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Showing posts with label Nature. Show all posts
Showing posts with label Nature. Show all posts

Tuesday, 22 October 2019

An underwater volcano generates bubbles over 400 meters in diameter

A plume of ash and gas rises from the Bogoslof volcano in 2017. | Dave Schneider / Alaska Volcano Observatory & US Geological Survey

At the beginning of the 20th century, sailors sailing near Alaska reported seeing black bubbles appearing to escape from the sea, each "at least the size of the dome of the United States Capitol (Washington)", according to certain statements. Surprisingly, they were not the only ones who reported the strange phenomenon. And they were not wrong, except on one detail: the bubbles are actually even bigger than they had estimated.


According to a new study, when the Bogoslof volcano, located in the Aleutian Islands and being largely submerged, erupts, it produces giant underwater bubbles up to 440 meters in diameter. These bubbles are filled with volcanic gas and create clouds up to several kilometers in altitude, says lead author of the study, John Lyons, geophysicist at the Alaska Volcano Observatory, Institute of Geological Survey of the States -United.

Images of volcanic clouds were captured by satellite after the last eruption of the volcano in 2017. However, the bubbles themselves have never been photographed to date.

During the eruption, a low buzzing sound spread through the air. Something emitted low-frequency signals, called infrasounds (sounds of a frequency lower than that perceptible by Man). These could last up to 10 seconds.

Lyons and his team, who regularly monitor active volcanoes in Alaska, have detected these signals in their data, thanks to adapted microphones. However, it took them a while to determine what it really was.

Map of Bogoslof volcano, with two satellite images of the top and crater partially submerged during an eruption. Credits: Lyons et al / Nature

It was only after going through the literature that the team proposed its hypothesis, arguing that the sound was the "murmur" of giant gas bubbles developing in the magma of the erupting volcano. They then proposed a computer model simulating the phenomenon.

The volcano erupted more than 70 times in 9 months. A distinct grunt (the "whisper") of a second, preceded each eruption, found the researchers. The computer models developed have shown that the vibration corresponds to the frequency that the eruptive bubbles generated as they stretched, dilated and exploded. The results were published Oct. 14 in the journal Nature Geoscience.


In their model, a bubble gushes from the column of magma, under water, and begins to grow. Once it reaches the surface of the water, part of the bubble emerges as a dome and continues to grow even faster. The pressure outside the bubble then becomes larger than the inside, and the bubble begins to contract. Eventually, his film becomes unstable and breaks, causing it to burst.

When it explodes, volcanic gas (composed of water vapor, sulfur dioxide and carbon dioxide) is partially released into the water, where it interacts with the lava, which breaks it down and produces ashes as well as volcanic clouds.

The team hypothesized that the low-frequency buzz came from the growth and oscillation of each bubble, and that the high-frequency signal represented the burst.

Diagram summarizing the formation of a bubble around a submerged eruption point. Gas flows from the column of magma to give birth to a bubble. The latter then continues to grow until it collapses. At one point, the bubble reaches its maximum radius (where the pressure is the lowest): at that moment, it contracts and eventually burst, giving rise to ash and volcanic clouds that can reach miles 'altitude. Credits: Lyons et al / Nature 


These shallow explosive underwater eruptions are very rare,  " Lyons said. " There is a lot of underwater volcanism, but most of it occurs under a large body of water (great depths), and all that extra pressure tends to suppress the incredible eruption  ."

Nevertheless, there are still outstanding issues and the results are limited by the research team's methodology, which is based on a number of assumptions. For example, it is difficult to know exactly what the water around the bubble looks like - whether it is normal seawater or whether the consistency is doughier, and so on. " It would be nice to be able to record these data elsewhere on Earth, and thus ensure that our methodology is sound, " Lyons said.

Sequence of recording the beginning of an eruption on March 8, 2017. Also audible are more than 100 consecutive bubble signals. (Each peak in the shape of the wave is a signal generated by a bubble). Credits: John Lyons


Source

Friday, 26 July 2019

A strange forest superorganism keeps a "vampire tree" alive!


In a New Zealand forest, a "vampire tree" clings to life. Formerly a powerful kauri tree (a kind of conifer that can grow up to 50 meters high), this low and leafless strain seems dead for a long time now. But, as a new study published this week shows ... we must not trust appearances.


According to the authors of the study, this strain is part of a " superorganism " forest: a network of interlaced roots that share resources. Note that this true community can include dozens or even hundreds of trees. Indeed, by grafting its roots on those of its neighbors, this strain of kauri can feed during the night water and other nutrients collected by other trees during the day, allowing it to survive through hard work of his comrades.

For the strain, the benefits are obvious: she would be dead without these transplants, because she no longer has green tissue per se ," said Sebastian Leuzinger, co-author of the study, and associate professor at the Auckland University of Technology of New Zealand. " But why would the trees keep this stump on the ground alive, when it does not seem to provide anything to its host trees? "Asks Leuzinger.

Once a powerful kauri tree, this low, leafless strain has now been dead for a long time. But that's all but the case. Do not be fooled by appearances ... Credits: Sebastian Leuzinger / iScience

Leuzinger and his colleagues attempted to answer this question by studying the flow of nutrients between the vampire strain and its two closest host trees. Using several sensors to measure the movement of water and sap through the three trees, the team noted a curious trend: the strain and its neighbors seemed to drink water, the whole time at opposite times.

During the day, while healthy trees are busy carrying water up and down to the roots, the stump is dormant. Then at night, when the host trees rest, the strain wakes up and circulates the water and nutrients in what remains of his body. According to the researchers, it is as if these trees take turns and operate as separate pumps in a single hydraulic network. Credits: iScience

But in this case, why add an almost dead tree to a real underground nutrient highway? According to the researchers, although the stump has no leaves, it is possible that its roots still have value for the surrounding trees, as a bridge to other trees in the network. It is also highly possible that the strain reached its neighbors a long time ago, even before it became a stump.

Also to know that the roots under these trees are very intertwined and therefore, according to the research team, it might be necessary to rethink the very concept of what a forest really is. " Maybe we do not really have to do trees as individual elements, but to the forest as a superorganism, " Leuzinger said.

According to the researchers, these forest superorganisms could also create some kind of additional protection against drought, by providing water to trees that have less access to it.


It is therefore extremely valuable information and resource for the future, as the frequency and intensity of droughts are about to increase in the face of changing global climate change. .

There is one element that the researchers wanted to highlight. All the positive elements of this real network, there is potentially a great disadvantage to everything being linked: in the same way that nutrients can be shared between individuals, pathogens could be transmitted as easily infected tree to another. It should also be noted that kauri trees in particular are threatened by a disease called kauri dieback , which is spread by a soil pathogen.

Researchers now want to continue their research on these forest superorganisms to learn more about their functioning and role.


Bibliography:

Hydraulic Coupling of a Leafless Kauri Tree Remnant to Conspecific Hosts
M.K.-F. Bader S. Leuzinger 2
Published:July 25, 2019
DOI:https://doi.org/10.1016/j.isci.2019.05.009


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