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A kolk is an underwater vortex causing hydrodynamic scour by rapidly rushing water past an underwater obstacle. High-velocity gradients produce a high-shear rotating column of water, similar to a
Kolks were first identified by the Dutch, who observed kolks hoisting several-ton blocks of riprap from dikes and transporting them away, suspended above the bottom. The Larrelt kolk near
Video of kolks and rock-cut basins
{{Authority control Oceanography Geomorphology Hydrodynamics Vortices
A kolk is an underwater vortex causing hydrodynamic scour by rapidly rushing water past an underwater obstacle. High-velocity gradients produce a high-shear rotating column of water, similar to a tornado
A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...
. Kolks can pluck multiple-ton blocks of rock and transport them in suspension for kilometres.
Kolks leave clear evidence in the form of kolk lakes, a kind of plucked-bedrock pits or rock-cut basin. Kolks also leave downstream deposits of gravel-supported blocks that show percussion but no rounding.
Examples
Kolks were first identified by the Dutch, who observed kolks hoisting several-ton blocks of riprap from dikes and transporting them away, suspended above the bottom. The Larrelt kolk near Emden
Emden () is an Independent city (Germany), independent town and seaport in Lower Saxony in the north-west of Germany and lies on the River Ems (river), Ems, close to the Germany–Netherlands border, Netherlands border. It is the main town in t ...
appeared during the 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 channeled scablands
The Channeled Scablands are a relatively barren and soil-free region of interconnected relict and dry flood channels, coulees and cataracts eroded into Palouse loess and the typically flat-lying basalt flows that remain after cataclysmic floods ...
of the Columbia Basin region in Eastern Washington. Depressions were scoured out within the scablands that resemble virtually circular steep-sided potholes. Examples from the Missoula floods in this area include:
* The region below Dry Falls includes a number of lakes scoured out by kolks.
* Sprague Lake is a kolk-formed basin created by a flow estimated to be wide and 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 Montana
Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...
shows 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.
* Oswego Lake, in the middle of Lake Oswego, Oregon (a Portland suburb), was an abandoned channel of the Tualatin River that was scoured by a kolk.
See also
* Hydrodynamic scourReferences
External links
Video of kolks and rock-cut basins
{{Authority control Oceanography Geomorphology Hydrodynamics Vortices