Update drumlin definition

[andypbarrett]

The current definition for drumlin is below.

term: drumlin
  definition:
    (1): Remnant elongated hills formed by historical glacial action; it is not clear exactly how they are formed and why they form only in some glaciated regions.
  synonym:
  also see:
  source:
  reference:

Sharp (1988) describes a drumlin in the glossary to Living Ice as low, streamlined ridge of glacial drift shaped by an overriding glacier. In the main text (pp143 - 145), he describes drumlins as a feature of glacial deposition that occur groups of elongate, streamlined hillocks that form in some areas deeply mantled by ground moraine. Drumlins have a blunt upstream end that is steeper than the tail, and are teardrop shaped. The sides may be steeper than the blunt nose. And large drumlins can have smaller drumlins perched on their flanks. Drumlins are aligned parallel with the direction of ice movement. Most are 10 to 20 m high, 10 to 500 m wide, and from 500 m to 1000 m long.

The groups are called swarms that can consist of up to 1000 drumlins. Drumlins are found in Ireland, England, Canada, Wisconsin, Michigan, up-state New York, eastern Washington and New England. Bunker Hill is a Drumlin. Most are formed by ice sheets but some drumlins in Switzerland are formed as a result of ice spreading out to form piedmont glaciers.

Sugden and John () suggest that there are as many theories of drumlin formation as there are drumlins but that the mechanism of their formation is still not adequately understood. Smalley and Unwin (1968) have suggested that continuously deformed basal till may undergo a drop in stress that causes the till to transition from a state of expansion (dilation) to compaction. This compaction results in the creation of a static stable, highly compact mass of till that is shaped but not completely eroded by overlying ice. Other theories suggest they form as a result of pressure gradients.

Andrew Fowler has the following simple definition

Drumlins are small rounded hills which occur in swarms, and which are formed under ice sheets. They are ubiquitous in North America and Northern Europe due to the former presence of the great ice sheets of the last ice age. The enigma of their formation has generated a rich literature over the last two hundred years.

From here https://amath.washington.edu/news/2024/05/02/andrew-fowler-drumlins

[andypbarrett]

My suggested definition is

Drumlins
small rounded hills that occur in groups or swarms, and are formed under ice sheets. They are found in Northern Europe and North America in terrain formerly occupied by ice sheets during the last ice age. Although much is known about the structure and form of drumlins, questions remain as to what determines the spacing within swarms.