A geoglyph is a large design or motif (generally longer than 4 metres) produced on the ground and typically formed by clastic rocks or similarly durable elements of the landscape, such as stones, stone fragments, live trees, gravel, or earth. A positive geoglyph is formed by the arrangement and alignment of materials on the ground in a manner akin to petroforms, while a negative geoglyph is formed by removing patinated clasts to expose unpatinated ground in a manner akin to petroglyphs.
The most famous geoglyphs are the Nazca Lines in Peru. The cultural significance of these geoglyphs for their creators remains unclear, despite many hypotheses. The "Works of the Old Men" in Arabia, "stone-built structures that are far more numerous than (the) Nazca Lines, far more extensive in the area that they cover, and far older,"  have been described as geoglyphs by Amelia Sparavigna, a physics professor at Politecnico di Torino in Italy. The use of this term to describe these features is probably inaccurate, as recent research has shown that most were not constructed primarily as art, but were rather built to serve a range of purposes including burial sites and funerary customs, aiding in the trapping of migratory animals, and as cleared areas for camps, houses and animal enclosures.
Since the 1970s, numerous geoglyphs have been discovered on deforested land in the Amazon rainforest, Brazil, leading to claims about Pre-Columbian civilizations. Ondemar Dias is accredited with first discovering the geoglyphs in 1977 and Alceu Ranzi with furthering their discovery after flying over Acre.
Other areas with geoglyphs include Megaliths in the Urals, South Australia (Marree Man, which is not ancient, rather a modern work of art, with mysterious origins), Western Australia and parts of the Great Basin Desert in the southwestern United States. Hill figures, turf mazes and the stone-lined labyrinths of Scandinavia, Iceland, Lappland and the former Soviet Union are types of geoglyphs.
Not all geoglyphs are ancient. The Land Art movement created many new geoglyphs as well as other structures; perhaps the most famous example is Spiral Jetty by Robert Smithson. Many towns and cites in the Western United States use hillside letters (also known as "mountain monograms") on the hills above their locations. Contemporary Australian sculptor Andrew Rogers has created geoglyphs around the world called "The Rhythms of Life". You Yangs National Park is the home of a geoglyph constructed by Rogers in recognition of the indigenous people of the area. It depicts Bunjil, a mythical creature in the culture of the local Wautharong Aboriginal people.
Geoglyphic texts and images are common in Central and Inner Asia but there has been little systematic study of their origins and spread.
In 2008–2009 Alfie Dennen created Britglyph, a locative art focused Geoglyph created by having participants across the United Kingdom leave rocks at highly specific locations and uploading media created at each location. When taken together and viewed on the main project website an image of a watch and chain inspired by John Harrison's marine chronometer H5 was created.
- Atacama Giant
- Intaglio (burial mound)
- Battalion Park
- ru:Надписи из деревьев (Wood Signs)
- ru:Надписи из деревьев
- New Technologies for Archaeology: Multidisciplinary Investigations in Palpa and Nasca, Peru, Natural science in archaeology, page 50, Markus Reindel, Günther A. Wagner, Springer Verlag, 2009. ISBN 978-3-540-87437-9
- Professor David Kennedy, quoted by Owen Jarus, LiveScience Contributor. "Visible Only From Above, Mystifying 'Nazca Lines' Discovered in Mideast", MSNBC (via LiveScience), 9/15/2011
- Amelia Sparavigna, quoted by Owen Jarus, LiveScience Contributor. "Visible Only From Above, Mystifying 'Nazca Lines' Discovered in Mideast", MSNBC (via LiveScience), 9/15/2011
- Professor David Kennedy, The “Works of the Old Men” in Arabia: remote sensing in interior Arabia
- Simon Romero (January 14, 2012). "Once Hidden by Forest, Carvings in Land Attest to Amazon’s Lost World". The New York Times.
- Amazon Jungle geoglyphs in Portuguese
- Martti Pärssinen, Denise Schaan and Alceu Ranzi (2009). "Pre-Columbian geometric earthworks in the upper Purús: a complex society in western Amazonia". Antiquity 83 (322): 1084–1095.
- Junior, Gonçalo (October 2008). "Amazonia lost and found". Pesquisa (ed.220) (FAPESP).
- "Unnatural Histories – Amazon". BBC Four.
- Dennen, Alfie (2009-03-11). "Britglyph". Moblog. Retrieved 2009-03-17.
|Wikimedia Commons has media related to Geoglyphs.|
- The Blythe Intaglios, A Photo Gallery
- Ken Scarlett, "Andrew Rogers and the Rhythm of Life" Sculpture article on geoglyph
- Photogrammetric Reconstruction of the Geoglyphs of Nasca and Palpa
- David Kennedy, The “Works of the Old Men” in Arabia: remote sensing in interior Arabia
- Aquizium - Curious World: The Top Ten Geoglyphs - Worldwide — Curious Britannia Ltd.
- Hundreds of Geoglifos Discovered in the Amazon