Rock Elm Disturbance
{{Short description|Impact crater in Wisconsin, United States}}
{{Infobox terrestrial impact site
| name = Rock Elm Disturbance
| other_name =
| photo = Middle Ordovician craters.jpg
| photo_size = 300
| photo_alt =
| photo_caption = North American Middle Ordovician impact craters, which may be part of the Ordovician meteor event. Key: 1: Ames crater, 2: Decorah crater, 3: Rock Elm Disturbance, 4: Slate Islands crater
| map = United States
| map_alt =
| map_caption = Location of the crater in the United States
| map_size =
| location =
| label =
| label_position =
| coordinates = {{coord|44|43|N|92|14|W|region:US-WI_type:landmark_scale:50000|display=inline,title}}
| coordinates_ref =
| confidence = Confirmed
| diameter = {{convert|6|km|mi|abbr=on}}
| depth =
| rise =
| imp_size =
| age = 430-455 Ma
Middle Ordovician
| exposed = -
| drilled = -
| bolide = Ordovician meteor event?
| translation =
| language =
| pronunciation =
| topo =
| access =
| country = United States
| state = Wisconsin
| province =
| district = Pierce County
| municipality = Rock Elm
}}
The Rock Elm Disturbance is an impact crater in Pierce County, Wisconsin, United States, roughly {{convert|40|km|mi}} southwest of Menomonie.{{cite Earth Impact DB |name=Rock Elm |linkname=rockelm |accessdate=2017-10-14}} The disturbance is named for Rock Elm, Wisconsin, a nearby town.
Description
File:Rock Elm crater N10NAPPW05490016.jpg
File:Blue Rock, at Plum Creek in Nugget Lake County Park.jpg
File:Blue Rock at Plum Creek in Nugget Lake County Park Panorama.jpg
File:View of Rock Elm Disturbance, facing NE.jpg]]
The meteorite that caused the impact crater is estimated to have been {{convert|170|m|abbr=on}} in diameter with a mass of {{convert|9e9|kg|abbr=on}} and impact velocity of {{convert|30|km/s|mph|abbr=on}}.
The crater is {{convert|6|km|mi|abbr=on}} in diameter, and fossils found in the rock filling the crater suggest it dates to the Middle Ordovician Period, about 455 to 430 million years ago.{{cite journal
| year=2002
| title=Paleontology of the Rock Elm Disturbance
| journal=Abstracts with Programs - Geological Society of America
| volume=34
| issue=2
| pages=95
| url=http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_32679.htm
| author=Peters, Christopher William, Middleton, Michael D., & Cordua, William S.
| access-date=2008-06-11
| archive-date=2012-02-11
| archive-url=https://web.archive.org/web/20120211151950/http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_32679.htm
| url-status=dead
}}
It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of a proposed Ordovician meteor event within the continental United States that includes the Decorah crater in Iowa, the Slate Islands crater in Lake Superior, and the Ames crater in Oklahoma.{{cite news|last=Vastag|first=Brian|title=Crater found in Iowa points to asteroid break-up 470 million years ago|url=https://www.washingtonpost.com/national/health-science/crater-found-in-iowa-points-to-asteroid-break-up-470-million-years-ago/2013/02/18/545131f8-76d5-11e2-aa12-e6cf1d31106b_story.html?wprss=rss_national|accessdate=19 February 2013|newspaper=Washington Post|date=18 February 2013}}
Crater characteristics
A raised area at the center of the crater 0.8 km (0.5 mi) wide by 2.4 km (1.5 mi) long suggests that the impact caused a major upheaval of lower-lying rock— breccia and Mount Simon Sandstone, which lies beneath the surface and is much older than the rock layers in the area surrounding it. Additionally, Blue Rock, an exposed portion of faulted Prairie du Chien sandstone lies at the south of the crater's edge, which can be viewed at Nugget Lake County Park.
= Discovery of reidite =
While studying the effects of erosion on areas of meteorite impact, researchers from the University of Puerto Rico discovered a rare high-pressure mineral, reidite, at the center of the Rock Elm impact site. Reidite is a dense form of zircon (ZrSiO4) that is formed by the intense heat and pressure as is caused by an impacting meteorite. The reidite found at the Rock Elm structure is the oldest known example of the mineral.{{Cite web|title=ROCK ELM IMPACT STRUCTURE – Crater Explorer|url=https://craterexplorer.ca/rock-elm-impact-structure/|access-date=2021-11-18|language=en-US}} It has been found in other impact sites such as the Xiuyan crater in China; the Chesapeake Bay impact crater in Virginia, United States; and the Nordlinger Ries crater in Germany.{{cite news |last=Oskin |first=Becky |url=http://www.livescience.com/48584-reidite-discovered-rock-elm-wisconsin.html |title=Rare Mineral Discovered in Ancient Meteorite Impact Crater |work=Live Science |date=November 3, 2014 |accessdate=2015-02-17 }}
References
{{reflist}}
External links
- [http://www.geotimes.org/mar04/NN_Wisccrater.html Article] from Geotimes.com, March 2004
- [http://www.uwrf.edu/news_bureau/0913022.html Press release] {{Webarchive|url=https://web.archive.org/web/20120205035616/http://www2.uwrf.edu/news_bureau/0913022.html |date=2012-02-05 }} from the University of Wisconsin-River Falls
- [http://www.seagrant.wisc.edu/MadisonJASON/Default.aspx?tabid=1468 Craters in Wisconsin] {{Webarchive|url=https://web.archive.org/web/20070701203645/http://www.seagrant.wisc.edu/MadisonJASON/Default.aspx?tabid=1468 |date=2007-07-01 }}
- [http://craterexplorer.ca/rock-elm-impact-structure/ Aerial exploration of the Rock Elm Crater]
{{Impact cratering on Earth}}
Category:Impact craters of the United States