Glacial Lake Penticton Varved Clay EarthCache

 

Contrary to common belief, there have actually been numerous ice ages over the last few hundred thousand years. However, the most commonly known ice age is called the Fraser Glaciation. This glacier was massive and covered pretty much all of British Columbia and extended into the U.S. with ice thicknesses ranging from 1-3 kilometres. This massive glacier joined with the gargantuan continental glacier and this covered all of North America! So much of the Earth’s water was frozen in these glaciers that the sea level dropped hundreds of metres. Only a few peaks in the Coast Range Mountains peeked above the ice. These summits were called nunatak. The ice started forming in 25,000 B.C.E. and had pretty much melted away by 13,000 B.C.E.

Yeah, the glacier was kind of big. Courtesy Okanagan Geology by Murray A. Roed.

Glacial Lake Penticton

The Fraser Glacier retreated about 13,000 years ago and left a big chunk of ice near Okanagan Falls, which dammed up the entire valley. As the glacier continued to melt, water continued to fill behind this dam up to a level of 457 metres (115m higher than Lake Okanagan today!) The cities of Kelowna, Penticton, Vernon, and Armstrong were underwater and the lake likely extended as far as Enderby. As the glacial till was washed downhill over time into the lake, this fine silt created beaches all around Lake Penticton’s shores. Gradually the ice dam melted down in steps, likely resulting in a devastating flood each time. This left terraces, or levels of silts behind. Finally when the dam melted altogether, the remaining water ponded in the depression left by the glacier and fault line and created today’s Okanagan Lake. A lake which is created from a melted glacier “ice cube” is known as a kettle lake and these are numerous all over the Thompson Plateau (eg. Kentucky/Alleyne Lakes).

Okanagan Lake Today

The large, obvious lake nearby is quite unusual. It has been described as a fjord lake since it looks like the fjords of Norway. It is quite large and deep at 120 km long and up to 232 metres deep. At locations where rivers flow in, such as Mission and Bellevue Creeks, there are deltas which extend quite far out and are shallow, while there are other locations that are sheer drop-offs.

The actual lake basin itself is extremely deep. The thickest sediment on the bottom is 750 metres deep! When you add water depth on top of that, that means the basin could be 900 metres deep below lake level! It is estimated that the lake contains 90 km3 of silt.

Varved Clay

The word 'varve' is derived from the Swedish word varv whose meanings and connotations include 'revolution', 'in layers', and 'circle'. These deposits are a vital window into our past and function like counting tree rings. With these layers, they can give us insights into past sea level change, glaciation change, and Earth's orbital variations which serve to answer questions about climate change.

Deposits are laid down year after year by the rivers that flow into a water body. The layers are thickest in the spring when water flow is the highest and thin in the winter when the rivers are frozen and not much silt moves downstream. This process repeats for many years until you have a bed as seen at the earthcache site.

To Log This Earthcache

Along the side of the road, you will see a cliff with numerous layers of alternating colour.

Answer the following questions and E-mail me the answers through my geocaching.com profile.

1.) Estimate how many layers are in the cliff and how many years this translates into.

2.) What season do you think a thick clay layer represents? (Think tree rings!)

3.) Tell me the colours of the two bands.

4.) Why do think the other clay layer is thin?

5.) Optional: Armchair loggers are lame and I would prefer a picture of your party at the site. Due to concerns the cliffs themselves may lie on private property.