Lake Erie Bluff Recession EarthCache
Lake Erie Bluff Recession
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This is the David M. Roderick Wildlife Reserve, a section of Pennsylvania State Game Lands 314. It is an ideal spot for viewing the receding of the Lake Erie bluffs. Be mindful of the edge and look after small children! I had a multi-cache in this area a few years ago. The location of the final cache is not even there anymore. Erosion washed that whole area away, including the tree it was in.
The high coastal cliffs overlooking Lake Erie are called bluffs and can range in height from 5 feet to nearly 200 feet above lake level. The bluffs are mostly glacial soils comprised of sand, gravel and clay. About 20 percent of the bluffs have a lake level shale bedrock exposure with a thickness ranging from barely visible above lake level to a height of 20 feet. Outside the armoring effect of the shale, the soils of the bluffs are highly erodible when exposed to the forces of direct wave contact, groundwater flows, surface water runoff, ice, wind and rain.
You can see a two-tone color difference in the bluff strata. The upper yellow-brown layer, sandy interval, is mostly beach sand with minor clay layers deposited in lakes, a product of the melting of 1000’s of feet of glacial ice. Today, water infiltrates freely down through this permeable layer.
The lower gray layer, diamict interval, is a glacially deposited mix of clay and silt with randomly intermixed gravel-sized rock fragments. Today, water infiltrating down from the sands above is stopped, ponding on top of this impermeable layer.
The vegetation mat that normally covers the bluff face helps protect the erodible soils and keeps them intact. During periods of high lake levels, wave damage can occur at the base of the bluff, remove the lower vegetation, and cause the remaining mat to slide and separate. Human activity, such as building footpaths or cutting the tree canopy, will also disturb the vegetation mat. Upon its disturbance or removal, the forces of erosion will further destabilize the bluff, causing substantial volumes of bluff material to collapse and slide into the lake. Such erosion, known as bluff recession, eventually causes the bluff crest to recede inland. Depending on the area, the bluffs recede between 1 and 20 feet per year!
Other influences that contribute to the instability of the bluffs:
* Increase in the steepness due to erosion of the toe of the bluffs, especially during times of high lake levels.
* Additional loading of the bluff edge due to construction or dumping.
* Seasonal snowmelt and/or prolonged rainfall can produce major amounts of groundwater. Excessive lawn or crop watering and leaking pools add to the problem. Water flows freely downward through the sandy layer and ponds on top of the clay layer. This can be seen by seeps and springs on the face of the slope. This saturation lubricates the sandy layer, destabilizing the slopes above.
* Pounding surf, shaking from cars, trains, and ATVs can also make the slope less stable.
* Deforestation of slopes removes anchoring by roots.
(information obtained from a paper by M. Raymond Buyce and from the PA Sea Grant Fact Sheet)
From this location, N 41 58.640 W 080 31.122 , you can see off in the distance to the west, a major cause of Lake Erie beach and bluff erosion. (The answer is NOT the rock with the plaque or the information kiosk.) Look out in the lake a few miles away. It dams the eastward flowing sand (littoral drift) starving beaches and thereby exacerbating bluff erosion. Narrow, starved beaches, provide minimal protection from wave erosion of the bluff toe.
1. What is this manmade structure? E-mail me the answer.
2. From this location, N 41 58.636 W 080 31.067, e-mail me the approximate elevation in feet above sea level. Use your GPS.
3. From the same location, estimate how far down the lake shore is. E-mail me the answer. Just estimate! Do not try to go down there. It’s steep!
4. Take a picture of yourself and your GPS with a section of the bluffs visible in the background. Post your picture with your log.
Special thanks to Chipper725 for relinquishing this spot in order for this EarthCache to be placed.
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