Jan. 13, 2019

How the fen happened

The northwest half or more of Lenawee County is a topographic area formed by glaciers, much of it now called the Irish Hills.  Rain that falls there, fifteen or twenty miles northwest of Ives Fen flows into the Raisin River drainage, or seeps into the ground.  Along a jagged line that runs diagonally across the county, that higher ground drops off into what was once the Great Black Swamp, and is now a rich farming area.  Where the River reaches that line, it has cut a valley several miles back into the glacial deposits.  The valley is not much more than 50 feet deep.  In this image you are looking up the gentle slope of the fen, to the steeper upper edge of the erosion.  Irish Hills rain that becomes ground water slowly flows southeast for those fifteen or twenty miles until it reaches the valley where the River is lower than the ground water level.  It emerges in virtually continuous seeps and springs along the bottom edge of that steeper upper slope.  From there it runs and seeps down the more gentle slope, keeping it constantly damp, even through the longest dry spells.  In its time underground, the water has accumulated a heavy concentration of dissolved limestone, making it very basic.  This all adds up to a very unusual system of plants and animals that can thrive in that wet basic environment.  The hillside fen at Ives is one of the more unusual ecosystems on the continent.  Most fens are on more level ground.