Shock waves in outflow gases could regulate 'volcano lightning'
Volcanic eruptions spew lava, rock and ash into the air. When fragments of these materials mix and collide in the outflow, they can create an electric potential large enough to generate lightning.
New research by Lawrence Livermore National Laboratory (LLNL) scientists and collaborators has discovered that standing shock waves in the supersonic outflow of gases prevent electric discharges like sparks and lightning from propagating. This suggests standing shocks formed by a volcanic eruption may suppress or reduce volcano lightning during the initial phase of an eruption. The new research appears in the journal Communications Earth & Environment.
In nature, electric discharges in the form of lightning are frequently observed not only in thunderclouds, but also in widely diverse environments that exhibit turbulent particle-laden flows, such as volcanic plumes and dust devils.
During electric discharge, radio frequency (RF) emissions can be recorded, providing a means to track the progressive evolution in space and time of the lightning source. Similar to the detection of thunderclouds and storms, RF detection also is now being used to detect and inform on the hazards associated with ash-laden volcanic plumes and ash clouds. In particular, lightning at active volcanoes in a state of unrest can indicate the onset of hazardous explosive activity and the production of ash plumes. In addition, both observable discharges and RF emissions can reveal the mechanisms that initiate the lightning and offer clues about the makeup of the erupting material.
Explosive volcanic eruptions can generate lightning that emits RF signatures. At early times in the eruption, moreover, shock waves in the supersonic flow may act to mediate the path of the lightning, recognizably modifying the RF signatures.
The team imaged sparks and a standing shock together in a transient supersonic jet of micro-diamonds entrained in argon. Shock waves represent a sharp transition in gas density and hence in the tendency of the gas to ionize. Fluid dynamic and kinetic simulations of the experiment illustrated how the observed sparks are bounded by the standing shock.
"We show that sparks transmit an impression of the explosive flow and open the way for novel instrumentation to diagnose currently inaccessible explosive phenomena," said lead author Jens von der Linden, former LLNL scientist now at the Max Planck Institute for Plasma Physics.
Explosive volcanic eruptions produce supersonic flows through the sudden release of over-pressurized gases contained in the erupting magma, resulting in shock waves.
Observations of erupting volcanoes in Alaska, Iceland and Japan have revealed that in the first few seconds following the onset of an explosive eruption, RF signatures distinct from those produced by leader-forming lightning are recorded in the vicinity (within tens to hundreds of meters) of volcano vents.
"If the sources of near-vent continual radio frequency emission are regulated by standing shock waves, then distributed antennas could pinpoint their locations, tracking the evolution of the regulating standing shock and providing insight into the pressure and particle content of the explosive flow," said Jason Sears, LLNL scientist and principal investigator for the project. "The fast decompression experiments and simulations that Jens led permit observation and analysis of explosive events producing RF at their onset."
More information: Jens von der Linden et al, Standing shock prevents propagation of sparks in supersonic explosive flows, Communications Earth & Environment (2021). DOI: 10.1038/s43247-021-00263-y
Journal information: Communications Earth & Environment
Provided by Lawrence Livermore National Laboratory
Dinosaurs' ascent driven by volcanoes powering climate change
The rise of dinosaurs coincided with environmental changes driven by major volcanic eruptions over 230 million years ago, a new study reveals.
The Late Triassic Carnian Pluvial Episode (CPE) saw an increase in global temperature and humidity—creating a major impact on the development of animal and plant life, coinciding with the establishment of modern conifers.
Researchers analyzed sediment and fossil plant records from a lake in northern China's Jiyuan Basin, matching pulses of volcanic activity with significant environmental changes, including the CPE's 'mega monsoon' climate, some 234 million to 232 million years ago.
The international research team, including experts at the University of Birmingham, today published their findings in Proceedings of the National Academy of Sciences (PNAS)—revealing four distinct episodes of volcanic activity during this time period, with the most likely source being major volcanic eruptions from the Wrangellia Large Igneous Province, the remnants of which are preserved in western North America.
Co-author Jason Hilton, Professor of Palaeobotany and Palaeoenvironments at the University of Birmingham's School of Geography, Earth and Environmental Sciences, commented: "Within the space of two million years the world's animal and plant life underwent major changes including selective extinctions in the marine realm and diversification of plant and animal groups on land. These events coincide with a remarkable interval of intense rainfall known as the Carnian Pluvial Episode.
"Our research shows, in a detailed record from a lake in North China, that this period can actually be resolved into four distinct events, each one driven by discrete pulses of powerful volcanic activity associated with enormous releases of carbon dioxide into the atmosphere. These triggered an increase in global temperature and humidity."
The researchers found that each phase of volcanic eruption coincided with large perturbation of the global Carbon cycle, major climatic changes to more humid conditions, as well the lake's deepening with a corresponding decrease in oxygen and animal life.
Geological events from a similar timeframe in Central Europe, East Greenland, Morocco, North America, and Argentina, among other locations indicate that increased rainfall resulted in widespread expansion of drainage basins converging into lakes or swamps, rather than rivers or oceans.
"Our results show that large volcanic eruptions can occur in multiple, discrete pulses -demonstrating their powerful ability to alter the global carbon cycle, cause climate and hydrological disruption and drive evolutionary processes," added co-author Dr. Sarah Greene, Senior Lecturer also in the School of Geography, Earth and Environmental Sciences at the University of Birmingham.
Dr. Emma Dunne, a Palaeobiologist also at the the University of Birmingham, who was not involved in the study, commented:
"This relatively long period of volcanic activity and environmental change would have had considerable consequences for animals on land. At this time, the dinosaurs had just begun to diversify, and it's likely that without this event, they would never have reached their ecological dominance we see over the next 150 million years"
Professor Hilton also added "In addition to dinosaurs, this remarkable period in Earth history was also important for the rise of modern conifer groups and had a major impact on the evolution of terrestrial ecosystems and animal and plant life—including ferns, crocodiles, turtles, insects and the first mammals."
The research team investigated terrestrial sediments from the ZJ-1 borehole in the Jiyuan Basin of North China. They used uranium-lead zircon dating, high-resolution chemostratigraphy, palynological and sedimentological data to correlate terrestrial conditions in the region with synchronous large-scale volcanic activity in North America.Discovery of a new mass extinction
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