|山系=初登頂=[[1936年 M.Rappら|種類=火山}}
'''ネバド・デル・ルイス火山'''（''Nevado del Ruiz''）は、コロンビアにある活火山である。コロンビアの火山の中で最も高く、最も北に位置している。

1985年11月13日の噴火では、火砕流により山頂の雪や氷と雲が溶け、大量の火山泥流（ラハール）が発生した。ラハールの厚さは最大で50mに及び、100km以上の距離を流下して麓のアルメロの町を直撃した。その被害は甚大で、人口28700人の約4分の3にあたる21000人が死亡した。これを含め噴火による被害は死者23000人、負傷者5000人、家屋の損壊5000棟となり、20世紀の火山噴火では２番目の被害となった。

生還を果たした人たちには、再度の噴火の可能性等の警告が行われたが、以前から偽情報が多く流れていたため、あまり聞き入れられなかった。

2001年ごろまで、町は60cm以上の灰や残骸に覆われていた。村人たちは、石や骨などを拾い集め神殿に点置した。間に合わせのフェンスで動物の侵入を防ぐことによって、現在では小さな木が育ち始めている。

この噴火の復旧には、その年のコロンビアの国民総生産の約20%にあたる77億ドルが費やされた。<sup></sup>

{{Infobox Mountain
| Name=Nevado del Ruiz
| Photo=Nevado del Ruiz by Edgar.png
| Caption=Steam in July, 2007
| Elevation=
| Location=Colombia
| Range=Cordillera Central
| Prominence = 
| Coordinates = 
| Topographic map = 
| Type=Stratovolcano
| Volcanic_Arc/Belt= Andean Volcanic Belt
| Age= 
| Last eruption= 1991
| First ascent= 1936 by M. Rapp and party 
| Easiest route=
}}

'''Nevado del Ruiz''' is an Andean Armero in the valley below. It is the northernmost and highest Colombian volcano with historical activity.  Its 1985 eruption produced a lahar which completely buried the city and caused an estimated 23,000 deaths in what came to be known as the Armero tragedy.

The Nevado del Ruiz was produced by subduction of the oceanic Nazca Plate beneath the continental South American Plate. Stratovolcanoes in the Andes are for the most part Plinian, as is Nevado del Ruiz, and produce pyroclastic flows.  Nevado del Ruiz consists of andesite and dacite lava.

Nevado del Ruiz has been called "the Sleeping Lion" by the local towns around it. It had been a dormant volcano for nearly 150&nbsp;years.

==1985 eruption==

thumb|left|Before the eruption in 1985
thumb|Space radar image of Nevado del Ruiz
On November 13, 1985, at 9:08 pm, Nevado del Ruiz erupted. Pyroclastic flows melted ice and snow at the summit which formed lahars that rushed down several river valleys. The lahars were up to 50&nbsp;meters thick and traveled more than 100&nbsp;kilometers.<ref name="usgs">[http://volcanoes.usgs.gov/Hazards/What/Lahars/RuizLahars.html Deadly Lahars from Nevado del Ruiz] at the USGS</ref>

Many houses and towns were destroyed by the lahars. The town of Armero was completely covered by debris, killing approximately 21,000&nbsp;people (out of 28,700). The eruption caused an estimated 23,000 deaths, 5,000 injuries, and destroyed more than 5,000 homes. This was the second-deadliest volcanic disaster in the 20th century (the 1902 eruption of Mount Pelée was the worst). The disaster gained some major international notoriety due in part to a photograph taken by photographer Frank Fournier, of a young girl named Omayra Sánchez who was trapped beneath rubble for three days before she died. <ref>[http://news.bbc.co.uk/2/hi/americas/4231020.stm Picture power: Tragedy of Omayra Sanchez] BBC News, September 30, 2005 - Retrieved: July 9, 2007</ref> 

Survivors who fled to other towns in the area were gradually housed in new government schemes, but problems for the displaced population occurred for many years after. The villagers were warned about the possibility of the disaster but because of past false information about it happening and the false statements of the Tolima Department Governor, among other officials, saying that the volcano was not going to erupt, many people did not believe these warnings. 

There were hundreds of cases where people a few feet apart were either killed by the massive mud and stone wave or survived the disaster. Among the terrible consequences for survivors was that the temperature of the mud and rock avalanche served as a gigantic culture media for all kinds of pathogenic fungus and bacteria. Some survivors who had minor cuts were killed by the infections, which could not be treated with known antibiotics.