Crater Lake, Mount Mazama

Past volcanic eruptions…in the future

You may have heard about the great volcanic catastrophes of Krakatau or Vesuvius and the possibility of a globally devastating eruption at Yellowstone? What if the eruptions that endangered our ancestors were to happen today? Would the effects be much worse or would the human species be more able to adapt and cope with the effects? In this article we will take a look at three major historic eruptions and discuss what effects these eruptions could have on today’s populations.

Krakatau, Indonesia 

In 1883 Dutch colonists and the native people of Indonesia were subject to a major volcanic eruption that occurred on the small island of Krakatau off the coasts of Java and Sumatra.

If the 1883 eruption was repeated today it would have a much more devastating effect. The eruption and subsequent collapse of the volcano killed around 36,000 people, but since 1883 the population has increased over >100 times in the affected areas. The main causes of death were a ~40m high tsunami triggered by the inward collapse of the volcanic island. Another cause of death was burning and asphyxiation from pyroclastic density currents (hot, dense, ground-hugging clouds of rock, ash and gas). As the 2004 Indian Ocean Tsunami showed, Indonesia might not be able to adequately support those that would be in harms way, nor would it be able to recover quickly from such a disaster. Luckily, it would probably take hundreds of years for a repeat of the 1883 eruption to take place, as first Krakatau needs to rebuild itself. For now the Javanese and Sumatran people are probably safe, although smaller eruptions or collapses at Anak Krakatau (child of Krakatau) could have serious consequences along the coastlines of Indonesia.

Java coast once destroyed by Krakatau
An area of Java once destroyed by the 1883 eruption of Krakatau. Credit: S.Wanmer 2014

Deccan Traps, India

The Deccan Traps was formed by a massive outpouring of basalt lava known as a Large Igneous Province (LIP) or Flood Basalt, which occurred ~65.5 million years ago. This volcanic event may have helped cause the extinction of the Dinosaurs and allowed mammals to become the most dominant species on the planet.

The eruption of the Deccan Traps occurred over millions of years at a time when humans did not exist. Nowadays the capital city of India sits on top of these, up to 2.4km thick basaltic lava flows.

The basalt lavas were lethal to the dinosaurs for many reasons:

  1. They would have released huge amounts of gases which may have led to global cooling (due to SO2) followed by more prolonged and more drastic global warming (due to the release of CO2 and CO)
  2. The volume of SO2 released into the atmosphere could have produced vast amounts of acid rain that would have helped lead to starvation through the death of vegetation

With eruptions occurring over millions of years and the highly adaptable nature of the human species it is likely that we would be able to adapt to changes in the climate, changes to our food production and living habits if an event on this scale took place in the future.

Mount Mazama/Crater Lake, Oregon, USA

About 7,700 years ago a cataclysmic eruption took place at Mount Mazama in Oregon. The eruption expelled so much magma from the chamber beneath the volcano that the volcano collapsed in on itself in a caldera forming eruption which created the stunningly beautiful Crater Lake. The hundreds of tourists that visit Crater Lake each year would find it hard to imagine the disaster that happened here 7,700 years ago.

Before the eruption the areas was home to one of the largest volcanoes in the Cascade Range within a proposed height of 4572-4877m [1]. It has been suggested that Mount Adams in Washington is the best representative as to what Mount Mazama may have once looked like in width and height before the decapitating eruption [1].

Mount Adams and Mount Mazama
Mount Mazama may have once looked like Mount Adams. Credit: S.Wanmer 2012

If a volcano in the Cascade Range, or Yellowstone, were to erupt, just as Mount Mazama did, today the whole world would be affected. The ash and aerosols in the eruption would shut down whole communication networks across the USA, especially in the state where the eruption occurs. This would bring a halt to shipping, rail and road transport. There are many flight paths over the Cascade Range which would be affected by an eruption, leading to flight cancellations and diversions all over the world. Agriculture in many states in the US would be destroyed which could lead to food shortages, not just in the local area. The volume of ash would bring cities to a standstill and clog sewage water systems, possibly helping the spread of diseases.

During the eruption and subsequence collapse, Mount Mazama covered an area over 800,000km2 in a measurable and significant amount of ash, covering at least 8 states in the USA and ‘the southern part of 3 Canadian Provinces’ [1]. Today this would have a huge effect on food production in the US. It’s not just food that would be an issue though as the ash and aerosols could cause health problems for the millions of people that live in the vast area that could be affected. The weight of ash could easily collapse roofs/buildings – especially if mixed with rain – leading to homelessness. All this would undoubtedly lead to total confusion, loss of life and even riots. An evacuation on a scale that on-one has seen before would be needed, costing billions of dollars.

With modern technology and the presence of the Cascade Volcano Observatory and Yellowstone Volcano Observatory, the chances of a sudden and unexpected volcanic catastrophe in the Cascade Range, or Yellowstone, is highly unlikely.

Crater Lake, Mount Mazama
Crater Lake, formed by the eruption of Mount Mazama. Credit: S.Wanmer 2015


By researching historic, present and future eruptions at volcanoes around the world geologists are forever increasing their knowledge and understanding of all types of volcanic eruptions. In the not so distant future we may be able to predict volcanic eruptions with a high percentage of certainty and enough time for large-scale evacuations. Mitigation and engineering may improve so that evacuations aren’t even necessary any more. Overall though it is unlikely that any globally catastrophic eruption will occur tomorrow, or even the day after that. But our planet is dynamic and may events have occurred to challenge our species existence in the past and the earth may once again surprise us in the future – when in the future though, no-one knows!


[1] Fire mountains of the West; the Cascade and Mono Lake volcanoes. 3rd edition. S.L. Harris. Mountain Press Publishing Company. 2011. Pg 454.

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