Are the secondary impacts of volcanic eruptions more dangerous than the primary impacts?

Volcanic eruptions are unusual in the way that generally they don’t cause as many immediate deaths than other natural hazards such as earthquakes. they are a hazard that can be reasonably easy to predict meaning any eruption can be foreseen with enough time to evacuate people who are at risk of the volcano and reduce the risk of the eruption. therefore it is generally accepted that the secondary impacts of a volcanic eruption pose the greatest danger to people. However, there are still examples in history where the primary impacts of a volcanic eruption have been more deadly than what is usually expected of a volcano.

Mount Tambora, Indonesia (photo credit:

The secondary impacts of a volcanic eruption are worse than the primary impacts because they are long-term so will affect more generations of people. an example of this is the effect larger volcanoes can have on the global climate. there have been many volcanic eruptions that have caused changes in the earth temperature leading to longer winters. Mount Tambora in Indonesia is well-known for being the cause  of what was known as the year without summer in 1816. This a time where global temperatures decreased by about 0.4-0.7 degrees C, caused by the increase in sulfur levels in the atmosphere, which caused crops to fail worldwide leading to increased famines. in many areas of the Northern hemisphere snow fell in what was normally the summer months with snow 30m deep settling in Quebec city. In Northeast USA a dry fog was present which glowed red with the sunlight and was not removed by rain or wind. the changes in climate also led to the pattern of the Indian monsoons being disrupted which led to 3 failed harvests and famine which aided the spread of Cholera around the world. famine was also present in the UK, Germany and Ireland and this resulted in food prices rising dramatically which in turn led to violent demonstrations, riots and looting as the cause at the time was unknown. in total it was estimated that around 71,000 people died as a result of the volcanic eruption of Tambora and only 11,000 of those was as a direct result of the volcano. this illustrates that the secondary effects of a volcanic eruption can sometimes be a lot more devastating than the initial effects they can cause.

Eyjafjallajokull, Iceland 2010 eruption (photo credit:

The secondary impacts of a volcanic eruption can also be considered worse than the primary effects due to how they can affect the economy of countries around the world in the long-term. the 2010 eruption of  the Eyjafjallajökull eruption in Iceland caused the disruption of air travel for weeks as ash in the atmosphere made it dangerous to fly in. however this led to an even longer term issue of the economic costs for countries all over the world due the disruption of trade and business travel. for example, in the UK 13 travel firms collapsed in 2010, BMW suspended manufacturing at 3 of its plants in Germany due to a lack of supplies, and there were fears that some supplies of fresh items that were normally shipped by air into the UK would become unavailable. In Africa there was consequences too such as the $150,000 a day in Zambia’s flower and vegetable industry, whilst in Kenya 400 tonnes of flowers had to be destroyed as they were unable to be shipped by air to their locations.

However, despite the large amount of secondary impacts of volcanic eruptions there are still large amounts of primary impacts when volcanic eruptions occur. Volcanoes can cause large areas of agricultural land to be devastated as lava flows can cover fields of crops and kill livestock leading to short-term food shortages. deaths can occur due to the lava flows but usually due to the toxic gases emitted by the volcano. also with the case of composite volcanoes the pyroclastic flows can be responsible for the destruction of infrastructure, buildings, and lives. the most devastating volcanic eruption ever to occur on the planet has been reported to have been that of the super volcanic eruption at lake Toba in Indonesia which occurred between 69,000 and 77,000 years ago killing most of the humans on earth at the time, leaving around only 10,000 survivors. although an eruption of this size was certainly going to have had many global impacts as well, it is clear the initial devastation was great too. another example of a deadly volcano was that of Mount Vesuvius in Italy in AD. 79 which killed an estimated 18,000 people including most of the residents of Pompeii. therefore there is evidence to suggest that the primary impacts of a volcano can be greater than the secondary impacts as there have been several volcanoes that have killed thousands in an eruption. however, the most recent volcanic eruptions seem to be causing less and less deaths than before so secondary impacts could become a greater issue in the future. the reduction in deaths could be due to the fact that we aren’t experiencing as many deadly volcanoes as there has been in history or because the advances in volcano monitoring have enabled accurate predictions of eruptions allowing for people to be prepared for a volcanic eruption and hence reducing the number of lives lost.

Lake Toba, Indonesia (photo credit:

In my opinion the secondary impacts of volcanic eruptions are more dangerous than the primary impacts as they can often be of a much larger scale, affecting not only those in close proximity to the volcano but those who live far away from it. this risk volcanoes pose to changes in the climate are too great to be ignored as there have been examples of world famine caused by volcanic eruptions and with the growing population of the world today, the risk of famine could be greater should that event happen again. I also think that the amount of primary effects such as deaths will continue to decrease overall as technology and education have grown meaning people know how to react to an eruption and will have the means to do so, on the whole. however, it could also be argued that just as technology will reduce the risk of primary impacts, it could also reduce the risk of secondary impacts as agricultural technology and knowledge is greater than when the previous famines caused be volcanoes occurred so it could be assumed that humans will be able to cope with changes to the climate that are caused by volcanic eruptions.



  • information on the amount of deaths caused by several volcanic eruptions sourced from:
  • information on the econimic impacts of the Eyjafjallajökull eruption sourced from:
  • information on the eruption at Mount Tambora sourced from
  • information on the ‘year without summer’ caused by mount Tambora sourced from:


location of 7 of the worlds super volcanoes (photo credit: coolgeography)

Super volcanoes at a first glance don’t appear like normal volcanoes. our stereotypical image of a volcano is a cone-shaped mountain, but a super volcano is the complete opposite. They are large depressions in the ground, that have a magma chamber that is capable for erupting 1000km2 of material. to put this into perspective, a normal volcano has a magma chamber of 1km2 worth of material. In other words super volcanoes are big.  There are about 40 super volcanoes known to the world however most of these are extinct. for example there are two extinct super volcanoes in Britain one in Glencoe in Scotland and another in the peak district.

Super volcano formation

A super volcano forms when the magma cannot escape through the crust like a normal volcano. Therefore it spreads our underneath the crust, putting pressure on the crust creating an uplift bulge as the magma forces the crust above it to rise, into a dome shape. As the pressure increases cracks appear on the surface of the crust and hot gases and ash start to escape from the magma trapped below. finally the crust above the magma chamber breaks away and collapses leaving a depression with steep sides called a caldera. this is the super volcano.

Yellowstone super volcano

Yellowstone is the most famous of all of the super volcanoes in the world and one of the most dangerous as it is located near a populated area in America. It’s caldera is massive: 80km long and 45km wide. It has erupted 3 times so far; once 2.1million years ago, once 1.3 million years ago and once 640,000 years ago. It has been suggested that Yellowstone has a cycle of 600,000 to 700,000 years, which means that an eruption could come any time soon. There have been signs that Yellowstone may erupt in the near future. There have been signs of increased activity inside Yellowstone’s vast magma chamber and the caldera is beginning to bulge up underneath Yellowstone lake. In other places the ground has risen as much as 70cm.

Yellowstone national park (photo credit: national geographic)

So what if Yellowstone does erupt soon? what will happen? In the short-term, large earthquakes would be felt immediately before the eruption and a 15cm layer of ash would cover everything within 1000km and 1 in 3 people affected would die. The sheer force of the eruption  would kill all life within a 50km radius due to the explosions for lava, ash and rock. This would cause severe damage and lead to transport links, electricity supplies and water supplies to be severely damaged or destroyed. The eruption would be a global natural disaster, global temperatures will decrease as ash spreads around the world and blocks out sunlight, these temperatures could drop by as much as 16 degrees C, which could trigger a mini ice age. This would lead to crops failing causing global food shortages and result in further deaths, it has been estimated that the global death toll would reach at least 1 billion. The ash would take around 5 days for it to reach the UK.

This all sounds bad enough, but it has also been suggested that a super volcano could trigger other volcanoes or super volcanoes that are near by to erupt as well. If that happened then the whole planet would be facing a major natural disaster.