baldwin Silt and Selawik Gravel members of the Hotham Inlet Formation) initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10. High-latitude glacier growth during a global `interglacial' period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover. The biostratigraphic record at Baldwin Peninsula provides further evidence that high-latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals.

Hantavirus (Bunyaviridae) infections in rodents from Orange and San Diego counties, California.

During a screening program to determine the extent of hantavirus activity in Orange and San Diego Counties, California, serum samples from 2,365 rodents representing nine genera and 15 species were tested for hantavirus antibodies. A reverse transcription-polymerase chain reaction on selected seropositive rodents was used to identify the specific hantavirus. Rodents positive for Sin Nombre virus (SNV) antibodies by Western blot included 86 (9.1%) of 948 deer mice (Peromyscus maniculatus), four (1.5%) of 275 California mice (Peromyscus californicus), one (0.5%) of 196 cactus mice (Peromyscus eremicus), 51 (12.2%) of 417 harvest mice (Reithrodontomys megalotis), and five (12.5%) of 40 California voles (Microtus californicus). All other specimens tested were negative for hantavirus antibodies. There was a correlation between age and sex of the reservoir host and prevalence of SNV antibody, especially among male deer mice and harvest mice. Few seasonal trends in antibody prevalence were observed and continued maintenance of SNV and El Moro Canyon virus was found at several foci over a 4-5-year period. Isla Vista virus was also found in voles and represents the first recorded in Orange County. Microhabitat selection on the part of these rodents based on plant density, plant height, and availability of food plants may explain, to some extent, all of the hantavirus-positive foci throughout the study area over a broad geographic range and the lack of antibody-positive rodents in dense chaparral, woodland, and riparian areas. The majority of rodents positive for SNV was identified from localities along coastal bluffs and the foothills of the Santa Ana Mountains, where trap success was high and P. maniculatus represented 43% of all rodents collected. Several residential, commercial, and industrial sites exist in these areas and the potential health risk should not be overlooked. This study represents an in-depth analysis of the prevalence, host distribution, and characteristics of rodent populations infected by three hantaviruses within a small, well-defined, geographic area.

Late Pleistocene sediments and environmental change at Plaza Creek, Falkland Islands, South Atlantic

Late Pleistocene organic-rich sediments exposed in coastal bluffs near the head of Plaza Creek, East Falkland, have yielded conventional and AMS 14C dates of between 36 and 28 ka BP, and possess a pollen spectrum dominated by grasses, indicating a vegetation assemblage similar to that of the present day. Although some sample dates are anomalous and contamination by non-contemporaneous carbon cannot be ruled out entirely, the age estimates are consistent with evidence and dates from Antarctica, South America and the amphi-North Atlantic for climate shifts to interstadial conditions at around that time. The organic-rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting. Grain-size characteristics suggest that these sediments may have been emplaced by solifluction, shallow translational landsliding and surface wash in at least five mass-wasting episodes. Some of the mass-wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka BP at San Carlos, East Falkland, and with periods of cirque and valley glaciation identified in the uplands of the Falkland Islands. The similarity between late Pleistocene interstadial, Holocene and present-day pollen assemblages, and the lack of vegetation change within these periods, is characteristic of most cool temperate Southern Ocean islands, and may reflect the lack of sensitivity of the vegetation to climate change and/or a lack of climate variability for the time intervals covered. © 1998 John Wiley & Sons, Ltd.

Late Pleistocene sediments and environmental change at Plaza Creek, Falkland Islands, South Atlantic

Late Pleistocene organic-rich sediments exposed in coastal bluffs near the head of Plaza Creek, East Falkland, have yielded conventional and AMS 14C dates of between 36 and 28 ka BP, and possess a pollen spectrum dominated by grasses, indicating a vegetation assemblage similar to that of the present day. Although some sample dates are anomalous and contamination by non-contemporaneous carbon cannot be ruled out entirely, the age estimates are consistent with evidence and dates from Antarctica, South America and the amphi-North Atlantic for climate shifts to interstadial conditions at around that time. The organic-rich units are developed in and enclosed by deposits attributed to processes of periglacial mass wasting. Grain-size characteristics suggest that these sediments may have been emplaced by solifluction, shallow translational landsliding and surface wash in at least five mass-wasting episodes. Some of the mass-wasting sediments might correlate with solifluction deposits above and below a podsolic soil dated to 26 ka BP at San Carlos, East Falkland, and with periods of cirque and valley glaciation identified in the uplands of the Falkland Islands. The similarity between late Pleistocene interstadial, Holocene and present-day pollen assemblages, and the lack of vegetation change within these periods, is characteristic of most cool temperate Southern Ocean islands, and may reflect the lack of sensitivity of the vegetation to climate change and/or a lack of climate variability for the time intervals covered. © 1998 John Wiley & Sons, Ltd.

Analysis of topographic amplification of inclined shear waves in a steep coastal bluff

AbstractThe effect of inclined shear waves on the seismic response of a steep bluff is analyzed using generalized consistent transmitting boundaries. The results of the frequency-domain analysis of a stepped half-space subjected to incident shear waves inclined from 0° to 30° show that the motion at the crest of the slope is amplified for waves traveling into the slope and attenuated for waves traveling away from the slope, as compared to the motion in the free field behind the crest of the slope. This amplification can be as much as twice that observed for vertically propagating waves. A time-domain analysis of bluffs at Seacliff State Beach, California, is used to estimate the effect of topography using realistic conditions, taking into account wave inclination and site effects. The analysis of the site shows that although topographic amplification does in fact nearly double the amplitude of the motion in some cases, this amplification is offset by reduced site amplification and by wave splitting at material interfaces. Thus, the actual peak acceleration occurring at the crest of the slope changes little with incident angle as compared to the amplification of the free-field motion and actually decreases in many cases. Though a more general study is recommended, these results suggest that wave orientation and inclination substantially increase topographic amplification; however, it may be adequate to only account for vertically propagating waves for site response and slope stability analyses where only the magnitude of acceleration is considered.

EVOLUTION OF THE PYGMY-FOREST EDAPHIC SUBSPECIES OFPINUS CONTORT AACROSS AN ECOLOGICAL STAIRCASE

Patterns of allozyme variation within and between two of the subspecies of Pinus contorta were examined for the evolutionary relationship between them. In coastal northern California, these subspecies are parapatric. Pinus contorta ssp. contorta occurs on grassy coastal bluffs on the lowest and youngest of a sequence of five marine terraces; P. contorta ssp. bolanderi is endemic to a pygmy forest ecosystem that occurs on the increasingly older and harsher soils of the third, fourth, and fifth terraces. The soils of the upper three terraces are characterized by extreme podzolization, low pH, low nutrient availability, summer drought (with periodic fires), and winter surface flooding above the hardpan. Dune and cliff soils support a tall redwood and Douglas-fir forest between the terraces. Analyses of seeds collected from 11 pygmy-forest and 6 coastal populations showed ssp. bolanderi to have significantly less allozyme variation than spp. contorta. The two subspecies did not show the phylogenetic dichotomy in allozyme allelic constitutions expected for subspecific classification. Within ssp. bolanderi, the pattern of genetic distances correlated better with edaphic differences among sites than with geographic distance. It appears that ssp. bolanderi is a recently evolved derivative of ssp. contorta, and that the low degree of allozyme differentiation among the bolanderi populations may be due to colonization of the sites by small numbers of individuals, or to hitchhiking of allozyme loci linked to loci undergoing strong selection imposed by the severe edaphic conditions typical of bolanderi sites.

The Influence of Ice on Southern Lake Michigan Coastal Erosion

Coastal ice does not protect the coast but enhances erosion by displacing severe winter wave energy from the beach to the shoreface and by entraining and transporting sediment alongshore and offshore. Three aspects of winter ice in Lake Michigan were studied over a 3-year period and found to have an important influence on coastal sediment dynamics and the coastal sediment budget: (1) the influence of coastal ice on shoreface morphology, (2) the transport of littoral sediments by ice, and (3) the formation of anchor and underwater ice as a frequent and important event entraining and transporting sediment. Coastal lake ice includes a belt of mobile brash (ice blocks) and slush and a dynamic nearshore ice complex consisting of an icefoot, a lakeward sequence of wave-generated ice ridges, and intervening ice lagoons. Our studies indicate that the nearshore ice complex contains a sediment load (0.2 - 1.2 t/m of coast) that is roughly equivalent to the average amount of sand eroded from the coastal bluffs and to the amount sand ice-rafted offshore to the deep lake basin each year. Up to 0.28 t/m of coast can be entrained by ice in a single anchor-ice event, and separate events occurred on 15 days in January 1991. The brash/slush belt is the most important system component responsible for ice-induced sediment transport. Estimates of longshore ice drift, ice volume, and ice-borne sediment load suggest that 0.36 to 4.14 × 10 3 t/d are transported alongshore.

Comparative habitat selection by muskoxen introduced to northeastern Alaska and the Taimyr Peninsula, Russia

Muskoxen (Ovibos moschatus) introduced to formerly occupied areas in northeastern Alaska (70°N) in 1969 and 1970, and the Taimyr Peninsula (75°N) in 1974 and 1975 increased in number (exceeding 20%/year in the early years following their establishment), and have expaned into available habitats. Vegetation of the two areas share many similarities, although richness of vascular plant species is greater in Alaska (350) than in the Taimyr (230). Seasonal partitioning of range use is similar in both areas with low-lying tussock tundra being used primarily from summer through early to mid-winter. By late winter, when snow accumulation in low areas and on lower slopes of hills limits access to forage, muskoxen concentrate activity on drier ridge tops and river and coastal bluffs with little snow accumulation. Riparian habitats appear to receive greater year round use in Alaska than in the Taimyr.

Patterns of stem photosynthesis in two invasive legumes (Spartium junceum, Cytisus scoparius) of the California coastal region

Stem assimilation of Spartium junceum and Cytisus scoparius was measured over diurnal cycles during four time periods of 1992 in California. Spartium junceum plants were growing at an inland, coastal mountain site while the C. scoparius plants were growing at a coastal bluff habitat. Both species had positive stem assimilation that resulted in approximately 200 mmol m 2 day‐1 carbon dioxide accumulation. Daily carbon gain decreased from spring to fall for S. junceum due to a decrease in shoot water potential. Although C. scoparius had the same relationship between assimilation and shoot water potential as that of S. junceum, carbon gain and water potential did not decrease during the year for C. scoparius. The major limitation for carbon gain of C. scoparius was light intensity because the coastal site was characterized by lower temperature, higher humidity, and more fog than the inland site. Although these species grew in habitats that had a different vapor pressure and temperature, the assimilation response to vapor pressure was similar between the species. Water use efficiency was higher and intercellular carbon dioxide was lower for S. junceum compared to C. scoparius. Although the leaves of both species are ephemeral, the canopy has a constant positive carbon balance because of stem assimilation. The constant carbon gain throughout the year, from stem assimilation, may enhance the growth capacity of these invasive species in disturbed habitats.

Patterns of Stem Photosynthesis in Two Invasive Legumes (Spartium junceum, Cytisus scoparius) of the California Coastal Region

Stem assimilation of Spartium junceum and Cytisus scoparius was measured over diurnal cycles during four time periods of 1992 in California. Spartium junceum plants were growing at an inland, coastal mountain site while the C. scoparius plants were growing at a coastal bluff habitat. Both species had positive stem assimilation that resulted in approximately 200 mmol m 2 day-1 carbon dioxide accumulation. Daily carbon gain decreased from spring to fall for S. junceum due to a decrease in shoot water potential. Although C. scoparius had the same relationship between assimilation and shoot water potential as that of S. junceum, carbon gain and water potential did not decrease during the year for C. scoparius. The major limitation for carbon gain of C. scoparius was light intensity because the coastal site was characterized by lower temperature, higher humidity, and more fog than the inland site. Although these species grew in habitats that had a different vapor pressure and temperature, the assimilation response to vapor pressure was similar between the species. Water use efficiency was higher and intercellular carbon dioxide was lower for S. junceum compared to C. scoparius. Although the leaves of both species are ephemeral, the canopy has a constant positive carbon balance because of stem assimilation. The constant carbon gain throughout the year, from stem assimilation, may enhance the growth capacity of these invasive species in disturbed habitats.

Resurrection and Revision of Hesperevax (Asteraceae: Inuleae)

Hesperevax comprises three species and three additional varieties endemic to the Californian floristic province of western North America. Separation of this genus from Evax, in which it has been included since 1901, is warranted on morphologic and biogeographic evidence. Ancistrocarphus and Cymbolaena are suggested as possible sister genera. Hesperevax acaulis var. ambusticola and H. acaulis var. robustior are newly described to accommodate extremes of geographic variation in that species. The new combination H. sparsiflora var. brevifolia is also made. The morphologic taxa of Hesperevax are ecologically distinct and divergent. Hesperevax caulescens appears to be restricted to shrink-swell clays of vernally moist areas, H. sparsiflora var. sparsiflora mostly to serpentine, H. sparsiflora var. brevifolia to sandy coastal bluffs, and H. acaulis var. ambusticola

Geology of the Lake Ontario Basin: A Review and Outlook

Lake Ontario, located at the northern margin of the Appalachian Basin, occupies a deep trough cut by rivers and glaciers into early to mid-Paleozoic limestones and shales. It is still being affected by movements along faults which have probably been active since late Precambrian (more than 600 million yr ago), as evidenced by small faults, "pop-ups" (small domes and anticlines) involving bedrock, Pleistocene drift (glacial and nonglacial deposits) and recent lacustrine sediments, and many small earthquakes (up to intensity V in the Mercalli scale). Infrequent large earthquakes may damage buildings and trigger slumps along coastal bluffs and subaqueous lacustrine slopes. Fractures generated by such crustal movements may become pathways for groundwater and leakage of stored dangerous substances. The lake receives sands from shore erosion of Pleistocene drift and silts and clays from rivers crossing vast Pleistocene lacustrine plains subjected to agricultural practices. Some of the nearshore, subaqueous sand deposits cannot be readily exploited for aggregates because shore erosion may be triggered and valuable ecosystems can be destroyed. Clays mop up pollutants, in part storing them in depocenters such as lagoons, marshes, and the deep lacustrine basins, and in part exporting them to the St. Lawrence River system.

Sedimentation on the Canadian Beaufort Shelf

Modern sediment supply to the Beaufort shelf is dominated by the Mackenzie River which annually provides of the order of 1.25 × 10 8 tonnes a −1 of mainly fine grained sediment. Minor contributions of sediment are derived from other rivers, principally along the Yukon coast (1.5 × 10 6tonnes a −1) and from erosion of coastal bluffs (5.62 × 10 6tonnes a −1). Calculations of the sediment mass that has accumulated in the Mackenzie Delta and on the Beaufort Shelf during the Holocene suggests that sediment supply from the Mackenzie must have been higher during the earlier Holocene than it is today. Sea-ice covers the Beaufort Shelf from October to June each year. Ice scouring may be active during the winter, particularly below pressure ridges, but net transport by ice-keels is probably unimportant on the eastern shelf where sedimentation rates are relatively high. Ice scour transport and ice-rafting may be more important on the western shelf where sediment supply is much lower. Discharge and sediment supply from the Mackenzie River are both low during the winter months but rise rapidly in late April and May prior to break-up. A significant proportion of the sediment supply occurs before and during break-up, when open water is minimal. During the open water summer months, a surface plume of brackish water with relatively high concentrations of suspended sediment extends over much of the shelf, east of the delta. The position and dynamics of the plume is alternately controlled by the prevailing northwesterly or easterly winds, but net transport is to the east. The distribution of Holocene mud on the shelf reflects this transport and is closely matched to the maximum extent of the plume. Over the middle and outer shelf (20 m water depth), wave motions influence bottom sediment transport less than 1% of the time. Near-bottom currents, weakly coupled to surface wind forcing, increase during storms and there is some evidence for resuspension of middle and outer shelf sediment during these events. In water depths less than 10 m, the influence of wave motion becomes important. Orbital wave motion combines with strong coastal currents during northwesterly storms to cause massive resuspensions of inner shelf sediments. Net transport during these events is generally parallel to the coast.

The last interglaciation in Alaska: Stratigraphy and paleoecology of potential sites

At least 20 localities in Alaska contain deposits that may provide information on the last interglaciation (Oxygen-Isotope Substage 5e). These widely dispersed localities include river bluffs, coastal bluffs and terraces, elevated marine shorelines, lake basins, and artificial excavations. Most of the inferred interglacial deposits contain macrofossils or pollen that are older than the range of radiocarbon dating and commonly indicate climate as warm as or warmer than the present. At a few localities, evidence for deep thaw of permafrost also indicates a warm paleoclimate. At eight localities, the Old Crow tephra occurs at or below organic deposits that may represent Substage 5e. The tephra occurs beneath conspicuous organic deposits at Fairbanks, the Yukon Palisades, and Holitna lowland, and directly above a peat bed at Hogatza Mine. At Birch Creek, Halfway House, Ky-11, and Imuruk Lake, the tephra occurs within a paleosol or organic deposit, but other organic horizons that more likely indicate interglacial conditions occur at higher stratigraphic levels. The varied stratigraphic relations of the Old Crow tephra suggest that it may have been deposited close to the boundary between Isotope Substages 6 and 5, which is dated at about 130 ka in the marine record and between 132 and 140 ka on land. These age relations suggests that the tephra may have been deposited about 135 ± 5 ka, validating the recent fission-track age determination of 140 ± 10 ka for this deposit. Six coastal localities contain deposits of probable interglacial age, and these commonly are associated with evidence for eustatic sea levels higher than those of the present. Beach and sublittoral sediments of the Pelukian transgression occur up to 12 m asl along the northwest coast of Alaska, and are correlative with barrier island and lagoonal sediments on the Alaskan Arctic Coastal Plain. Both sets of deposits commonly contain extralimital mollusks and microfauna that indicate marine water slightly warmer than present and suggest that seasonal sea ice did not extend south of Bering Strait during the last interglacial as it does today. Farther south, elevated marine-terrace deposits on Amchitka Island contain marine invertebrates that indicate a climate warmer than at present. Peat horizons in coastal exposure at Goose Bay and coastal terraces at Lituya Bay contain pollen spectra that suggest forests like those of the present day, and spruce macrofossils exposed on Baldwin Peninsula indicate boreal forest more extensive than at present. Sediments from several lakes in northwestern Alaska may contain continuous records of the last interglaciation. A major warm interval, possibly Isotope Substage 5e, has been identified in a core from Squirrel Lake by a peak in Picea pollen that indicates forest extension beyond present limits. Similar pollen records are potentially available from two maars which formed in the Cape Espenberg area more than 125 ka. Terrestrial organic deposits thought to record the last interglaciation occur interstratified with marine and glaciogenic sediments in the Nushagak Lowland of southwest Alaska and on Baldwin Peninsula in Kotzebue Sound. Extensive exposures along the Copper and Nenana Rivers may also contain organic deposits that record the last interglaciation.

Nourishment of perched sand dunes and the issue of erosion control in the Great Lakes

Although limited in coverage, perched sand dunes situated on high coastal bluffs are considered the most prized of Great Lakes dunes. Grand Sable Dunes on Lake Superior and Sleeping Bear Dunes on Lake Michigan are featured attractions of national lakeshores under National Park Service management. The source of sand for perched dunes is the high bluff along their lakeward edge. As onshore wind crosses the bluff, flow is accelerated upslope, resulting in greatly elevated levels of wind stress over the slope brow. On barren, sandy bluffs, wind erosion is concentrated in the brow zone, and for the Grand Sable Bluff, it averaged 1 m3/yr per linear meter along the highest sections for the period 1973–1983. This mechanism accounts for about 6,500 m3 of sand nourishment to the dunefield annually and clearly has been the predominant mechanism for the long-term development of the dunefield. However, wind erosion and dune nourishment are possible only where the bluff is denuded of plant cover by mass movements and related processes induced by wave erosion. In the Great Lakes, wave erosion and bluff retreat vary with lake levels; the nourishment of perched dunes is favored by high levels. Lake levels have been relatively high for the past 50 years, and shore erosion has become a major environmental issue leading property owners and politicians to support lake-level regulation. Trimming high water levels could reduce geomorphic activity on high bluffs and affect dune nourishment rates. Locally, nourishment also may be influenced by sediment accumulation associated with harbor protection facilities and by planting programs aimed at stabilizing dunes.

Coastal retreat and shoreface profile variations in the Canadian Beaufort Sea

The coastline of the southern Canadian Beaufort Sea consists primarily of unconsolidated bluffs. Although the sea is ice-free for 3 months of the year and wave energy is restricted by pack ice, the coast is undergoing regional retreat with erosion rates as high as 10 m a −1 in some locations. Simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession. Sediment texture, ground-ice content, cliff height, wave energy and shoreface gradient revealed medium to poor correlation with erosion rates, showing that the recessive evolution of the coastline can not be explained solely by wave-induced and subaerial processes. The comparison of nearshore echo-sounding records from 1987 with bathymetry from 1971 showed substantial erosion (up to 1 m) of the submarine profile between 12 and 15 m of water. There is strong evidence that this erosion has been caused by sea ice gouging on the seafloor. From depths of 5 to 9 m, accretion has taken place, possibly induced by ice-push processes, and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred. These results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium.

Bluff response to wave action

The unconsolidated materials forming the bluffs along the coasts of the Great Lakes are subject to active wave erosion which results in losses in millions of dollars annually due to property damage and reduction in property values. An understanding of the mechanics of bluff recession and the long-term trends in the evolution of coastal bluffs is required for an evaluation of engineering and management solutions for the problems created by retreating coastal bluffs. Bluff retreat is usually analyzed and measured from airphotos. However, since airphotos are taken at discrete points in time they are not capable of providing a full account of bluff retreat mechanisms. Field investigations, coupled with analytical methods, can enable investigators to identify patterns of bluff retreat. These patterns, subsequently incorporated into slope evolution models, shed light on data obtained over long periods from airphotos. The present paper explains recession rates and bluff profile changes as measured from airphotos with the help of bluff evolution models already established for the bluffs forming the Great Lakes shorelines.