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.

Glacial erratics from Norway on Schokland in the Netherlands
Glacial erratic boulder in Snowdonia (Eryri), Wales
Multiple erratics on the terminal moraine of the Okanogan Lobe. The Cascade Mountains are in the background.
Two small icebergs at right clearly retain fragments of the moraine (rock debris) that forms a dark line along the upper surface of the glacier. The inclusion of the moraine illustrates how land-based rocks and sediment are carried by ice.
This photo shows an automobile passing in front of a rock which is essentially fully exposed. The rock has a rough, dark surface indicating it is weathered basalt and is roughly circular in exposed cross-section. The rock is immediately adjacent to a roadway—the road cut removed much of the earth from one side of it exposing it—from the excavation it is evident that the rock sits on a mound of glacial till. The rock is approximately two times the length of the car (i.e., ≈9 metres) in one direction and five times the height of the car in the other direction (i.e., ≈9 metres). Since the rock has not tipped onto the road and no structural support is provided, it must be approximately as deep as it is wide and high. Since the density of basalt is 3 grams per cubic centimetre, this puts the mass of the rock at about 400 to 500 metric tons (consistent with the references).
Yeager Rock , a 400-metric-ton (440-short-ton) boulder on the Waterville Plateau, Washington . Although transported by a glacier, this boulder is not a true erratic because it is of the same lithology as the underlying, till-blanketed bedrock . Note the glacial till below the rock.
Angular glacial erratic on Lembert Dome
Glacial erratic Ehalkivi with overground volume 930 cubic metres (1,220 cu yd) (weight approximately 2,500 metric tons or 2,800 short tons) in Estonia
Area exposed by the retreat of Alaska 's Steller Glacier in August 1996, the westernmost part of Bering Glacier 's piedmont lobe. The ground surface is covered by glacial sediment deposited as lodgement and ablation till . The erratic is an angular, 20-foot-high (6.1 m) piece of gneiss . Bering Glacier, Alaska flows through Wrangell–St. Elias National Park and Preserve .
Erratic rocks on Estonian northern coast
Example of mixed erratics. The boulder in the foreground is basalt . The boulder on the other side of the fence is granite .
Large glacial erratic boulder in shady forest
Glacial erratic in Green Timbers Urban Forest, in Surrey, BC, Canada
Kukkarokivi in March 2013
Lauču Stone in Vidzeme coastline, Latvia
Devil Stone, Kashubia , Poland
The Drake Stone near Harbottle , Northumberland, is the height of a double-decker bus .
The Glen Rock, in Glen Rock, New Jersey