The various precursors include the following.
The high magnitude 7.3 1975 HaiCheng earthquake had a low death toll of 2041. This was because the earthquake was accurately predicted and the city of HaiCheng, of about 1 million, was evacuated. 4 days later, the earthquake struck, killing a small percentage of the city population.
However, prediction is limited.
Volcanic Explositivity Index/ Type Of Eruption
The volcanic eruption of Mount Pinatubo caused a death toll of 853. It had a VEI of 6 and was a plinian eruption. The Soufrière Hills Volcano had a VEI of 3 and was a sub-plinian eruption. 19 people were killed.
Mount Pinatubo is located on a destructive plate boundary, where the Phillipines plate subducts beneath the Eurasion plate. The Phillipine plate turns into molten magma as a result of the high temperature and pressure. The molten magma, being less dense than the surrounding aesthenosphere, rises through the cracks of the Earth’s surface. As it rises through the surface, more silica is assimilated. The silica-rich is viscous and solidifies near the vent. It also is gas-rich as it traps gases. Hence, pressure builds up. Once the volcano can no longer contain the pressure, the volcano erupts violently, resulting in a VEI of 6.
The volcanic eruption of Mount Pinatubo had a lower death toll (853) than the volcanic eruption of Nevado Del Ruiz (23000) despite it having a larger VEI. Though both countries had predicted the volcanic eruptions, only the Phillipine government acted on it and swiftly evacuated the citizens. On the other hand, the Colombian government urged the citizens to remain where they were as they did not want to falsely alarm the citizens. Furthermore, there were no trained volcanologists monitoring the volcano to advise the government into taking swift action.
The volcanic eruption of Mount Merapi caused a death toll of 353. One of the factors that contributed to the death toll was the lack of the civilians’ corporation. Some returned to their village from the emergency shelter to tend to their crops and livestocks. Others did not leave the village due to cultural reasons. They believed that as long as the gatekeeper of Mount Merapi was alive, the volcano would not erupt.
The volcanic eruption of Mount St. Helens has a lower death toll (57) than the eruption of Nevado Del Ruiz (23000). Population density had a part in the disparity of the number of deaths. There were few people living near Mount St. Helens. However for Nevado Del Ruiz, the town of Armero was wiped out by the fast-flowing lahar. Other towns such as Chinchina were partially wiped out. These towns were densely populated and located near the volcano probably because agriculture was their livelihood. This is especially in Colombia, an LDC where the economy depends on the primary sector.
1985 Nevado Del Ruiz Volcanic Eruption, Colombia
The 1985 Nevado Del Ruiz volcanic eruption in Colombia caused a high death toll of 23000. Despite the indicators, such as increased seismic activities, gas emissions of carbon dioxide and sulfur dioxide and phreatic eruptions, the damage was severe. This was due to several reasons.
- Officials did evacuate the people despite warnings. Authorities did not believe the volcano was going to erupt as it has been inactive for 140 years. Furthermore, there were no trained volcanologists monitoring the volcano.
- The city of Armero had a high population density.
Hence, towns were buried under quick-moving lahars which gave people little time to escape.
2010 Mount Merapi Volcanic Eruption, Indonesia
The 2010 Mount Merapi volcanic eruption caused a death toll of 353 people. About 350,000 people were evacuated. This was after the volcano started spewing lava, hot gases and ash. The volcano had a few minor eruptions prior to the major eruption.
Even though people evacuated, some died due to the following reasons.
Hence, people were killed by the high temperatures of the pyroclastic flow as the result of the collapse of the ash column. Others were asphyxiated.
1991 Mount Pinatubo Volcanic Eruption, Philippine
The 1991 Mount Pinatubo volcanic eruption caused a low death toll of 800 people. This was a result of houses collapsing due to the weight of wet ash. Despite it being the second largest. eruption in the 20th century, the damage to the human environment was low due to successful prediction and evacuation. This was due to several reasons.
Despite this, the response strategies were not efficient, leading to an increased number of deaths.
- There was an outbreak of diseases. The evacuation camp was unsanitary. There was insufficient clean water and improper waste disposal. This led to deaths primarily by measles. Other causes of death included diarrhea and respiratory infections.
- There were not enough emergency supplies.
Hence the death toll continued to climb despite effective evacuation .
Prediction estimates the time of a volcanic eruption. This allows for sufficient time for people to evacuate. Prediction strategies can be both short-term and long-term. Short-term methods monitoring of volcanoes for any frequent gas emissions of carbon dioxide and sulfur dioxide, increased seismic activities, phreatic eruptions and ground deformations. Long – term strategies include studying the geologic history of the volcano, such as the intensity and frequency of the volcanic eruptions. One successful example was the 1991 Mount Pinatubo volcanic eruption in Philippine. Despite it being the second largest eruption in the 20th century, the damage to the human environment was low due to successful prediction and evacuation… In contrast, the death toll of the 1985 Nevado Del Ruiz volcanic eruption was high at about 23000 due to unsuccessful evacuation… Hence, prediction needs to be coupled with evacuation to successfully minimize death toll, otherwise it may prove to be ineffective as a standalone strategy.
I hope this blog can be useful for your geography journey.