Visitors to Whistler are often amazed at the magnificent emerald hue of Green Lake, particularly in the spring and summer months. From the posted coordinates for this earthcache, you can see across the waters of Green Lake, most of Whistler Mountain, and the top of Blackcomb. It is a great view and photo spot. But what gives Green Lake it's unique colour?
Green Lake's primarily inflow comes from Fitzsimmons Creek, which enters the lake almost straight across from this viewpoint. Fitzsimmons Creek is the largest creek/river flowing into the Whistler Valley and is fed directly by the Fitzsimmons Glacier, the Curtain Glacier, and the Overlord Glacier, all in Garibaldi Provincial Park. The meltwater in Fitzsimmons Creek appears cloudy as it flows through Whistler Village. When it arrives Green Lake, and slows down it give Green Lake a spectacular green colour.
The cloudiness in Fitzsimmons Creek, and the emerald hue of Green Lake are due to the presence of rock flour. Rock flour is formed when rocks under a glacier are ground up into tiny pieces by the huge weight of the ice. These tiny pieces of rock are almost weightless and stay suspended in the water. Rock flour is very nutrient-rich. In Greenland, rock flour from melting glaciers is being harvested and used as a fertilizer. Another interesting property of rock flour is that rock flour particles absorb CO2 in contact with air. Thanks to its tiny particles, the rock flour dissolves in rainwater, releases its nutrients and undergoes a chemical reaction that traps carbon dioxide from the atmosphere.
Since Fitzsimmons Creek is very turbid and often flows under a tree canopy, it usually looks cloudy grey-ish colour. A great spot to view the creek is at the Covered Bridge near the Day Lot parking at Whistler Village: N 50° 06.916' W 122° 57.027'. When the water of Fitzsimmons Creek enters Green Lake, it slows down, and sunlight relecting off the rock flour creates a brilliant blue/green colour. The colour is blue/green because rock flour absorbs the shortest light waves - the purples and indigos - while the water itself absorbs the longest waves - the reds, oranges and yellows. The result is that when the sunshine hits, it reflects a brilliant green/blue colour.
Unlike some of the other lakes in Whistler, Green Lake is incredibly cold as it is directly fed by a steady flow of glacier water (the source of the abundant rock flour). That said, in the summer months you may see some windsurfers, paddleboarders or even wakeboarders out enjoying the lake. Just don't fall in!
To log this earthcache, please answer the following three questions, and add the required photograph:
(1) Why do you think Green Lake is at its "greenest" in the spring and summer months?
(2) Given that it is the same water, why do you think Fitzsimmons Creek appears cloudy, while Green Lake appears green in colour?
(3) Of the big lakes in the Whistler Valley, only Green Lake is this colour. Why are the other lakes in Whistler not the same colour?
(4) Post a photograph of yourself or your GPSr at the viewpoint at the posted coords (Mandatory- photo must be included!)
Sources:
- Informational Signage posted at N 50° 06.916' W 122° 57.027''
- Wikipedia: "Rock Flour"
- A Moment of Science: "Rock Flour": https://indianapublicmedia.org/amomentofscience/rock-flour.php
- Le Monde: Rock Flour: A promising nutirent from Greenland's melting ice: https://www.lemonde.fr/en/economy/article/2022/07/30/rock-flour-a-promising-nutrient-from-greenland-s-melting-ice_5991999_19.html
Beautiful Fitzsimmons Creek (July 2022):
Green Lake - Spectacular but very cold!
