Recent eruptions have demonstrated our continued vulnerability to ash dispersal, which can disrupt the aviation industry and cause billions of dollars in economic loss. Scientists widely believe that volcanic particle size is determined by the initial fragmentation process, when bubbly magma deep in the volcano changes into gas-particle flows.
But new Georgia Tech research indicates a more dynamic process where the amount and size of volcanic ash actually depend on what happens afterward, as the particles race toward the surface. Their initial size and source depth, as well as the collisions they endure within the conduit, are the differences between palm-sized pumice that hit the ground and dense ash plumes that jet into the atmosphere and can halt aviation. The findings are published in the current edition of Nature Geoscience.
Assistant Professor Josef Dufek used lab experiments and computer simulations to study particle break-up, known as granular disruption, in volcanic eruptions. His team, which included the University of California, Berkeley’s Michael Manga and Ameeta Patel, determined that shallow (approximately 500 meters below the surface) fragmentation levels likely cause abundant, large pumice that are often seen in large volcanic eruptions. If the fragmentation begins a few kilometers underground, the volcano is more likely to emit fine-grained ash.
“The longer these particles stay in the conduit, the more often they collide with each other,” said Dufek, a faculty member in Georgia Tech’s School of Earth and Atmospheric Sciences. “These high-energy collisions break the volcanic particles into fractions of their original size. That’s why deeper fragmentations produce small particles. Particles that begin closer to the surface with less energy don’t have time for as many collisions before they exit the volcano. They stay more intact, are larger and often contained in pyroclastic flows.”
The team collected volcanic rock from California’s Medicine Lake volcanic deposit for collision experiments. They also used glass spheres because, like glass, pumice is heated and hardens before crystals are able to form. Using a pumice gun that propels volcanic fragments using compressed gases, Dufek and his team determined that particles must collide at a minimum of 30 meters per second to break into larger pieces.
Using numerical simulations, the researchers concluded that large pumice particles (greater than fist size) will not likely remain intact unless the fragmentation is very shallow. Abundant large pumice rocks in a deposit provide an indication of the depth of fragmentation, which may vary over the course of the eruption. Due to the depth and violent nature of the process, scientists have had little record of the depth of the fragmentation process, even though much of the eruptive dynamics and subsequent hazards are determined in this process.
Dufek and his team will next use the research to better understand the dynamics of one of the most rare natural disasters: super volcanoes, which produced the features in Yellowstone National Park.
“We know very little about the eruption processes during super eruptions,” said Dufek. “Indications of their fragmentation levels will provide important clues to their eruptive dynamics, allowing us to study them in new ways.”
This project is supported by the National Science Foundation (NSF) (Award Numbers 0809321 and 0809564). The content is solely the responsibility of the principal investigators and does not necessarily represent the official views of the NSF.
Jason Maderer | Newswise Science News
Research icebreaker Polarstern begins the Antarctic season
09.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Far fewer lakes below the East Antarctic Ice Sheet than previously believed
08.11.2018 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
Physicists at ETH Zurich demonstrate how errors that occur during the manipulation of quantum system can be monitored and corrected on the fly
The field of quantum computation has seen tremendous progress in recent years. Bit by bit, quantum devices start to challenge conventional computers, at least...
Scientists developed specially coated nanometer-sized vehicles that can be actively moved through dense tissue like the vitreous of the eye. So far, the transport of nano-vehicles has only been demonstrated in model systems or biological fluids, but not in real tissue. The work was published in the journal Science Advances and constitutes one step further towards nanorobots becoming minimally-invasive tools for precisely delivering medicine to where it is needed.
Researchers of the “Micro, Nano and Molecular Systems” Lab at the Max Planck Institute for Intelligent Systems in Stuttgart, together with an international...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
12.11.2018 | Life Sciences
12.11.2018 | Materials Sciences
12.11.2018 | Physics and Astronomy