STEVENS TWIN SINKS PRESERVE
The Stevens Twin Sinks Preserve is a 30 acre
parcel owned by the Michigan Karst Conservancy in Alpena County. It was purchased in 1993
with gifts from William and Archie Stevens and other members and friends of the MKC. The
Preserve surrounds two sinkholes separated by a fragile saddle-ridge, each about 200 feet
in diameter and 85 feet deep, which give the Preserve its "twin sinks" name. An
interpretive nature trail that visits the rims of these sinkholes and other karst and
natural features of interest is currently being developed.
Other sinkholes in the area are on private property and may not be visited by the public. The Stevens Twin Sinks Preserve is the only sinkhole site open to the public in this area. We trust that the public will treat the sinkholes and other features to help preserve them for public interest and enjoyment now and in the future.
Quite recently the Bruski Sink across Leer Road was donated to the Conservancy and made part of the Preserve. This sinkhole has been used for illegal dumping of trash for many years, contributing to the contamination of groundwater in the area. The MKC plans to clean out most of the visible trash and install barriers to future dumping.
GEOLOGY AND HYDROLOGY
Alpena and Presque Isle counties are underlain by a thick sequence of Devonian limestones and some shales, called the Traverse Group. At a depth of ca. 800 feet at the Preserve occurs the Detroit River Group, which includes considerable evaporites - anhydrite and gypsum. These dissolve much more readily than limestones and have been totally removed further north by water circulating at depth. The sinkholes of the area are created by collapse of Traverse Group rocks into the cavities created by the dissolving of Detroit River Group evaporites. The result is the settling and collapse of large rock blocks with some shattering, leading to a hummocky terrain, such as can be seen in and to the east of the Preserve. Also present on the Preserve are "earth cracks", resulting from the slumping of the rocks .
The water that dissolved the evaporites found its way underground along joints and especially joint intersections. These points of greatest water input created the earliest and largest voids in the Detroit River rocks, which allowed the rocks above to collapse - all the way to the surface, to form the sinkholes visible today. They tend to be aligned along joint trends, as indicated by the grouping of the Twin and Bruski sinkholes.
Evidence for the dissolving of the evaporites is found where the water that goes underground in the sinkholes returns to the surface - from submerged sinkholes in Lake Huron, twenty miles to the east. The resurgent water is saturated with gypsum.
This area of Michigan was glaciated and a considerable amount of glacial outwash - sand and gravel - mantles the limestone, which can be seen from the parking area. That the sinkholes are not also filled with outwash shows that they increased in depth following the melting of the glaciers (it is not known what depth of glacial outwash fills the bottom of the sinkholes). The exact relations between the glacial deposits and the sinkhole formation have not been elucidated yet and is an area for future research.
BIOLOGY
The preserve forest is second growth with beech, maple and birch trees dominating. An open glade in the southern part of the Preserve may have been tilled at one time. What is most significant about the biology of the Preserve, however, is that several plants that grow in the sinkholes - especially ferns - are not found in surrounding surface habitats, but rather several hundred miles to the north. The reason is that the sinkholes have restricted sunlight, high moisture, protection from wind, and cooler temperatures than the surrounding surface area. They also accumulate cold air, and retain snow earlier in the Fall and later in the Spring.
Trees growing in the sinkholes provide unique viewing opportunities at tree-top level of the annual warbler migration occurring from mid to late May. Further studies of wildlife inhabitating the Preserve is being conducted.
MANAGEMENT
The Stevens Twin Sinks Preserve is managed by the Thunder Bay Karst Preserve Committee of the MKC.
It is the purpose of the MKC to manage and protect
karst areas for scientific study and conservation education. These purposes are
implemented by making MKC Preserves available, without charge, for public uses that are
compatible with long-term preservation. Protection of natural features of a Preserve, and
the safety of visitors, are major concerns. For these reasons, the following policies have
been adopted for the use of the Stevens Twin Sinks Preserve:
1. The Stevens Twin Sinks Preserve is open to the public,
subject to the following policies:
2. The following are not permitted in the preserve: fires,
camping, littering or dumping, alteraction of any natural feature, collecting of firewood,
vehicle use off designated roads, nonconforming structures, firearm use, hunting or
trapping, and pollution of soil or streams.
3. Permission from the Preserve Committee is required for
descent into sinkholes, collecting of minerals, flora, or fauna, excavation or movement of
soil or rocks, and installation of instrumentation.
4. Descent into sinkholes is permitted in accord with the
following policies: permission must be obtained from the Thunder Bay Karst Preserve
Committee; a liability release and an acknowledgement of use policies for the Preserve
must be signed by those descending; all persons descedning into sinkholes must weqar a
hard hat with a chin strap and sturdy boots, and follow the path established by the
Preserve Committee.
319 PROJECT RUNOFF DIVERSION AT STEVENS TWIN SINKS.
A problem at
MKC's Stevens Twin Sinks Preserve has been runoff from adjacent farm fields, eroding
hillsides and carrying sediments and accompanying farming wastes into Bruski and Twin
Sinks. Similar problems have occurred throughout the karst areas of northeast Michigan. In
1995 the Presque Isle County Soil Conservation District was funded through the federal
Clean Water Act - Section 319 (Nonpoint Source Pollution) - to undertake first an
evaluation of the problem, and then to undertake corrective measures, which began in 1997.
The following is a synopsis of the program quoted from the Michigan State University web
site http://www.gem.msu.edu/casestd/karst.html.
"The Karst Aquifer Protection Project is the first in the state to include protection of groundwater as a key element of nonpoint source pollution prevention through the Clean Water Act Section 319 program. Previous funds were assigned only to the control of surface water pollution. The Conservation District office of Presque Isle County was approached to participate in the program by the Department of Environmental Quality (DEQ) due to the geological characteristics of a karst. The goal of the project was to take a pro-active stance on environmental practices and management by protecting the area's drinking water and to create a public awareness of the connection between the different land use pollutants and their drinking water."
A broader description of the federal 319 Projects has been posted at the EPA site http://www.epa.gov/OWOW/NPS/sec319.html.
Eventually included in the program in northeast Michigan have been two barnyard/feedlots, ten pasture sites and eight cropland sites, to prevent pollutants from entering karst features.
MKC was consulted by the program quite early in its development and then tentatively agreed to participate if the funding could be found for the MKC share of the cost. Fortunately, the 319 Project paid 75% of the cost.
The project at Stevens Twin Sinks Preserve has two components. First, the treatment of exposed soil areas so that runoff would not erode soil, and then diversion and settling of runoff to remove sediments. This part of the project has been completed. MKC's share of the cost has been provided primarily by a donation of $500 from the Michigan Interlakes Grotto of the National Speleological Society, and a grant of $ 1,358 from the Community Foundation of Northeast Michigan, while the aggregate used in the runoff channel and erosion-prevention was donated to the 319 Project by the Michigan Limestone Company.
The second component of the project is cleaning out the trash, to the extent possible, from Bruski Sink, and then fencing the sinkhole to minimize future dumping. Planning is still underway for this. When estimates have been obtained we will have to consider again how to raise the money to pay MKC's share of the cost.
We would like to thank all those individuals and organizations that have helped to accomplish this these steps toward improving the quality of karst groundwater in northeast Michigan.
Information about visiting the Preserve can be obtained from the Jessie Besser Museum in Alpena, or by writing to the MKC at the address below.
The work of the Michigan Karst Conservancy is carried out by volunteers, who believe in the value to the puglic 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@caves.org
Under
Construction