Powell Lake EarthCache EarthCache
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Powell Lake is a large lake in southern coastal British Columbia
that is used for water sport recreation, floating cabins and even
hydro electric power generation for the local paper mill. It has a
long narrow profile that resembles some of the neighbouring ocean
inlets (fjords) which, as it turns out, is not a coincidence. The
posted coordinates take you to a recreational boat launch and
parking lot at the south west end of the lake and the terminal
point of the Powell Forest Canoe Route
During the last ice age or "Glacial Age", much of North America was
covered in kilometer-thick ice and glaciers. The immense weight of
this ice sheet pushed the North American Plate down into the
Earth.
As the glaciers carved out the nearby Toba Inlet, Jervis Inlet, and
Sechelt Inlet (also known as fjords) they were also hard at work
carving out the basin of Powell Lake.
About 10,000 years ago, the Earth started to warm up, the ice began
to retreat, and sea water was able to flood back into the inlets.
Because the North American plate was still mostly covered in
ice,the plate was much lower than its current height, allowing
seawater to flow into "Powell Inlet". As the ice age ended and the
ice sheet retreated back to the Arctic, the weight was lifted and
the North American Plate rebounded upwards, cutting off what is now
Powell Lake from the ocean, and trapping the seawater in an
incredibly deep land-locked body of water. Powell Lake is one of
the deepest lakes in the province of British Columbia, with a depth
of approximately 360m (1200 ft).
As the millennia passed, fresh water in the form of rain and rivers
flowed into the land-locked salt lake covering the trapped
seawater. Salt water, being more dense than fresh water, remains
hidden hundreds of meters below the surface of today's Powell Lake.
Scientists predict that slow mixing between the ancient salt water
layer and the fresh water layer will eventually deplete the trapped
portion of the Pacific Ocean rendering Powell Lake entirely fresh
water.
To Log this EarthCache, please email the Cache Owner with the
answers to the following questions and post the obligatory
photo.
1. Who was Powell Lake named after?
2. Using your GPS, go to the edge of the lake and determine the
elevation of the surface. Seasonal snow melt cycles and
hydroelectric activity not withstanding, assume the surface of the
lake was originally at sea level. Estimate how high the North
American plate has rebounded vertically since the lake was cut off
from the ocean.
3. Post a picture with your cache log of yourself and/or GPS unit
with the Lake and boat launch/marina clearly visible in the
background.
References:
Powell
Lake
UBC Library publication
Ancient Seawater Blog
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