Geologists monitoring Nevado del Ruiz volcano in Colombia noticed increasing seismic activity and gas emissions in late 1984, indicating rising magma. In September 1985, phreatic eruptions and earthquakes prompted local officials to begin evacuation planning and finalize a hazard map highlighting danger from ash, rockfall, and lahars. The map was unfortunately not well distributed to at-risk communities. In November 1985, further volcanic unrest signaled that magma was near the surface, leading to a catastrophic eruption that triggered lahars which devastated the town of Armero, killing over 20,000 people.

1. Nevado del Ruiz
Science help us predict hazard
In late 1984,geologists noticedthat seismic activity in the area had
begun to increase.Increased fumarole activity,deposition of sulfur on
the summit of the volcano,and phreatic eruptionsalso alerted
geologists to the possibility of an eruption.Phreatic events,when
rising magma encounterswater,continued well into September 1985
(one major eventtook place on September 11,1985),shooting steam
high into the air. Activity began to decline in October,probably
because the new magma had finished ascending into Nevado del
Ruiz's volcanic edifice. Publishing a reportfor officials on October 22,
1985,the scientists determinedthat the risk of lahars was unusually
high. Volcanic activity increased again in November 1985 as magma
nearedthe surface.Increasing quantitiesof gases rich in sulfur
dioxide and elementalsulfur began to appear in the volcano.The
water contentof the fumaroles' gases decreased,and water springsin
the vicinity of Nevado delRuiz became enriched with magnesium,
calcium and potassium,leached fromthe magma. The
extensivedegassing of the magma caused pressureto build up inside
the volcano in the space abovethe magma,which eventually resulted
in the explosiveeruption.
Knowing hazard risk can help people to make decisions
In September1985,as earthquakes and phreatic eruptions rocked the
area,local officials began planningfor an evacuation.In October,
a hazard map was finalized for the area aroundNevado delRuiz. This
map highlightedthe dangerfrom falling material—includingash
and rock—nearMurillo,Santa Isabel,and Libano,as well as the threat
of lahars
in Mariquita, Guayabal, Chimchináand Armero.Unfortunately,the
map was poorly distributed to the people at high risk from Ruiz: many
survivorshad never heard of it, even though severalof the country's
major newspapersfeatured versions of the map.

2. Linkagesexistbetweennatural hazards
The primaryeffectof thishazard wasthe eruptionandthe previouslittle earthquakes.The secondary
effectwasthe laharscausedby the meltingice,rocksandtreeswhichwere inthe volcano.The tertiary
effectwaseconomical andsociological,because all Armerowasdevastatedandthere wasover20.000
people diedonlyinthisvillage,whichwasof 29.000 habitantsbefore the catastrophe.Thishighnumber
of deathmakesthiseventthe secondworse eruptionof the 20th
centuryand the fourthworse since
1500s
Humans can turn disastrous eventsinto catastrophes
Armerowas buildingonmuds.People stayathome notto die because the ashis fallingasscientistsaid
to them,buttheydidn’tthinkabouttheycoulddie buryon the muds,andit was whathappened.
Consequencesofhazards can be minimized
The consequence of thishazardwouldbe lessthanitactuallywas,because people didn’tknow thatit
will occurand the government,whoknew,didn’tdoanythingtoprotectthem.