The Science Behind Volcanic Smoke Rings

Volcanoes are openings in the earth’s crust that serve as an outlet for the escape of magma and gases. The magma varies in viscosity based on factors like temperature, silica content and the  amount of dissolved gases.

These factors not only determine whether the magma will flow freely or will have more resistance  (viscosity). It also determines whether condensed gases will be able to escape from the magma and form smoke rings.

Let's do a quick run-through of our knowledge of volcanoes and try to understand what happens to these trapped gases inside the mouth of a volcano.

How do volcanoes form?

There are over 1500 active volcanoes on the Earth, and possibly more under the oceans. Some scientists believe that 80 percent of the volcanic eruptions on Earth take place in the ocean. 

Hawaii, Alaska, California, Oregon, and Washington host the vast majority of volcanoes in the U.S.

There are different ways to define an active volcano, but generally, a volcano is known as active if it has had at least one eruption in the last 10,000 years.

It might be difficult to imagine, given the violence of an eruption, but most volcanoes are formed in a slow process. These volcanoes form when magma from within the Earth's upper mantle works its way to the surface. Once at the surface, it emerges to form lava flows and ash deposits. 

The volcanoes form through many cycles of such eruptions. The lava cools down after coming in contact with air, which eventually hardens into layers that ultimately form the volcano. This process occurs repeatedly over thousands of years and, over time, as the volcano continues to erupt, it often becomes bigger and bigger. 

What causes volcanic eruptions?

Magma rises from the mantle when it melts. This can be triggered by tectonic plates pulling apart or pushing down against one other, or in 'hot spots' where the Earth's crust is thin.

The magma, which is relatively light, rises to the surface and ultimately escapes through volcanic openings. The explosive eruptions that we often think of when we hear the word eruption happen infrequently and in specific kinds of volcanoes.

These takes place when the pressure gets too high. It can also happen when the magma comes in contact with water. The steam formed as a result is enough to give the volcano the required pressure to erupt.

But not all volcanoes erupt. The ones that do are known as active volcanoes.

These volcanoes are a subject of a lot of research and surveying despite the obvious challenges and hazards.

What are the different kinds of volcanoes?

There are different types of volcanoes. The simplest are cinder cones. They occur when particles and blobs of lava are ejected from a volcanic vent. Over time, this builds up a circular or oval-shaped cone, usually with a bowl-shaped crater at the top. Cinder cone volcanoes tend to be short, only growing around 1,000 feet high.

Composite, or stratovolcanoes are some of the world’s most well-known mountains: Mount Rainier and Mount Fuji are both stratovolcanoes. In these volcanoes, magma from deep within the Earth in channeled to the surface. The lava breaks through to the surface through vents or  fissures and form steep-sided cones. Composite volcanoes can explode violently and may erupt steam, ash, and rock instead of magma. This type of eruption is collectively known as a pyroclastic flow.

Shield volcanoes, on the other hand, have gentle slopes. The eruptions of these volcanoes are more frequent but typically non-explosive. Their magma has low viscosity, so it can travel for great distances down the shallow slopes of the volcano.These volcanos build up slowly over time, with hundreds of eruptions, creating many layers, rather than exploding  catastrophically. Mount Kilauea in Hawaii is a shield volcano.

Some volcanoes form lava domes. These are created by small masses of lava, with high viscosity and acidity, which piles up over and around the vent. The dome grows as the lava inside expands. Lava domes can explode violently, releasing a huge amount of hot rock and ash. An example of a dome volcano is Puy de Dome in France.

Eruptions of all kinds are damaging to life, though some, like explosive eruptions, have more destructive power. While eruptions are an exciting topic to study, smoke rings typically happen when no eruptions are taking place.

Explaining the smoke rings

A theory by Boris Behncke, a volcanologist at Italy’s National Institute of Geophysics and Volcanology, says that these rings are, in fact, not smoke but water vapor and other compressed gases. 

The smoke rings are challenging to study as they quickly disappear into the atmosphere. A probable smoke ring explanation was found by a group of scientists led by Fabio Pulvirenti. Pulvirenti is a senior fellow at NASA’s Jet Propulsion Laboratory.

The approach of this group was quite radical. They accepted that studying this phenomenon using physical equipment would be difficult, because of its rarity. Instead, they created simulations on a computer.

They fed the various parameters of the volcanic smoke rings, such as speed, height, and cooling time into a computer program. This program was based on theoretical concepts of fluid mechanics that defined how the gases interacted with the magma and the physics of vortex formation.

Then they varied the parameters that could affect smoke ring formation. They found that changing the pressure and geometry of the vent to particular values led to the appearance and disappearance of smoke rings.

In the simulation, condensed gases, predominantly water vapor, escaped from the magma and was propelled from the volcano’s vent. This volcanic vapor, which is warmer and less dense than the surrounding air, drifts upwards and starts expanding.

The mechanism is akin to what happens in the mouth of the smoker when he blows smoke rings. It has been established that the volcano needs to have a reasonably narrow opening in order for the rings to form.

But the mystery doesn’t end there.

Why don’t these volcanoes always blow smoke rings?

The right question, then, isn’t how they happen but why they don’t happen most of the time when the conditions are met. And the probable answer is quite simple: wind. 

Fast winds don’t let the smoke rings form, or at least they are not big enough to be observable.

Wrapping up

The early metaphysicists and scientists developed the understanding we have today of the world by observing nature. Today, we see a disconnect between our researchers and nature.

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At the same time, the technology and research methods we use today are crucial to our understanding of nature, as demonstrated by Pulvirenti’s team.

Choosing between the two will always remain a dilemma for scientists. And they have to find a balance to do truly inspiring work.

The study shows that no matter how advanced technology gets, nature will always have a thing or two to teach us.