Civil Engineering Graduate Seminar, Thursday,September 19, 4:00 pm, Room 641 Dow
Glacial Lake Ontonagon and the Development of Large Scale Landslides
Vitton, Stanley J., Michigan Technological University, Houghton, MI, 49931
A massive landslide occurred in 2005 along the East Branch of the Ontonagon River in northern Michigan adjacent to US-45. The landslide initially blocked the river causing it to redevelop a new flow channel. While other massive landslides occur along this section of the river, they tend to be infrequent with respect to the general form of mass wasting such as slope regression due to river under cutting and surface erosion. An investigation of the landslide indicated two very distinct soil units that appear to correspond to the two phases of glacial Lake Ontonagon. The two soil units have a relatively distinct boundary as seen in Figure 1C. The lower unit consists of a red till, which forms the floor of the valley, grading upward into alluvial sand, while the upper unit is a distinct lacustrine soil deposit.
The massive landslide failure zone developed in the lower soil unit. It is unclear at this point as to whether the failure was due to softening of the lower red till or liquefaction induced failure caused by increased pore pressure development during the spring runoff in the alluvial sand. Due to the extensive development of soil liquefaction features, however, it is believed that failure was induced via liquefaction in the transitional zone between the red till and the clean sand in the lower soil unit where the percent of fines in the sand prevent adequate drainage. Additional analysis of the soil’s strength and dynamic properties are needed, however, to make a more definitive determination (Smith, 2012).
The origins of glacial Lake Ontonagon was first addressed by Leverette (1929) and later by Hack (1965), Farrand and Drexler (1985) and Attig, Clayton and Mickelson (1985). The formation of Lake Ontonagon soils are believed to have developed in the post-Twocreekan time, around 11,800 Before Present (BP). The post-Twocreekan glacier advance completely filled the Lake Superior basin with two ice lobes that were split by the Keweenaw Peninsula. The Superior lobe reached the position of the Nickerson moraine southwest of Duluth, while the Lake Michigan-Green Bay lobe moved southward across the northern peninsula of Michigan, ultimately reaching the Two Rivers moraine at Manitowoc, Wisconsin, about 11,800 BP. Following the Two Creek advance, de-glaciation formed lakes and drainage channels in front of the glacier lobes in which glacial lakes Duluth and Ontonagon formed. Lake Ontonagon drained westward into Lake Ashland and eventually to the St. Croix River, which drained southward to the Mississippi River at about 11,000 BP. Between 11,000 and 10,700 BP the glacier retreated into the Lake Superior Basin forming a much larger Lake Duluth and eventually as the ice retreated and the glacial rebound occurred lowering Lake Duluth to form Lake Algonquin. It is believed that the lower soil unit formed during this period of time.
At about 10,000 BP, however, the last glacial re-advance, known as the Marquette Phase, advanced back into the Lake Superior Basin covering most of the northern portion of the Upper Peninsula. At about 9,900 BP the ice retreated again forming a series of lakes along the front of the ice sheet. Lake Ontonagon reformed at this time along with Lake’s Ashland and Nemadjic. Eventually the lakes became confluent and drained westward to the St. Croix outlet. At that time the lake levels for Ashland and Nemadjic dropped about 20 feet. Lake Ontonagon, on the other hand, dropped about 200 feet, (Leverett, 1929) leaving much of its lake bed dry land surface. It is believed that the upper lacustrine soil unit formed during this period of time.
References
Attig, W.J., Clayton, L. and D.M. Mickelson, 1985. Correlation of late Wisconsin glacial phases in the western Great Lakes area, Geological Society of America Bulletin vol. 96, no. 12; pp 1585-1593.
Farrand, W.R. and Drexler, C.W. 1985. Late Wisconsin and Holocene History of the Lake Superior Basin, Quaternary Evolution of the Great Lakes, P.F Karrow and P.E. Calkin, editors, Geological Assoc. of Canada Special Paper 30.
Hack , John, 1965. Postglacial drainage evolution and stream geometry in the Ontonagon area, Michigan, Geological Survey Professional Paper 504-B, Washington, D.C., 45 p.
Leverett, Frank, 1929. Moraines and shorelines of the Lake Superior basin: U.S. Geological Survey Professional Paper 154-A, 72 p.
Smith, J. 2012. Large Scale Landslide on the Ontonagon River, Michigan, Masters of Science Report, Michigan Technological University, Houghton, Michigan, 17 p.