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Erratic identification and geology

A rock or boulder transported by glacial ice and deposited far from its source, typically resting on bedrock or sediment of a different composition. Erratics are important for reconstructing ice flow directions and glacial extent because they can be traced back to their source outcrops. They range in size from pebbles to house-sized blocks and are sometimes found perched on surfaces of completely different lithology. Field: glacial geology. Example: The Okotoks Erratic near Calgary, Alberta—the world's largest known glacial erratic at approximately 16,500 tonnes—was transported from Jasper National Park by the Cordilleran Ice Sheet, a distance of over 300 km.. Related terms: Glacial, Till, Moraine, Ice sheet.

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  • Till
  • Moraine

Sources, scope & corrections

These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.

Editorial owner
GeoMiner
Last updated
2026-03-30T15:19:41.999576+00:00
Review status
Published; not independently peer-reviewed
  • USGS Thesaurus — U.S. Geological Survey. Controlled earth-science terminology used to describe USGS information resources.
  • Glossary of Geologic Terms — U.S. National Park Service. Geologic definitions prepared by the NPS Geologic Resources Inventory.

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Common questions

What does Erratic mean in geology?
A rock or boulder transported by glacial ice and deposited far from its source, typically resting on bedrock or sediment of a different composition. Erratics are important for reconstructing ice flow directions and glacial extent because they can be traced back to their source outcrops. They range in size from pebbles to house-sized blocks and are sometimes found perched on surfaces of completely different lithology.
What is an example of Erratic?
The Okotoks Erratic near Calgary, Alberta—the world's largest known glacial erratic at approximately 16,500 tonnes—was transported from Jasper National Park by the Cordilleran Ice Sheet, a distance of over 300 km.
Which earth-science field uses the term Erratic?
Erratic is used in glacial geology.
Which terms are related to Erratic?
Related terms in this reference are Glacial, Till, Moraine, Ice sheet.

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