Fort Roberdeau sinkhole - Blair County, PA
N 40° 35.004 W 078° 16.425
17T E 730732 N 4496084
This sinkhole is on the grounds of Fort Roberdeau, the Lead Mine Fort.
Waymark Code: WM1667B
Location: Pennsylvania, United States
Date Posted: 05/16/2022
Views: 5
The grounds of Fort Roberdeau are open to visitors from 8:00am - sunset daily.
The Incredible Sinking Stream
Water in this stream of water coming from the mountain falls through little holes and cracks in the stream bed. It drops into underground channels in the limestone bedrock beneath.
If the stream is very full of water, not all of it can fall through these holes and cracks before reaching the rock wall before you. In that case, the remaining water flows under the rock wall, and it too disappears. The water will flow underground for 5 miles before it surfaces again.
There are many streams in this valley which sink into underground channels. That is why surveyors who made the first maps of the valley named it Sinking Spring Valley.
Do you see the layers (strata) of gray limestone in front of you? The floor of this whole valley is this way, made of Ordovician limestone deposited about 500 million years ago. In 1778, the lead miners had to dig through this limestone to find the veins of lead ore and remove it. Not an easy task!
Sinkholes
When the rocks and soil above a cavern cannot be supported by the cavern roof, they fall in. This leaves a depression on top of the ground called a sinkhole. There are several sinkholes close by. One is beside the platform. Others are along our entrance road.
(from sign)
While you're here to visit the sinkhole, you can complete the Earthcache: (
visit link)