In November of 1984, the Nevado Ruiz started experiencing regular tremors. Over the next 51 weeks, the volcano continued to show signs of eruption, until finally erupting on November 13,1981. It would become one of the most devastating eruptions in living memory, causing over 23,000 deaths and costing almost a quarter of the Columbian GDP. Unsurprisingly, the main threats of the disaster were mudslides caused by mass ice-melt on the glacier of the volcano. The mud-slides would mainly threaten the town of Armero, 75 km east of the Nevado Ruiz.
Almost every single person involved handled the situation incorrectly. The town itself was built on a plane made by the previous eruption of the Nevado Ruiz. There was even a detailed history of the mudslide that formed the plane, explaining when, where, and how it formed. The village failed to do their due diligence on volcanic history, as did the Columbian geology institution, and the UN disaster commission. However, the USGS published a map of possible mud slide zones, and distributed it to the people of Armero. However, they did not educate people properly, there was no practice evacuation or education on evacuation routes. The mayor in the town did not think the disaster was a big deal, and was telling the national news network over HAM radio that he did not think the mudslide was a big threat as he was swept away and killed. For whatever reason, the police did not have a HAM radio, and were incommunicado when the volcano erupted at 9 pm, and did not evacuate the town in the two hours until the mudslides reached Armero. Almost every single building was destroyed, and 23 thousand people died before 1 AM, in a town of 24,000.
There is not a single mitigation method in the world that would prevent a mudslide of the magnitude that hit Armero, the only things that would help would be to move the town three hundred feet vertically, or away from the mudslide threat zones. Evacuation plans, and power independent siren systems would have gone a long way towards helping people evacuate, HOWEVER THE EVACUATION ORDER WAS NOT GIVEN, BECAUSE NOBODY PICKED UP THE PHONE OR RADIO. So sorting out the chain of command would go a long way towards resolving disasters.
On November 14, the day after the eruption, a crop duster flew over Armero to survey the damage. They almost did not find it, however there was a single culvert of trees with intact buildings. It then called the local dispatch, and the military was sent in. This was nine hours after the initial eruption, and five hours after the mudslides had subsided in Armero. Rescue operations had to be carried out purely by helicopter, which limited the scope that rescue operations could take place.