Washboard moraine
Encyclopedia
A washboard moraine
, also known as minor or corrugated moraine, is a geomorphic feature caused by glacier
s. The name "washboard moraine" refers to the fact that, from the air, it resembles a washboard
.
The exact washboard formation mechanism is not known. One theory proposes that as the glacier melts it leaves behind an accumulation of rock debris in the form of annual recessional moraines. These annual glacial advances and recessions cause parallel ridges to form a few meters apart. Because the accumulation of debris is annual, the moraines do not get very large and stand only a few meters high.
An alternative theory is that basal till
, weakened by high pore water pressure, deformed upwards into parallel basal crevasse
s a short distance in from the glacial margin. Crevasse fields of similar geometry to fields of washboard moraines have been observed on ice shelves of Antarctica experiencing large amounts of longitudinal extension, similar to the stresses that would have been experienced by the glaciers that formed these moraines.
Washboard moraines can be seen in many places such as South Dakota, Iowa, Maine, and Iceland.
Moraine
A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...
, also known as minor or corrugated moraine, is a geomorphic feature caused by glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s. The name "washboard moraine" refers to the fact that, from the air, it resembles a washboard
Washboard
A washboard is a tool designed for hand washing clothing. With mechanized cleaning of clothing becoming more common by the end of the 20th century, the washboard has become better known for its originally subsidiary use as a musical instrument....
.
The exact washboard formation mechanism is not known. One theory proposes that as the glacier melts it leaves behind an accumulation of rock debris in the form of annual recessional moraines. These annual glacial advances and recessions cause parallel ridges to form a few meters apart. Because the accumulation of debris is annual, the moraines do not get very large and stand only a few meters high.
An alternative theory is that basal till
Till
thumb|right|Closeup of glacial till. Note that the larger grains in the till are completely surrounded by the matrix of finer material , and this characteristic, known as matrix support, is diagnostic of till....
, weakened by high pore water pressure, deformed upwards into parallel basal crevasse
Crevasse
A crevasse is a deep crack in an ice sheet rhys glacier . Crevasses form as a result of the movement and resulting stress associated with the sheer stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement...
s a short distance in from the glacial margin. Crevasse fields of similar geometry to fields of washboard moraines have been observed on ice shelves of Antarctica experiencing large amounts of longitudinal extension, similar to the stresses that would have been experienced by the glaciers that formed these moraines.
Washboard moraines can be seen in many places such as South Dakota, Iowa, Maine, and Iceland.