Disappearing Stream
At this location you are standing over a stream. Depending on the time of year, the flow will vary considerably.
Just a few meters downstream from the footbridge the water will diverge into two. The one on the right disappears into the ground in what looks like a sinkhole, while the one on the left goes over the escarpment (and then also disappears into the rocks).
Your task is to take a stick about the size of a popsicle stick...hundreds on the ground to choose from. Drop it into the stream from the footbridge and determine which path the stick takes...directly into the sinkhole in the stream to the right, or over the escarpment. Time how long it takes from when you drop the stick into the stream from the footbridge to when it disappears. If your stick gets stuck on a rock or in some vegetation, then help nudge it along. There is a path on either side of the stream that you can follow along. It's good to come with a partner so each person can walk on either side of the stream. Answer the following questions based on your observations while performing this task.
**If there is no water or not enough flow, take an educated guess based on what you observe.
A) Which path of least resistance does the stick take...Left (over the escarpment) or Right (into the sinkhole)?
B) How long does it take for your stick to disappear?.
C) At the sink hole on the right, does the water disappear at the tree that is growing over the rocks or before?
D) What body of water would this stream most likely empty into?
The source of this stream is from a ground spring about 3km north of the posted coordinates and continues on to 16 Mile Creek which eventually empties into Lake Ontario in Oakville.
This area consists of karst topography with the extensive dissolution of rock which has led to the development of subterranean channels through which groundwater flows in conduits. Karst is produced mostly in areas underlain by carbonate rocks, usually limestones and dolostones such as along the Niagara Escarpment. Areas of karst topography are characterized by natural features such as sinkholes, which often are seen as circular ponds or depressions as well as non-continuous surface streams. The evolution of karst topography differs significantly from more typical landscapes where erosion and deposition by running water sculpt the land surface. In karst topography, the underlying soluble rocks are removed by being dissolved instead of being eroded.
Sinkholes form where rock has been removed by dissolution, forming an underground void. Where these underground voids have collapsed, a closed depression, or sinkhole, is formed at the surface. Karst sinkholes often are small, perhaps only a few meters in diameter as is the case here.
Disappearing streams occur when groundwater percolates through cracks removing the soluble rock while leaving an enlarged channel for further (and progressively more efficient) flow of water. In some cases, the flow of a surface stream may be diverted underground when subterranean caves collapse and break through beneath the streambed in a process known as stream piracy. Usually this is a gradual process, with only part of the surface stream being diverted through small cracks in the rock just below the soil cover. The amount of surface water diverted grows larger with time, and the underground caves and channels also grow with time until the entire surface stream disappears into the ground. Sometimes these disappearing, or sinking, streams provide access to the caves beneath.
In order to understand these underground stream systems, hydrologists attempt to determine the sources of springs by water tracing. Water tracing usually involves injecting a tracer chemical, most commonly a harmless fluorescent dye, into a disappearing stream. Springs are then sampled and the water samples are tested for the presence of the dye.
Geocachers (whether placing or searching for a geocache), like all other trail users, must travel on blazed trails and NOT STRAY OFF THE TRAIL. Note: Straying off the trail can lead to hazardous situations, e.g. cliffs, crevices and/or disturbing species at risk.