Text Box: More images, this time with an annotation:  The image above is of the dried clays on the bed of Rainy Lake.  The caption handwritten on the back of this picture said:  "The small boy is me, Albert Tennant with my father Del Tennant, at my back and to his right is George Tennant my grandfather and to his right is A.C. Robinson my other grandfather. Note the cracks in the clay bottom. My father has told me that some of those cracks you could put your arm full length in, and that some places you could hear a roar like an under ground current."   Rainy and Sunken Lakes remained geological curiosities for many years. In the late 1960's and 1970's, however, citizens began buying lots on Rainy Lake in several subdivisions. It was an ideal location for a summer cottage until late 1980, when the sinkholes in the bed of Rainy Lake again became unplugged and the lake began draining, after a period of time when the lake was higher than normal. In 1982, the level of Rainy Lake had dropped over 45 feet, and the shoreline had receded over 500 meters in places. During the 1980-1982 incident, water in Rainy Lake was draining at an estimated rate of 10 gallons per second.     A significant number of cottages and summer homes were built around Rainy Lake between the times of the 1950 and 1980 incidents. The residents were understandably concerned, and after a 30-year dormancy, interest in Rainy Lake was again revived. In an attempt to help bring the lake level up, the Michigan DNR opened a stop-log wildlife flooding dam in 1982 and allowed water to flow approximately six miles down the Rainy River into Rainy Lake. As expected, the resulting increase in lake level was of small magnitude, and only temporary. Rainy Lake has now stabilized, and it is back at its normal level. Late in 1982, the major sinkhole through which the lake drained once again became naturally plugged, allowing the lake to fill. Post-glacial sinkholes Postglacial sinkholes are likewise a unique feature of the karst landscape. These sinks are typically nearly perfectly round, about 400 to 500 feet in diameter, with a depth up to 100 feet. Postglacial sinks look very similar to kettle holes with which they are often confused by the untrained eye (sinks are about 5 degrees steeper and are VERY round).  KARST IN ALPENA AND PRESQUE ISLE COUNTIES Very little work has been completed on the relation of karst in northeastern lower Michigan to the structure of the Michigan Basin, prior to the work currently in progress. Basic structural and tectonic processes in the Michigan Basin were reviewed, and almost 500 lineaments in northern Alpena and southern Presque Isle Counties which are discernible on aerial photographs, were mapped. Two predominant average azimuth orientations of photolinears were calculated.     Many of the linear features discernible in northeastern lower Michigan developed at least in part by ground water solution processes. The primary development of fractures probably took place concurrently with the uplift of the Michigan Basin at the close of the Paleozoic Era. Many of the northwest-southeast and northeast-southwest trending sets of lineaments developed along fracture intersections. Although evidence exists for an upper Devonian karst system, much of the post-Paleozoic karst appears to be oriented along the northwest-southeast linear trend, which is roughly parallel to the regional strike of the bedrock in the area. Much of the subsurface ground water movement in this area probably follows linear zones of weakness which developed along fracture intersections.     Much has yet to be learned about karst phenomena in northeastern lower Michigan, and what controls the seemingly periodic cycle of lake lowering due to karst, such as has happened at Rainy Lake. Modern technology will not prevent karst lakes from draining in the future, but much insight is to be gained so we can better predict cyclical trends in karst phenomena and be better prepared to deal with them as they develop. The work of the Michigan Karst Conservancy is carried out by volunteers, who believe in the value to the public of protecting examples of karst features in Michigan for education and scientific uses. Donations to the MKC are tax deductible in accord with federal law. For further information about MKC, and membership in it, write: Michigan Karst Conservancy, 2805 Gladstone Avenue, Ann Arbor, MI 48104-6432. (e-mail: mkc@cyberspace.org) Much thanks to Dennis Hudson and the MSU Center for Remote Sensing and GIS, who supplied some of the text and imagery for this page.

Sinkholes Info 2

Rainy Lake Property Owners Association, Inc.

To contact us:

Phone: 586 465 0065

E-mail: rploa@core.com