View source for Nevado del Ruiz

{{Short description|Volcanic mountain in Colombia}}
{{Featured article}}
{{Infobox mountain
| name = Nevado del Ruiz
| other_name = {{lang|es|La Mesa de Herveo}}
| photo = Nevado del Ruiz by Edgar.png
| photo_size = 
| photo_alt = 
| photo_caption = Steam on the mountain in July 2007
| elevation_m = 5389
| elevation_ref = <ref name="Global Volcanism Program">{{cite gvp |vn=351020 |name=Nevado del Ruiz |access-date=2011-05-01}}</ref>
| prominence_m = 2035
| prominence_ref = <ref name=deFerranti>{{cite web |author=Jonathan de Ferranti, John Biggar and Aaron Maizlish |url=http://www.PeakList.org/WWlists/ultras/colombia.html |title=22 Mountain Summits with Prominence of 1,500 meters or greater |publisher=Peaklist |year=2005 |access-date=2009-03-03}}</ref>
| listing = [[Ultra prominent peak|Ultra]]
| range = [[Cordillera Central (Colombia)|Central Ranges]], [[Andes]]
| parent_peak = 
| location = [[Caldas Department|Caldas]] and [[Tolima Department|Tolima]], [[Colombia]]
| map = Colombia
| map_caption = Location of Nevado del Ruiz in Colombia
| map_size = 250
| label_position = 
| coordinates = {{coord|04|53|33|N|75|19|24|W|type:mountain_region:CO-TOL_scale:100000|display=inline,title}}
| range_coordinates = 
| coordinates_ref = <ref name=deFerranti />
| topo = 
| type = [[Stratovolcano]]
| age = [[Pleistocene]]–[[Holocene]]
| volcanic_belt = [[Andean Volcanic Belt]]
| volcanic_zone = [[Northern Volcanic Zone]]
| last_eruption = 2022<ref name="Global Volcanism Program"/>
| first_ascent = 1936 by Cunet and [[Augusto Gansser-Biaggi|Gansser]]<ref name=MAColombia/>
| easiest_route = 
}}

'''Nevado del Ruiz''' ({{IPA|es|neˈβaðo ðel ˈrwis}}), also known as '''La Mesa de Herveo'''<ref>{{cite web |url=http://www.parquesnacionales.dos |title=General Data Los Nevados |publisher=Parques Nacionales Naturales de Colombia |access-date=March 29, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20071215032310/http://www.parquesnacionales.gov.co/pnn/portel/libreria/php/decide.php?patron=02.02020802 |archive-date=December 15, 2007}}</ref> ({{langx|en|[[Mesa]] of [[Herveo]], the name of the nearby town}}) is a volcano on the border of the [[Departments of Colombia|departments]] of [[Caldas Department|Caldas]] and [[Tolima Department|Tolima]] in [[Colombia]], being the highest point of both. It is located about {{cvt|130|km|mi|0|sp=us}} west of the capital city [[Bogotá]]. It is a [[stratovolcano]] composed of many layers of [[lava]] alternating with hardened [[volcanic ash]] and other [[pyroclastic rock]]s. Volcanic activity at Nevado del Ruiz began about two million years ago,<ref name=Thouret/> during the [[Early Pleistocene]] or [[Late Pliocene]], with three major eruptive periods. The current volcanic cone formed during the present eruptive period, which began 150,000 years ago.

The volcano usually generates [[Vulcanian eruption|Vulcanian]] to [[Plinian eruption]]s, which produce swift-moving currents of hot gas and rock called [[pyroclastic flow]]s. These eruptions often cause massive [[lahar]]s (mud and debris flows), which pose a threat to human life and the environment. The impact of such an eruption is increased as the hot gas and lava melt the mountain's snowcap, adding large quantities of water to the flow. On November 13, 1985, a small eruption produced an enormous lahar that buried and destroyed the town of [[Armero]] in Tolima, causing an estimated 25,000 deaths. This event later became known as the [[Armero tragedy]]—the deadliest lahar in [[recorded history]]. Similar but less deadly incidents occurred in 1595 and 1845, consisting of a small explosive eruption followed by a large lahar.

The volcano is part of [[Los Nevados National Natural Park]], which also contains several other volcanoes. The summit of Nevado del Ruiz is covered by large glaciers. The volcano continues to pose a threat to the nearby towns and villages, and it is estimated that up to 500,000 people could be at risk from lahars from future eruptions. Today, the Nevado del Ruiz volcano is constantly monitored by the [[Colombian Geological Survey]] via the [[Colombian Geological Survey#Volcanic and Seismic Observatory of Manizales|Volcanic and Seismic Observatory of Manizales]].<ref>{{cite web |url=https://www2.sgc.gov.co/ProgramasDeInvestigacion/geoamenazas/Paginas/OVS-Manizales.aspx |title=Observatorio Vulcanológico y Sismológico de Manizales |website=www2.sgc.gov.co |access-date=3 February 2019}}</ref>

== Geography and geology ==

Nevado del Ruiz, which lies about {{cvt|129|km|mi|0|sp=us}} west of Bogotá, is part of the [[Andes]] mountain range. The volcano is part of the [[Cordillera Central (Colombia)|Ruiz–Tolima volcanic massif]] (or Cordillera Central), a group of five ice-capped volcanoes which also includes the [[Nevado del Tolima|Tolima]], [[Santa Isabel (volcano)|Santa Isabel]], [[Nevado del Quindío|Quindio]] and [[Cerro Machín|Machin]] volcanoes.<ref name=Williams>{{Cite web |url=https://pubs.usgs.gov/pp/p1386i/colombia/ruiz.html |author1=S. Williams |author2=Richard Jr |title=Ruiz-Tolima Volcanic Massif (Cordillera Central) |publisher=[[United States Geological Survey]] |access-date=September 20, 2013}}</ref><ref name=Thouret>{{cite conference |last=Thouret |first=Jean-Claude |author2=Murcia, A |author3=Salinas, R |title=Stratigraphy and quaternary eruptive history of the Ruiz-Tolima volcanic massif, Colombia. Implications for assessement{{sic |nolink=yes}} of volcanic hazards |year=1990 |conference=Symposium international géodynamique andine: résumés des communications |pages=391–393 |place=Paris |url=http://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_4/colloques/31077.pdf |display-authors=etal}}</ref> The massif is located at the intersection of four [[fault (geology)|fault]]s, some of which are still active.<ref name=Huggel2007>{{cite journal |last=Huggel |first=Cristian |author2=Ceballos, Jorge Luis |author3=Pulgarín, Bernardo |author4=Ramírez, Jair |author5=Thouret, Jean-Claude |title=Review and reassessment of hazards owing to volcano–glacier interactions in Colombia |year=2007 |volume=45 |issue=1 |journal=Annals of Glaciology |pages=128–136 |url=http://www.igsoc.org/annals/45/a45A019.pdf |doi=10.3189/172756407782282408 |bibcode=2007AnGla..45..128H |s2cid=18144817 |access-date=2008-12-12 |archive-date=2009-03-27 |archive-url=https://web.archive.org/web/20090327111238/http://www.igsoc.org/annals/45/a45A019.pdf |url-status=dead }}</ref>

Nevado del Ruiz lies within the [[Pacific Ring of Fire]], a region that encircles the Pacific Ocean and contains some of the world's most active volcanoes. It is the third most northernly of the volcanoes lying in the [[North Volcanic Zone]] of the [[Andean Volcanic Belt]], which contains 75 of the 204 [[Holocene epoch|Holocene-age]] volcanoes in South America.<ref>{{Cite book |author1=T. Simkin |author2=L. Siebert |name-list-style=amp |year=1994 |title=Volcanoes of the World, 2nd edition |publisher=Geoscience Press in association with the Smithsonian Institution [[Global Volcanism Program]] |location=Tucson AZ |page=349}}</ref> The Andean Volcanic Belt is produced by the eastward [[subduction]] of the oceanic [[Nazca Plate]] beneath the [[South American Plate|South American continental plate]].<ref>{{Cite news |url=https://query.nytimes.com/gst/fullpage.html?res=9D0CE7DD1638F930A25755C0A967958260&scp=11&sq=nevado%20del%20ruiz&st=cse |title=Plate Under a 'Ring of Fire' |work=[[New York Times]] |last=Sullivan |first=Walter |date=June 13, 1991 |access-date=September 24, 2008}}</ref> As is the case for many subduction-zone volcanoes, Nevado del Ruiz can generate explosive [[Plinian eruption]]s with associated [[pyroclastic flow]]s that can melt snow and glaciers near the summit, producing large and sometimes devastating [[lahar]]s (mud and debris flows).<ref name=SDSU/>

Like many other Andean volcanoes, Nevado del Ruiz is a [[stratovolcano]]: a voluminous, roughly conical volcano consisting of many [[Stratum|strata]] of hardened lava and [[tephra]] including [[volcanic ash]].<ref>{{cite web |url=https://pubs.usgs.gov/gip/volc/types.html |title=Principal Types of Volcanoes |publisher=United States Geological Survey |access-date=January 19, 2009}}</ref> Its lavas are [[andesite|andesitic]]–[[dacite|dacitic]] in composition.<ref name="Global Volcanism Program"/> The modern [[volcanic cone]] comprises five [[lava dome]]s, all constructed within the [[caldera]] of an ancestral Ruiz volcano: [[Nevado El Cisne]], Alto de la Laguna, La Olleta, Alto la Pirana, and Alto de Santano.<ref name=gvp-names>{{cite gvp |vn=351020&vtab=Subfeatures |title=Nevado del Ruiz: Synonyms & Subfeatures |access-date=November 26, 2008}}</ref> It covers an area of more than {{cvt|200|km2|mi2|0|sp=us}}, stretching {{cvt|65|km|mi|sp=us}} from east to west.<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=92 |url=http://books.nap.edu/openbook.php?record_id=1784&page=92 |isbn=978-0-309-04477-6}}</ref> The mountain's broad summit includes the Arenas crater, which is {{cvt|1|km|mi}} in diameter and {{cvt|240|m|ft|sp=us}} deep.<ref name="Global Volcanism Program"/> Nevado del Ruiz, as its neighbours to the southwest Nevado El Cisne and [[Nevado de Santa Isabel]] is located over the Palestina Fault that crosscuts the underlying El [[Antioquia Batholith|Bosque Batholith]],<ref>{{Citation |title=Palestina Fault |date=2025-06-25 |work=Wikipedia |url=https://en.wikipedia.org/w/index.php?title=Palestina_Fault&oldid=1297360759 |access-date=2025-07-08 |language=en}}</ref> dated at 49.1 ± 1.7 Ma.<ref name=Plancha225>{{cite book |last1=Mosquera |first1=Darío |last2=Martín |first2=Pedro |last3=Vesga |first3=Carlos |last4=González |first4=H. |year=1998 |title=Plancha 225 – Nevado del Ruiz 1:100,000 |url=https://drive.google.com/open?id=0BwFQPMJEi17QaEtlRlM3NnlUeGc |publisher=[[INGEOMINAS]] |pages=1 |access-date=2017-06-06}}</ref>

The summit of the volcano has steep slopes [[inclination|inclining]] from 20 to 30 degrees. At lower elevations, the slopes become less steep; their inclination is about 10 degrees. From there on, [[foothills]] stretch almost to the edge of the [[Magdalena River]], north of the volcano and the [[Cauca River]] to the west.<ref name="NAPCh1p5">{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=5 |url=http://books.nap.edu/openbook.php?record_id=1784&page=5 |isbn=978-0-309-04477-6}}</ref> On the two major sides of the summit, [[headwall]]s show where past [[rock avalanche]]s occurred. At times, ice on the summit has melted, generating devastating lahars, including the continent's deadliest eruption in 1985.<ref name=SDSU/><ref name="Global Volcanism Program"/><ref name=USGS1>{{Cite web |url=https://vulcan.wr.usgs.gov/Volcanoes/Colombia/description_colombia_volcanoes.html |year=2001 |publisher=[[United States Geological Survey]] |title=Colombia Volcanoes and Volcanics |access-date=September 3, 2008}}</ref> On the volcano's southwest flank is the pyroclastic cone La Olleta, which is not currently active, but may have erupted in historical times.<ref name="Global Volcanism Program"/>

=== Glaciers ===
[[File:Nevado del Ruiz Volcano, Colombia.jpg|thumb|left|upright=1.15|The volcano's summit and upper flanks are covered by several glaciers that appear as a white mass surrounding the Arenas crater.]]
The summit of Nevado del Ruiz is covered by [[glacier]]s ({{Lang|es|nevado}} means "snow-covered" in Spanish), which formed over many thousands of years, and have generally retreated since the [[last glacial maximum]]. From 28,000 to 21,000 years ago, glaciers occupied about {{cvt|1500|km2|mi2|sigfig=1|sp=us}} of the Ruiz–Tolima massif. As late as 12,000 years ago, when the ice sheets from the last glacial period were retreating, they still covered {{cvt|800|km2|mi2|sigfig=1|sp=us}}. During the [[Little Ice Age]], which lasted from about 1600 to 1900&nbsp;CE, the ice cap covered approximately {{cvt|100|km2|mi2|sigfig=1|sp=us}}.<ref name=Thouret1996>{{cite journal |last=Thouret |first=Jean-Claude |author2=Van der Hammen, Thomas |author2-link=Thomas van der Hammen |author3=Salomons, Barry |author4=Juvigne, Etienne |title=Paleoenvironmental Changes and Glacial Stades of the Last 50,000 Years in the Cordillera Central, Colombia |year=1996 |volume=46 |issue=1 |journal=Quaternary Research |pages=1–18 |doi=10.1006/qres.1996.0039 |bibcode=1996QuRes..46....1T |s2cid=129575897}}</ref>

Since then the [[Retreat of glaciers since 1850|glaciers have retreated]] further because of atmospheric warming.<ref name=Huggel2007/> By 1959, the massif's glaciated area had dropped to {{cvt|34|km2|mi2|sp=us}}.<ref name=Morris2006>{{cite conference |last=Morris |first=Jennifer N. |author2=Pool, Alan J. |author3=Klein, Andrew G. |title=Retreat of Tropical Glaciers in Colombia and Venezuela from 1984 to 2004 as Measured from ASTER and Landsat Images |year=2006 |conference=63rd Eastern Snow Conference. Newark, Delaware USA |url=http://www.easternsnow.org/proceedings/2006/morris_et_al.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070926135853/http://www.easternsnow.org/proceedings/2006/morris_et_al.pdf |archive-date=2007-09-26}}</ref> Since the 1985 eruption, which destroyed about 10% of the summit ice cover, the area of Nevado del Ruiz covered by glaciers has halved—from {{cvt|17|to|21|km2|mi2|sp=us}} just after the eruption to about {{cvt|10|km2|mi2|sp=us}} in 2003. The glaciers reached altitudes as low as {{cvt|4500|m|ft|sp=us}} in 1985 but have now retreated to elevations of {{cvt|4800|-|4900|m|ft|sigfig=3|sp=us}}.<ref name=Huggel2007/>

The ice cap is approximately {{cvt|50|m|ft|sp=us}} thick on average. It is thickest in parts of the summit plateau and under the Nereides Glacier on the southwestern slopes, where it is as deep as {{cvt|190|m|ft|sp=us}}. Glaciers on the northern and, to a lesser extent, the eastern slopes lost the most ice in the 1985 eruption,<ref name=USGSFig12>{{Cite web |url=https://pubs.usgs.gov/pp/p1386i/colombia/ruiz.html#FIG12 |year=1999 |publisher=[[United States Geological Survey]] |title=Ruiz-Tolima Volcanic Massif (Cordillera Central) |access-date=March 29, 2009}}</ref> and therefore reach only up to {{cvt|30|m|ft|sigfig=1|sp=us}} deep.<ref name="ramirez">{{cite journal |last=Ramirez |first=J. |author2=Thouret, J.-C. |author3=Naranjo, J.L. |author4=Vargas, C.A. |author5=Valla, F. |title=Nevado del Ruiz, Colombia, 20 years after: Evolution of the ice cap, re-assessment of volcano-snow interactionprocesses that feed lahars |year=2005 |volume=7 |journal=Geophysical Research Abstracts |pages=1–2 |url=http://www.cosis.net/abstracts/EGU05/09540/EGU05-J-09540.pdf |archive-date=2011-06-13 |access-date=2009-03-28 |archive-url=https://web.archive.org/web/20110613164441/http://www.cosis.net/abstracts/EGU05/09540/EGU05-J-09540.pdf |url-status=dead }}</ref> The deep ice covering the summit plateau may hide a caldera. Five domes ringing the summit plateau have emerged as the ice has retreated.<ref name="ramirez"/>

The [[meltwater]] from the glaciers drains primarily to the Cauca River and Magdalena River via the western and eastern flanks of the volcano, respectively.<ref name="NAPCh1p5"/> [[Surface runoff|Runoff]] from these glaciers and those on the surrounding volcanoes is a source of fresh water for forty surrounding towns, and Colombian scientists and government officials are concerned about the towns' [[water supply]] should the glaciers melt completely.<ref>{{Cite news |url=http://www.tierramerica.net/2001/0408/iacentos.shtml |title=The Thawing of the Peaks |work=Tierramerica |last=María Isabel García |access-date=December 12, 2008 |year=2001 |url-status=dead |archive-url=https://web.archive.org/web/20080905223246/http://www.tierramerica.net/2001/0408/iacentos.shtml |archive-date=September 5, 2008}}</ref>

== Flora and fauna ==

Nevado del Ruiz is generally poorly forested because of its high elevation, and its forest cover decreases with increasing elevation. At lower elevations, well-developed [[mesic forest]]s ({{convert|20|–|35|m|ft|sp=us|disp=semicolon}} high) are present. Above these but below the [[tree line]], parts of the volcano are covered with dwarf forests {{cvt|3|–|8|m|ft|sigfig=1|sp=us}} high. Above the tree line, in the [[Páramo]] zone, the vegetation is dominated by plants such as bunchgrass and [[Espeletia]].<ref name=BotanySI/> Regional vegetation consists of different families of woody plants, including [[Rubiaceae]], [[Leguminosae]], [[Melastomataceae]], [[Lauraceae]], and [[Moraceae]]. Flowers such as ''[[Polypodiaceae]] s.l.'', [[Araceae]], [[Poaceae]], [[Asteraceae]], [[Piperaceae]], and [[Orchidaceae]] are also present in the region.<ref name=BotanySI/>

Animals living on the volcano include the [[Tapirus pinchaque|mountain tapir]] and [[spectacled bear]], both of which are designated as [[Threatened species|threatened]].<ref name=BotanySI/> Other animals inhabiting the surrounding region include the [[Bolborhynchus ferrugineifrons|rufous-fronted parakeet]], [[buffy helmetcrest]], and [[Herveo plump toad]]. The volcano is home to 27 species of birds endemic to Colombia, with 14 of these species confined to the region around the volcano. 15 bird species in the area are considered threatened.<ref name=BotanySI/>

== Los Nevados National Park ==
{{Main|Los Nevados National Natural Park}}
Nevado del Ruiz is one of several stratovolcanoes within [[Los Nevados National Natural Park]], a national park located west of Bogotá in the centre of the Colombian Andes. The park is a popular tourist destination and contains several tourist shelters. The slopes of the volcano are used for winter sports, and nearby [[Lake Otún]] offers trout fishing.<ref name=BotanySI/> A number of commercially operated spas can be found nearby.<ref name=BotanySI>{{Cite book |first1=J. Orlando |last1=Rangel-Ch. |first2=Aída |last2=Garzón-C. |editor-last1=Davis |editor-first1=S.D. |editor-last2=Heywood |editor-first2=V.H. |editor-last3=Herrera-MacBryde |editor-link3=Olga Herrera-MacBryde |editor-first3=O. |editor-last4=Villa-Lobos |editor-first4=J. |contribution=Region of Los Nevados Natural National Park |contribution-url=http://botany.si.edu/projects/cpd/sa/sa28.htm |title=Centres of Plant Diversity: A Guide and Strategy for Their Conservation. Volume 3: The Americas. |year=1997 |place=Cambridge, England |publisher=World Wide Fund for Nature, International Union for Conservation of Nature and Natural Resources |url=http://botany.si.edu/projects/cpd/ |isbn=978-2-8317-0199-8 |access-date=December 16, 2008 |editor5-last=Hamilton |editor5-first=A. |url-status=dead |archive-url=https://web.archive.org/web/20100709031954/http://botany.si.edu/projects/cpd/ |archive-date=July 9, 2010}}.</ref> In 1868–1869, German geologists [[Wilhelm Reiss]] and [[Alphons Stübel]] were the first to attempt to climb Ruiz. In 1936, W. Cunet and [[Augusto Gansser-Biaggi]] made the first successful ascent, partly by ski; they repeated the ascent in 1939.<ref name=MAColombia>{{cite book |url=http://www.rgs.org/NR/rdonlyres/D39032F5-BFC0-4FC5-842F-F8558767983B/0/MAColombia.pdf |title=Mountaineering in the Andes |first=Jill |last=Neate |year=1994 |edition=2 |publisher=Expedition Advisory Centre |access-date=November 25, 2008 |page=12 |isbn=978-0-907649-64-9}}</ref>

== Eruptive history ==
[[File:Ash Fall Deposits and Debris Flow at Nevado del Ruiz volcano in Colombia.jpg|thumb|right|upright=2|The top of the 11,000 year-old ash fall deposits interstratified with paleosols overlying a channelized debris flow and a sequence of wet surges.]]

The first eruptions of Nevado del Ruiz occurred about 1.8&nbsp;[[myr|million years ago]] at the beginning of the [[Pleistocene]] epoch.<ref name=Huggel2007/> Three primary eruption periods in the history of the massif have been identified: ''ancestral'', ''older'' and ''present''. During the ''ancestral'' period between one million to two million years ago, a complex of large stratovolcanoes was created.<ref name=Thouret/> Between 1.0&nbsp;million and 0.8&nbsp;million years ago, they partially collapsed, forming large (5–10&nbsp;km wide) calderas. During the ''older'' period, which lasted from 0.8&nbsp;million to 0.2&nbsp;million years ago, a new complex of large stratovolcanoes developed (including Older Ruiz, Tolima, Quindio, and Santa Isabel). Once again explosive summit calderas formed from 0.2&nbsp;million to 0.15&nbsp;million years ago.<ref name=Thouret/>

The ''present'' period began about 150,000&nbsp;years ago and involved the development of the present volcanic edifice through the emplacement of lava domes made of andesite and dacite (igneous rocks) inside older calderas.<ref name=Huggel2007/> During the past 11,000&nbsp;years, Nevado del Ruiz passed through at least 12 eruption stages, which included multiple [[Landslide|slope failures]] (rock avalanches), pyroclastic flows and lahars leading to partial destruction of the summit domes.<ref name=Thouret/><ref name=Huggel2007/> During the past several thousand years, eruptions of the volcanoes in the Ruiz–Tolima massif have mostly been small, and the pyroclastic flow deposits have been much less voluminous than during the Pleistocene.<ref name=Thouret/> Since the volcano's earlier eruptions are not recorded, [[volcanologist]]s have used [[tephrochronology]] to date them.<ref name=GVPEH/>

During recorded history, eruptions have consisted primarily of a central vent eruption (in the caldera) followed by an explosive eruption, then lahars. Ruiz's earliest identified [[Holocene]] eruption was about 6660&nbsp;BC, and further eruptions occurred in 1245&nbsp;BC&nbsp;±&nbsp;150&nbsp;years (dated through [[radiocarbon dating]]), about 850&nbsp;BC, 200&nbsp;BC&nbsp;±&nbsp;100 years, 350&nbsp;AD&nbsp;±&nbsp;300 years, 675&nbsp;AD&nbsp;±&nbsp;50 years, in 1350, 1541 (perhaps),{{#tag:ref|Several entries in the Smithsonian's eruptive history for Nevado del Ruiz are marked as "uncertain".<ref name=GVPEH/> An eruption may have occurred at these dates, but this has not been confirmed. They define an eruption as the arrival of volcanic products, excluding gases, at the Earth's surface.<ref name=GVPFAQ2>{{cite web |url=http://www.volcano.si.edu/faq/index.cfm?faq=02 |title=Frequently Asked Questions: What is an eruption? |access-date=February 23, 2009 |work=[[Global Volcanism Program]] |publisher=Smithsonian Institution |archive-date=January 13, 2012 |archive-url=https://web.archive.org/web/20120113085326/http://www.volcano.si.edu/faq/index.cfm?faq=02 |url-status=dead }}</ref>
|group=nb}} 1570, 1595, 1623, 1805, 1826, 1828 (perhaps),{{ref|Perhaps|[b]}} 1829, 1831, 1833 (perhaps),{{ref|Perhaps|[b]}} 1845, 1916, December 1984 – March 1985, September 1985 – July 1991, and possibly in April 1994.{{ref|Perhaps|[b]}} Many of these eruptions involved a central vent eruption, a flank vent eruption, and a [[phreatic explosion|phreatic (steam) explosion]].<ref name=GVPEH>{{cite gvp |vn=351020&vtab=Eruptions |title=Nevado del Ruiz: Eruptive History |access-date=December 13, 2008}}</ref> Ruiz is the second-most active volcano in Colombia after [[Galeras]].<ref name=USGS1/>

=== 1595 lahar ===
On November 13, 1595, Nevado del Ruiz erupted. The episode consisted of three Plinian eruptions, which were heard up to {{cvt|100|km|mi|sp=us}} from the summit of the volcano. A large amount of ash was ejected, which completely darkened the surrounding area. The volcano also erupted [[lapilli]] (a form of tephra) and [[volcanic bomb|pumice bombs]]. In total, the eruption produced 0.16&nbsp;km<sup>3</sup> of tephra.<ref name=GVPEH/> The eruption was preceded by a large precursor earthquake three days before.<ref name="Nat Acad Eruption"/> The eruption caused lahars, which traveled down the valleys of the nearby Gualí and Lagunillas rivers, clogging up the water, killing fish and destroying vegetation. More than 600&nbsp;people died as a result of the lahar.<ref name=BBC>{{cite news |title=BBC:On this day: November 13: 1985: Volcano kills thousands in Colombia |url=https://news.bbc.co.uk/onthisday/hi/dates/stories/november/13/newsid_2539000/2539731.stm |work=[[British Broadcasting Corporation]] |date=November 13, 1985 |access-date=September 3, 2009}}</ref> The 1595 eruption was the last major eruption of Nevado del Ruiz before 1985. The 1595 and 1985 eruptions were similar in many respects, including in the chemical composition of the erupted material.<ref name=Naranjo1986/>

=== 1845 lahar ===
On the morning of February 19, 1845, a large earthquake resulted in a substantial [[mudflow]].<ref name="Nat Acad Eruption">{{Cite book |author=National Research Council |publisher=The National Academies Press |location=Washington, DC |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |year=1991 |chapter=1 |pages=9–10|chapter-url=http://books.nap.edu/openbook.php?record_id=1784&page=9 |isbn=978-0-309-04477-6}}</ref> This mudflow flowed down the valley of the Lagunillas River for approximately {{cvt|70|km|mi|0|sp=us}},<ref name=SDSU>{{cite web |url=http://www.geology.sdsu.edu/how_volcanoes_work/Nevado.html |title=Nevado del Ruiz (1985) |last=Camp, Vic |publisher=[[San Diego State University]] |access-date=September 3, 2008}}</ref> spilling out of the [[channel (geography)|river channel]] and killing much of the local population.<ref name="Nat Acad Eruption"/> After reaching an [[alluvial fan]], the mudflow split into two branches. The larger portion of it joined the Lagunillas River and flowed into the nearby Magdalena River, while the smaller portion was diverted by hills in front of Lagunillas Canyon, turned 90&nbsp;degrees to the north until it reached the Sabandija River, and then flowed east with the Sabandija River, until it rejoined the other branch of the mudflow at the junction of the Sabandija and the Magdalena. It is estimated that 1000&nbsp;people were killed in the mudflows.<ref name="Nat Acad Eruption"/>

=== Eruption (1985) ===
{{Main|Armero tragedy}}

Beginning November 1984, geologists observed an increasing level of seismic activity near Nevado del Ruiz.<ref name=Naranjo1986/> Such [[Volcano tectonic earthquake|volcanic tectonic seismicity]] is often a precursor of an upcoming eruption. Other signs of a forthcoming eruption included increased [[fumarole]] activity, deposition of sulfur on the summit of the volcano, and small [[phreatic eruption]]s. In the latter, hot magma came in contact with water, resulting in explosions as the water was almost instantly turned into steam. The most notable of these events was an ash ejection on September 11, 1985.<ref name=Naranjo1986/> The activity of the volcano decreased in October 1985.<ref name=Naranjo1986/> The most likely explanation of the events is that new magma rose into the volcanic edifice before September 1985.<ref name=Naranjo1986/>

An Italian volcanological mission analyzed gas samples from fumaroles along the Arenas crater floor and proved them to be a mixture of [[carbon dioxide]] and [[sulfur dioxide]], indicating a direct release of [[magma]] into the surface environment. The mission's report, delivered on October 22, 1985, judged the risk of lahars to be very high. The report proposed various simple preparedness techniques to local authorities.<ref>{{cite journal |last1=Barberi |first1=F. |last2=Martini |first2=M. |last3=Rosi |first3=M. |date=July 1990 |title=Nevado del Ruiz volcano (Colombia): pre-eruption observations and the 13 November 1985 catastrophic event |journal=Journal of Volcanology and Geothermal Research |volume=42 |issue=1–2 |pages=1–12 |doi=10.1016/0377-0273(90)90066-O |bibcode=1990JVGR...42....1B}}</ref>

In November 1985, volcanic activity once again increased<ref name=Naranjo1986/> as magma neared the surface. The volcano began releasing increasing quantities of gases rich in sulfur dioxide and elementary [[sulfur]]. The water content of the fumaroles' gases decreased, and water springs in the vicinity of Nevado del Ruiz became enriched in [[magnesium]], [[calcium]] and [[potassium]], which were leached from the magma.<ref name=Naranjo1986/> The [[thermodynamic]] equilibration (stationary heat energy) temperatures, corresponding to the chemical composition of the discharged gases, were from {{cvt|200|°C|°F|sigfig=1}} to {{cvt|600|°C|°F|sigfig=1}}. The extensive [[degassing]] of the magma caused pressure to build up inside the volcano, which eventually resulted in the explosive eruption.<ref>{{cite journal |last1=Giggenbach |first1=W.F. |last2=Garcia P. |first2=N. |last3=Londoño C. |first3=A. |last4=Rodriguez V. |first4=L. |last5=Rojas G. |first5=N. |last6=Calvache V. |first6=M.L. |year=1990 |title=The chemistry of fumarolic vapor and thermal-spring discharges from the Nevado del Ruiz volcanic-magmatic-hydrothermal system, Colombia |journal=Journal of Volcanology and Geothermal Research |volume=42 |issue=1–2 |pages=13–39 |doi=10.1016/0377-0273(90)90067-P |bibcode=1990JVGR...42...13G}}</ref>

==== Eruption and lahars ====
[[File:Nevado del Ruiz hazard map, from Wright and Pierson.png|thumb|upright=2|Hazard map for Nevado del Ruiz, with 1985 [[lahar]]s shown in red]]

At 3:06&nbsp;pm, on November 13, 1985,<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=13 |url=http://books.nap.edu/openbook.php?record_id=1784&page=13 |isbn=978-0-309-04477-6}}</ref> Nevado del Ruiz began to erupt, ejecting dacitic tephra more than {{cvt|30|km|mi}} into the atmosphere.<ref name=Naranjo1986>{{cite journal |last=Naranjo |first=J.L. |author2=Siggurdsson, H. |author3=Carey, S.N. |author4=Fritz, W. |date=August 1986 |title=Eruption of the Nevado del Ruiz Volcano, Colombia, On 13 November 1985 3:06 p.m. : Tephra Fall and Lahars |journal=[[Science (magazine)|Science]] |volume=233 |issue=4767 |pages=991–993 |url=http://www.sciencemag.org/cgi/content/abstract/233/4767/961 |doi=10.1126/science.233.4767.961 |pmid=17732038 |bibcode=1986Sci...233..961N |s2cid=6358629|url-access=subscription }}</ref> The total mass of the erupted material (including magma) was 35&nbsp;million [[tonne]]s<ref name=Naranjo1986/>—only 3% of the amount that erupted from [[Mount St. Helens]] in 1980.<ref name=Wright>{{Cite book |last=Wright |first=T.L. |author2=Pierson, T.C. |year=1992 |title=Living with Volcanoes: The U. S. Geological Survey's Volcano Hazards Program: USGS Circular 1073 |publisher=[[United States Geological Survey]] |doi=10.3133/cir1073 |url=https://vulcan.wr.usgs.gov/Vhp/C1073/ |access-date=December 13, 2008}}</ref> The eruption reached a value of 3 on the [[Volcanic Explosivity Index]].<ref>{{cite web |url=https://pubs.usgs.gov/gip/msh//comparisons.html |title=Mount St. Helens&nbsp;– Comparisons With Other Eruptions |last=Watson, John |publisher=[[United States Geological Survey]] |access-date=September 20, 2008}}</ref> The mass of the ejected sulfur dioxide was about 700,000&nbsp;tonnes, or about 2% of the mass of the erupted solid material,<ref name=Naranjo1986/> making the eruption atypically sulfur-rich.<ref>{{cite journal |title=TOMS measurement of the sulfur dioxide emitted during the 1985 Nevado del Ruiz eruptions |volume=41 |issue=1–4 |doi=10.1016/0377-0273(90)90081-P |date=July 1990 |pages=7–15 |journal=Journal of Volcanology and Geothermal Research |author=Krueger, Arlin J., Walter, Louis S., [[Charles C. Schnetzler|Schnetzler, Charles C.]], and Doiron, Scott D. |bibcode=1990JVGR...41....7K}}</ref>

The eruption produced pyroclastic flows that melted summit glaciers and snow, generating four thick lahars that raced down river valleys on the volcano's flanks.<ref name="usgs"/> It also destroyed a small lake that was observed in Arenas crater several months before the eruption.<ref name=Naranjo1986/> Water in such volcanic lakes tends to be extremely salty and contain dissolved volcanic gases. The lake's hot, acidic water significantly accelerated the melting of the ice; this effect was confirmed by the large amounts of [[sulfate]]s and [[chloride]]s found in the lahar flow.<ref name=Naranjo1986/>

The lahars, formed of water, ice, [[pumice]], and other rocks,<ref name="usgs"/> mixed with clay as they travelled down the volcano's flanks.<ref>{{cite journal |last=Lowe |first=Donald R. |author2=Williams, Stanley N. |author3=Leigh, Henry |author4=Connort, Charles B. |author5=Gemmell, J. Bruce |author6=Stoiber, Richard E. |date=November 1986 |title=Lahars initiated by the 13 November 1985 eruption of Nevado del Ruiz, Colombia |journal=[[Nature (journal)|Nature]] |volume=324 |issue=6092 |pages=51–53 |doi=10.1038/324051a0 |bibcode=1986Natur.324...51L |s2cid=4315639}}</ref> They ran down the volcano's sides at an average speed of 60&nbsp;km per hour, eroding soil, dislodging rock, and destroying vegetation. After descending thousands of meters down the side of the volcano, the lahars were directed into all of the six river valleys leading from the volcano. While in the river valleys, the lahars grew to almost 4 times their original volume. In the Gualí River, a lahar reached a maximum width of {{convert|50|m|ft|abbr=on}}.<ref name="usgs">{{Cite web |url=https://volcanoes.usgs.gov/hazards/lahar/ruiz.php |title=Deadly Lahars from Nevado del Ruiz, Colombia: November 13, 1985 |publisher=[[United States Geological Survey]] |date=September 30, 1999 |access-date=March 18, 2010 |archive-date=May 27, 2010 |archive-url=https://web.archive.org/web/20100527195111/http://volcanoes.usgs.gov/hazards/lahar/ruiz.php |url-status=dead }}</ref>
[[File:Armero aftermath Marso.jpg|thumb|left|upright=1.35|[[Armero]] was located in the center of this photograph, taken late November 1985.]]

One of the lahars virtually erased the town of Armero in [[Tolima Department|Tolima]], which lay in the Lagunilla River valley. Only one quarter of its 28,700 inhabitants survived.<ref name="usgs"/> The second lahar, which descended through the valley of Chinchiná River, killed about 1,800 people and destroyed about 400 homes in the town of [[Chinchiná, Caldas|Chinchiná]], in the department of [[Caldas Department|Caldas]].<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=1 |url=http://books.nap.edu/openbook.php?record_id=1784&page=1 |isbn=978-0-585-14407-8}}</ref> In total, over 23,000 people were killed and approximately 5,000 were injured.<ref name="usgs"/> More than 5,000 homes were destroyed.<ref name="usgs"/> The [[Armero tragedy]], as the event came to be known, was the second-deadliest volcanic disaster in the 20th century, being surpassed only by the 1902 eruption of [[Mount Pelée]],<ref>{{Cite web |url=http://www.ngdc.noaa.gov/hazard/stratoguide/nevadofact.html |title=Nevado del Ruiz&nbsp;– Facts and Figures |publisher=[[National Oceanic and Atmospheric Administration]] |last=Staff |access-date=September 3, 2008}}</ref> and is the fourth-deadliest volcanic eruption in recorded history.<ref>{{Cite web |url=https://vulcan.wr.usgs.gov/LivingWith/VolcanicFacts/deadly_eruptions.html |title=Deadliest Volcanic Eruptions Since 1500 A.D. |last=Topinka, Lyn |publisher=[[United States Geological Survey]] |access-date=September 20, 2008 |archive-date=May 31, 2012 |archive-url=https://web.archive.org/web/20120531100910/http://vulcan.wr.usgs.gov/LivingWith/VolcanicFacts/deadly_eruptions.html |url-status=dead }}</ref> It is also the deadliest known lahar,<ref name=Huggel2007/> and Colombia's worst natural disaster.<ref>{{cite news |last=Staff |title=World News Briefs |url=http://www.cnn.com/WORLD/Newsbriefs/9511/11-14/index.html?iref=newssearch |work=[[CNN]] |date=November 14, 1995 |access-date=September 20, 2008}}</ref> A young girl named [[Omayra Sánchez]] became a worldwide symbol of the disaster after images of her trapped under the debris of her former home, after the eruption made the news worldwide.

The loss of life during the 1985 eruption was due partly to the fact that scientists did not know precisely when the eruption would occur, and the authorities would not take costly preventive measures without clear warnings of imminent danger.<ref name=Fielding>{{cite web |url=https://www.bbc.co.uk/science/horizon/2001/volcanohelltrans.shtml |title=Volcano Hell Transcript |last=Fielding |first=Emma |publisher=[[BBC]] |access-date=September 3, 2008}}</ref> Because the volcano's last substantial eruption occurred more than 140 years earlier, it was also hard for many to accept the danger the volcano presented; locals even called it the "Sleeping Lion".<ref name=BBC/> [[Hazard map]]s showing Armero would be completely flooded after an eruption were distributed more than a month before the eruption, but the Colombian Congress criticized the scientific and [[civil defense]] agencies for scaremongering. Local authorities failed to alert people to the seriousness of the situation, with Armero's mayor and a priest both reassuring the populace after an ash eruption on the afternoon of November 13 and the consequent ashfall early that evening.<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |pages=51–53 |url=http://books.nap.edu/openbook.php?record_id=1784&page=51 |isbn=978-0-585-14407-8}}</ref> Another factor was the storm that hit that evening, causing electrical outages and hindering communications. Civil defense officials from four nearby towns tried to warn Armero the lahar was approaching in the hour or so before it reached Armero, but failed to make radio contact.<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=61 |url=http://books.nap.edu/openbook.php?record_id=1784&page=61 |isbn=978-0-585-14407-8}}</ref>

Scientists later looked back to the hours before the eruption and noticed that several [[long-period earthquakes]], which start out strong and then slowly die out, had occurred in the final hours before the eruption. Volcanologist Bernard Chouet said that, "the volcano was screaming 'I'm about to explode'", but the scientists who were studying the volcano at the time of the eruption were not able to read this signal.<ref>{{cite news |title=Signs of an eruption&nbsp;— A scientist has found a way to use earthquakes to predict when volcanoes will erupt |url=https://news.bbc.co.uk/2/hi/science/nature/3183047.stm |work=[[BBC]] |date=August 27, 2003 |access-date=September 13, 2008}}</ref>

== Current threats and preparedness ==

[[File:El ruiz volcano.jpg|thumb|Nevado del Ruiz as seen from [[Manizales]], 2006]]
[[File:Nevado del Ruiz from the air.jpg|thumb|upright=1.5|Photo of Nevado del Ruiz taken on approach to [[El Dorado International Airport]], [[Bogotá]]. [[Nevado del Tolima]] is visible in the background on the left. Approximate altitude of photo: {{cvt|23550|ft|order=flip}}.]]

The volcano continues to pose a serious threat to nearby towns and villages. The most likely hazard is small-volume eruptions, which might destabilize glaciers and trigger lahars.<ref name=Thouret/> Despite the significant retrenchment of the volcano's glaciers, the volume of ice atop Nevado del Ruiz and other volcanoes in the Ruiz–Tolima massif remains large. Melting merely 10% of the ice would produce mudflows with a volume of up to {{cvt|2000000|m3|cuft|0|sp=us}}—similar to the mudflow that destroyed Armero in 1985.<ref name=Huggel2007/> Such lahars can travel up to {{cvt|100|km|mi|0|sp=us}} along river valleys in a matter of few hours.<ref name=Huggel2007/> Estimates show that up to 500,000 people living in the Combeima, Chinchiná, Coello-Toche, and Guali valleys are in danger, and 100,000 of these are considered to be at high risk.<ref name=Thouret/>{{#tag:ref|The available sources do not indicate that lahars from Nevado del Ruiz pose any danger to Bogotá.<ref name=Thouret/><ref name=McDowell/>|group=nb}} Lahars pose a threat to nearby towns of [[Honda, Tolima|Honda]], [[Mariquita, Tolima|Mariquita]], [[Ambalema]], Chinchiná, [[Herveo]], [[Villahermosa, Tolima|Villa Hermosa]], [[Salgar]] and [[La Dorada, Caldas|La Dorada]].<ref>{{cite book |last=Mileti |first=Dennis S. |author2=Bolton, Patricia A. |author3=Fernandez, Gabriel |author4=Updike, Randall G. |title=The Eruption of Nevado Del Ruiz Volcano Colombia, South America, November 13, 1985 |publisher=Commission on Engineering and Technical Systems (National Academy Press) |year=1991 |location=Washington, D.C. |page=80 |url=http://books.nap.edu/openbook.php?record_id=1784&page=80 |isbn=978-0-309-04477-6}}</ref> Although small eruptions are more likely, the two-million-year eruptive history of the Ruiz–Tolima massif includes numerous large eruptions, indicating that the threat of a large eruption cannot be ignored.<ref name=Thouret/>
A large eruption would have more widespread effects, including the potential closure of [[El Dorado International Airport|Bogotá's airport]] due to ashfall.<ref name=McDowell>{{cite journal |last=McDowell |first=Bart |title=Eruption in Colombia |journal=National Geographic |date=May 1986 |pages=640–653 |url=http://encarta.msn.com/sidebar_762503944/eruption_in_colombia.html |archive-url=https://web.archive.org/web/20050128111307/http://encarta.msn.com/sidebar_762503944/Eruption_in_Colombia.html |archive-date=2005-01-28 |url-status=dead}}</ref>

As the Armero tragedy was exacerbated by the lack of early warnings,<ref name=Fielding/> unwise land use,<ref name=Touret2004/> and the unpreparedness of nearby communities,<ref name=Fielding/> the government of Colombia created a special program ({{Lang|es|Oficina Nacional para la Atencion de Desastres}}, 1987) to prevent such incidents in the future. All Colombian cities were directed to promote prevention planning in order to mitigate the consequences of natural disasters,<ref name=Touret2004>{{cite journal |last=Touret |first=Jean-Claude |author2=Laforge, Christophe |title=Hazard Appraisal and Hazard-Zone Mapping of Flooding and Debris Flowage in the Rio Combeima Valley and Ibague City, Tolima Department, Colombia |journal=GeoJournal |year=1994 |volume=34 |issue=4 |pages=407–413 |doi=10.1007/BF00813136 |jstor=41146332 |bibcode=1994GeoJo..34..407T |s2cid=189882493}}</ref> and evacuations due to volcanic hazards have been carried out. About 2,300 people living along five nearby rivers were evacuated when Nevado del Ruiz erupted again in 1989.<ref>{{Cite news |last=Associated Press |title=Colombian Volcano Erupting |work=New York Times |url=https://query.nytimes.com/gst/fullpage.html?res=950DE4DF143DF931A3575AC0A96F948260 |date=September 2, 1989 |access-date=September 20, 2008}}</ref> When another Colombian volcano, the [[Nevado del Huila]], erupted in April 2008, thousands of people were evacuated because volcanologists worried that the eruption could be another "Nevado del Ruiz".<ref>{{Cite news |last=Associated Press |title=Colombian Volcano Erupts, Thousands Evacuated |work=[[Fox News]] |url=https://www.foxnews.com/story/colombian-volcano-erupts-thousands-evacuated |date=April 15, 2008 |access-date=September 20, 2008 |archive-url=https://web.archive.org/web/20110204112828/http://www.foxnews.com/story/0,2933,351333,00.html |archive-date=2011-02-04 |url-status=live}}</ref> In October 2022, the [[International Union of Geological Sciences]] (IUGS) listed Nevado del Ruiz as one of 100 "geological heritage sites" for being among the "best-studied volcanoes in the world" and a "model for volcanic risk management".<ref>{{cite book|isbn= 978-1-7923-9975-6|title=The First 100 IUGS Geological Heritage Sites |editor=[[International Union of Geological Sciences]]|url=https://iugs-geoheritage.org/videos-pdfs/iugs_first_100_book_v2.pdf |location=Spain|publisher=[[International Union of Geological Sciences]]|year=2022|pages=164–165}}</ref>

In 2006, heavy rains on Ruiz sent a mudslide down the Chinchiná River, killing nine children aged 12–19 on a scouting expedition near the volcano.<ref>{{cite news |url=https://apnews.com/e480472d4eab39c182b4e041950d8d90 |title=Colombia Mudslide Kills Nine Young Hikers |publisher=Associated Press |author=Goodman, Joshua |date=March 20, 2006 |access-date=January 19, 2014}}</ref>

=== Recent activity ===

During September and October 2010, the [[Colombian Geological Survey]] noted gradual increases in seismic activity near the Arenas crater. Sulfurous odors and phreatic eruptions reported at Nevado del Ruiz prompted an alert level of Yellow on October 1.{{#tag:ref|An alert level of Yellow indicates "that activity is not imminently dangerous";<ref name=GVPMonth/> it was altered based on "changes in the behavior of volcanic activity".<ref name=GVPWeek/>|group=nb}} Chemical analysis of the volcano demonstrated [[Deformation (engineering)|deformative]] changes and geochemical alterations.<ref name=GVPWeek>{{cite web |url=https://volcano.si.edu/volcano.cfm?vn=351020&vtab=Weekly |title=Nevado del Ruiz: Weekly Reports |work=Global Volcanism Program |publisher=Smithsonian Institution |date=2013 |access-date= March 31, 2013}}</ref> Over the next four months a smattering of long-period earthquakes, considered pseudo-[[Tornillo event]]s, raised worries that the volcano might erupt.<ref name=GVPMonth>{{cite web |url=https://volcano.si.edu/volcano.cfm?vn=351020&vtab=Bulletin |title=Nevado del Ruiz: Bulletin Reports |work=Global Volcanism Program |publisher=Smithsonian Institution |date=2012 |access-date=March 31, 2013}}</ref> In 2010, [[Tiltmeter|tilt]] increased, and on average 890 volcanic tremors were recorded monthly, roughly eight times as many as had been recorded from 2009 to 2010.<ref name=GVPMonth/>

Scientists flying over the volcano on March 8, 2012, noted fresh ash deposits on the east flank of the volcano near the crater, likely from an phreatic eruption on February 22.<ref name=GVPMonth/> Later that day, a small ash plume erupted from the crater; by March 13, scientists detected ash deposits at the head of the Gualí River.<ref name=GVPWeek/> After seismicity continued to increase, the alert level was raised to Orange, and in April Nevados National Natural Park authority closed the reserve, fearing lahars and ashfall hazards.<ref name=GVPMonth/> The sudden activity peak in March did not culminate in a major eruption, and activity declined enough that the alert level was lowered to Yellow on May 3.<ref name=GVPMonth/>{{#tag:ref|The alert level was lowered based on "changes in the behavior of volcanic activity".<ref name=GVPWeek/>|group=nb}} On May 29, seismicity rapidly increased, and the alert level was restored to Orange because ash fell into more than 20 nearby communities. Over the next few months ash fell frequently until earthquakes increased again in June. Because of the severity of these tremors, evacuations were ordered by the Emergency Committee of Caldas on news media for 300–1500 people near the volcano. The alert level was raised to Red, indicating an imminent major volcanic event, and an eruption {{cvt|7.5|km|mi|sp=us}} in diameter took place on July 2, 2012, continuing intermittently until the end of August.<ref name=GVPMonth/> Ash plumes and sulfur dioxide emissions recurred until January 2013.<ref name=GVPWeek/>

Through the beginning of July 2013, ashfall took place at Nevado del Ruiz a few times per month. On July 11, 2013, there was a relatively large explosion, followed by inactivity until August, when emission of ash resumed, continuing intermittently until April 2014. Reports of ashfall stopped until October 2014. In November 2014, earthquakes were recorded, and volcanic ash was observed near the summit; ashfall reached local communities within a {{cvt|30|km|mi|order=flip}} radius of Nevado del Ruiz multiple times each month until December 2015. A lava dome was extruded from August to the end of October in 2015, coinciding with thermal anomalies increasing near the summit crater at the end of the same year.<ref name=2017report>{{Cite journal |editor-last=Venzke |editor-first=E. |title=Report on Nevado del Ruiz (Colombia) |journal=Bulletin of the Global Volcanism Network |volume=42 |issue=6 |publisher=[[Smithsonian Institution]] |date=June 2017 |doi=10.5479/si.GVP.BGVN201706-351020}}</ref> According to the Global Volcanism Program, the last documented eruption at Nevado del Ruiz took place in 2017.<ref name="Global Volcanism Program"/> However, reports from the Servicio Geológico Colombiano observatory at Manizales through the end of October 2018 suggested earthquakes near the volcano, with phreatic eruptions ejecting water vapor, volcanic ash, and volcanic gases up to {{cvt|1.5|km|mi|order=flip}} over its crater.<ref name=octreport>{{cite web |editor-last=Sennert |editor-first=S. K. |editor-link=Sally Kuhn Sennert |url=https://volcano.si.edu/showreport.cfm?doi=GVP.WVAR20181024-351020 |title=Report on Nevado del Ruiz (Colombia) — 24 October-30 October 2018 |date=2018 |work=[[Global Volcanism Program]] |publisher=[[Smithsonian Institution]] and [[United States Geological Survey]]}}</ref> In March 2023, seismic activity around the volcano dramatically increased, prompting the Colombian Geological Survey to raise the alert level from yellow to orange. Families living in the area near the volcano were evacuated, and local schools transitioned to online classes; Los Nevados Natural Park was closed.<ref name=bbc2023>{{cite news|url=https://www.bbc.com/news/world-latin-america-65162781|last=Buschschlüter|first=Vanessa|title=Nevado del Ruiz: Residents evacuated from slopes of volcano|work=[[BBC News]]|publisher=[[BBC]]|date=April 3, 2023|accessdate=December 21, 2023}}</ref><ref name=reutersevac>{{cite news|url=https://www.reuters.com/world/americas/colombia-evacuate-those-closest-nevado-del-ruiz-volcano-2023-04-04/|last=Symmes Cobb|first=Julia|editor-last=Baum|editor-first= Bernadette|title=Colombia to evacuate those closest to Nevado del Ruiz volcano|date=April 4, 2023|accessdate=December 21, 2023|work=[[Reuters]]|publisher=[[Thomson Reuters]] Corporation}}</ref> Ultimately, in June 2023, the threat level was lowered back to yellow without an eruption.<ref name=reutersupdate2023>{{cite news|url=https://www.reuters.com/world/americas/after-89-days-colombia-lowers-activity-alert-nevado-del-ruiz-volcano-2023-06-27/|last=Symmes Cobb|first=Julia|editor-last=O'Brien|editor-first= Rosalba|title=After 89 days, Colombia lowers activity alert at Nevado del Ruiz volcano|date=June 27, 2023|accessdate=December 21, 2023|work=[[Reuters]]|publisher=[[Thomson Reuters]] Corporation}}</ref>

== See also ==
*[[List of volcanic eruptions by death toll]]
*[[List of volcanoes in Colombia]]
*[[List of volcanoes by elevation]]
*[[22195 Nevadodelruiz]], a minor planet named after the volcano
{{clear}}

== Notes ==
{{Reflist|group=nb}}

== References ==
{{Reflist}}

== Further reading ==
{{Commons category|Nevado del Ruiz}}
*{{cite book |last=González |first=Humberto |year=2001 |title=Geología de las planchas 206 Manizales y 225 Nevado del Ruiz - 1:100,000 - Memoria explicativa |url=http://tuinfopro.com/?memoriae206 |publisher=[[INGEOMINAS]] |pages=1–93}}

{{Andean volcanoes|state=collapsed}}
{{Volcanoes of Colombia|state=expanded}}
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{{DEFAULTSORT:Nevado Del Ruiz}}
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