Scarborough Bluffs Research Articles

Why did the Scarborough Bluffs Collapse? Earthquakes, Rock Bump, Volcanic Explosions, and Large-Scale Rockslides as a Routine Rock Heaving Process

The theoretical foundations of the causes of rock swelling took shape in the 60-70s of the last a century and did not receive further development. In this area of the scientific problem, the an illusion has arisen that in the mining and geophysical fields of research, the process of rock swelling takes up an insignificant place, it has been completely studied, and it makes no sense to look for new approaches to explain it. But scientific facts strictly indicate that the process of rock swelling is underestimated and is the main cause of earthquakes, rock bump, sudden outbursts of rock and gas, explosions of volcanoes, and landslides. In fact, the process of rock swelling is a process of deformation of rocks with a period of time from several hours to several years with the possibility of avalanche-like swelling of rocks in a short period of time with the appearance of a force pulse in the form of a shock wave, which can cause an earthquake, volcano explosion, rock-slide, rock bump, the sudden outburst of rock and gas in the mines. The article substantiates the hypothesis of an avalanche-like restructuring of the crystal lattice of a geological body and, as a consequence of this process, to a lightning-fast change in its volume, that is, to the process of heaving of rocks at a high speed, which, in our opinion, is the cause of the collapse of The Scarborough Bluffs, Toronto, Canada on 23.08. 2020, earthquakes, rock bumps, volcanic explosions, and landslides.

Micromorphology of ice keel scour in pebbly sandy mud and fine‐grained sands: Scarborough Bluffs, Ontario, Canada

AbstractThe keels of icebergs and ice‐pressure ridges plough through unconsolidated sea/lake sediments gouging out long grooves known as ice keel scour marks. Although the surface and (more recently) subsurface morphology of scours are well‐documented, little is known of the effect of grain size on the detectability, style and intensity of sub‐scour deformation. This investigation macroscopically and microscopically (two‐dimensional thin sections) examines suspected ice keel scour in: (i) glaciolacustrine pebbly sandy mud and (ii) fine‐grained sands at Scarborough Bluffs, Ontario, Canada. In this investigation, there is an almost identical suite of deformation structures (individual structures and overprinted structural patterns) to those identified in iceberg‐scoured clays from former Glacial Lake Agassiz (Manitoba, Canada); this confirms that deformation in the pebbly sandy mud and fine‐grained sands at Scarborough Bluffs is likely to be indicative of ice keel scour. Discrete differences in the detectability, style and intensity of deformation between the Scarborough Bluffs and Glacial Lake Agassiz sediments are probably a function of grain size in response to ice keel scour. This research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes. This information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes. It also demonstrates the potential value of micromorphology where, for example, the study of cores is necessary.

Significance of Sedimentological Studies on the Wisconsinan Stratigraphy of Southern Ontario

Detailed facies mapping along Lake Erie and Lake Ontario Bluffs, plus other studies illustrate that sedimentological studies, especially those with geomorphic or landform control, have had three main effects on the Wisconsinan stratigraphy of Ontario: (1) improved understanding of depositional processes and environments of several major rock stratigraphic units, without altering the stratigraphic framework, (2) aided correlation of drift sequences, and (3) questioned previous interpretations and stratigraphic correlations of drift sequences. Thus sedimentological analysis can not be separated from stratigraphy because the interpretation of depositional environnments of many mapped strata relies on their geometry and the inclusion of regional data. The geomorphic control provided by sedimentological study of surface landforms is also important because assessment of older buried sediments such as those at the Scarborough Bluffs has been hampered by the failure to determine landform control. The Late Wisconsinan stratigraphy of Southern Ontario generally remains unchanged, except for questions on the role of climate versus ice margin dynamics. The pre-Late Wisconsinan stratigraphy is scarce and not well defined, yet sedimentary studies support the presence of glacial ice in the Ontario Lake basin for all of the Middle Wisconsinan and possibly earlier, including the formation of the Scarborough delta. Large channel cut and fill sequences in the Toronto area (Pottery Road Formation), initially interpreted as resulting from subaerial erosion, were probably formed by subaqueous or subglacial meltwater erosion. If so, the pre-Late Wisconsinan stratigraphy in southern Ontario changes because the Pottery Road Formation may not be an Early Wisconsinan correlative of the St. Pierre beds. The channel example illustrates that stratigraphie correlation without sedimentological investigations may be misleading.

Morphology and Composition of Two Late Wisconsinan Soils Forming in Till and Lacustrine Deposits, Scarborough Bluffs Area, South-Central Ontario

Halton Till and Glacial Lake Iroquois lacustrine sand and gravel deposits are the major surficial materials exposed at the surface of Scarborough Bluffs in South-Central Ontario. Luvisols formed in these deposits have different morphologies, including depth of weathering, complexity of horizonation, and strength of structural grades which result from parent material differences and pedogenesis. Particle size variations between the two paleosols result, in part, from different modes of deposition, and show that variable amounts of clay were produced pedogenically in the two systems. Clay mineral genesis, involving the transformation of illite and illitesmectite to vermiculite, appears to be restricted to the Iroquois sand paleosol, while some chloritization of illite occurs in both profiles. Changes in the primary mineral contents in the two paleosols suggest a similar magnitude of weathering in both systems. Distributions of vermiculite and dithionite-extractable Fe suggest some preweathering effects in the Halton Till paleosol. Morphological, mineralogical and some soil chemical properties are closely related to the physical attributes of the two different parent materials (till vs lacustrine sand and gravel).

Three detailed, radiocarbon-dated, Holocene tufa and alluvial fan mollusc successions from southern Ontario: The first in northeastern North America

Fossil mollusc remains, particularly those of land snails, provide a wealth of detailed information concerning local Quaternary paleoenvironments and regional paleoclimatic conditions. However, this important resource is generally overlooked in North America and consequently quantitative, well-dated terrestrial mollusc successions are extremely rare here. In an attempt to redress this imbalance, a project examining the Holocene molluscan faunal history of northeastern North America has been initiated. Thus far, detailed mollusc successions and associated radiocarbon age determinations have been obtained from three sites in southern Ontario; two alluvial fans (Chine Drive Fan and Cudia Park Fan, both from the Scarborough Bluffs east of Toronto) and a tufa (West River Road, near Cambridge). The observed land snail successions to provide an initial view of the molluscan faunal history of this region during the period from the late glacial to the mid Holocene, between approximately 10,500 and 5000 radiocarbon years BP (yr BP). The molluscan data have also been used to reconstruct the paleoenvironmental history of southern Ontario during this time, documenting the progression from exposed, open habitats characterised by species such as Vertigo modesta, Vallonia albula, Columella columella and Vitrina angelicae limpida, to closed woodland biotopes indicated by the presence of taxa including Carychium nannodes, Nesovitrea binneyana, Paravitrea multidenta and Helicodiscus parallelus. This study has already demonstrated the potential of this technique in the study of Quaternary climatic and environmental change in eastern North America and represents a strong foundation for extending the analysis of fossil land snail successions to other sites throughout this region. It has also provided new and important insights into the establishment of the modern molluscan fauna, which are essential to the understanding of present day distributional patterns and environmental associations.

Case study of a relict iceberg scour exposed at Scarborough Bluffs, Toronto, Ontario: implications for pipeline engineering

Ice scour is a common process on high latitude shelves and has been studied extensively though laboratory and numerical modelling. Direct observations of ice scours in outcrop are very rare. This paper describes a Late Pleistocene iceberg scour observable in soil cliff exposures at Cudia Park, Scarborough Bluffs, Toronto, Ontario. The structure is cut into a glaciolacustrine clayey silt, is about 10 m wide and 4 m deep, and is filled with sands deposited in shallow water. A description of the scour and a simplified finite element model of sub-ice scour soil deformation are presented. It is estimated that the Cudia scour was caused by a small iceberg with a mass of 0.04 Mt, in a water depth between 10 and 30 m, acting with a downward force of 5 MN, which is consistent with modern iceberg scours. The relevance of the Cudia scour to pipeline engineering (design burial depths) is demonstrated, with reference to the design methodology of the Centre for Cold Ocean Research and Engineering (C-CORE). The Cudia scour provides an additional outcrop example of a subscour bearing capacity-type failure and is the only outcrop example to date with lateral berm piles, which are a characteristic part of modern iceberg scours.Key words: iceberg scour, Scarborough Bluffs, pipeline engineering, finite element modelling, Pleistocene geology.

Sedimentary and Paleoclimatic Controls on Caddisfly (Insecta: Trichoptera) Assemblages during the Last Interglacial-to-Glacial Transition in Southern Ontario

Southern Ontario, Canada, has late Pleistocene deposits that contain evidence for climatic cooling during the last interglacial/glacial transition and much of the succeeding Wisconsin glaciation. Fossils of lacustrine and riverine caddisflies (Insecta: Trichoptera) are abundant and well-preserved in these deposits. We examined 26 samples from the interglacial section exposed in the Don Valley Brickyard and compared their caddisfly assemblages with those recovered from the overlying early Wisconsin Scarborough Formation deposits at nearby Scarborough Bluffs. Fifty-one caddisfly taxa in 16 families were recovered from the Don Valley site. Fossil abundance and species richness appear related to the storm or fair-weather conditions inferred from the sedimentary facies. Caddisfly fossils were most abundant and species richness highest in fair-weather, peaty, rippled sands. Highest proportions of river species as opposed to lake species were recovered from sands (storm and fair-weather). Assemblages from both sites indicate the presence of a large and productive river flowing into ancestral Lake Ontario. However, the river assemblage appeared to be far more sensitive to environmental change than the relatively stable assemblage representing the thermally buffered lake. Warm temperate river species such as Hydropsyche bidens, Hydropsyche mississippiensis, Macrostemum carolina, and Potamyia flava are present in the lower Don samples but absent from the Scarborough Bluffs deposits, while indicators of cooler than present climatic conditions such as Arctopsyche Indogensis and Hagenella canadensis are present in the Scarborough Bluffs sediments but absent from the lower Don samples. For the interval from about 80,000 to 55,000 yr B.P., we infer a climatic cooling from temperature about 2°C warmer than present to about 3°C cooler than present.

Late quaternary stratigraphy and geochemistry of the R47 section, Rouge River Basin, south‐central Ontario, Canada: Correlation with Scarborough Bluffs

AbstractQuaternary glacial diamictons in section R47, overlying Ordovician shale in the Rouge River Basin of south‐central Ontario, are considered to be representative of older and younger Wisconsinan glacial diamictons in the field area. Field characteristics, clast composition, mineralogy, particle size and geochemistry permit delineation of two units within the sequence and subdivision of deposits that correlate with Sunnybrook and Halton diamictons of Wisconsinan age. No Wisconsinan interstadial deposits are present in the section; however, outwash sandy gravel capping the Halton diamicton was probably emplaced by a high‐energy stream draining into Lake Iroquois just prior to the incision of the Rouge Valley in the later Wisconsinan (ca. 11 000‐12 000 yr BP). A buried palaeosol, which developed in this sandy gravel and in overlying aeolian sediment, shows partial leaching of carbonates and a slight increase of clay in the palaeosol solum. The main clay‐mineral transformations in the buried palaeosol appear to involve the degradation of illite and illite‐smectite accompanied by the production of vermiculite and minor amounts of chlorite. The ground soil capping the buried palaeosol is formed in colluvium emplaced 200 ± 80 yr BP following a local forest fire; the ground soil Ahk horizon gives an age of 4000 yr in the future, probably as a result of nuclear bomb testing effects on modern radiocarbon. The presence of an A/C profile in the ground soil system, although thin, indicates that surface soils may form rapidly.The geochemistry of the two Wisconsinan diamictons shows similar calcite and SiO2‐corrected mean element concentrations, with slightly elevated levels of Ca, Sr, Hf and Lu in the younger deposit. Both diamictons are geochemically quite different from the shale bedrock in the area, indicating that the bulk of transported sediment came from outside the area.

Comparative analysis of cladoceran microfossils in the Don and Scarborough Formations, Toronto, Canada

Pleistocene deposits at Toronto, consisting of Don Formation (considered to be of Sangamonian interglacial age) and Scarborough Formation (interpreted to be Early Wisconsinan, >50 000 years B.P.) were examined at three sites: Don Valley Brickyard, Leaside, and at the south end of Brimley Road at the foot of the Scarborough Bluffs. Comparison of the cladoceran microfossil assemblages described from these sites has enabled reconstruction of the lacustrine environment of the region. Cladoceran microfossil evidence from each site confirmed the disparity in community composition and structure, and in environmental conditions that existed during deposition of the Don and Scarborough Formations. Cladocera community composition averaged 40–45% remains of littoral species in the warmer Don interval at all three sites. The Scarborough Formation contained a more homogeneous cladoceran assemblage, with higher community similarity across sites than observed in the Don Formation. However, there was greater variation in the littoral: planktonic ratio among sites, ranging from >0.90 at Leaside to <0.10 at Brimley Road. Stratigraphically constrained cluster analysis of cladoceran microfossil assemblages clearly separated the communities in the Don Formation from those in the Scarborough Formation at each site. During the interglacial, the Don Brickyard site appears to have been a shallow, protected embayment on the lake shore, whereas the other sites are more distinctly lacustrine. The Scarborough assemblage at each site is representative of deeper, oligotrophic, subarctic lakes.

Laurentide ice sheet extent inferred from stable isotopic composition (O,C) of ostracodes at Toronto, Canada

Early and Middle Wisconsin glaciolacustrine sediments exposed at Scarborough Bluffs, Toronto, Canada, contain a low-diversity benthic ostracode fauna dominated by Candona subtringulata and C. caudata. We have studied the oxygen and carbon isotopic compositions of the two ostracode species from the base of the Scarborough section to its top immediately below a Late Wisconsin till. We find an upward decrease in δ 18O in both species that is more marked in C. caudata. The shift in δ 18O of ostracode calcite from interglacial values of −6 to −8‰, to values of −17‰ immediately below the Late Wisconsin till is the result of (1) lowering of δ 18O of the lake as a result of addition of isotopically light meltwater from an advancing and thickening Laurentide Ice Sheet combined with (2) lowering of δ 18O of local precipitation entering the lake, due to falling temperatures. In the last stages of the lake, δ 18O of the lake water was between −17 and −21‰, corresponding to a lake body composed of between 35 and 55% glacial meltwater. The lake appears to have been isotopically and thermally stratified for part of its history. Differences in δ 13C values between C. caudata and C. subtriangulata increase upward in the stratigraphic section. This may record enhanced partitioning of carbon isotopes between surface and bottom waters as a result of increased water depths, photosynthesis by algae, and changes in the input of dissolved organic carbon from the oxidation of organic matter. If the age assessments of these sediments are correct, then these data provide valuable information regarding the isotopic composition of ancestral Lake Ontario and also confirm that the basin was only fully glaciated during the Late Wisconsin.

Geochemistry of Holocene and late Pleistocene soils in the Rouge River and Scarborough Bluffs areas, South-Central Ontario, Canada

Concentrations of major, minor and trace elements were measured in four soil profiles from south-central Ontario. The mean concentration values reported are probably representative of elemental levels in soils formed from sediments reworked by lacustrine and fluvial processes and weathered over the last 12 000 years. The older soils in the sequence (R12, R15 and BRIM1) show declining Na, K, and Al, mainly from Ca dilution, especially in the lower horizons. Iron and Mg levels were not affected by the variations in the Ca concentrations. Arsenic, Br, and Sb concentrations did not increase appreciably in surface A horizons, indicating no measurable airfall influx of industrial pollutants. The relative increase in Mn/Al in the lower horizons of the older soils may be related to leaching by soil or ground water movement.

A hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada: Reply

A hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada: Reply

A hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada: Discussion

This is a discussion of a paper by the same title which appeared in Volume 25, Canadian Geotechnical Journal, pp 455-466. The authors of the original paper are N. Eyles and K.W.F. Howard.

Hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada

Hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada

Sunnybrook drift indicates a grounded early Wisconsin glacier in the Lake Ontario basin

Glaciotectonic analysis of Sunnybrook diamicton and underlying sediments in Scarborough Bluffs, Ontario, Canada, indicates that the diamicton investigated is lodgment and/or deformation till. The early Wisconsin overriding of deformable glaciolacustrine mud by the Ontario ice lobe was a significant glacial event in the eastern Great Lakes region. This has important implications for understanding interactions between Laurentide ice, proglacial lakes, and water-laid sediments.

A hydrochemical study of urban landslides caused by heavy rain: Scarborough Bluffs, Ontario, Canada

Scarborough Bluffs is a 15 km long stretch of the Lake Ontario shoreline east of downtown Toronto. This heavily urbanized area currently represents Canada's most serious erosion problem. The worst affected zone is 1.5 km long and lies along South Marine Drive where 50 m high bluffs are failing by shallow retrogressive failures of jointed glacial clays over underlying deltaic sands and clays. The erosion rate is about four times that for the coastline as a whole.Heavy rains in the Toronto area in August and September 1986 produced a spate of slope failures and mud flows. Particularly heavy storms on September 10 and 29 triggered extensive retrogressive slope failures at South Marine Drive. Hydrochemical investigations of discharge waters suggest that slope failure was caused by surface runoff on the bluff top recharging lower slope areas by infiltration through joints in the upper clay capping. Discharge of water from the lower slope is impeded by less permeable barriers in the deltaic stratigraphy at the site and by a cover of clayey slope debris. Data suggest that provision for adequate drainage of the bluff top, by interceptor drains, is a prerequisite for controlling slope behaviour in the area. Key words: slopes, erosion, groundwater, hydrochemical, recharge, drainage.

The internal structure of glacial landforms: an example from the Halton till plain, Scarborough Bluffs, Ontario

Current views on the internal structure of many glacial landforms need further definition. For example, drumlinized Halton till plain near the Scarborough Bluffs, Ontario would traditionally be. viewed as a lodgement till sheet, but it was found to consist of complex sedimentary assemblages including sediment flows, melt‐out, deformation and lodgement tills. These facies vary spatially depending on whether deposition occurred beneath grounded ice or within subglacial cavities. Proglacial sediments bury portions of the till plain. Surface Rutings and drumlins clearly indicate the action of subglacial processes on the surface of Halton drift. Sedimentary structures at the contact between stratified sediments and diamictons within the Late Wisconsinan Halton drift are similar to those in older beds exposed at Scarborough Bluffs. The demonstration of the role of grounded ice in Halton drift and the similarity of sedimentary structures to those of the underlying Thorncliffe and Sunnybrook sediments suggests that the action of grounded ice cannot be ruled out in the case of the lower beds, as has been done by Eyles &amp; Eyles (Geology 11, 146–152, 1983). Thus, surface Halton drift may be a model for recognition of similar environments of deposition in older beds beneath Halton. This analysis indicates flaws in a recent re‐evaluation of Scarborough Bluffs sediment interpreted as solely lacustrine and not directly affected by glaciers.

Sedimentological controls on piping structure and the development of scalloped slopes along an eroding shoreline: Scarborough Bluffs, Ontario

Sedimentological controls on piping structure and the development of scalloped slopes along an eroding shoreline: Scarborough Bluffs, Ontario

Magnetic and pebble fabrics and origin of the Sunnybrook Till, Scarborough, Ontario, Canada

The early Wisconsinan Sunnybrook Till is a mud-rich, pebble-poor, dark gray to gray–brown massive diamicton that is exposed in the Scarborough Bluffs, Ontario. It is interpreted here to be till.Previous separate, magnetic, and pebble fabric studies made on the till suggest a westward ice movement ranging from west of south to northwest. In this study, two dominant directions are found, northwest by west and northeast by north. Of these two directions, the northwest by west direction is the most common and this combined with the direction of shear in the underlying sediments and lithology of the till suggests that the glacier moved in a westerly direction.However, the fabrics are not typical of a lodgement till and to some extent resemble fabrics found in subaquatic debris-flow deposits. It is suggested that the glacier that deposited the Sunnybrook Till was buoyed up by high pore water pressure in the accumulating sediment at the sole of the glacier. Under these conditions, the till either flowed away from the zone of release at the base of the glacier and (or) was being lightly smeared by a partially grounded glacier.

Thermoluminescence dating studies of glacial silts from Ontario

To develop procedures for the direct dating of glacially related silts by thermoluminescence (TL), I have applied previously proposed techniques to three polymineralic 4–11 μm samples from the Toronto area. Furthermore, one of these samples was studied in detail by isolating some mineral fractions. The principal conclusion is that the TL of the lodgment Halton Till (from Woodbridge) was not significantly reset during deposition, whereas the TL of the waterlaid upper Thorncliffe silt (from the Scarborough Bluffs) was reset, as was the TL of the third sample (WC-ST), a massive silt from Woodbridge that has been generally correlated with the glaciolacustrine Sunnybrook diamict at the Bluffs. This conclusion follows from the observation of feldspar TL apparent ages of &gt;140 ka for the ~12 ka BP Halton Till and of 36 and 66 ka for the upper Thorncliffe and WC-ST samples, respectively.The four laboratory factors that contributed most to inaccuracies in the TL apparent ages were: (1) anomalous fading in the feldspar-dominant fractions, (2) nonlinearity in TL growth curves, (3) "overbleaching" of the TL, and (4) radon loss during alpha particle counting of dry powders. The effects of each of these have been circumvented or minimized. As expected, uncertainty in the past pore-water content represented the single largest source of imprecision for such TL apparent ages after correction for the other effects.