Lynn Creek flows all the way down to the Burrard Inlet. In Lynn Canyon Park, the flow of the creek is most dramatic as it cuts through bedrock forming some well known and interesting geological features. However, there is also a section through the park where the flow of the creek looks completely different. The valley of the creek is far more typical of creeks and streams found elsewhere. What could account for the difference?
This Earthcache takes you on a tour of Lynn Creek where you can observe the results of thousands of year of geological forces in the region.
Glaciers used to cover this whole region. The most recent period of glaciation, the Fraser Glaciation, occurred approximately 20,000 to 10,000 years ago. During this period it is most likely that the wide U-shaped valley of the Lynn Valley flood plain was formed from the force of the 2km thick ice and the erratic boulders were picked up and deposited in the area as the glacier moved to the Pacific Ocean. Other evidence of the passage of this glacier include the till deposits and peat found near the suspension bridge. This most recent period of glaciation carved the Coast Range landscape to the present form and shape.
As the glaciers retreated, the streams flowed from the North Shore Mountains entering a sea that was about 200 metres higher than present day. The sea level began to drop as more sediment built up forming land mass deltas on the North Shore. As the sea level dropped, so too did the streams and creeks. However, where the streams and creeks flowed through rocks, they were “let down” though the rocks. In other words, the creek at Lynn Canyon carved the canyon over 13,000 years finding the lowest points it could in the rock surface.
However, there is a cross section in the park, north of where the present day suspension bridge where Lynn Creek is not cut through bedrock and does not resemble a canyon. In fact, with the large boulders in this area, it resembles more of a low flat floodplain. It is thought that the bedrock in this area is buried under sediment brought by the flow of the Seymour River. The Seymour River in the present day, runs approximately parallel east of Lynn Creek. It is surmised that perhaps this was once where the Seymour River flowed, but it eventually became filled with sediment and found a new route to Burrard Inlet.
To log this Earthcache and claim a find, you must email (do not use message centre as I don't read those) to the cache owner the answers to the following questions. Please note that found logs without an accompanying email answering the questions must be deleted as per the Earthcache guidelines.
Stop 1 49 20.724 123 01.220
Observe the creek at this point.
1. Estimate how high are you standing relative to the flow of the water.
2. Is the water able to change path at this point (eg, flow wider, or narrower)
3. Is the water flowing fast or slow on the day of your visit?
Stop 2 49 20.752 123 01.186
This rock could be an erratic or an exposed batholith.
An erratic is a rock or boulder that differs from the surrounding rock and is believed to have been brought from a distance by glacial action.
A batholith is a large emplacement of rock that forms from cooled magma deep in the Earth's crust.
4. Which do you think this is and why?
Stop 3 49 20.456 123 00.963
Observe the creek at this point.
5. Estimate how high are you standing relative to the flow of the water.
6. Is the water able to change path at this point (eg, flow wider, or narrower)
7. How is the creek different at this point to what you observed at stop 1?
Stop 4 49 20.428 123 00.952
8. What feature(s) do you see here that suggest that the flow of the creek was much different here as compared to 13,000 years ago?
References:
"Vancouver, City on the Edge" by John Clague & Bob Turner ISBN 0-9697601-4-0
http://www.bcminerals.ca/i/pdf/GSCGeoFieldTrip-LynnCanyon.pdf
http://www.oocities.org/rainforest/vines/4301/tour.html