It looks like a desert … but it is really the remains of an ancient lake.
If this were a real desert, it would have a hot, dry climate. The Carcross Dunes are a result of a glacial process.
About 10,000 years ago, the great ice sheets that covered much of North America were melting. Ice dams created a series of glacial lakes that submerged some valleys under 300 metres of melt water. A layer of sand and silt, which had been trapped in the glaciers, settled to the bottom of these lakes in a thick layer.
Glacial lake Watson disappeared with the glaciers. The Watson River cut through the lake bottom sediments and continues to bring sand and silt into Bennett Lake. This constant supply of sand makes the Carcross Dunes a truly dynamic system.
Glacial retreat from the Watson, Wheaton and Yukon river valleys allowed the glacial lakes to expand. The Cowley Creek outlet, south of Whitehorse, drained glacial lake Watson as the ice retreated south and east.
Old beaches along Bennett Lake match the Cowley Creek outlet elevation which means that Carcross was once submerged under 120 metres of water.
An Ancient but Active Environment
The Watson River is full of sand which the current brings into Bennett Lake. In the spring, low water-levels expose the sand deposits and the prevailing winds blow the sand onto the beach and into the dunes.
Sometimes the wind blows the vegetation away and digs holes (blowouts) in the sandy landscape. Old forest, previously buried, is sometimes re-exposed.
To the north east, the Carcross Dunes climb up onto a low ridge below Caribou Mountain. The highest part of the dune has crested the ridge and is advancing onto a less steep section. This may stop the advance of sand until enough builds up to move the system forward again.
This high area of the dunes receives direct impact from the onshore wind and is prone to blowouts. Stable dunes can also be reactivated by forest fires.
What is a Dune System?
The low slope leading away from the lake has created an ideal landscape for the dune system. Windblown sand moves up the slope. The heaviest grains form a bump that eventually crests and the lighter grains tumble down the slip face to form a dune.
The most active areas of the dunes are near the lakeshore and at higher elevations on exposed ridges. Windblown sand builds up against any obstacle and forms a crest. Over time, the dune migrates - keeping its shape while moving down-wind.
Hardy vegetation tries to build a stable habitat while the wind keeps the dune moving inland. Sometimes the vegetation protects the sand from the wind and keeps it stable. Vegetation can most easily find a home in the troughs, protected from the prevailing wind.
Patterns in the Sand
Sand comes in particles of all sizes. Most sand is light enough for the wind to move but too heavy to be carried very far. The wind pushes grains of sand and they bounce along the surface, a process called saltation. The average distance of the bounce is the width between the crests of two ripples. Heavier sand grains creep along the surface and a very small amount of light particles is blown away.
Growing on Shifting Sands
The plant communities that live on the dunes are constantly changing as the dunes move and alter their shape. Established plant communities are disturbed and new species move in and thrive.
Plants that live on the dunes have to survive droughts, the abrasive effects of wind-blown sand and unstable ground. The plants of the Carcross Dunes have adapted to these extreme conditions.
The most active and fragile dunes, characterized by little or no vegetation, are found in the dunes’ higher elevations and near the shore of Lake Bennett.
Here you will find plants that can live in harsh and unstable conditions. For example, the roots of the Baikal sedge and Siberian aster are long and spread out to efficiently gather moisture and act to stabilize the sand.
On less-exposed dunes, shrubs and trees develop a mat-like growth form in response to the abrasive action of the wind.
In the winter and spring, accumulated snow and ice protect the bottom leaves and branches while exposed parts of the plant are blasted by wind-driven ice and sand.
In sheltered areas, more species invade the dunes from the surrounding forest. The roots of willows, spruce and aspen increase moisture and stabilize the sand.
Even here, the wind and harsh conditions can cause “blow-outs” and all of the plants are destroyed and the process of re-vegetation has to begin again.
Watch your Step!
The dunes habitat is home to some rare plants and insects. The Carcross Dunes is an exciting place to explore but this unique area is fragile. Please avoid the dunes’edges and crests where delicate and fragile plants grow. Limit motorized activities to areas where there is no vegetation an /or along established trails.
Ten or more species of insects found in the Carcross Dunes are found in few other places on earth. Scientists studying the dunes have found eight species of insects that may be new to science.
The Coast Dart Moth (Euxoa cursoria) is found in the dunes of Europe and Asia, Carcross and Athabasca (Alberta). Their larvae are cutworms that feed on the roots of a variety of dune plants.
There are only six Baikal sedge (Carex sabulosa) populations in Yukon, one in Alaska, and another in Asia. This species has been listed as “threatened” under the federal Species at Risk Act.
Siberian asters (Aster sibiricus) are abundant in some of the most active portions of the sand dunes. Their decaying leaves contribute nutrients to the developing soil.
The Dune Tachinid Fly (Germaria angustata) and other rare insects can be found at the edge of the Carcross Desert. In July, you might see a female Dune Tachinid Fly looking for a place to lay her eggs. She will try and put them where they can hatch and attack a host caterpillar, perhaps a larva of the Coast Dart Moth. The Dune Tachinid Fly is difficult to distinguish from other blackish flies that hover over the dunes.
The genus Gnorimoschema, in the sub-family Gelechiidae, is a very diverse group of small moths which predominantly inhabit dry or arid places in the northern hemisphere. Five new species of Gnorimoschema were identified here in the 1980s and have not been scientifically described or named. Although winged and fully capable of flight, they often run, hop and flutter across their sandy home. At rest, their colouration makes them blend with the sand and difficult to see.
The Yukon Lupine (Lupinus kuschei) is a rare species of lupine that evolved in the dunes of Yukon and Alaska. It can also be found along the Atlin Road.