Glacial erratic

Erratics, which take their name from the Latin word errare ("to wander"), are carried by glacial ice, often over distances of hundreds of kilometres.

The characteristics of rock avalanche–supraglacial transport includes:[5] Erratics provide an important tool in characterizing the directions of glacier flows, which are routinely reconstructed used on a combination of moraines, eskers, drumlins, meltwater channels and similar data.

[6] Glacial ice entrains debris of varying sizes from small particles to extremely large masses of rock.

Such erratic megablocks greater than 1 square kilometre (250 acres) in area and 30 metres (98 ft) in thickness can be found on the Canadian Prairies, Poland, England, Denmark and Sweden.

Among others, the Swiss politician, jurist and theologian Bernhard Friedrich Kuhn [de] saw glaciers as a possible solution as early as 1788.

Ignaz Venetz (1788–1859), a Swiss engineer, naturalist and glaciologist was one of the first scientists to recognize glaciers as a major force in shaping the earth.

In the 19th century, many scientists came to favor erratics as evidence for the end of the ice age 10,000 years ago, rather than a flood.

Charles Lyell's Principles of Geology (v. 1, 1830)[13] provided an early description of the erratic which is consistent with the modern understanding.

Prior to this proposal, Goethe, de Saussure, Venetz, Jean de Charpentier, Karl Friedrich Schimper and others had made the glaciers of the Alps the subjects of special study, and Goethe,[15] Charpentier as well as Schimper[14] had even arrived at the conclusion that the erratic blocks of alpine rocks scattered over the slopes and summits of the Jura Mountains had been moved there by glaciers.

In his accounts written during the voyage of HMS Beagle, Darwin observed a number of large erratic boulders of notable size south of the Strait of Magellan, Tierra del Fuego and attributed them to ice rafting from Antarctica.

One of the more unusual examples is found far from its origin in Idaho at Erratic Rock State Natural Site just outside McMinnville, Oregon.