"Pothole" on the 138
Posted by: 
davidb1957
N 49° 15.060 W 068° 09.624
19U E 561100 N 5455698
The Earth scientists, who study rivers and streams, define a pothole as a smooth, bowl-shaped or cylindrical hollow, generally deeper than wide, found carved into the rocky bed of a watercourse.
Waymark Code: WMZ5PP
Location: Québec, Canada
Date Posted: 09/14/2018
Views: 11
Potholes are also sometimes referred to as swirlholes. This word was created to avoid confusion with an English term for a vertical or steeply inclined karstic shaft in limestone. However, given widespread usage of this term for a type of fluvial sculpted bedrock landform, pothole is preferred in usage to swirlhole.
The consensus of geomorphologists and sedimentologists is that fluvial potholes are created by the grinding action of either a stone or stones or coarse sediment (sand, gravel, pebbles, boulders), whirled around and kept in motion by eddies within and force of the stream current in a given spot. Being a spectacular feature of bedrock river channels, they have been and still are studied extensively and considered as a key factor in bedrock channel development and morphology and important factor in the incision of bedrock channels.
In this region, the rocks in the Canadian Shield are 1 billion to 1.7 billion years old, and are mostly granite and metamorphic gneiss and fell victim to fault effects, to uplift and to erosion.
This gneiss is a metamorphic rock with medium to coarse grain size, with a foliation characterized by darker beds (grey or black) and by lighter beds (white or pink). Rocks with a foliated texture are also included in the gneiss.
What we call kettles or potholes is a cylindrical depression in a riverbed, or what once was a riverbed, normally with a fast moving current. When the current is active, we usually see the presence of stones in rotation. It is because of this movement that the stones eventually erode a depression in the rock in the form of a pothole.
When the river has a steep descent, these kettles can stagger below a waterfalls, sometimes forming aesthetic ponds overflowing into each other. With the progression of erosion, some kettles can finally break through and partially or completely empty depending on the size of the opening and the flow of water.
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