|
B. Geology
Glacial
Approximately 20,000 years ago, the Wisconsinan glacier began to advance
south through
Ohio
. In the Bellefontaine area the
glacier ran into a high area called the Bellefontaine Outlier which caused the
glacier to continue advancing in two separate lobes.
The lobe that traveled to the west of the Bellefontaine Outlier advanced
through
Troy,
Dayton
and
Xenia
areas of
Ohio
until it stopped around the Hamilton and
Butler
county border. The lobe that
advanced to the east of Bellefontaine traveled through the Darby Watershed and
east into the middle of Knox, Licking, and
Fairfield
counties and then south to the
Hillsboro
area. The point at which the
glacier stopped is represented on the map by the farthest solid dark line
between the tan/yellow areas and the light green (Map
3). This event represents the
Early Wisconsinan glacier in
Ohio
.
The Early Wisconsin Glacier then retreated to an unknown
distance and then traveled south again. The
Late Wisconsin Glacier again advanced to the Bellefontaine Outlier and then
separated into two lobes that travel similar paths but both stop at an area just
north of the previous glacial advance. Inside
the light green areas of the map (Wisconsinan Glacial event) a solid dark line
represents the farthest advance of the Late Wisconsinan Glacial advance (Map
3). The retreat of the eastern
lobe formed the majority of the present landscape in the Darby Watershed.
As the eastern lobe retreated it remained over different areas for periods of
50-100 years then continued to retreat. As
it retreated end moraines formed representing a temporary glacial stopping
point. End moraines are today
evident as broad, hummocky ridges of glacial debris (marked by darker green arcs
over the light green). Several end
moraines exist within the Darby Watershed from the Late Wisconsinan Glacial
event.
Reesville Moraine
- This moraine intersects the
Big
Darby
Creek
as it enters into the
Scioto
River
in Circleville (See Map
3).
London
Moraine – This end moraine forms a ridge through northwest
Madison
County
, through
London
, and then along the
Franklin
and Pickaway
County
boundaries (See Map 3).
The significance of this moraine on the
Darby
Creeks
is unknown (ODNR, 1992).
Cable Moraine
Complex – This moraine is referred to as a complex because a wide
variety of glacial activities are occurring in an area between Bellefontaine
and
Urbana. On Map
3 , different colors represent a wide variety of glacial activities.
This complex glacial environment is likely a result of the fact that
the ice in this area remained for a long time and moved very little because of
the Bellefontaine Outlier holding it in place (Brockman, Personal
Communication, 2003). This formed a more
rugged terrain with rolling hills and steeper slopes in comparison to the
remainder of the Watershed. This
area formed the headwaters of the Big and Little Darby Creeks.
Powell Moraine - The northernmost
portion of the Darby Watershed in
Union
County
experienced an additional glacial event as the Late Wisconsinan glacier
retreated for a second time north of the
Lake Erie
Basin. The glacier’s third advance
was likely over the freshly deposited clayey lake deposits in the
Lake Erie
Basin
which explains the higher concentration of clay in soils in
Union
County
than soils from the second glacial advance in the remainder of the watershed
(Brockman, Personal Communication, 2003).
The third glacial advance again hit the Bellefontaine Outlier and split
into two lobes;
Miami
and
Scioto
. The Scioto lobe dipped into
Union
County
and then formed the Powell Moraine which represents the southernmost glacial
advance. The Powell Moraine was
the first of a series of end moraines formed by the third glacial retreat
represented by a grayish area on the map.
The remainder of the land in the watershed is largely referred to as a ground
moraine (light green areas on Map 3), or simply as the material that the glacier left behind as it
slowly retreated north. The material
is a mixture of clay, silt, and sand with some areas of pebbles, cobbles, and
boulders. Areas with a higher
concentration of boulders are represented by red dots on the map (See Map
3).
  
Back to
Table of Contents | 
