FYFD

Tag: geophysics

  • Dancing Peanuts

    Dancing Peanuts

    Bartenders in Argentina sometimes entertain patrons by tossing a few peanuts into their beer. Initially, the peanuts sink, but after a few seconds they rise, wreathed in bubbles. Once on the surface, they roll, causing the bubbles to pop, and the peanut sinks once again. The cycle repeats, sometimes for as long as a couple hours.

    There are a couple physical processes governing this dance. The first is bubble nucleation. Most beers are carbonated; they contain dissolved carbon dioxide gas that remains in solution while the beer is under pressure. Once poured, that storage pressure is gone and bubbles start to form in the liquid. The shape of the peanut means that bubbles form more easily on it than on the glass walls or in the liquid. And once the peanut is covered in bubbles, buoyancy comes into play. The bubbles attached to the peanut reduce its density relative to the surrounding fluid, enabling the peanut to rise up and float.

    This same process is seen with other objects in carbonated fluids, too, such as blueberries in beer and lemon seeds in carbonated water. But it’s also reflected elsewhere in nature. For example, magnetite crystals are thought to float in magma due to a similar nucleation of dissolved gases on their surface. (Image and research credit: L. Pereira et al.; via APS Physics)

  • Underwater Volcanic Flows

    Underwater Volcanic Flows

    The Hunga Tonga–Hunga Ha’apai volcanic eruption in December 2021 was the most violent in 140 years, and we are still learning from its aftermath. A recent study focuses on the eruption’s incredible underwater flows, which damaged nearly 200 kilometers of underwater cables. From the cables’ locations and the time of service loss, the team calculated that gravity currents hit the cables at speeds as high as 122 kilometers per hour and with run-outs that lasted over 100 kilometers. These fast flows were triggered by material from the volcanic plume falling into the ocean, causing dense flows that swept down the submerged slopes of the volcano and seafloor.

    Illustration of volcanic plume material falling into the ocean and triggering underwater flows.
    Illustration of volcanic plume material falling into the ocean and triggering underwater flows.

    Previously, a landslide broke underwater telegraph cables off Newfoundland and a coastal construction accident severed a cable in the Mediterranean. But neither of those incidents revealed the same level of speed, distance, and destructive capacity as the Tongan eruption. It seems that these underwater gravity currents pose an ongoing threat to submerged infrastructure. As more cables are laid in volcanically-active regions of the Pacific, we will need more extensive mapping and monitoring of the seafloor to protect against future disruptions. (Image credit: eruption – Tonga Geological Services, illustration – APS/C. Cain; research credit: M. Clare et al.; via APS Physics)

  • Field of Dunes

    Field of Dunes

    Barchan dunes collide in this astronaut image of Brazil’s southern coastline. Barchan (pronounced “bar-kahn”) dunes are crescent-shaped; their tips point downwind into their direction of travel. When many barchan dunes overlap, they coalesce into a dune field like the one seen here. A dune’s speed depends on many factors, including the wind speed, dune size, and its proximity to other dunes. In experiments, dunes have even chased one another and changed speeds to avoid collision. (Image credit: NASA; via NASA Earth Observatory)

  • Predicting Landslides

    Predicting Landslides

    Landslides can cause catastrophic damage, but historically it’s been difficult to monitor susceptible slopes and predict when they’ll fail. But a recent study looking at the 2017 Mud Creek landslide in California shows that new methods could provide a heads up.

    The researchers used satellite data from the months preceding the landslide to study how areas on the slope moved relative to one another. Within their survey region, they found sub-regions where ground locations largely moved together. These sub-regions, called communities in the researchers’ parlance, were remarkably persistent, showing little variation over long periods. But 56 days before the landslide, the researchers saw a sudden change between the communities on the slope. They believe their methodology could help identify slopes in danger of imminent slides.

    So far, though, they’ve only applied this method to the Mud Creek landslide. It’s a promising start, but they’ll need to show that the technique works for other slides as well. If so, it will be a major step forward in landslide prediction. (Image credit: USGS; research credit: V. Desai et al.; via APS Physics)

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    To Clog or Not to Clog?

    The clear plastic disks use to study clogging appear rather plain — at least until you look at them through polarizers. Then the disks light up with a web of lines that reveal the unseen forces between the particles. In this video, researchers use this trick to explore how spontaneous clogs occur. If particles jam together into an arch, that bridge can be strong enough to hold the weight of all the particles above it, bringing the flow to a halt. Some arches aren’t strong enough to hold for long; they can break in moments. Other more stable arches persist. By watching the flow through polarizers and carefully tracking the ebb and flow of the forces between particles, researchers can predict which clogs will have staying power. (Video credit: B. McMillan et al.)

  • Puddle Depth Matters for Stalagmites

    Puddle Depth Matters for Stalagmites

    In a cave, mineral-rich water drips from the ceiling, spreading ions used to build stalagmites. A recent study considers how the depth of a pool affects the droplet’s splash and how material from the droplet spreads. The authors found several scenarios that vary widely depending on pool depth.

    A droplet falling into a shallow pool creates a splash that quickly breaks up into droplets. This flings the red droplet material in many directions.
    A droplet falling into a shallow pool creates a splash that quickly breaks up into droplets. This flings the red droplet material in many directions.

    A drop falling into a shallow pool had a splash that quickly broke up into droplets (above). By dyeing the pool green and the droplet red, they could track where the droplet’s material wound up. The spray of small droplets carried fluid far, but the main point of impact had a strong concentration of the drop’s fluid.

    With a deeper pool, the drop's impact creates a thick crown splash that collapses in on itself. The drop's fluid is quickly mixed into the pool.
    With a deeper pool, the drop’s impact creates a thick crown splash that collapses in on itself. The drop’s fluid is quickly mixed into the pool.

    In contrast, a deeper pool sent up a thick-walled splash crown that collapsed in on itself. This droplet’s material saw lots of mixing with the pool, but only near the point of impact. From their work, the authors concluded that models of stalagmite growth should incorporate pool depth in order to capture how minerals actually concentrate and move. (Image credit: cave – H. Roberson, others – J. Parmentier et al.; research credit: J. Parmentier et al.; via APS Physics; submitted by Kam-Yung Soh)

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    Studying Earth’s Interior

    The Earth’s interior is almost entirely inaccessible to humanity, so how do we know what it consists of? As explained in this video, our knowledge of the planet’s interior is based on measuring waves sent out by earthquakes and nuclear blasts. Both produce two kinds of waves — pressure waves (P-waves) and shear waves (S-waves) that travel through the earth and get picked up by seismometers. Scientists noticed that pressure waves travel through the center of the planet while shear waves — which get dissipated in liquids — do not. This led them to conclude that part of Earth’s interior is a liquid. The idea of a solid inner core came from observations of pressure waves scattering in a way that only made sense if they’d hit something solid. (Video and image credit: Science)

  • Fast-Moving Martian Rivers

    Fast-Moving Martian Rivers

    For the first time, scientists have found evidence of deep, fast-flowing ancient rivers on Mars. After examining images taken recently by the Perseverance rover in Jezero Crater, fluvial experts have spotted familiar signs of turbulent river flow. The mosaic above shows an area nicknamed “Shrinkle Haven,” where curved bands of rock mark the landscape. Although scientists are confident that a powerful river deposited these rocks, they’re still debating whether that river was a meandering one like the Mississippi or a braided river like the Platte.

    Nicknamed "Pinestand," this hill's sedimentary layers were likely formed by a deep fast-moving river.
    Nicknamed “Pinestand,” this hill’s sedimentary layers were likely formed by a deep, fast-moving river.

    In another area, known as “Pinestand,” scientists spotted hills as high as 20 meters tall with clear sedimentary layers. Like Shrinkle Haven’s rock bands, formations like this are most often associated with a large, fast-flowing river. (Image credits: NASA/JPL-Caltech/ASU/MSSS; via Gizmodo; see also NASA JPL)

  • Hawaiian Magma Complex

    Hawaiian Magma Complex

    Few volcanoes are as well-studied as those of the Big Island of Hawai’i. With a host of seismic monitors and frequent eruptions, scientists know the near-surface region of Hawai’i well. But a recent study looked at nearly 200,000 seismic events after the 2018 collapse of Kilauea’s crater and found hints of what goes on much deeper.

    Mapping out earthquakes beneath the island revealed a cluster of activity near a village named Pahala. These earthquakes took place 36 to 43 kilometers below the surface and seem to be connected to magma filling a sill complex there. From that deep reservoir, the team was also able to map seismic activity leading upwards to both Kilauea and Mauna Loa volcanoes. Despite the 34 kilometers between those two volcanoes, they appear to be fed through the same web of magma! (Image credit: top – USGS, illustration – J. Wilding et al.; research credit: J. Wilding et al.; via Physics Today)

    This cartoon illustrates the web of magma linking Kilauea and Mauna Loa deep underground.
    This cartoon illustrates the web of magma linking Kilauea and Mauna Loa deep underground.
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    Why Rivers Shift

    In their natural state, rivers are variable in their course, shifting and meandering. Sometimes they deposit sediment, and sometimes they erode it. In this video, Grady from Practical Engineering digs into the principles behind these changes. With help from Emriver‘s stream tables, which demonstrate years of changes in a river over minutes, Grady shows how changing the sediment load, flow rate, and other factors in a river affect its course. (Video credit: Practical Engineering)