Editing Mercury (planet) (section)

====Volcanism====
[[File:Picasso crater.png|thumb|[[Picasso (crater)|Picasso crater]]—the large arc-shaped pit located on the eastern side of its floor is postulated to have formed when subsurface magma subsided or drained, causing the surface to collapse into the resulting void.]]
There is evidence for [[pyroclastic flow]]s on Mercury from low-profile [[shield volcano]]es.<ref name="Kerber 2009">{{cite journal |title=Explosive volcanic eruptions on Mercury: Eruption conditions, magma volatile content, and implications for interior volatile abundances |journal=Earth and Planetary Science Letters |date=August 15, 2009 |last1=Kerber |first1=Laura |last2=Head |first2=James W. |last3=Solomon |first3=Sean C. |last4=Murchie |first4=Scott L. |last5=Blewett |first5=David T. | volume=285 | issue=3–4 | pages=263–271 | doi=10.1016/j.epsl.2009.04.037 | bibcode=2009E&PSL.285..263K }}</ref><ref name="Volcanism 2011">{{cite journal |title=Flood Volcanism in the Northern High Latitudes of Mercury Revealed by ''MESSENGER'' |journal=Science |date=September 30, 2011 |last1=Head |first1=James W. |last2=Chapman |first2=Clark R. |last3=Strom |first3=Robert G. |last4=Fassett |first4=Caleb I. |last5=Denevi |first5=Brett W. |volume=333 |issue=6051 |pages=1853–1856 |doi=10.1126/science.1211997 |bibcode=2011Sci...333.1853H |pmid=21960625 |s2cid=7651992 |url=https://authors.library.caltech.edu/72395/2/Head.SOM.pdf |access-date=August 20, 2019 |archive-date=July 19, 2018 |archive-url=https://web.archive.org/web/20180719031049/https://authors.library.caltech.edu/72395/2/Head.SOM.pdf |url-status=live }}</ref><ref name="becca">{{cite journal |last1=Thomas |first1=Rebecca J. |last2=Rothery |first2=David A. |last3=Conway |first3=Susan J. |last4=Anand |first4=Mahesh |title=Long-lived explosive volcanism on Mercury |journal=Geophysical Research Letters |date=September 16, 2014 |volume=41 |issue=17 |pages=6084–6092 |doi=10.1002/2014GL061224 |bibcode=2014GeoRL..41.6084T |s2cid=54683272 |url=http://oro.open.ac.uk/40782/ |access-date=July 19, 2017 |archive-date=August 22, 2017 |archive-url=https://web.archive.org/web/20170822012357/http://oro.open.ac.uk/40782/ |url-status=live }}</ref> Fifty-one pyroclastic deposits have been identified,<ref name="Groudge 2014">{{cite journal |title=Global inventory and characterization of pyroclastic deposits on Mercury: New insights into pyroclastic activity from MESSENGER orbital data |journal=Journal of Geophysical Research |date=March 2014 |last1=Groudge |first1=Timothy A. |last2=Head |first2=James W. |doi=10.1002/2013JE004480 |volume=119 |issue=3 |pages=635–658 |bibcode=2014JGRE..119..635G |s2cid=14393394 |url=http://www.planetary.brown.edu/pdfs/4334.pdf |access-date=August 25, 2019 |archive-date=July 18, 2019 |archive-url=https://web.archive.org/web/20190718161242/http://www.planetary.brown.edu/pdfs/4334.pdf |url-status=dead }}</ref> where 90% of them are found within impact craters.<ref name="Groudge 2014"/> A study of the degradation state of the impact craters that host pyroclastic deposits suggests that pyroclastic activity occurred on Mercury over a prolonged interval.<ref name="Groudge 2014"/>

A "rimless depression" inside the southwest rim of the Caloris Basin consists of at least nine overlapping volcanic vents, each individually up to {{convert|8|km|mi|abbr=on}} in diameter. It is thus a "[[compound volcano]]".<ref name="Rothery 2014">{{cite journal |title=Prolonged eruptive history of a compound volcano on Mercury: Volcanic and tectonic implications |journal=Earth and Planetary Science Letters |date=January 1, 2014 |last1=Rothery |first1=David A. |last2=Thomas |first2=Rebeca J. |last3=Kerber |first3=Laura |volume=385 |pages=59–67 |bibcode=2014E&PSL.385...59R |doi=10.1016/j.epsl.2013.10.023 |url=http://oro.open.ac.uk/38842/1/Rothery2.pdf |access-date=August 20, 2019 |archive-date=March 6, 2020 |archive-url=https://web.archive.org/web/20200306081432/http://oro.open.ac.uk/38842/1/Rothery2.pdf |url-status=live }}</ref> The vent floors are at least {{convert|1|km|mi|abbr=on}} below their brinks and they bear a closer resemblance to volcanic craters sculpted by explosive eruptions or modified by collapse into void spaces created by magma withdrawal back down into a conduit.<ref name="Rothery 2014"/> Scientists could not quantify the age of the volcanic complex system but reported that it could be on the order of a billion years.<ref name="Rothery 2014"/>