The scale of volcanic eruptions is one factor, which can influence their human impact. Massive eruptions such as Pinatubo may cause changes to the global climate, i.e global cooling and its implications for food production. Such changes may be short term or long terms, in the past massive eruptions have permanently altered global climate and large parts of the Earth’s topography. However the scale is only one of several factors. The impact of eruptions also depends on physical factors such as viscosity and gaseous content of magma, whether eruptions are effusive or explosive, the nature of the material erupted e.g. pyroclastic flows, superheated gases, ash, lava etc. There are also human factors such as prediction, hazard mitigation, and evacuation procedures, population distribution and density.
Nevado Del Ruiz is an example of a volcanic eruption that was on a large scale with a big impact. The eruption occurred on 13th November 1985 in Columbia. The eruption caused the glaciers to melt which resulted in a huge lahar that swamped the town of Armero, 40 miles away down the river valley. A small group of scientists began investigating Ruiz when it started producing smoke in the winter of 1984. Dr Marta Clavache who began investigating previous eruptions to try and predict what might happen in the incident of an eruption, this led to her drawing up a hazard map. The problem that the hazard map showed with the situation of Armero was that it lay directly in the path of a confluence of two rivers, which would carry down a torrent of mud and ruin the town. The scientist did all they could to warn the townspeople, but they couldn’t answer the one question that everybody was asking. “When would it erupt”. When the volcano eventually did erupt this left the townspeople helpless. This naivety and the fact that the scientist could not answer the most