Volcanic avalanches may be more destructive than previously thought_tio2 kit thermo     DATE: 2022-08-17 23:32:19


Volcanic avalanches may be more destructive than previously thought

High-pressure pulses in these flows act like a jackhammer on obstacles

Pyroclastic flows are volcanic avalanches of gas, ash and rock. They possess rhythmic, high-pressure pulses as a result of turbulence, a new study suggests.

Stocktrek Images/Richard Roscoe/Getty Images Plus

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By Nikk Ogasa

Avalanches of ash, gas and rock can cascade downhill during volcanic eruptions. Known as pyroclastic flows, they may be even more dangerous than scientists had suspected.

Those pulses are the result of turbulence, lab and field measurements now show. Within these slides, pulses of high pressure form. Those pressures can be far stronger, and more destructive, than hazard assessments typically assume. Researchers shared their new finding this past December 15 in Nature Communications.

“It’s not a small difference,” says Gert Lube. He’s a volcanologist at Massey University. That’s in Palmerston North, New Zealand. A conventional hazard assessment might suggest a certain flow will only burst windows. But, he says, the pressures might be so strong “they knock down the walls of the building.”

Explainer: The volcano basics

Pyroclastic flows are the deadliest volcanic hazard. That’s due in part to the pressures they generate. Because these flows are so violent, studying them directly can be hard. Researchers often have to estimate average obstacle-smashing pressures in the flows. They do this with computer models. Those are based on studies of geologic deposits left by past flows.

Lube and his colleagues wanted to directly study the inner workings of these flows. So they reproduced smaller versions of the flows in experiments. They measured destructive factors. These included particle velocities and temperatures. They also measured flow densities. That let the team calculate pressures inside the flows. The researchers also analyzed the first measurements of pressures in natural flows. Those measurements were from 2019. That’s when pyroclastic flows burst from the Whakaari volcano in New Zealand. They engulfed a set of infrasound sensors.

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To the researchers’ surprise, flow pressures rose and fell in a rhythmic pattern. This happened as volcanic particles clustered into cascading waves and trains of rolling eddies. These pulses would successively damage obstacles like blows from a jackhammer, Lube says. Sometimes the pulses smashed more than three times as hard as the average pressure estimates.

Many hazard assessments are probably underestimating the destructiveness of pyroclastic flows by a lot, Lube says. “It’s a big wake-up call.”

Researchers at Massey University in Palmerston North, New Zealand, released mixtures of hot rock, ash and gas down a channel to replicate volcanic avalanches known as pyroclastic flows. These flows have an internal rhythm that makes them unexpectedly destructive, a new study suggests.

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Power Words

More About Power Words

ash: (in geology) Small, lightweight fragments of rock and glass spewed by volcanic eruptions. 

average: (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.

colleague: Someone who works with another; a co-worker or team member.

eddy: A circular motion that develops in some liquid or gas and that moves in a direction opposite to the main current. In water, this may create a whirlpool.

eruption: (in geoscience) The sudden bursting or spraying of hot material from deep inside a planet or moon and out through its surface. Volcanic eruptions on Earth usually send hot lava, hot gases or ash into the air and across surrounding land. In colder parts of the solar system, eruptions often involve liquid water spraying out through cracks in an icy crust. This happens on Enceladus, a moon of Saturn that is covered in ice.

factor: Something that plays a role in a particular condition or event; a contributor.

field: An area of study, as in: Her field of research is biology. Also a term to describe a real-world environment in which some research is conducted, such as at sea, in a forest, on a mountaintop or on a city street. It is the opposite of an artificial setting, such as a research laboratory.

geologic: An adjective that refers to things that are related to Earth’s physical structure and substance, its history and the processes that act on it. People who work in this field are known as geologists.

infrasound: Sound waves with frequencies below the lower limit of human hearing.

New Zealand: An island nation in the southwest Pacific Ocean, roughly 1,500 kilometers (some 900 miles) east of Australia. Its “mainland” — consisting of a North and South Island — is quite volcanically active. In addition, the country includes many far smaller offshore islands.

particle: A minute amount of something.

pressure: Force applied uniformly over a surface, measured as force per unit of area.

pyroclastic flow: Hot clouds of ash and rock that sweep down a volcano’s slopes during an eruption. These flows can move at hurricane speeds.

sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.

simulation: (v. simulate) An analysis, often made using a computer, of some conditions, functions or appearance of a physical system. A computer program would do this by using mathematical operations that can describe the system and how it might change over time or in response to different anticipated situations.

turbulence: A chaotic, flowing mass of swirling air. Airplanes that run into turbulence high above ground can give passengers a bumpy ride.

volcano: A place on Earth’s crust that opens, allowing magma and gases to spew out from underground reservoirs of molten material. The magma rises through a system of pipes or channels, sometimes spending time in chambers where it bubbles with gas and undergoes chemical transformations. This plumbing system can become more complex over time.

volcanology: The study of volcanoes. Scientists who work in this field are known as volcanologists.

wave: A disturbance or variation that travels through space and matter in a regular, oscillating fashion.


Journal:​ ​​ E. Brosch et al. Destructiveness of pyroclastic surges controlled by turbulent fluctuations. Nature Communications. Published online December 15, 2021. doi: 10.1038/s41467-021-27517-9.