Great Lakes Origin by Diastrophic Processes

Lake Ontario

Patterns of drumlins in the region surrounding Lake Ontario provide evidence for two separate flow patterns, that are superimposed, one over the other. The first of  these was a current flow over a broad area from north to south, that I suggest was generated by an uplift of the crust, probably involving a large part of the Canadian Shield. This current formed patterns of north-south oriented drumlins in Paleozoic sediments across southern Ontario and in northwestern New York by a process of streamlining. During this time, as the Allegheny Highlands south of Lakes Erie and Ontario began to emerge above the water, the currents were confined to north-south valleys, where erosion became intensified.

Landforms such as drumlins on plateaus that remained above the water remained intact, while in the valleys between, erosion continued and intensified. Drumlins in low lying areas were often modified or eroded away. The restriction of flow in valleys resulted in the excavation of long troughs such as the Finger Lakes and other north-south valleys in northwestern New York and Ohio. Eventually the southerly flow was diverted around the highlands, some towards the southeast, down the Hudson Valley, and some towards the southwest.
 

DEM image showing the Great Lakes area
DEM showing the Great Lakes area.
Figure courtesy of John Shaw.

Downwarping of the crust in central Michigan, together with uplift centered in the Adirondack Mountains, east of Lake Ontario, initiated the second flow pattern. The flood waters spilled towards the west, and the westerly current flow along the axis of Lake Ontario modified previously formed drumlins in the lowlands on both north and south shores of Lake Ontario, and excavated the southern part of the basin of Lake Ontario to below sea level. Drumlins along the shores of Lake Ontario were cut in half by these currents, and new drumlin fields developed west of Lake Ontario, in a fan-shaped pattern. Flow was towards the northwest above the Niagara Escarpment between Dundas and Orangeville. On the Niagara Peninsula the flow was towards the west as indicated by a group of drumlins near Caledonia, that are half buried in silt. These currents also excavated Lake Erie, which has a deep basin near its eastern end.

Shaw and Gilbert studied drumlin orientations in this region and interpreted the flow patterns northwest  of Lake Ontario as converging in a southeasterly direction, towards the basin of LakeOntario. My observations of  drumlins around Guelph, Ontario, and a small cluster of drumlins at Westover suggest the flow direction in this location was from out of the lake, towards the west.

Shaw and Gilbert's comments about two superimposed flood streams are in substantial agreement with my own conclusions. They wrote (Shaw, J. and R. Gilbert, 1990, p.1170):

Evidently it is possible to recognize separate flood events by the pattern of drumlins and to establish relative ages for these events. The two flood events inferred for southern Ontario are identified by names appropriate to their broad regional extent. Thus, the earliest flood that surged across the Algonquin highlands is named the Algonquin event, and the later flood that swept through the LakeOntario basin is named the Ontarian event.

Drumlins are, suprisingly, absent from the floor of Lake Ontario ...  and glaciogenic sediment is unexpectedly thin beneath the lake bed compared to its thickness on shore at, for example, the Scarborough Bluffs (Karrow, 1967; Sly and Prior, 1984). Interpreted in terms of meltwater events, the Ontarian event transported large quantities of sediment from the basin and removed from along its path drumlins formed by the earlier Algonquin event.

The lack of drumlins in Lake Ontario is well explained by erosion of drift generated by an in situ disintegration process. The disintegration mechanism promoted the removal of the unconsolidated drift material from the site of the lake basin by fast currents.

When the patterns of flow are related to diastrophic processes and  the locations of areas of depressed basement, one can understand why different flow patterns formed. Currents were spilled first to the south, then to the west, during the large-scale crustal movements.

Tilted shorelines of ancient high level beaches indicate less violent crustal movements continued after the lakes had formed. The crustal warping provides the clue to the cause of the currents which excavated Lake Ontario. Most geologists have assumed the uplift of the Great Lakes area was a slow process, caused by "rebound" of the earth's crust when the ice melted. I. C. Russell wrote [Russell, I.C. , p. 100]:

The amount of change in level shown by the warping of the beaches about Lake Ontario is considerable, and illustrates the character of the slow upheavings and subsidences known to be in progress over wide areas of the earth's surface. It is stated by Gilbert that "the old gravel spit near Toronto, belonging to what is known as the Davenport Ridge, is 40 feet higher than the contemporaneous gravel spit on which Lewiston is built; at Belleville, Ontario, the old shore is 200 feet higher than at Rochester; at Watertown, N.Y., 300 feet higher than at Syracuse; and the lowest point in Hamilton, Ontario, at the head of the lake, is 325 feet higher than the highest point near Watertown. From these and other measurements..., we learn that the Ontario basin with its new attitude inclines more to the south and west than with the old attitudes." The general tilting has thrown the waters of Lake Ontario westward and flooded small tributary valleys so as to drown them and make miniature fjords.

Movements in the earth's crust were also in progress during the long period in which the ancient lakes of the Laurentian basin were making their various records, as shown by the fact that the abandoned beaches do not lie in planes parallel with each other.

Russel's words, "The general tilting has thrown the waters of Lake Ontario westward", if taken more literally than the writer intended, give the idea of a violent displacement of the overlying waters at a time when the region was submerged. The environment in which the basins of Lake Ontario and other Great Lakes were excavated, and the drumlins were formed was one of catastrophic flooding.

Observation of existing ice sheets and glaciers suggests they invariably flow downhill from elevated regions; however the postulated, hypothetical flow of the ice of the glacial theory was uphill out of basins and depressions like the basin of Lake Ontario. The ice is supposed to have flowed uphill out of Lake Ontario, over the steep cliffs of the Niagara Escarpment, and flowed uphill towards the Allegheny Highlands in northwestern New York.

References:

Lewis, C.F.M. et al. 1996. Were the Ontario and Erie basins swept by catastrophic meltwater flooding? Geological Society of America Abstracts with Programs. 28 (3) 76.

Russell, I.C. 1900. Lakes of North America. Ginn and Co., Boston

Shaw, J. and R. Gilbert, Evidence for large-scale subglacial meltwater events in southern Ontario and northern New York State. Geology, v. 18, Dec. 1990, p. 1169-1172.
 

Bathymetry Maps:

Lake Ontario

© 1999 by Douglas E. Cox
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