Western Lake Superior Region Research Articles

A Climatology of Easterly Wind Lake-Effect and Lake-Enhanced Precipitation Events over the Western Lake Superior Region

Abstract Lake-effect precipitation is convective precipitation produced by relatively cold air passing over large and relatively warm bodies of water. This phenomenon most often occurs in North America over the southern and eastern shores of the Great Lakes, where high annual snowfalls and high-impact snowstorms frequently occur under prevailing west and northwest flow. Locally higher snow or rainfall amounts also occur as a result of lake-enhanced synoptic precipitation when conditionally unstable or neutrally stratified air is present in the lower troposphere. Although likely less common, lake-effect and lake-enhanced precipitation can also occur with easterly winds, impacting the western shores of the Great Lakes. This study describes a 15-yr climatology of easterly lake-effect (ELEfP) and lake-enhanced (ELEnP) precipitation [conjointly, easterly lake collective precipitation (ELCP)] events that developed in east-to-east-northeasterly flow over western Lake Superior from 2003 to 2018. ELCP occurs infrequently but often enough to have a notable climatological impact over western Lake Superior, with an average of 14.6 events per year. The morphology favors both single shore-parallel ELEfP bands due to the convex western shoreline of Lake Superior and mixed-type banding due to ELEnP events occurring in association with “overrunning” synoptic-scale precipitation. ELEfP often occurs in association with a surface anticyclone to the north of Lake Superior. ELEnP typically features a similar northerly displaced anticyclone and a surface cyclone located over the upper Midwest that favor easterly boundary layer winds over western Lake Superior.

“Mr. Burk Is Most Interested in Their Welfare”: J.G. Burk’s Campaign to Help the Anishinabeg of Northwestern Ontario, 1923-53

Although there is a small but growing body of literature on Euro-Canadians who acted "with good intentions" towards the First Nations (Haig-Brown and Nock 2006), precious little has been written about those within the ranks of the Department of Indian Affairs who acted benevolently towards the Aboriginal peoples. James Gerry Burk, Indian agent for the Anishinabeg of the western Lake Superior region for three decades (1923-53), was one such individual. He chose to ignore the department's prevailing racist ideology in favour of nurturing the incipient desire for industry and enterprise that he saw first-hand among the Aboriginal constituents of his agency. In the process, he was compelled to overcome numerous obstacles that Indian Affairs placed in his way. As a result, Burk's career stands as a glowing testament to the indomitable spirit of one departmental official's commitment to assisting the Aboriginal peoples.

Breeding Bird Communities Across an Upland Disturbance Gradient in the Western Lake Superior Region

Upland breeding bird communities were sampled from 225 points in 15 survey routes in the coastal region of western Lake Superior to examine relationships to human land use. Eighty-four species were detected and 50 were abundant enough to be included in data analysis. Monotonic quadratic regression models were constructed for these 50 species by using species counts as the dependent variable and the proportion of human conversion of the landscape (residential, agriculture, and commercial/industrial land uses) within each study area as the independent variable. Twenty-seven bird species had significant regressions (P < 0.05), 18 of which generally avoided areas developed by humans and 9 of which were attracted to development. Detrended correspondence analysis using counts of these 27 bird species was used to investigate multivariate, community responses to development. The first DCA axis was interpreted as a gradient from urban avoiding to urban exploiting bird species and was strongly correlated with land cover variables related to human development. Our results advance the idea that breeding bird communities can be used as indicators of ecological condition and can diagnose potential causes for changes in these conditions. Further, our study points out the usefulness of bird monitoring data in regional planning efforts that incorporate goals for maintaining native biological diversity.

Geoarchaeology and late glacial landscapes in the western lake superior region, Central North America

AbstractThe transition from full glacial to interglacial conditions along the southern margin of the Laurentide ice sheet resulted in dramatic changes in landscapes and biotic habitats. Strata and landforms resulting from the Wisconsin Episode of glaciation in the area directly west of Lake Superior indicate a context for late Pleistocene biota (including human populations) connected to ice margins, proglacial lakes, and postglacial drainage systems. Late Glacial landscape features that have the potential for revealing the presence of Paleoindian artifacts include abandoned shorelines of proglacial lakes in the Superior and Agassiz basins and interior drainages on deglaciated terrains. The linkage between Late Pleistocene human populations and Rancholabrean fauna has yet to be demonstrated in the western Lake Superior region, although isolated remains of mammoth ( Mammuthus) have been documented, as well as fluted points assigned to Clovis, Folsom, and Holcombe‐like artifact forms. Agate Basin and Hell Gap (Plano‐type) artifacts also imply the presence of human groups in Late Glacial landscapes associated with the Agassiz and Superior basins. © 2007 Wiley Periodicals, Inc.

Discovery of distal ejecta from the 1850 Ma Sudbury impact event

A 25-70-cm-thick, laterally correlative layer near the contact between the Paleoproterozoic sedimentary Gunflint Iron Formation and overlying Rove Formation and between the Biwabik Iron Formation and overlying Virginia Formation, western Lake Superior region, contains shocked quartz and feldspar grains found within accretionary lapilli, accreted grain clusters, and spherule masses, demonstrating that the layer contains hypervelocity impact ejecta. Zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca. 1878 Ma and 1836 Ma. The Sudbury impact event, which occurred 650-875 km to the east at 1850 ′ 1 Ma, is therefore the likely ejecta source, making these the oldest ejecta linked to a specific impact. Shock features, particularly planar deformation features, are remarkably well preserved in localized zones within the ejecta, whereas in other zones, mineral replacement, primarily carbonate, has significantly altered or destroyed ejecta features.

Age of volcanic rocks and syndepositional iron formations, Marquette Range Supergroup: implications for the tectonic setting of Paleoproterozoic iron formations of the Lake Superior region

A rhyolite in the Hemlock Formation, a mostly bimodal submarine volcanic deposit that is laterally correlative with the Negaunee Iron-formation, yields a sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon age of 1874 ± 9 Ma, but also contains inherited Archean zircons as old as 3.8 Ga. This precise age determination for the classic Paleoproterozoic stratigraphic sequence of northern Michigan, the Marquette Range Supergroup (MRS), necessitates modification of previous depositional and tectonic models. Our new data indicate that the Menominee Group, previously ascribed to continental rifting during early, pre-collision phases of the Penokean orogenic cycle, is coeval with arc-related volcanic rocks now preserved as accreted terranes immediately to the south and is more aptly interpreted as a foredeep deposit. We interpret these to be second-order basins created by oblique subduction of the continental margin rather than basins formed on a rifting margin. Along with a recently reported age for the Gunflint Formation in Ontario of 1878 ± 2 Ma, our data suggest that an extensive foredeep in the western Lake Superior region was the locus of iron-formation deposition during arc accretion from the south. Further, we interpret the lower MRS (Chocolay Group), a glaciogenic and shallow-marine succession that lies atop Archean basement, to be equivalent to the upper part of the Huronian Supergroup of Ontario and to represent the original continental rifting and passive-margin phase of the Penokean cycle. The upper MRS (Baraga Group) represents deeper marine basins, dominated by turbidites and lesser volcanic rocks, resulting from increased subsidence and continued collision. A stitching pluton, which cuts correlatives of the Hemlock Formation in a thrust sheet, yielded a U–Pb zircon age of 1833 ± 6 Ma, consistent with other post-tectonic plutons in Wisconsin and northern Michigan, indicating that Penokean convergence lasted no longer than ~40 million years.

Proterozoic reactivation of the southern Superior Province and its role in the evolution of the Midcontinent rift

Major reverse faults associated with the late compressional phase of the 1.1 Ga Midcontinent rift in the western Lake Superior region appear to cut across the rift at the eastern end of the lake and join with reverse faults on the eastern shoreline, defined on the basis of geological and potential field data. The continuation of the faults across eastern Lake Superior is inferred on evidence drawn from nearshore shipborne magnetic surveys together with new interpretations of published bathymetric and GLIMPCE aeromagnetic data. In the Archean Superior Province about 100 km east of Lake Superior, paleomagnetic and petrographic data from the 2.45 Ga Matachewan dyke swarm show that the Kapuskasing Zone, a narrow belt of uplifted crust, can be extended to within 50 km of the Lake Superior shoreline and has bounding reverse faults that are almost continuous with two faults of similar dip and sense of displacement that define the inversion of the Midcontinent rift in the central and western parts of the lake. Since the Kapuskasing Zone is dominantly a Paleoproterozoic (about 1.9 Ga) structure, the continuity suggests that the Lake Superior faults, whose last major activity was during the Grenville Orogen, may represent reactivation of much older faults that were part of an extended Kapuskasing structure. Within the Superior Province to the north and east of Lake Superior, published radiometric data on biotites suggest a series of alternating crustal blocks of varying tectonic stability, separated by northeast-trending faults. The Lake Superior segment of the Midcontinent rift developed within the most unstable block, bounded by the Gravel River fault to the northwest and the Ivanhoe Lake fault (the eastern margin of the Kapuskasing Zone) to the southeast.

Geochronology of the North American Midcontinent rift in western Lake Superior and implications for its geodynamic evolution

Volcanism in the Midcontinent rift system lasted between 1108 and 1086 Ma. Rates of flood-basalt eruption and subsidence in the western Lake Superior region appear to have been greatest at the beginning of recorded activity (estimated 5 km/Ma subsidence rate at 1108 Ma) and rapidly waned over a period of 1–3 Ma during a magnetically reversed period. The age of the paleomagnetic polarity reversal is now constrained to be between 1105 ± 2 and 1102 ± 2 Ma. A resurgence of intense volcanism began at 1100 ± 2 Ma in the North Shore Volcanic Group and lasted until 1097 ± 2 Ma. This group contains a ca. 7 Ma time gap between magnetically reversed and normal volcanic sequences. A similar disconformity appears to exist in the upper part of the Powder Mill Group. The average subsidence rate during this period was approximately 3.7 km/Ma. Latitude variations measured from paleomagnetism on dated sequences indicate that the North American plate was drifting at a minimum rate of 22 cm/year during the early history of the Midcontinent rift. An abrupt slowdown to approximately 8 cm/year occurred at ca. 1095 Ma. These data support a mantle-plume origin for Midcontinent rift volcanism, with the plume head attached to and drifting with the continental lithosphere. Resurgence of flood-basalt magmatism at 1100 Ma may have been caused by extension of the superheated lithosphere following continental collision within the Grenville Orogen to the east.

Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events

Research Article| November 01, 1997 Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events Howard D. Mooers; Howard D. Mooers 1Department of Geology, University of Minnesota, Duluth, Minnesota 55812 Search for other works by this author on: GSW Google Scholar J. D. Lehr J. D. Lehr 2Minnesota Department of Natural Resources, Division of Minerals, 500 Lafayette Road, St. Paul, Minnesota 55155 Search for other works by this author on: GSW Google Scholar Author and Article Information Howard D. Mooers 1Department of Geology, University of Minnesota, Duluth, Minnesota 55812 J. D. Lehr 2Minnesota Department of Natural Resources, Division of Minerals, 500 Lafayette Road, St. Paul, Minnesota 55155 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1997) 25 (11): 987–990. https://doi.org/10.1130/0091-7613(1997)025<0987:TROLIS>2.3.CO;2 Article history First Online: 02 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 Howard D. Mooers, J. D. Lehr; Terrestrial record of Laurentide Ice Sheet reorganization during Heinrich events. Geology 1997;; 25 (11): 987–990. doi: https://doi.org/10.1130/0091-7613(1997)025<0987:TROLIS>2.3.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 SocietyGeology Search Advanced Search Abstract The glacial stratigraphy and geomorphology of the western Lake Superior region record a complex sequence of late Wisconsinan ice advances and retreats of the Laurentide Ice Sheet from accumulation centers in Quebec and Hudson Bay. Geomorphic evidence indicates that three major late Wisconsinan events occurred, each marked by gradual buildup of ice, formation of a prominent moraine, and subsequent rapid ice retreat. The established radiocarbon chronology indicates that these three events culminated ca. 23–21, 16–15.5, and 13 14C ka, indicating that major glacial advances culminated immediately prior to Heinrich events H-2 and H-1, and that ice underwent rapid retreat during Heinrich events.The possible linkage between western Lake Superior region ice dynamics and Heinrich events is supported by the presence of indicator rock types in drift associated with each major glacial recession. These indicators suggest that progressive southward shifts of the Laurentide Ice Sheet ice divide accompanied each rapid glacial recession. Furthermore, lithologic evidence indicates that there were two episodes of ice divide shifts: one ∼400–600 km occurring during H-2, and a smaller shift occurring during H-1. 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.