Lake Agassiz Research Articles

Relict ice-scour marks and late phases of Lake Agassiz in northernmost Manitoba

In northern Manitoba, intersecting grooves 300–1800 m long are ice-scour marks created by the dragging of iceberg keels along rises in the bed of a glacial lake whose water plane was at about 305 m asl. The lake was bounded by glacial ice on its northern and eastern margins. The occurrence of scours on topographic divides indicates that a single extensive lake, thought to be a northern extremity of Lake Agassiz, occupied the area as far north as Seal River at the time the ice scours were formed. The lake extended as far west as Sprott Lake and eastwards into the Hudson Bay Lowlands into an area later occupied by Tyrrell Sea. The preservation of the scour marks suggests that the lake drained suddenly.Ice-scour marks are easily recognized on air photographs and provide a means of identifying areas that have been inundated by glacial lakes. Scours in emerged marine sediment are generally obliterated by littoral processes.

Late quaternary history of Lake Manitoba, Canada

The postglacial history of Lake Manitoba has been deduced from a study of the changes in physical, mineralogical, and chemical variables in sediment cores collected from the lake. Six lithostratigraphic units are recognized in the South Basin of the lake. Weakly developed pedogenic zones, reflecting dry or extremely low water conditions in the basin, separate five of these six units. The initial phase of lacustrine sedimentation in the Lake Manitoba basin began shortly after 12,000 yr B.P. as water was impounded in front of the receding glacier to form Lake Agassiz. By 11,000 yr ago, continued retreat of the ice sheet opened lower outlets to the east and much of Lake Agassiz drained, including the Lake Manitoba basin. Water levels again rose at 9900 yr B.P., but by about 9200 yr B.P. the South Basin was again dry. For the next 4700 yr there was an alternation of wet and dry conditions in the basin in response to the interaction of a warmer and drier climate and differential crustal rebound of the basin. About 4500 yr ago a new phase of Lake Manitoba sedimentation was initiated when the Assiniboine River began to discharge into the South Basin. The Assiniboine River was diverted out of the Lake Manitoba watershed about 2200 yr ago. Erosion and redistribution of the sandy deltaic sediments deposited by the Assiniboine River has created the barrier beach that now separates the extensive marsh to the south of the lake from the main lake.

Oberservations on the life histories and biology of Ephemeroptera and Plecoptera in northeastern Alberta

Abstract During studies of the environmental effects of oil sands development in northeastern Alberta in 1976–1977, 36 species of Ephemeroptera and 21 of Plecoptera were collected using various techniques. Individuals of 18 mayflies and 17 stoneflies were taken in numbers sufficient to determine their basic life histories and habitat preferences. Among the mayflies, 8 (possibly 10) species exhibited fast seasonal development, 8 slow seasonal, and 2 non‐seasonal. Among the Plecoptera, these patterns were exhibited by 5, 7 and 5 species, respectively. Nymphs of most fast seasonal mayflies developed in pools and silty backwaters, often in association with aquatic macrophytes. Slow seasonal mayflies and most stoneflies were found in riffles, or on bedrock and debris in the Athabasca River. The fauna included a mixture of Eastern, northern and cordilleran species. Eastern species probably reached the Athabasca River drainage via glacial Lake Agassiz.

The Wisconsinan deglaciation of southern Saskatchewan and adjacent areas: Discussion

In his recently published paper summarizing the stratigraphic and morphologic record of southern Saskatchewan and adjacent areas, Christiansen (1979) proposed a chronology of deglaciation that is in error because it fails to integrate relevant data from outside of Saskatchewan. Christiansen's interpretation shows a progressive northward retreat of the glacial margin from Montana and North Dakota beginning before 16 000 years BP. By 15 500 years ago, the ice is shown to have retreated north of the Missouri River watershed (which previously had channelled all meltwater well south of the glaciated region) with runoff discharging eastward into Manitoba via the Souris and Pembina channels (Phase 3, Fig. 12 in Christiansen). At 14 000 years BP (Phase 4, Fig. 13), the glacial margin of Christiansen has retreated still farther north, with icefree conditions having developed over most of southern Saskatchewan; all rivers of the deglaciated region of Saskatchewan and Alberta are shown draining eastward into Lake Agassiz in Manitoba. The 14 000 year BP margin of Christiansen (1979) brings his interpretation, as well as that of Klassen (1972), into apparently irresolvable conflict with evidence to the south and east of Saskatchewan. In one of the most closely and certainly dated events in the glacial chronology of central North America, ice advanced southward over a forest bed near Des Moines, Iowa, at 14 000 years BP to deposit the Bemis Moraine (Ruhe 1969). Radiocarbon dates from six samples of wood, including two trees in growth position in loess beneath till, three trees rooted in the top of the loess and pushed over by the advancing ice, and one log incorporated in till, record this advance (Table 1). Lobate patterns and flow indicators confirm that, to reach Iowa, this ice must have flowed through the Lake Agassiz basin (Fig. 1) and over the only southern outlet from this basin, the Minnesota River Valley. In short, it does not seem possible to have water discharging eastward into the Lake Agassiz basin at 14 000 years BP, nor probably at 15 500 years BP, as Christiansen (1979) has shown because the basin was filled with ice, making eastward and southeastward drainage impossible. This point also has been made by Teller (1976) and Teller and Fenton (1980). On the basis of the evidence available in North Dakota, South Dakota, and Iowa, the last major glacial advance across the region reached its maximum western position about 14000 years ago (Clayton et al., in press). We suggest that Christiansen's Phase 2 (16 500 years BP) glacial boundary (Fig. 11) may more closely reflect conditions at 14 000 years BP. While the pattern of deglaciation in southwestern Saskatchewan and Alberta may have occurred as depicted by Christiansen, drainage from these western regions must have been southward into the Missouri River system until sometime after 14 000 years BP, rather than eastward through Lake Agassiz and into the upper Mississippi River system. Although it is not the main purpose of this discussion to explore the reason for Christiansen's unacceptably early chronology of deglaciation, we feel that a comment about the radiocarbon dates he used is pertinent. Nearly all of the dates that are used to document the deglaciation of southern Saskatchewan before 14 000 years BP are from finelydisseminated organic matter in fine-grained sediment (S-522 to S-526, GSC-1369, and S-

Late Wisconsinan glacial stratigraphy and history of southeastern Manitoba

The history of Late Wisconsinan glaciation in southwestern Manitoba has been established by identifying and correlating ice-laid lithostratigraphic units in the subsurface. Five Late Wisconsinan tills are defined on the basis of their texture, mineralogic composition, and stratigraphic position. These new formations are, from youngest to oldest, Marchand, Whitemouth Lake, Roseau, Senkiw, and Whiteshell Formations.Late Wisconsinan ice first invaded southeastern Manitoba 22 000 to 24 000 years ago. This Laurentide glacier advanced from the northeast across the Precambrian Shield and deposited the sandy Whiteshell and Senkiw tills, which contain abundant Precambrian rock fragments and minerals and few Paleozoic carbonate grains. Shortly after this, Keewatin ice advanced from the northwest over Paleozoic carbonate rocks, depositing the loamy carbonate-rich Roseau Formation throughout most of the area. This ice remained over southeastern Manitoba until after 13 500 years ago, when it rapidly retreated northward with Lake Agassiz on its heels. Two brief glacial readvances occurred. The first overrode Lake Agassiz lacustrine sediment as far south as central North Dakota shortly after about 13 000 years ago. The clayey Whitemouth Lake till was deposited in southern Manitoba at this time. After a rapid retreat, the ice briefly pushed southward over southeastern Manitoba about 12 000 years ago to just south of the International Boundary. The sandy carbonate-rich Marchand Formation was deposited at this time as the ice overrode its own sandy outwash. By 11 000 years ago, ice had disappeared from southeastern Manitoba.

Northern extent of Lake Agassiz in eastern Saskatchewan

Surveys for a proposed hydroelectric dam, disclosed extensive deposits of late Pleistocene lacustrine clay in the valleys of the Churchill and Reindeer Rivers. The presence of montmorillonite in these clays and the topographic configuration suggest continuous connection to the main body of Glacial Lake Agassiz. The presence of till layers above the lacustrine deposits is explained by subaqueous slumping rather than read vance of the glacier, which retreated from this area between 10 000 and 9 000 years ago.

Climatic implications of D/H ratios of meteoric water over North America (9500–22,000 B.P.) as inferred from ancient wood cellulose C [sbnd]H hydrogen

δD and δ 13C values have been measured for the unexchangeable hydrogen and the total carbon of cellulose extracted from 40 North American 14C-dated trees that range in age from 9500 to 22,000 years B.P. Meteoric waters which precipitated over ice-free regions of North America in the interval 14,000–22,000 B.P. had more positive δD values than corresponding modern waters by an average of 19‰. Lower ocean temperatures and smaller temperature gradients than exist at present between ocean and ice-free North America are indicated for the late Wisconsin glacial maximum. This is compatible with warmer winters and cooler summers for this glacial period. The δD value of the North American ice sheet during the Late Wisconsin maximum was approximately −100‰ as determined from the inferred δD values of the waters of proglacial lakes Agassiz and Whittlesey. From this figure the increase in δ 18O of the oceans during the glacial maximum can be calculated to have been +0.8‰. At the point where they began to move over the ice, air masses supplying moisture to the North American ice sheet contained a little more than 50% of their original moisture content, which is a much greater percentage than exists in air masses supplying the modern Greenland and Antarctic ice sheets. This relatively vapor-rich air coupled with lower summer temperatures, which reduced ablation, probably contributed to the maintenance and growth of the ice sheet. The transition from glacial to interglacial conditions on North America was rapid and occurred within a 2000–3000-year interval. However, the transition may not have been synchronous over North America. A 40-year δD record in a spruce branch from the Two Creeks (Wisconsin) forest (∼11,800 B.P.) shows large variations which suggest an unusual hydrologic environment in the area of the tree. Cellulose δ 13C values range between −20.8 and −25.9‰, but do not correlate with δD variations for the samples analyzed in this work. Thus, climatic significance of δ 13C variations cannot be resolved from these data.

Paleoecological aspects of the Red Lake Peatland, northern Minnesota

The Red Lake Peatland, situated on the eastern arm of the Lake Agassiz plain in north central Minnesota, is made up of large black spruce raised bogs separated by sedge-covered water tracks marked by string patterns and teardrop-shaped forested islands. About 3 m of peat overlie a prairie soil; the basal peat is 3170 ± 100 years old (14C date). Stratigraphic distribution of pollen, macrofossils, and peat components in a series of cores along a small forested island was used to study the development of the peatland.In pollen zone RLB-1 (lowest) the upland pollen types suggest an oak savanna with a developing mesic deciduous forest. The local pollen indicates a succession from a Typha marsh to a sedge meadow. Zone 2 shows a small rise in Pinus pollen; Ericaceae pollen and Sphagnum spores indicate the development of a bog–heath vegetation type at the coring site. An increase in pollen of spruce and larch reflects the establishment of the island forest. Zone 3 is marked by a rise in Ambrosia pollen, recording agricultural land clearance in northwestern Minnesota in about 1890.The Salix–herb macrofossil assemblage occurs at the base of some cores; it is succeeded stratigraphically by the Typha–Scirpus assemblage, which also makes up the base of the remaining cores. There follows the Carex diandra – Carex aquatilis assemblage, suggesting a sedge meadow. The overlying Menyanthes–Larix assemblage continues to the surface under the sedge fen; under the island, seeds of Chamaedaphne and needles of Picea occur in this assemblage. The incoming of the Menyanthes–Larix assemblage is believed to reflect the first development of the patterned wetland.Reed peat comprises the bottom 20–50 cm of all cores; it corresponds with the lower part of pollen zone 1 and contains the Typha–Scirpus macrofossil assemblage. Pure sedge peat or sedge peat with Bryales corresponds with zone 2 and upper zone 1 of the pollen diagram and contains the Carex diandra –C. aquatilis macrofossil assemblage. Ericaceous peat occurs only under the island, and it contains the Menyanthes–Larix macrofossil assemblage. Laterally under the present sedge fen it grades into sedge peat with ericaceous components.The general upward succession of communities observed in these peat cores can be duplicated along a west-to-east surface traverse across the present prairie–forest transition. The stratigraphic succession thus records the westward movement of the prairie–forest transition across Beltrami County about 4000–2000 years ago.The area was covered by prairie more than 3100 years ago. Development of a cooler, moister climate led to a Typha marsh in the poorly drained lowland; oak savanna occupied the surrounding upland. As the water level rose in the lowland, peat started to accumulate as sedge meadow developed, and aspen parkland and conifer–hardwood forest moved into the upland. About 2000 years ago the growth of Sphagnum moss increased, accompanied by the development of patterned wetland and bog forest, with conifer–hardwood forest on the upland.

Lake Agassiz deposits in the main offshore basin of southern Manitoba

The lowlands adjacent to the Red River Valley were flooded whenever Quaternary glaciation dammed the northward-draining river systems of the region. The most recent impoundment, referred to as Lake Agassiz, began shortly before 13 500 years BP, as late Wisconsinan ice retreated northward in the Valley for the last time. In southern Manitoba, three fine-grained lacustrine units, numerous beach deposits, and an extensive area of fluvio-lacustrine (deltaic) sediment were deposited in and around the main depositional center of the Lake Agassiz basin during the life of the lake.The oldest offshore deposit of Lake Agassiz (Unit 1) is a silty clay containing ice-rafted clasts of till, clayey silt, and rock. Most of the silty and sandy sediment of the Assiniboine Delta also was deposited at this time. A readvance of ice into the northern and eastern Lake Agassiz basin, about 9800 years ago, caused a new influx of ice-rafted sediment into the offshore silty clays of southern Manitoba. Clast-rich Unit 2 was deposited at this time along the northern and eastern margins of the basin. When the ice retreated from the area shortly after 9800 years BP, lake levels dropped, and siltier, better laminated, and relatively clast-free Unit 3 was deposited. Units 1, 2, and 3 in southern Manitoba are correlated, respectively, with the Brenna Formation, lower part of the Sherack Formation, and upper part of the Sherack Formation of Lake Agassiz in North Dakota and Minnesota. Lake Agassiz deposition continued in southern Manitoba until after 8700 years BP.

Postglacial diatom stratigraphy in relation to the recession of Glacial Lake Agassiz

The sediment and diatom stratigraphy of a small pond on The Pas moraine, near Grand Rapids, Manitoba, reveals a change in sedimentary environment related directly to the last stages of Glacial Lake Agassiz. Beach sands were replaced by clay 7300 14C y. a., then by organic silt and, at 4000 14C y. a. by coarse organic detritus; the corresponding diatom assemblages were (I) a predominantly planktonic spectrum in beach sands, (II) a rich assemblage of nonplanktonic forms, and (III) a distinctly nonplanktonic acidophilous spectrum. These results confirm Elson's (1967) reconstruction of the extent and chronology of the final (Pipun) stage of Glacial Lake Agassiz. The sedimentary environments change from a sandy beach of a large lake at 7300 BP to a small, shallow eutrophic pond with clay and silt deposition from 7000 to 4000 BP. From 4000 BP to the present, organic detritus was deposited in a shallow pond that tended toward dystrophy.

DhLB-1: Early Period Occupation Near Glacial Lake Agassiz, Southeast Manitoba

DhLB-1: Early Period Occupation Near Glacial Lake Agassiz, Southeast Manitoba

Pollen stratigraphy of holocene sediments from the grand rapids area, Manitoba, Canada

Two sections of sediments from a shallow lake on The Pas moraine gave a 14C age of 7 220 ± 110 years, a likely minimum age for the recession of Glacial Lake Agassiz II. Three pollen zones are recognized as follows: Zone 1, from 7 300 to about 6 200 B.P., dominated by NAP(40–75%) with 6–22% spruce, 1–10% juniper and minor proportions of other trees, interpreted as a treeless vegetation, except for scattered spruce, dominated by juniper, grasses, sagebush and herbs. Zone 2, from 6 200 to 3 500 B.P., dominated by pine, with a mixed forest of poplar, pine and spruce. Zone 3, an assemblage occurring from 3 500 B.P. to the present, consisting of spruce, pine and birch, representing the modern mixed boreal forest. These findings agree with archaeological data suggesting a shift from a plains to a woodland culture.

Slope Stability Analysis in Anisotropic Winnipeg Clays

Two major aspects of an investigation dealing with the stability of natural and cut slopes in the Winnipeg area are described. The first concerns an experimental investigation of the anisotropic shear strength characteristics of the layered Lake Agassiz clays and the second is a study of the mechanism of failure for slopes in these layered clays.Four main types of clay were investigated and it was found that the effective shear strength parameters were greater for failure across the layers than for failure along the layers. Residual shear strength parameters were also determined.Stability analyses were carried out for representative slope cross sections using circular and noncircular failure surfaces, taking into account the anisotropic shear strength effects measured in the laboratory tests.Factors of safety were found for the conventional method of analysis assuming circular arc failure surfaces and isotropic shear strength properties. These factors of safety were found to be up to 0.5 greater than those obtained from noncircular failure surfaces which partially passed along the layers and so mobilized the lower shear strength properties of these layers.

Early History of Lake Agassiz in Southeast North Dakota

Research Article| May 01, 1974 Early History of Lake Agassiz in Southeast North Dakota JOHN P. BLUEMLE JOHN P. BLUEMLE 1North Dakota Geological Survey, University Station, Grand Forks, North Dakota 58201 Search for other works by this author on: GSW Google Scholar Author and Article Information JOHN P. BLUEMLE 1North Dakota Geological Survey, University Station, Grand Forks, North Dakota 58201 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1974) 85 (5): 811–814. https://doi.org/10.1130/0016-7606(1974)85<811:EHOLAI>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN P. BLUEMLE; Early History of Lake Agassiz in Southeast North Dakota. GSA Bulletin 1974;; 85 (5): 811–814. doi: https://doi.org/10.1130/0016-7606(1974)85<811:EHOLAI>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 Extensive accumulations of collapsed lake and shore sediment are present above the Herman level adjacent to the Agassiz lake plain in southeast North Dakota. The presence of these deposits indicates that ice-dammed lakes existed on top of stagnant glacial ice while Lake Agassiz was developing. Lake Agassiz did not simply expand northward from its southern end; but rather, when the superglacial lakes coalesced, the resulting Lake Agassiz flooded areas along much of the length of the Herman Beach. 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.

Composantes du Mouvement de Rebondissement Isostatique d'Après des Données de Remblaiements Alluviaux. (Exemple de la Rivière Saskatchewan Sud)

During the retreat of the last ice age isostatic rebound occurred propagating like a damped wave parallel to the ice front. Beaches of large glacial lakes show this clearly. In areas where such lakes were too short lived to develop well defined beaches evidence of rebound must be sought elsewhere. In regions where the general slope of the land is towards the retreating ice front, rebound will trigger incision of the down valley section. If a bed is uplifted which is more resistant than the rate of incision, aggradation will occur in an upstream section of the river. This mechanism seems to best explain the fill in the South Saskatchewan River Valley at Elbow. In this case a bouldery till near Saskatoon appears to behave as a resistant layer. Minimum deformation derived from the evidence available is comparable to that measured on Lake Agassiz shorelines.

The Mosbeck Site: a paleoenvironmental interpretation of the late quaternary history of Lake Agassiz based on fossil insect and mollusk remains

The Mosbeck Site is in the southern part of the Lake Agassiz basin in northwestern Minnesota. The stratigraphic section at the site consists of seven lithologic units, which are from bottom to top (A) unsorted, pebbly, sandy, silty clay, (B) coarse gravel, (C) silty sand, (D) peat, (E) fine sand, (F) interbedded sand and gravel, and (G) unbedded dirty gravel. The lower few centimeters of unit E are unoxidized and contain black spruce and tamarack driftwood, which has been radiocarbon dated at 9940 ± 160 BP (I-3880). Units C-E contain numerous, well-preserved insect and mollusk remains. These fossils have been compared with modern species, and at least 76 insect and 15 mollusk taxa are present. Assuming that their ecological tolerances have changed little in the past 10,000 years, they provide valuable information about the environment of Lake Agassiz. Few of the insects are now found in the region, indicating that the environment has changed. With few exceptions the species present indicate that the climate and vegetation at the time were similar to the present-day climate and vegetation of southeastern Manitoba. The lithology and faunal contents of the sediment are interpreted as follows. Unit A is Late Wisconsinan glacial sediment. Unit B is a lag concentrate formed by wave action during a regressive phase of Lake Agassiz. Unit C is the sediment of a small body of water that formed when the level of Lake Agassiz had dropped below the site. The banks were covered with a spruce forest. Open water gave way to swampy conditions, and unit D was formed. Both units C and D were deposited during the low-water Moorhead Phase of Lake Agassiz. Units E and F are shoreline sediment deposited as the lake level rose, drowning the vegetation. Unit G is modern ditch spoil.

A Postglacial Freshwater Drum (Aplodinotus grunniens) from Ontario, and Comments on the Zoogeography of the Species

A freshwater drum (Aplodinotus grunniens) specimen from postglacial deposits of northern Ontario indicates the species former presence in Lake Barlow–Ojibway. The fact that the species survives in Lakes Abitibi and Timiskaming may be best explained by its having entered Lake Barlow–Ojibway from the west during the Gimli phase of Lake Agassiz about 8000 years ago, but this hypothesis cannot be confirmed with the existing evidence.

Geography and Bathymetry of Selected Lake Basins, Experimental Lakes Area, Northwestern Ontario

The Experimental Lakes Area (ELA) is located at 93°30′–94°00′W and 49°30′–49°45′N at an altitude of 360–380 m above mean sea level. This area is underlain by Precambrian acid granites overlain in some areas by thin glacial drift composed largely of sand and gravel of quartz, plagioclase, and K-feldspar. The area was under glacial ice about 14,000 years B.P. (before present). With the melting of this glacial ice, ELA was situated on the eastern margin of glacial Lake Agassiz. As Lake Agassiz levels receded, the present lake basins were formed. The ELA watersheds now drain into the Winnipeg River, which is in the Hudson Bay drainage system.Mean annual temperatures in the vicinity of ELA are between 0.5 and 2.2 C, and annual precipitation is between 500 and 750 mm. Brunisols were observed over sand deposits in the ELA, but considerable variation in soil types and soil depth were also found. ELA is in a boreal (fire-controlled) subclimax forest of jack pine, black spruce, trembling aspen, and white birch. Aquatic macrophytes were scarce in the littoral zone of ELA lakes. Nearby logging operations and hunting and sport fishing have not influenced the immediate watersheds of ELA lakes.Morphometric maps and measurements are given for 16 lakes in ELA. These lakes vary from 2.5 to 33 m in maximum depth, and from 1.7 to 56 ha in lake surface area. Using estimates of precipitation, evaporation, evapotranspiration, drainage areas, and lake morphometry, a preliminary calculation of theoretical water renewal time is given for these lakes. These values range from 2.6 to 38 years.

Flexural rigidity, thickness, and viscosity of the lithosphere

The earth's lithosphere and asthenosphere are modeled as a thin elastic sheet and a fluid substratum, respectively; the physical principles involved are briefly described. The flexural rigidity of the lithosphere is deduced from observations of the wavelength and amplitude of bending in the vicinity of supercrustal loads. Data from Lake Bonneville given by M. D. Crittenden, Jr., are reinterpreted to give a value for the flexural rigidity of the lithosphere in the Basin and Range province of the western United States of 5×1022 Newton meters. Observations of loading in Canada give values for the flexural rigidity of greater than 3×1020N m for the Caribou Mountains in Northern Alberta; about 4×1023 N m for the topography over the Interior Plains; about 1023 N m for the Boothia uplift in arctic Canada; and about 1025 N m for the bending of the beaches of Pleistocene Lakes Agassiz and Algonquin. The flexure of the lithosphere at Hawaii and the bending of the oceanic lithosphere near island arcs give values of about 2×1023 N m. For short-term loads (103–104 years) the flexural rigidity of the continental lithosphere is almost two orders of magnitude larger than for long-term loads, indicating nonelastic behavior of the lithosphere with a viscous (about 1023 N sec m−2) as well as an elastic response to stress. From the values of the flexural rigidity, the thickness of the continental lithosphere is inferred to be about 110 km and that of the oceanic lithosphere about 75 km or more. The anomalously low flexural rigidity of the lithosphere of the Basin and Range province may be due to a very thin lithosphere, only about 20 km thick, with hot, lower crustal material acting as an asthenosphere.

Quaternary geology of the Grand Rapids area, Manitoba

Grand Rapids is at the mouth of the Saskatchewan River on the western side of Lake Winnipeg in central Canada and is in the western part of the region formerly covered by Glacial Lake Agassiz.Relict beaches and cliffs, and abandoned spillway and stream channels have been observed in the area. Much of the Paleozoic bedrock is covered by Quaternary deposits consisting of three or four Wisconsin tills interspersed and covered by glacio–lacustrine silts and clays.The events are correlated with the final four episodes in the general history of Lake Agassiz and it appears that after substantial changes in the drainage pattern, the recent course of the lower reaches of the Saskatchewan River developed during the last 8 000 ± 250 y.