The devastating potential of volcanic eruptions: An explainer

In recent weeks there have been lots of of stories in the news about volcanic eruptions that are currently occurring, most notable Kilauea, Hawaii and just last week Fuego, Guatemala. Both of these eruptions have been devastating in one way or another for the local populations who live in the shadow of these two volcanoes, but the risks at each volcano are different.

The questions I am being asked by my non-geology friends are; what are the differences between these eruptions and is the frequency of eruptions increasing?  In comparison, my volcanology-related friends were initially complaining that the media were reporting lava eruptions from Fuego, which had not yet occurred. What has been really nice to see here, is that the incorrect usage of terminology was fed back to the media via through various routes, and at the time of writing I cannot find any reports on lava eruptions from Fuego.

So what is lava and why were the scientists upset by the use of this terminology?

Lava is molten rock erupting at the surface, often at high temperatures (800-1200 °C), and has the ability to flow like a river. On cooling, the lava solidifies, often forming hard and dense igneous rocks (Figure 1). Eruptions of lava are often effusive and are generally much quieter, passive eruptions as volatiles in the magma can escape. Although dangerous, the resulting lava flows can be monitored and tracked. In comparison, explosive eruptions are much more violent, as any trapped volatiles suddenly depressurise, expelling rocks, gas and ash potentially hundreds or thousands of meters in the atmosphere. These eruptions can often blanket large regions with volcanic debris in a matter of minutes to hours.

The eruption of Kilauea has been lava dominated, whereas the eruption at Fuego resulted in pyroclastic flows.  These are hot clouds (typically between 200-700°C) of rock, ash and gas that descend down the side of volcanoes at great speeds (approximately 70-200 mph). Both type of eruptions have the power to cause devastation but in different manners.

Let’s start with Hawaii. Kilauea volcano is a shield volcano that makes up over 10% of the land mass of Hawaii’s Big Island, with an active lava lake at its summit. The eruption of Kilauea is not new, it has been erupting for the last 30 years, what has happened in the last few weeks is the magma migrated and started to erupt in a new location that is unfortunately in a residential area of the island. At the same time, explosive eruptions have occurred at Kilauea summit vent, sending plumes of ash skyward. The current eruption in the Leilani Estates commenced on the 3rd May 2018 and a month later active fire fountains and lava flows are continuing to pour out, destroying homes and communities in the southeast of Hawaii’s Big Island, displacing many families.

The eruption at Fuego has resulted in heart-rendering images being beamed around the world of local communities that have been utterly devastated. Initial reports suggest little warning of an imminent eruption was observed, but reports appearing in the media currently e.g. BBC and El Periodico, suggest some signs of a potential eruption may have transpired. As it stands no notice of evacuation was given and hence when the eruption occurred, the resulting pyroclastic flow raced down the side of the volcano, sweeping through villages giving no time for the locals to escape. The result being families and local communities were utterly changed within moments. The images coming from the region reminds us just how unpredictable and powerful volcanoes are, and just how much devastation they can cause in a short timescale.

So with the media reporting on these volcanic eruptions, back to the question my friends have been asking. Are the number of volcanic eruptions increasing? Personally, I would argue this is unlikely, technology and the way we communicate has changed drastically over the last few decades. Where once news would have to sent by mail and may takes weeks to arrive, today we share global events almost instantly. As we lack a complete record of past volcanic eruptions, it will never be an easy task to answer this question. In recent years there has been much work to try and catalog known eruptions and to investigate whether there has been changes in frequency. There has been many published reports on this. A database of Holocene eruptions can be found at the Smithsonian Volcano Database.  One of the most comprehensive reports that is freely available to all, is the Global Hazards and Risk Book, originally written as a report for the United Nations For Disaster Risk Reduction  led by Sue Loughlin of the BGS and Steve Sparks of the University of Bristol.

One of the things these databases and reports are highlighting, is the complexity of recording volcanic eruptions. Not only do they highlight the difficulty in identifying all volcanic eruptions in the geological history, the reporting of volcanic eruptions during world events (e.g. world wars) are also shown to decrease. Thus, one thing is for sure; there is not a simple answer to the question “is the frequency of volcanic eruptions changing”. So let’s leave you with a fun fact, whilst you have been reading this blog, it is likely that 20-40 volcanoes globally have erupted, but the majority of these will not have been reported in the media.