When the earth spits fire
Today, there are about 1,500 volcanoes worldwide, that are considered active, and 50 to 60 eruptions are recorded each year. Volcanoes that have erupted in the last 10,000 years are classified as active. Volcanic eruptions are therefore not uncommon. Whether on the Canary Islands, Hawaii, Guatemala or in the Eifel – the earth spews hot lava again and again.
Canary Islands: In the morning of September 19, 2021, several shallow earthquakes with magnitudes greater than 3.0 shake the ridge of Cumbre Vieja (28.569204, -17.837197) on La Palma, in the afternoon lava fountains form in several places of 2 longer earth fissures, ash clouds rise up to 1500 meters high.
Already the next day an 8-15 meter high lava front has moved up to 2.9 km to the west, 6000 inhabitants of the region are evacuated and about 300 houses are destroyed by the lava. On September 25, the volcanic cone collapses, with part of the western flank slipping away; the ash cloud now reaches a height of 3500 meters. Finally, on September 29, the lava reaches the coast for the first time, flowing into the Atlantic Ocean and forming a 500-meter-wide estuarine delta.
By the end of the eruption on December 13, 2021, the responsible land registry office reports more than 1600 destroyed buildings, 1300 of them residential. In addition, more than 70 kilometers of roads and 370 hectares of plantations are buried under lava flows, it will be the longest known and also the – with regard to the damage – most consequential eruption of a volcano on La Palma.
Hawaii: After Kilauea (19.4069, -155.2877) has been active for several weeks, on May 3, 2018, in the small community of Leilani, about 20 km east of Pu’u O’o crater, the ground suddenly ruptures, hot steam and toxic gases are followed by thin lava that subsequently buries about 35 km² of land, additionally filling Kapoho Bay and forming about 3.5 km² of new land. By the time it ends on September 4, 2018, the eruption destroys about 700 homes, vaporizes a lake (Green Lake, the largest freshwater reservoir in the Hawaiian Islands), and damages a geothermal power plant that provides energy to about a quarter of the island. At a cost of more than $800 million, the eruption is the most consequential in the U.S. since Mount St. Helens erupted in 1980.
Fig. 1: The Hawaiian islands in the Pacific Ocean (source: Google Earth); fissure eruption in the middle of the residential area (Source: USGS)
Guatemala: The people around Volcan de Fuego (14.4747, -90.8850) are used to the regular eruptions of the volcano in their neighborhood. The lava is viscous and usually flows only a few hundred meters. But on the morning of June 03, 2018, the volcano is shrouded in clouds, the people of San Miguel Los Lotes cannot see the extent of the eruption and the ash cloud and are thus surprised by pyroclastic flows. The whole village is wiped out, 114 people die. On June 17, the search for another 197 people still missing is suspended.
It is impossible to say where and when such events take place, but we will deal with some questions here: What is the geological mechanism behind it? Can something like this happen elsewhere? What does this mean for volcanic risk assessment?
Hot Spots, Supervolcano and Stratovolcanoes
Hawaii and the Canary Islands are hot spots
Deep inside the earth it is about 5,000 degrees hot. Partly this heat originates from the formation of the earth nearly 5 billion years ago. Atomic decay processes – similar to those in a nuclear reactor – also ensure a constant supply, so that it will take billions of years until the earth has cooled down completely. Like any hot body, the Earth wants to transfer this heat energy to its colder surroundings. The heat transport from the inside to the outside is carried out by viscoplastic rock masses that move from the bottom to the top at a rate of only a few centimeters per year. Near the earth’s surface, they cool down and then sink back into the earth’s interior, ready for the next round. However, this does not always happen evenly everywhere: In some places, where the hot rock mush “shoots up” faster than elsewhere, perhaps only a few centimeters per year, the heat transport is particularly effective. Geologists refer to these places as hot spots or heat anomalies.
At the earth’s surface, a hot spot acts like a cutting torch held to a steel plate from below: It first becomes red hot there, until eventually a hole is created and the flame passes through to the top. If the plate moves slowly, the first hole will close again and a new one will appear elsewhere.
Exactly in this way the chains of the Hawaiian or Canarian volcanic islands were formed: The Pacific Ocean floor near Hawaii slowly but steadily migrates northwestward, but the hot spot remains stationary. That’s why the oldest and long-extinct volcanoes in Hawaii are at the northwestern end of the island chain, and Big Island at the other end is currently right above the hot spot. Here lies Kilauea, the most active volcano in the island chain. But because the northwestward migration of the Pacific Ocean floor continues steadily, the volcanoes on Big Island will also eventually die out, and a new volcano will form farther southeast. In fact, it’s already happening: southwest of Big Island, in the depths of the Pacific, Lo’ihi is getting ready to rise above the surface in the not-too-distant future.
In the case of the Canary Islands, the ocean floor of the Atlantic moves in the opposite direction from west to east; the oldest islands are Fuerteventura and Lanzarote, La Palma is one of the youngest, along with El Hierro.
However, Hawaii and the Canary Islands are not the only volcanic hot spots on earth. Geologists have now identified more than 60 such hot spots, most of which, however, are located under water or in remote regions and are therefore relatively harmless. At this point, we will therefore limit ourselves to only a few that could cause problems:
Eifel (50.4126, 7.2716): Let‘s start with the home of the KA: Located only about 100 km south of Cologne, the Eifel has been the scene of recurring volcanic eruptions for about 800,000 years. The area north of Koblenz is covered with smaller and larger volcanic cones. But the hot spot takes long breaks, because the last really violent eruption that threw ash as far as southern Sweden was 11,000 years ago. Nevertheless, nothing is extinguished here yet, because carbon dioxide emissions at Laacher See and an impressive geyser near Andernach show that there is no peace in the underground yet.
Fig. 2: Carbon dioxide emission at Laacher See (Source: Paus)
Etna (37.7511, 14.9965): Etna on Sicily is Europe‘s most active volcano. Every few years it attracts attention by breaking out. Nevertheless, due to its diameter of up to 30 km, the nearest settlements are far enough away from the main crater and are therefore not threatened should an eruption occur. However, it has an unpleasant characteristic: just like in Hawaii, crevices in the ground at Etna far away from the summit can suddenly rupture, and liquid lava can flow. Like parasites, the remains of these eruptions stick to the wide flanks of the mountain. During such an eruption in 1669, even parts of the port city of Catania were overrun by lava, 30km away from the main crater.
South-Australia (-37.8463, 140.7768): Here, about halfway between the cities of Adelaide and Melbourne, things currently seem to be as peaceful as in the Eifel, although the most recent eruptions were only 4,500 to 5,000 years ago. For the city of Mount Gambier, which lies directly next to the mountain of the same name, this volcano and the more remote Mount Schank are now a tourist attraction. However, there are no traces of major fissure eruptions, such as on Etna and Hawaii.
Fig. 3: Crater Lake at Mount Gambier, South Australia (Source: Paus)
Iceland (64.1502, -18.8961): The situation is quite different in Iceland, where hot springs, geysers and a constant trembling of the ground are part of everyday life. A volcanic eruption in 1967 created a new island off the coast (Surtsey), in 1973 there were eruptions on the Westmännar Islands for weeks and in 2010 a rift eruption at the volcano Ejafjallajökull blew up so much ash that air traffic had to be stopped in half of Europe. Even worse was the eruption of the Laki in 1773: sulphurous gases then blew as far as Central Europe and led to numerous casualties. Nowadays such an outbreak would cause our entire electronic communication network to break down, because acid rain and fog would lead to massive short-circuits in the transmitters.
Fig. 4: Outbreak on Heimaey, Iceland 1973 (Source: Ewerts)
Yellowstone (44.4182, -110.5719): Although no conical mountain can be seen, Yellowstone is one of the largest volcanoes on earth: after its last really extensive eruption 640.000 years ago, only a collapse crater of 80 km length and 55 km width remained, in which today the national park of the same name with its geysers and bubbling mud pools is located. Ejected material from this eruption can be found in half of North America, and dust and sulfuric acid are thought to have caused twilight and uncomfortable weather in the atmosphere for weeks or months around the world. In today‘s circumstances, that would be a global disaster. Geologists have found that such apocalyptic eruptions occur approximately every 600,000 years. So the next one is overdue. Nevertheless, there is no reason to panic: in view of such long periods, an outbreak is no more likely (or unlikely) today than at the time of the Roman Empire.
Supervolcanoes
Due to the global dimension of its eruptions, Yellowstone is also one of the so-called supervolcanoes. These are volcanoes that do not necessarily have to be fired by a hot spot, but occupy an outstanding position in terms of their risk potential. Two of these volcanic giants are to be discussed here:
Toba (2.6258, 98.7919): The Toba volcano on the Indonesian island of Sumatra left behind a 100 km long and 30 km wide burglary crater, which is now filled with water, during its last eruption some 74,000 years ago. This eruption had an explosive force of about one gigatonne TNT, whereby the Indian subcontinent was covered with an ash layer about 15 cm thick. One – albeit controversial – theory says that at that time mankind had passed through a „genetic bottleneck“ and, especially in Africa, only a few thousand individuals survived the consequences of the Toba outbreak. After the devastating tsunami in the Indian Ocean in 2004, which was triggered by an earthquake off the coast of Sumatra, geologists were concerned that the Toba volcano could be awakened from its twilight sleep. So far, however, nothing of the kind has happened, fortunately it remains quiet.
Campi Flegrei (40.8273, 14.1394): A smoking volcanic vent in the middle of the city, countless other remains of eruption craters of various sizes and ages as well as areas where the ground has risen and sunk by up to 8 metres within decades: these are the Campi Flegrei, a densely populated area that begins just west of the city of Naples and extends as far as the island of Ischia. Geologists have found the remains of a huge eruption 37,000 years ago, which can be compared to the largest historically known eruptions (Tambora 1815, Krakatau 1883). A similar eruption would now devastate large parts of the western Mediterranean and wipe the city of Naples off the map. However, it is more likely that another volcano will do this: Vesuvius east of Naples; a stratovolcano that has been sealed since its last eruption in 1944 and will eventually regain air with an explosion.
Fig. 5: Sulphur vapours on the Campi Flegrei near Naples (Source: Paus)
Volcan de Fuego is a Stratovolcano
Volcan de Fuego is one of the volcanoes along the Pacific Ring of Fire, a volcanic belt that surrounds the Pacific Ocean from three sides. Volcanism is triggered by the subduction of oceanic plates (e.g. Pacific plate, Nasca plate) under continental plate (e.g. Eurasian, Australian or South American plate). Through the conical mountains with steep flanks and one or more summit craters, stratovolcanoes look like they are out of a picture book. But each of them carries more risk than the volcanoes described above, because they erupt much more frequently than the supervolcanoes and develop higher destructive power than the hot spot volcanoes. Mostly the intervals between the eruptions last only decades or centuries; sometimes also some millennia, rarely however still longer. In addition, stratovolcanoes tend to explode suddenly, pouring hot ash and rock avalanches over their surroundings for miles.
Among the most dangerous stratovolcanoes are currently Vesuvius (Italy, 40.8223, 14.4289), Tambora (Indonesia, -8.2462, 117.9905) and Popocatepetl (Mexico, 19.0236, -98.6225). These three volcanoes have the potential to wreak immense destruction far beyond their immediate surroundings. And not in a few tens or hundreds of thousands of years, but possibly soon.
Fig. 6: View of Popocatepetl volcano (Source: Paus)
Assessment of volcanic risk
Volcanoes are as diverse as the risks they pose. Sudden and „unannounced“ eruptions are just as possible as weeks of threatening rumbling in the mountain, which triggers large-scale evacuations of the surrounding area but is not followed by an eruption. Also, nobody can predict today whether tomorrow, next year or the next decade one of the supervolcanoes will make itself felt or whether a hot spot will decide to be active. Unexpectedness is the name of the game.
This is how it happened in 1943 in western Mexico: from one day to the next, a crevice in the earth was ruptured in a field of maize from which gas and ashes burst. A few days later, lava followed and soon buried the nearby village of Paricutin, after which the newly formed mountain was named. The eruption lasted nine years, then the volcano went silent again. The emergence of Paricutin (19,4931, -102,2516) shows amazing parallels to the events in Hawaii in 2018, although there is no hot spot and certainly no super volcano in this area. The Paricutin belongs to a 40,000km² Michoacan-Guanajuata volcanic field, which comprises more than 900 monogenetic cinder cones, i.e. volcanoes that erupt only once or only within a short period of time and then remain silent forever. When and where the earth will re-open in this area is uncertain. The further away the site is from the volcano, the less likely it is that damage will be caused by ejected rocks or lava flows. Damage caused by volcanic ash, on the other hand, can still occur several hundred kilometres around the site. It is therefore not easy to understand the risk of volcanism.
Fig. 7: Example of a volcano vulnerability curve in K.A.R.L.
With K.A.R.L. we use a combination of different information and data sources, such as volcanic type, eruption history, removal of potentially endangered sites from the eruption centre and the site-specific sensitivity of buildings, means of production and goods to the consequences of volcanic activity. However, it is still not possible to predict volcanic eruptions, but in this way the risk of suffering damage from volcanism can be limited and quantified quite well.
If you would like to discuss this paper with us, we look forward to hearing from you.