Kolk (vortex)
Washington at 46°54′21.40″N 119°16′47″W / 46.9059444°N 119.27972°W
.A kolk is a scour hole created by an underwater vortex caused by rapidly rushing water passing an underwater obstacle in boundary areas of high shear. High-velocity gradients produce a violently rotating column of water, similar to a tornado. Kolks can pluck multiple-ton blocks of rock and transport them in suspension for thousands of metres.[1][2]
Kolks leave clear evidence in the form of plucked-bedrock pits, called rock-cut basins or kolk lakes and downstream deposits of gravel-supported blocks that show percussion but no rounding.[1]
Examples
Kolks were first identified by the Dutch, who observed kolks hoisting several-ton blocks of
1717 Christmas flood which broke through a long section of the dyke. The newly formed body of water measured roughly 500 × 100 m and was 25 m deep. In spite of the repair to the dyke, another breach occurred in 1721, which produced more kolks between 15 and 18 m deep. In 1825 during the February flood
near Emden, a kolk of 31 m depth was created. The soil was saturated from here for a further 5 km inland.
Kolks are credited with creating the pothole-like features in the highly jointed basalts in the
Missoula floods in this area include:[1]
- The region below Dry Falls includes a number of lakes scoured out by kolks.
- Sprague Lakeis a kolk-formed basin created by a flow estimated to be 8 miles (13 km) wide and 200 feet (60 m) deep.
- The Alberton Narrows on the Clark Fork River show evidence that kolks plucked boulders from the canyon and deposited them in a rock and gravel bar immediately downstream of the canyon.
- The south wall of Hellgate Canyon in Montanashows the rough-plucked surface characteristic of kolk-eroded rock.
- Both the walls of the Wallula Gap and the Columbia River Gorge also show the rough-plucked surfaces characteristic of kolk-eroded rock.
- Lake Oswego, Oregon (a Portland suburb), was an abandoned channel of the Tualatin Riverthat was scoured by a kolk.
See also
References
- ^ ISBN 0-87842-415-6.
- ^ ISBN 978-1-879628-27-4.
External links
| Authority control databases: National |
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