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A drumlin, from the Irish word droimnín ("little ridge"), first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg [1] [2] formed by glacial ice acting on underlying unconsolidated till or ground moraine.
The Withrow Moraine and Jameson Lake Drumlin Field is a National Park Service–designated privately owned National Natural Landmark located in Douglas County, Washington state, United States. [1] Withrow Moraine is the only Ice Age terminal moraine on the Waterville Plateau section of the Columbia Plateau.
The steeper slope is typically up-ice whereas the shallower slow is down-ice. [38] It is proposed that the width to length ratio of a drumlin can be used to determine the velocity at which a glacier was traveling. An elongated drumlin indicates a slower glacial velocity, whereas a shortened drumlin indicates a much faster glacial velocity.
The Ice Age National Scientific Reserve is an affiliated area of the National Park System of the United States comprising nine sites in Wisconsin that preserve geological evidence of glaciation. To protect the scientific and scenic value of the landforms, the U.S. Congress authorized the creation of a cooperative reserve in 1964.
Their heights vary from 15 to 50 meters, and they can reach a kilometer in length. The steepest side of the hill faces the direction from which the ice advanced (stoss), while a longer slope is left in the ice's direction of movement (lee). Drumlins are found in groups called drumlin fields or drumlin camps.
The ice becomes buried in the sediment and when the ice melts, a depression is left called a kettle hole, creating a dimpled appearance on the outwash plain. Lakes often fill these kettles; these are called kettle hole lakes. Another source is the sudden drainage of an ice-dammed lake and when the block melts, the hole it leaves behind is a kettle.
The concentration of rock debris in the ice and the rate at which sediment is delivered to the tunnel by melting and from upstream transport determines the amount of sediment in an esker. The sediment generally consists of coarse-grained, water-laid sand and gravel, although gravelly loam may be found where the rock debris is rich in clay.
A drumlin is not originally shaped by meltwater, but by the ice itself and has a quite regular shape. It occurs in fine-grained material, such as clay or shale, not in sands and gravels. And drumlins usually have concentric layers of material, as the ice successively plasters new layers in its movement.