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ISS015-E-07649 (11 May 2007) --- Saskatchewan River Delta, Manitoba, Canada is featured in this image photographed by an Expedition 15 crewmember on the International Space Station. This image highlights a portion of the Saskatchewan River delta extending into Cedar Lake in the Province of Manitoba. The Saskatchewan River watershed extends from the Rocky Mountains of Alberta through the plains of Saskatchewan and Manitoba. The construction of the Grand Rapids Dam to the southeast (not shown) in the 1960s flooded the Cedar Lake basin. This has resulted in the formation of numerous shallow, muddy lakes and bogs (dark green to dark grey irregular areas and at upper right) in and around the Saskatchewan River delta. The level of saturation in these bogs is such that peat (semiconsolidated plant and organic matter) deposits have formed; over long periods of time and under the right geological conditions, such deposits can become coal. The velocity of Saskatchewan River water slows significantly as it enters Cedar Lake; as the flow velocity drops, entrained sediment comprised of silt, clay, sand, and gravel is deposited at the river mouth. These deposits, called alluvium by geologists, account for much of the light tan to grey materials bordering the active channels visible in the image (Saskatchewan River, Summerberry River). According to scientists, fossil-bearing amber -- originating from Late Cretaceous (approximately 65-99 million years ago) coal deposits over a thousand kilometers to the west of Cedar Lake -- is also found in the deltaic sediments. As the deposits accumulate, old channels are abandoned and new channels are formed, as the river seeks more favorable flow paths into the lake, this process (known as avulsion) builds out the river delta over time. A typical "birds foot" delta form is currently being constructed at the mouth of the Saskatchewan River (lower left). The birds foot structure is approximately 13 kilometers wide. The Mississippi River's active delta, while having the same general form, is much larger by comparison -- it is approximately 50 kilometers wide.
Saskatchewan River Delta, Manitoba, Canada:
This astronaut photograph highlights a portion of the Saskatchewan River delta extending into Cedar Lake in the province of Manitoba, Canada. The Saskatchewan River watershed extends from the Rocky Mountains of Alberta through the plains of Saskatchewan and Manitoba to the east. Flooding of the Cedar Lake basin following the construction of the Grand Rapids Dam (to the southeast, not shown) in the 1960s created shallow, muddy lakes and bogs (dark green and blue irregular areas).
The velocity of Saskatchewan River slows significantly as the river enters Cedar Lake; as the velocity slows, silt, clay, sand, and gravel are deposited at the river mouth. These deposits (light tan and gray in the image), called alluvium by geologists, border the active channels of the Saskatchewan and Summerberry Rivers.
As the deposits accumulate, they impede the river's flow. Old channels are abandoned, and new ones form as the river seeks an easier path into the lake. Through this process (known as avulsion), the delta builds and branches out over time. A typical "bird's foot"-shaped delta is currently forming at the mouth of the Saskatchewan River (image lower right). The bird's-foot structure is approximately 13 kilometers wide. The Mississippi River's active delta has the same general form, but it is much larger--approximately 50 kilometers wide.
The bogs in the Saskatchewan delta are saturated enough that peat (dead plant material that accumulates in a water-saturated environment) has formed. Over long periods of time and under the right geological conditions, peat deposits can become coal. The accumulation of plant and animal remains in the water-logged, oxygen-poor environment greatly slows down decay. In addition to setting the stage for coal formation, these conditions also preserve fossils of many kinds. The delta sediments at Cedar Lake are a rich source of fossil-bearing amber that was preserved along with coal deposits during the Late Cretaceous (about 65-99 million years ago). These deposits were not formed locally, however; they have washed into the delta from coal deposits over a thousand kilometers to the west of Cedar Lake. | |
