Standing Water – lakes and ponds Lakes result from either barriers to drainage or when depressions (or excavations) form along a drainage system Majority of lakes are found in glaciated areas and are formed by glacial action
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Lakes result from either barriers to drainage or when depressions (or excavations) form along a drainage system
Majority of lakes are found in glaciated areas and are formed by glacial action
Others are formed in river channels (oxbows), by geological faulting, volcanic action, or sea level changes
Beavers form ponds by blocking drainage and then excavating the basins and seal the dam with the mud they dig up—lakes and man-made reservoirs are formed in much the same way—excavation and impoundment.
The vast majority of lakes in the world occur in glaciated areas—74%
Ice can impound the flow in a drainage system
The flow can be blocked by glacial till or moraines
Ice flow can scour or deepen a basin
Ice blocks in till can melt out to form a “kettle” or “pothole” which then fills up with seepage or surface flow
western extent of the continental glacier
Probable Waterton glacial lake at the height of the Wisconsin glaciation
>12,000 yr bp.
Present Waterton lakes
This lake would have been fed by the all of the tributaries of the Oldman system
This lake probably served as a major refugium from which fish and invertebrates colonized the SSRB, after the ice age.
Genetic studies indicate that many lake trout populations across western Canada came from this glacial refugium
Eastern extent of the cordilleran glaciers
Waterton Lakes have a similar origin—Both Waterton and Memphremagog have contain glacial relict animal species in their deep waters.
Freshwater mysid shrimp are important glacial relicts and have a restricted range because of this.
They have been introduced to many lakes because fisheries managers thought that this would improve fisheries yields
This has largely backfired because Mysis tends to compete with epilimnetic zooplanktivorous fish, and because of their vertical migrations are difficult for these fish to consume.
Most of the mysids for the introductions to other western lakes came from Upper Waterton Lake
Pothole or kettle lake formed in glacial --usually small < 30 ha, but can be quite deep--10-40 m. Watersheds are very small.
Polygonal ponds near the Lena River, Russia
Polygon ponds form along the Arctic coastal lowlands.
Form in the summer as wedges of ice melt within the permafrost to form small
polygonal basins (around 50 m across) that fill up with surface water.
See Fig. 6.2 in your text
Many occupy ancient basins called grabens—formed by large geological faults
Rocks before faulting
Lake in a symmetrical graben
Lake in a tilted graben
Lake Baikal—one of the most famous tectonic lakes in the world, has existed for over 20 million years