Many names are used to refer to pyroclastic clouds: fire clouds, pyroclastic flows, pyroclastic density flows, etc. All of these terms refer to the same thing, referring to the massive amounts of gas and particles that pour out of the crater and travel at breakneck speed. However, pyroclastic clouds are not the best known part of volcanoes, and in fact their presence can have many undesirable consequences.
In this article we are going to tell you what pyroclastic clouds are, what their characteristics and consequences are.
What are pyroclastic clouds
It is a mixture produced during volcanic eruptions, formed by gas and solid particles at high temperatures. Specific, the temperature of pyroclastic clouds is between 300 and 800°C. Once a pyroclastic cloud emerges from an erupting volcano and reaches the Earth's surface, it travels along the ground at speeds ranging from ten to hundreds of meters per second.
As we mentioned in the previous paragraph, pyroclastic clouds are made up of solid particles. These solid particles are called pyroclasts or ashes and they are nothing more than fragments of solidified magma expelled by volcanoes. Depending on the size of the fragments, pyroclastics can be divided into:
- Ash: Particles less than 2 mm in diameter.
- lapilli: Particles ranging in diameter from 2 to 64 mm.
- Bombs or Blocks: Fragments greater than 64 mm in diameter.
For its part, the size of the particles determines the speed and extent of the pyroclastic flow. Those consisting of blocks have little mobility and are generally confined to a range of tens of kilometers from the discharge center. And those flows made of ash and lapis lazuli can reach a radius of 200 kilometers from the center of their discharge.
It is worth mentioning that pyroclastic clouds represent one of the greatest dangers of volcanic eruptions, since they can affect large areas of land in a short period of time due to the speed of the flow. Furthermore, it not only affects human life and infrastructure, but always has long-term adverse effects on the region's climate, soil and water.
How do pyroclastic clouds form?
Not all volcanoes produce pyroclastic clouds during eruptions, but pyroclastic clouds only form on volcanoes with moderate to highly explosive eruptions, such as Strombolian, Plinian, or Vulcan eruptions.
Pyroclastic clouds can form in different ways, here we mention two of them:
- Due to gravitational collapse of the eruption column at high altitude. Collapse occurs when the density of the column is greater than the density of the surrounding atmosphere.
- Through the collapse of a lava dome, this is a bulge that arises when lava is so viscous that it does not flow easily. When the lava dome becomes so large that it becomes unstable, it collapses, eventually causing an explosion.
types that exist
Pyroclastic clouds can be classified based on their composition, the sediments they produce, how they originated, and more. For example, depending on its density, that is, the gas-solid particle ratio it has and the deposits it forms, we can find:
pyroclastic tide
They are characterized by their dispersion (due to their low concentration of solid particles), dynamism and turbulence. The waves can be divided into heat waves and cold waves. They can be below the boiling point of water, like a cold tide, or they can reach temperatures above 1000°C, like a hot tide. Pyroclastic tidal deposits are characterized by their richness in lapis lazuli and lithics (rock fragments that were solid at the time of the eruption). However, it is worth clarifying that jet flows are not generally considered a type of pyroclastic flow.
Pyroclastic flow
They are a flow produced mainly by Purin-style eruptions, with a higher density compared to pyroclastic surges. Deposits formed by lava are difficult to study because they have no apparent internal layers, but in general, their deposits are called ignimbrites and consist of particles of various sizes: from ash to lumps.
Consequences
The eruption of Guatemala's Fuego volcano has claimed at least 65 lives so far. In addition, the violent volcanic activity left 46 people with second and third degree burns, 1,7 million inhabitants were affected to some extent and the ash cloud rose to a height of 10.000 meters.
Last Sunday was the second Fuego eruption of 2018 and the largest in recent years. Such is the magnitude of the tragedy that the lava that comes out of the crater has reached the surface 260 kilometers from the epicenter of the volcano.
The disaster occurred when lava soaked one of its usual outlet ducts, causing it to escape through other natural holes and funnel into four towns near the crater. Thus, the forces of nature ended up burying dozens of people who could not escape from the disaster area.
But lava isn't the only deadly weapon at Guatemala's Fuego volcano. Pyroclastic clouds are one of the main hazards during volcanic eruptions. Also known as the "burning cloud", it reached a height of 1.500 meters when it was ejected.
It is a mixture of volcanic gases, solid matter (ash and rocks of different sizes) and air that is expelled by the volcano during an eruption, it slides along the ground in a rapid and destructive way due to the energy of the volcano. These pyroclastic flows can reach speeds of up to 200 kilometers per hour, and due to their strength and high temperatures, they can advance and even overcome obstacles in their path, calcining under volcanic material or burying the environments they pass through.
As you can see, pyroclastic clouds are quite dangerous and must be taken into account to protect the population against a volcanic eruption. I hope that with this information you can learn more about pyroclastic clouds and their characteristics.