Drumlins often resemble inverted spoons of eggs
DRUMLIN An oval-shaped hill, largely composed of glacial drift, formed beneath a glacier or ice sheet and aligned in the direction of ice flow. There are no strict definitions relating to their size but they tend to be up to a few kilometres long and up to 50 m in relief. They are widespread in formerly glaciated areas and are especially numerous in Canada, Ireland, Sweden and Finland. Drumlins are considered to be part of a family of related landforms including FLUTES, MEGA-SCALE GLACIAL LINEATIONS, and ROGEN MORAINE which are collectively referred to as SUBGLACIAL BEDFORMS. Their formation remains controversial (see below) but in spite of this they are extremely useful for reconstructing former ice sheets. The word drumlin is a derivation of a Gaelic word for a rounded hill.
Whilst there are many variations in shape, the `classic´ drumlin is a smooth, streamlined hill that resembles an egg half buried along its long-axis. They tend to exist as fields or swarms of landforms rather than as isolated individuals, with a typical swarm comprising tens to thousands of drumlins. Viewed en masse, drumlins within a swarm display a similar long-axis orientation and morphology to their neighbours, and are closely packed, usually within two to three times the dimensions of their drumlin length. The majority of drumlins in a swarm have their highest elevation and blunter end pointing in an upstream direction, with the more gently sloping and pointed end, or tail, facing down-ice. The upstream blunt end is called the stoss end and the downstream end called the lee. A common measure of their shape is the elongation ratio, which is the maximum drumlin length divided by maximum width. Typical elongation ratios are 2:1 to 7:1. Variations in drumlin shape include spindle-like forms, two-tailed forms resembling barchan dunes in plan view, and they also exist as perfect circular hills with an elongation ratio of 1:1. There is a whole branch of investigation, called drumlin morphometry, which uses measures of shape, size and spacing to try and develop or test theories for their formation.