Editing Río Cuarto craters

{{Short description|Purported impact craters in Argentina}}
{{Use shortened footnotes|date=December 2022}}
{{Infobox terrestrial impact site
| name = Río Cuarto craters
| other_name = 
| photo = Rio Cuarto - Landsat TM 229.jpg
| photo_size = 
| photo_alt = 
| photo_caption = [[Landsat program|Landsat]] image of the craters in 2010
| map = Argentina
| map_alt = 
| map_caption = Location of the craters in Argentina
| map_size = 
| location = 
| label =
| label_position = 
| coordinates = {{Coord|32|52.7|S|64|13.4|W|region:AR-X_type:landmark_scale:30000|display=inline,title}}
| coordinates_ref = 
| confidence = Confirmed,<ref name="Planetary and Space Science Centre" /> contested<ref name="Cione 2002"/><ref name="Acevedo etal 2011" />
| diameter = {{convert|4.5|km|mi|abbr=on}}
| depth = 
| rise =
| imp_size =
| age = <100,000 or <10,000 years<br />[[Pleistocene|Late Pleistocene]] or [[Holocene]]
| exposed = Yes
| drilled = No
| bolide = [[Chondrite]]
| translation =
| language =
| pronunciation =
| topo = 
| access = 
| country = [[Argentina]]
| state = 
| province = [[Córdoba Province, Argentina|Córdoba]]
| district = 
| municipality = [[Río Cuarto, Córdoba|Río Cuarto]]
}}

The '''Río Cuarto craters''' are a purported group of [[impact crater]]s located in [[Córdoba Province, Argentina|Córdoba Province]], [[Argentina]].<ref name="Planetary and Space Science Centre">Planetary and Space Science Centre University of New Brunswick Fredericton<!--, year--></ref> Research published in 2002 indicates that they are more likely a result of [[aeolian processes]].<ref name="Cione 2002">Cione et al., 2002</ref><ref name="Acevedo etal 2011" />

== Discovery ==
In 1990, Captain Ruben Lianza of the [[Argentine Air Force]], an amateur astronomer, provided a report to an astronomy publication that included aerial pictures of a set of odd teardrop-shaped depressions near the city of [[Río Cuarto, Córdoba]] in north-central Argentina. The depressions seemed very similar to the sets of [[Impact crater|crater]]s produced in laboratory simulations of impacts taking place at low angles. Such features exist on the [[Moon]], [[Mars]], and [[Venus]], but had not been seen on [[Earth]] up to that time.

The depressions had long been known to Argentine geologists, but until Lianza, nobody had seriously investigated them. Samples of materials obtained from the depressions indicated the presence of shocked materials, as well as pebbles that were clearly of [[meteor]]itic origin {{Citation needed|date=September 2017}}. A team of [[United States|American]] researchers went to Argentina to investigate, collaborating with Captain Lianza and Argentine academics to study the strange depressions.

There were ten depressions, four of them of substantial size. One depression, named the "Drop", was about {{convert|200|m|ft}} wide and {{convert|600|m|ft}} long. Two more large depressions, the "Eastern Twin" and "Western Twin", both about {{convert|700|m|ft}} wide and {{convert|3.5|km|mi|frac=4|abbr=on}} long, were located {{convert|5|km|mi|frac=2|abbr=on}}  northeast. Another major depression, the "Northern Basin", about half and again as big as one of the Twins, was sited 11 kilometers further to the northeast. The long axes of the depressions all point to the northeast.

== Impact origin theory ==
{{singlesource|section|date=August 2023}} 
The depressions were thought to be due to a grazing impact of a set of objects at a very low angle, which calculations show to be a rare occurrence. Most impacts will strike at an angle of 45 degrees to the horizontal or greater, and the impact craters will always be close to circular, since the shock wave that results from the impact propagates symmetrically.

A grazing impact, however, will form an [[ellipse|elliptical]] crater, with sprays of debris that look like butterfly wings. This has been confirmed by high-velocity guns used for impact experiments, and more recently by computer simulations. On impact, the object may shed chunks of itself that fly further downrange to perform secondary impacts.

Based upon physical and numerical modeling, proponents of the Río Cuarto event suggest that the object struck at an angle of no more than 15 degrees from the horizontal, with the impact itself having 10 times more explosive energy than the [[Barringer Crater]] event and 30 times more than the [[Tunguska event]].<ref name="Planetary and Space Science Centre" /> Although the age of the depressions has not yet been determined precisely, it is believed by some researchers{{Who|date=September 2017}} they are about 10,000 years old, placing them at the start of the [[Holocene]], though the EID gives a broader age of less than 100,000 years old.<ref name="Planetary and Space Science Centre" />

== Aeolian origin theory ==
Satellite surveys of the area have found more than 400 similar oval features in the area, and studies of the layers of rock show no evidence of raised rims. These studies point to the oval features as being dune formations, aligned to the prevailing northeast wind.<ref name="Acevedo etal 2011">Acevedo et al., 2011</ref>

There is no doubt that there is impact material in the form of glassy [[impactite]] and [[shocked quartz]] in the Río Cuarto structures. The age of this material has been questioned, and estimated to more than 500,000 BP, from an unknown source crater. There may have been a second, more recent event at around 10,000 BP which produced a second layer of impactite glass.<ref name= "Acevedo etal 2011" />

== References ==
{{Portal|Argentina|Geology}}
{{Reflist}}

=== Bibliography ===
* {{cite journal |last1=Acevedo |first1=Daniel |last2=Rocca |first2=Maximiliano C.L. |last3=Ocampo |first3=Adriana C. |year=2011 |title=Meteorite Impact Craters in South America: A Brief Review |url=https://www.researchgate.net/publication/239935637 |journal=[[Revista Brasileira de Geomorfologia]] |volume=12 |pages=137–160 |accessdate=2019-03-30}}
* {{cite journal |last=Cione |first=Alberto Luis |author2= Eduardo Tonni |author3=Jorge San Cristóbal |author4=Pedro J. Hernández |display-authors=1 |year=2002 |title=Putative Meteoritic Craters in Río Cuarto (Central Argentina) Interpreted as Eolian Structures |url=https://www.researchgate.net/publication/226369871 |journal=[[Earth, Moon, and Planets]] |volume=91 |pages=9–24 |doi=10.1023/A:1021209417252 |bibcode=2002EM&P...91....9C |s2cid=122467947 |accessdate=2019-03-30}}
* {{cite web<!--|year=--> |title=Rio Cuarto |url=http://www.passc.net/EarthImpactDatabase/New%20website_05-2018/riocuarto.html |website=[[Earth Impact Database]] |publisher=[[University of New Brunswick|Planetary and Space Science Centre University of New Brunswick Fredericton]] |accessdate=2017-10-09}}{{dead link|date=May 2023}}<!-- archive.org oldest is April 12, 2019, and was always 404 -->

{{Impact cratering on Earth}}

{{DEFAULTSORT:Rio Cuarto craters}}
[[Category:Impact craters of Argentina]]
[[Category:Pleistocene impact craters]]
[[Category:Holocene impact craters]]
[[Category:Pleistocene Argentina]]
[[Category:Geology of Córdoba Province, Argentina]]
[[Category:Landforms of Córdoba Province, Argentina]]