SCIENCES

Volcanoes: A Dangerous Sight

On the surface of our planet, there are several hundred active volcanoes and every year geologists record between 30 and 50 eruptions of varying size. During the eruption, the volcanoes offer a breathtaking spectacle, but are very dangerous for the surrounding population. More than 2000 years ago, the city of Pompeii and its population were decimated by Mount Vesuvius in southern Italy, while in 1883, the Krakatoa volcano in Indonesia claimed tens of thousands of victims. In order to understand this natural phenomenon of our planet, we will examine their formation, their different forms and their distribution on the surface of the globe.

The area near the Calbuco volcano in southern Chile was placed on red alert after the volcano erupted on April 22, 2015. © Rafael Arenas/Reuters

By: Nenad Tomic

Advertising

Read More

The mechanism of eruptions

For millions of years, the Earth's landform has been shaped by volcanic eruptions. When a volcano awakens and becomes active, it is under the earth's crust, at a depth of about ten thousand meters, that the phenomenon begins its journey to the surface. In extremely hot spots, the rock is in a liquid state. It is the magma that, under the effect of the pressure of the earth's crust, is pushed towards the outlet. Magma is slowly advancing through cracks that have appeared as a result of the movement of tectonic plates. It is through this conduit, which geologists call "the chimney", that magma exits by projecting ash, water vapor or small solidified rocks. Once the magma reaches the surface, it is called "lava."

Volcanologists distinguish between two main types of eruptions: effusive and explosive. An effusive eruption occurs when lava flows out of the crater from the volcano more or less slowly. It is impossible to stop the lava that destroys everything in its path.

On the contrary, the explosive eruption results in earthquakes and the projection of rocks around the crater and large amounts of ash into the air. This type of eruption presents a great danger: the speed of the phenomenon often takes the population by surprise, as they do not have time to evacuate the area around the volcano.

Most volcanoes are located on the ocean floor and form in areas where two tectonic plates move away from each other (rift zone). Several islands were formed in this way, such as the Canary Islands archipelago or Cape Verde.

In areas where two tectonic plates are in a subduction zone, i.e. when they move towards each other, magma, rising to the surface, forms volcanoes.

But there are also the so-called "strange" areas where volcanoes appear in the middle of a large tectonic plate. These "fire spots" or "hot spots" are rare, and scientists are still looking for explanations for their formation because they are located in the center of a plate. This is the case of the volcanoes on the islands of Hawaii, the Piton de la Fournaise on the island of Reunion or the volcano of Mount Cameroon.

The Ring of Fire

98% of the world's volcanoes lie on the edge of the Pacific Plate, which scientists call the Pacific Ring of Fire. Volcanoes are aligned along this plate surrounding the ocean for 40,000 kilometers. Thus, many volcanoes are found along the west coast of the South American continent (Peru, Chile), in Central America (Mexico), in Asia (Japan, Philippines, Indonesia), and in Oceania along the Tonga and Kermadec faults north of New Zealand.

The Pacific Ring of Fire. © Anoushka Notaras / RFI Savoirs

On the side of the Atlantic Ocean, there are volcanoes at the level of the mid-ocean ridges (Canary Islands and Cape Verde Islands).

In Europe, two regions stand out for their active volcanoes: Italy and Iceland. In Italy, Mount Vesuvius, which overlooks the city of Naples, is a constant threat to the population, which is often forced to evacuate. In addition, Stromboli, north of Sicily, regularly emits large quantities of lava, the last of which occurred in 2019.

In Iceland, many active volcanoes erupt very frequently. Icelanders and Europeans still remember the eruption of Mount Eyjafjallajökull in the spring of 2010. The volcano expelled a gigantic amount of ash, causing air traffic in Europe to stop for several weeks.

The "super volcanoes"

Geologists have also discovered volcanoes that, during eruption, can spew huge amounts of lava and ash. Generally speaking, a volcano spews about 1 km³ of lava and ash. For example, Mount Pinatubo in the Philippines, when it erupted in the summer of 1991, which is considered the largest eruption of the twentieth century, spewed 10 km³. For a super volcano, these projections of ash and pumice can even go between 1,000 and 3,000 km³, a quantity more than enough to cover a territory the size of France!

There are at least two "super volcanoes" listed in the world. At the center of Lake Toba on the island of Sumatra in Indonesia lies a sleeping monster: during its last eruption, 73,000 years ago, it emitted ash that blocked solar radiation in the Earth's atmosphere, plunging the entire planet into a cold period known as the "Ice Age" that lasted 1000,<> years.

In the United States, in Yellowstone National Park, there is a "super volcano" that scientists are monitoring very closely. In history, this volcano has already erupted three times, considerably modifying the topography of the western part of the American continent. If this volcano were to erupt, the amount of projections could cover the entire territory of the United States and the global surface temperature could drop by 10°C for 10 years, threatening the extinction of many animal and plant species.

Our selection on the subject:

• Listen:

→In Iceland, volcanoes are
waking up→ Do volcanic eruptions have an effect on the climate?
→ What's new about volcanoes?
→ Why do volcanoes rumble?
→ What's going on under Nyiragongo Volcano?
→ Why live below volcanoes?
→Why volcanoes?
→ How can we change the way we look at the Earth's seismic and volcanic activity?

• To read:

→ Eruption of a volcano in the Canary Islands: respite or end of the lava flow?
→ "Volcanoes of France", a book by Frédéric Lécuyer → Spain: a hundred houses destroyed in the eruption of a volcano in the Canary Islands

→ Always be wary of a sleeping volcano!

NewsletterGet all the latest international news straight to your inbox

Subscribe now

Keep up to date with all the latest international news by downloading the RFI app

Share:

Read on the same topics:

• Environment
• Natural disasters
• Knowledge Science