Monday, December 8, 2008

FLOW through a winter watershed hike...

FLOW members (Friends of the Lower Olentangy Watershed) hike Deer Run through Camp Lazarus.

Wintertime opens our temperate landscapes for easier viewing while deciduous leaves are down. Landscapes and landforms are much easier to see when they are not veiled under summertime green. This is the best time to explore geology. Members of FLOW joined Jackie and I in exploring the fresh white winter landscape and geology of Camp Lazarus Saturday, December 6.

Friends of the Lower Olentangy Watershed exploring Camp Lazarus. Left to right; Joe Brehm, Joanne Leussing, Megan Zale, Mike Welsh, Greg Hostetler, Joanne Wissler, Rich Wissler, your blogger. Photo by Jackie

FLOW is a 501C3 non-profit organization dedicated to preserving Lower Olentangy River watershed quality while hyper-development spreads through the watershed's landscape. They partner with stakeholders and work with decision-makers to guide responsible development of the watershed to protect watershed resources for all of us.

Jackie is Education Coordinator with Preservation Parks of Delaware County, and an occasional host of FLOW hikes. I joined the hike to offer geoecological insights and just to explore and have fun with fellow naturalists.

We hiked Deer Run, a small tributary of the Olentangy River south of Delaware, Ohio from near its origin along State Route 23 near the entrance to BSA's venerable Camp Lazarus, to its junction with Lazarus Run near the Olentangy River terrace.*

Topographic map of Lazarus Run and Deer Run, Delaware County, Ohio. Lazarus Run courses east-west. Deer Run joins from the north. The Olentangy River at far left.

Snow fell throughout our two-hour scramble along the steep waterway. Birds were mostly quiet, the usual cast of characters made brief appearances, Downy Woodpecker, Red-bellied Woodpecker, Dark-eyed Junco, Eastern Tufted Titmice, Carolina Chickadee, and so on. Squirrels and cub scouts were abundant.

Our walk assembled on glacial till, a flatish ground moraine left by the last ice sheet at least fifteen thousand years ago. The ground moraine supports remnant vernal pools, dry this time of year. Scattered pin oaks flag the dry vernal pools area. Shagbark hickories and a few shellbark hickories mark the slightly drier areas.

A constant crunch of hickory nuts underfoot announced a really abundant mast crop this year. Sugar maple and American beech thrive among red oaks and scattered white oaks as we approached the steepening slopes. Soon we stepped off of the thin ground moraine and onto slopes formed of shale bedrock. Oaks dominated the steep dry shale slopes.

It's a fairly short walk behind the camp nature center to where the slope begins to increase as the terrain descends westward toward the Olentangy River 120 feet below. Deer Run begins as a small drain easily straddled by a hiker near the roadway. It's dammed along a short segment for a small pond used by scouts for nature programming, then it runs free to the Olentangy River.

Deer Run deepens and steepens dramatically over a short distance. Its steep youthful profile exhibits the rapid down-cutting and headward erosion caused by the rapid cutting of the Olentangy River Valley.

Geologically speaking, Deer Run formed fast and furious and continues to form, today, more slowly. Its meandering path suggests it first found its course on a fairly uniform and low slope moraine surface before down-cutting quickly deepened the channel, greatly slowing meander-widening.

Glacial meltwater cut the Olentangy River Valley quickly through about ninety feet of shale bedrock, the Ohio Shale and the Olentangy Shale, then through about thirty feet of Delaware Limestone, a silty dark limestone with fossil beds. The resistant Columbus Limestone beneath it greatly slowed down-cutting as it is a very resistant bedrock.

The geo-speak for the pattern of watercourses in this area is "consequent drainage." It happened this way: The Olentangy River Valley formed as the Wisconsin ice sheet (or earlier ice sheet**) melted, its channel carried immense volumes of water and glacial outwash sediments southward to the Scioto River. While draining the huge volume of meltwater the river eroded deeply quickly, forming steep slopes flanking its course. Drainage along these steep slopes quickly consolidated into the tributaries we recognize today which cut down quickly to keep pace with the deepening Olentangy.

Along the way we noted the jointed (regularly fractured) Ohio Shale and we snapped pieces of fresh black shale from the streambed to smell the organic echo of long ago life (The Ohio Shale here was deposited about 365 million years ago). The Ohio Shale is 30 percent organic by volume.

The streambed was littered with glacial erratics, rocks not of the immediate area, which were originally left in moraine high above, and since have eroded free and rolled or slid downslope to the streambeds.

Our journey continued to the geological contact between the Ohio Shale and the gray silty Olentangy Shale, then back up slope through the camp.

The geological contact between two bedrock formations where Deer Run joins Lazarus Run. Above, the brownish weathered organic Ohio Shale formation. Below, the grayish silty Olentangy Shale formation. This is a sharp contact exhibiting abrupt change in sedimentary conditions.

Watch the Preservation Parks of Delaware County website and the Friends of the Lower Olentangy Watershed website for future opportunities to explore Delaware County nature and geology.

*Camp Lazarus is private property. Permission must be obtained in advance from The Boy Scouts of America to visit the camp.

**At least four major ice sheets advanced into Central Ohio based on sediments described. More ice sheets probably visited the area before these but their sediments do not survive to be described. The original formation of the Olentangy River Valley might have occurred much earlier. The valley might have been cut into bedrock, then filled with glacial sediments, then eroded again several times during the Pleistocene.

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