The Deadly 1985 Lahar of Nevado del Ruiz, Columbia

Nevado del Ruiz with steam plume.  Image courtesy Infographic Vennpage.com, Feb 2017

Nevado del Ruiz (also known as La Mesa de Herveo or Volcan Ruiz) is a massive active stratovolcano located some 129 km west of Bogota, Columbia.  Its summit is covered with large glaciers.  It is locally known as the ‘sleeping lion’, meaning that the locals remember and respect its danger.

Eruptions mobilize and melt the glacial ice from time to time, leading to deadly lahars traveling down valleys on its flanks.  The most recent of these in 1985, when a VEI 3 eruption emptied a small crater lake on top of the edifice, melted perhaps 10% of the ice cap, and sent at least 10 lahars, 4 of them deadly down its flanks, killing over 23,000.  The deadliest of these lahars hit Armero, some 40 km from the volcano, killing 20,000 of the town’s population of 28,700.

Shaded relief map of Nevado del Ruiz location.  Image courtesy Hicks, et al, 2017

Typical historic eruptions from this volcano are Vulcanian to Plinian in strength.  Pyroclastic flows are not uncommon.  There have been at least three deadly historic lahars from Nevado del Ruiz since 1595, all of these triggered by eruptions.

Glacial coverage has generally retreated since the height of the last ice age, having fallen from around 1,500 km2 21,000 years ago, to 800 km2 12,000 years ago, to around 34 km2 in the last century.  Meltwater from these glaciers forms the headwaters of the Cauca and Magdalena River on the E and W flanks of the volcano.  These rivers are the source of fresh water for 40 surrounding towns and villages, which is part of the problem.

River valleys to the east of Ruiz.  Image courtesy wfoster2011, June 2012

Nevado del Ruiz is sparsely forested due to its high elevation.  There are forests below the tree line, dwarf forests at the tree line, and arctic conditions above the tree line.  Animals and birds live on the volcano.  It is one of several stratovolcanoes in the Los Nevados National Natural Park, a park west of Bogota.  The slopes of the volcano are used for winter recreation and there is a nearby lake stocked with trout.

The volcano tops out at 5,321 m.  There are over 507,000 within 30 km of the volcano and over 4,250,000 within 100 km.

Lahar that buried Amero. Image courtesy USGS VDAP, Dec 1985

Disaster

One of the problems living next to a volcano is a close physical proximity to things produced by its eruptions.  Locals located their towns and villages next to the rivers fed by the glacial ice cap on Nevado.  Unfortunately, these rivers also wound their way through lahar deposits from previous eruptions.  Armero was located on the deposits of the 1845 lahar, though hazard maps were either ignored or misinterpreted.

Previous eruptions in 1595 and 1845 produced deadly lahars.  Three Plinian eruptions in 1595 produced a lahar that killed 636.  In 1845, lahars flooded the Lagunillas River valley, killing over 1,000.  This is the valley that the town of Armero was built upon.

Generalized hazard map of Nevado del Ruiz published on the front page of newspaper El Espectator, Oct 7, 1985,  Image courtesy Henry Villegas, 2003

Earth Magazine and Scientific American have reasonable descriptions of the deadly lahars of 1985.  While there is a significant body of work describing the disaster and its aftermath in more technical detail, these are good places to start.

Volcanic activity began in 1984 with earthquakes and increases fumarole activity.  Climbers reported gas from the summit crater in Nov.  Three earthquakes were felt within 20 – 30 km of the volcano in Dec.  This activity continued into the new year.

Emergency planning began in January.  A new pit was observed in the bottom of the crater in Jan.  The regional seismograph broke in Feb and was not replaced.  By March, visiting seismologists described the increasing activity as typical precursory events for an eruption.  He observed vapor columns hundreds of meters tall and recommended immediate installation of a seismograph.  By Aug, multiple seismographs had been installed and were monitoring the volcano.

Armero was in the center of the photo taken late Nov 1985. Image courtesy Wikipedia

The first phreatic eruption took place on Sept 11.  The government started to develop a response plan and a hazard map.  Unfortunately, there were only 10 copies of the hazard map distributed.  The dangers of lahars were obvious to emergency planners.

The deadly eruption sequence started in the afternoon on Nov 13 with another phreatic eruption.  This one settled down after a bit and rain started.  Six hours later the larger magmatic eruption started and lasted for 20 minutes.  This eruption was obscured by the rainstorm and darkness.  It produced pyroclastic flows and tephras.  It was this eruption that emptied the small crater lake, melted part of the ice cap and created the lahars.  They traveled down 11 flank valleys.

The first lahar reached Chinchina about an hour after the eruption, killing over 1,000 and destroying 200 houses.  The first of multiple lahars reached Armero about 140 minutes after the start of the eruption, killing over 20,000 and injuring another 5,000.  Initial lahar was cold.  Subsequent ones were hot.  The lahars down the River Lagunillas continued another 30 km for a total of 70 km from the volcano before they spread out across the floodplain of the river.

A 1990 retrospective by Barry Voight made the case that nobody had to die, “… but rather by cumulative human error – by misjudgment, indecision and human bureaucratic shortsightedness.”  This is likely all true. Unfortunately, hindsight is the only exact science.   A 1991 book The Eruption of Nevado Del Ruiz Volcano Columbia, South America November 13, 1985 is available on Amazon and Google Books.

Damage from lahar into Armero.  Photo taken Dec 18, 1985.  Courtesy USGS/VDAP, Nov 2016

After the requisite arguments and blame-placing about who was responsible and why, the government of Columbia got very serious about the threats of lahars created by volcanic eruptions.  They started writing evacuation plans and practicing the timely execution of those evacuation plans.  This was a worldwide effort, as PHIVOLVC’s adoption of timely planning and evacuation plans six years later significantly decreased the loss of life during the 1991 eruption of Pinatubo.

Over time, Volcan Ruiz has become Columbia’s best monitored volcano.

Volcano Discovery lists several Volcan Ruiz webcams, none of which were active at this writing.

Nevado del Ruiz from the air taken on approach to Bogata. Volcan Tolima is visible under the flap screw fairing center left. Image courtesy Wikipedia

Volcano

Initial volcanic activity from Nevado del Ruiz began some 2 Ma and has proceeded in three eruptive periods.  The most recent of these began 150,000 years ago.  It is located on the complex intersection of four groups of faults.

The volcano is part of the Ruiz – Tolima volcanic massif.  It is a group of 5 ice-capped volcanoes at the intersection of four faults.  The other volcanoes are Tolima, Santa Isabel, Quindio and Machin and are located mostly to the south of Ruiz.  The total Ruiz massif covers over 200 km2.  The volcano erupts andesitic and dacitic lavas and has produced andesitic pyroclastics.  The modern cone is a cluster of lava domes built in the caldera of an older edifice.  The current active crater, Arenas is at the summit.  There is a prominent pyroclastic cone on the SW flank that may have been active in historic times.

Older volcanic edifices surrounding Nevado del Ruiz.  Note at least six volcanoes within 20 km south, with Machin another 15 km farther south.  Image courtesy Smithsonian GVP, May 1995 Bulletin Report

Modern volcanism here started 3 Ma with the pre-volcanic stage 3.00 – 1.25 Ma.  This stage had two large pyroclastic events and a lava flow.  There is a total of four eruptive periods – pre-ancestral, ancestral, older and present.

The first eruptions of the Ancestral period took place 1.8 Ma.  The constructive stage of the ancestral period 1.8 – 0.4 Ma formed a complex of large stratovolcanoes.  These partly collapsed in a destructive phase 1.0 – 0.8 Ma creating 5 – 10 km calderas.  Lava flows and domes are scattered across 50 km2 in the vicinity of the current volcano.  Local faults are thought to be the pathway for magma to reach the surface.  There are block and ash flows, pyroclastics and domes.

Ancestral Volcan Ruiz mapped on present edifice.  Image courtesy Toro Toro, et al  2010

In the older period 0.8 – 0.2 Ma, alternated constructive and destructive phases starting with a new complex of stratovolcanoes (Ruiz, Tolima, Quindio and Santa Isabel).  Explosive eruptions created summit calderas 0.2 – .015 Ma.  There are extensive welded and non-welded andesitic pyroclastic flow deposits that partly fill surrounding valleys from these eruptions.  There are also lava flows.

The present period began 150,000 years ago and grew the current edifice via emplacement of dacite / andesite domes inside the older caldera.  The volcano has had at least 12 eruption cycles over the last 11,000 years, alternating constructive and destructive phases.  It is currently in a destructive cycle.  These eruptions included multiple slope failures and debris avalanches, pyroclastic flows and surges, and their interaction with the ice cap.  This period also includes glacial erosion and mass-wasting (smaller flank landslides).  Summit domes have been partially destroyed.  Over the last several thousand years, Ruiz – Tolima eruptions appear to be smaller and pyroclastic flows less massive.  There is as yet no tephrochronology available to support these observations.  The current cluster of summit domes is physically unstable and prone to collapse.

Top of 11,000-year-old ash fall deposit. Thick segment is a channelized debris flow topped with a series of wet surges. Image courtesy Wikipedia

The main magma chamber was originally thought to be located at the intersection of major faults at 5 – 10 km beneath the volcano.  It powers both eruptions and a hydrothermal system.  More recent RADARSAT-2 data suggests it is 14 km below the surface.  The main magma chamber feeds an intermediate dacite chamber around 6 km.  This is connected to a shallow andesitic chamber around 2 km deep.

Ruiz has an active and extensive hydrothermal system on its summit and flanks.  At elevations below 3,000 m, water is discharged from two groups of boiling springs and several isolated warm springs on the western slope.  There are also extensive springs on the northern and eastern flanks.  The major source for sulfates, halogens and acidity for the spring waters is thought to be high temperature magmatic gasses.  The Nov 1985 eruption caused and increase in sulfate concentration in some of the acid springs that peaked about a year after the eruption.  Glacial waters interacts with the shallow magma chambers.

Ash emissions from Ruiz, Nov 14, 2014 from two different webcams.  Image courtesy SGC via Smithsonian GVP Bulletin Report Jun 2017

Eruptions

In recorded history, eruptions from Volcan Ruiz have been primarily central vent eruptions from the caldera.  A typical sequence is a central vent eruption, an explosive eruption followed by lahars.  The earliest identified eruption was 6660 BC, identified by tephras.  At least 8 other eruptions have been identified between that and 1595.  They were typically VEI 3 – 4.  4 of them were from the Arenas crater and 2 from the flank.

The first deadly historic eruption was Mar 9, 1595.  This was a VEI 4 that produced three Plinian eruptions which were heard up to 100 km from the summit.  The eruption produced 0.16 km3 of tephras and a lahar.  The lahar traveled down the Guali and Lagunillas rivers, eventually killing 636.  This eruption was similar to the 1985 eruption.

There were another 7 eruptions between 1595 and 1845, most of them in the 19^th Century.  With one exception, these were all VEI2.  There were large earthquakes preceding both deadly lahar producing eruptions.

Daily number of recorded earthquakes at Ruiz, July 20, 1985 – Mar 31, 1988.  Eruptions and ash emissions clearly labeled including Nov 1985 eruption.  Image courtesy Smithsonian GVP Bulletin Report Mar 1988

The next deadly lahar producing eruption took place Feb 19, 1845.  This eruption was a VEI 3 and produced another lahar down the Lagunillas River for 70 km.  The breadth and extent of these lahars are similar to those produced in 1985.  An estimated 1,000 died in these lahars.

There was a VEI 2 in 1916 before the 1984 – 1985 eruption sequence described in the earlier Disaster section of this post.

Following the 1985 eruption, activity continued to decrease.  Seismicity and deformation continued into Feb 1986, though the last eruptive period was Jan 4.  There was a variable vapor column above the crater that continued through March.  Ash content in the plume was low.  There was an increase in seismic activity Apr – May with minor ash emissions.  Harmonic tremor took place on May 4 and continued well into June.  There were ash emissions as part of the column along with SO2 emissions.  Strong ash emissions took place in late July these were also accompanied with tremor.  They lasted into August and peaked in Sept.  Small ash emissions and seismic activity took place into 1987.

Steam emissions from Ruiz Aug 2012.  Note Arenas crater, glacial ice cap and steep sides around the top of the volcano.  Image courtesy INGEOMINAS via Smithsonian GVP Bulletin Report Aug 2012

Overall seismic activity, gas emissions and ash emissions at Ruiz increased fitfully through 1987 and into 1989.

The next phreatomagmatic eruption took place Sept 1, 1989.  This created a lahar that destroyed a bridge.  The lahar at the bridge was 5 m thick and 20 m wide.  The volcano quieted down a bit following this eruption, though it still emitted a steam plume and occasional ash.

Activity resumed Aug 1990 with ash emissions, tremor, deformation and increased seismicity.  This tailed off through 1991 and 1992.

Nov 13, 1985 eruption preserved in ice-rich levees of pyroclastic flows.  Layers deposited on glacial ice.  Multiple layers of tephra and ice overlain with pyroclastic flow deposits.  Photo taken a month after the eruption in Dec.  Image courtesy Tom Pierson, USGS, 1985 via Smithsonian GVP

The next round of activity started Mar 1994 with earthquakes and an explosion.  There was a landslide down the Lagunillas River valley that was not volcanically caused.  Multiple tornillos were recorded Jan 1996.  The largest earthquake swarm since 1985 was recorded Jun 2002.  Vapor plumes were visible through most of 2006.

There were several years of increasing activity 2007 – 2012 with explosions in Feb – Mar 2012.  The national park below the volcano was closed due to possible ash and lahar threats.  The rainy season began in March and remobilized ash.  Explosions on May 29 sent ash to 11 km.  Large ash plumes continued through June.  Evacuations were ordered for 1,500 families in 8 local communities.

Schematic of evolution of magma chamber beneath Ruiz.  Evolution 1998 – 2012 noted.  Image courtesy Vargas, et al, 2017

Frequent gas and ash plumes continued Sept 2012 – July 2013.   Ash was detected at 7.6 km on June 16.  Ash emissions were sparse Aug 2013 – April 2014.  They picked up Nov – Dec 2014 and continued well into 2015 with continuous tremor.  Plume heights to nearly 8 km were reported multiple times in Sept 2015.  The Feb 2012 eruption was a VEI 3.  The Nov 2014 eruption was a VEI2.

Small plumes of gas and ash were observed in late July 2019.  Smithsonian GVP lists this as a confirmed eruption with no listed VEI.  Seismicity once again started to increase Sept 2019.  Ash emissions took place Oct 4 with ashfall on several surrounding communities.

Tectonic layout of intersecting faults around Ruiz (NRV).  Bottom chart is number of earthquake events/month and cumulative energy of those events.  Image courtesy Vargas, et al, 2017

Tectonics

Ruiz is essentially a subduction volcano, driven by the subduction of the Nazca Plate under the NW margin of South America.  This has provided magma for recent volcanic activity in the Northern Volcanic Zone.

The Northern Volcanic Zone of Columbia is a narrow volcanic arc located above a steep slab dipping 45 degrees.  The Nazca Plate is descending below the north Andes at 56 mm/year.  Crust thickness beneath the volcanoes varies 20 – 50 km in Ecuador to the south.  In Columbia, it is generally 40 – 50 km, though there are variations with a section less than 35 km thick.  The Nevada del Ruiz complex is some 150 km above the Benioff zone, on the northern segment of Northern Volcanic Zone.

Most of the stratovolcanoes in the Northern Volcanic Zone have a similar history of construction and destruction of stacked edifices.  The greater region can be thought of as the end result of a series of crustal accretion events that have shaped the Northern Andes.  These have left the region riddles with a complex network of faults, most of which control the ascent of magma to the surface.

Satellite view of Nevado del Ruiz. North is up. Armeno is off the screen to the east (right). Preferred lahar channels are clearly visible. Image courtesy Wikipedia

Conclusions

Nevado del Ruiz continues to be an incredibly dangerous volcano.  Not only is it capable of deadly lahars, it is also currently unstable, capable at any time of massive debris avalanches.  It has a healthy magma supply and appears to be a destructive phase of activity.  Sadly, there are far too many people living close to it.

Nevado del Ruiz from Manizales, 2006. Image courtesy Wikipedia

Additional information

https://en.wikipedia.org/wiki/Nevado_del_Ruiz

https://volcano.si.edu/volcano.cfm?vn=351020

https://www.volcanodiscovery.com/nevado_del_ruiz.html

https://www.earthmagazine.org/article/benchmarks-november-13-1985-nevado-del-ruiz-eruption-triggers-deadly-lahars

https://www.ngdc.noaa.gov/hazard/stratoguide/nevadofact.html

https://blogs.scientificamerican.com/history-of-geology/november-13-1985-the-nevado-del-ruiz-lahars/

http://sci.sdsu.edu/how_volcanoes_work/Nevado.html

https://earthobservatory.nasa.gov/images/43859/nevado-del-ruiz-volcano-colombia

https://earthobservatory.nasa.gov/images/78205/simmering-eruption-of-nevado-del-ruiz

http://volcano.oregonstate.edu/keep-eye-volcanic-activity-nevado-del-ruiz-colombia

https://www.nature.com/articles/srep46094

http://www.scielo.org.mx/scielo.php?pid=S0016-71692009000100011&script=sci_arttext

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015GL063858

https://pangea.stanford.edu/ERE/db/WGC/papers/WGC/2015/13050.pdf

https://core.ac.uk/download/pdf/39866998.pdf

https://www.researchgate.net/publication/233690210_Volcano-glacier_interactions_on_composite_cones_and_lahar_generation_Nevado_del_Ruiz_Colombia_case_study