FYFD

Tag: geophysics

  • Magma Mixing

    Magma Mixing

    Magmas typically consist of a mixture of molten liquid, bubbles, and solid crystals. As they mix, those crystals can sink from one viscous layer into another. To investigate this sort of process, researchers studied solid particles sinking across an interface between two viscous liquids. This is what we see above. One fluid is clear; the other is dyed red, and gravity points toward the left so the particles fall from right to left.

    What happens when the particle reaches the interface between fluids depends on three main factors: the gravitational force acting on the particle, the surface tension at the interface, and the ratio of the viscosities of the two fluids. The researchers observed two main outcomes. In one (top), the particle slows at the interface and breaks through slowly, its surface wetted by the second fluid so that it drags little to none of the previous fluid with it. The researchers named this the film drainage mode. It tends to occur when the viscosity ratio between fluids is large.

    The second method, shown in the bottom image, is the tailing mode. As the particle approaches, the interface deforms. A thick layer of the first fluid coats the particle even as it pass through, forming a tail that destabilizes behind the falling particle. This mode occurs when the viscosity ratio is small or the gravitational force is large compared to the surface tension. (Image and research credit: P. Jarvis et al.)

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    Slow Mo Geyser

    Geysers are one of the most surreal wonders of our planet – pools of turquoise that periodically erupt into towers of water and steam. But what we see from the surface is only a small part of the story. Geysers require two main ingredients: an intense geothermal heat source and the right plumbing. Below ground, that plumping needs both a reservoir for water to gather and narrow constrictions that encourage the build-up of pressure.

    A cycle begins with water filling the reservoir; this can be both geothermally heated water and groundwater seeping in. As the geyser fills, the pressure at the bottom increases. Eventually, the water becomes superheated, meaning that it’s hotter than its boiling point at standard atmospheric pressure. That’s when the steam bubbles you see above rise to the surface. When they break through, it causes a sudden drop in the reservoir pressure. The superheated water there flashes into steam, causing the geyser to erupt. Check out the full video below for some awesome high-speed video of those eruptions, and, if you’re curious what the inside of an active geyser looks like check out Eric King’s video. (Image and video credit: The Slow Mo Guys; submitted by @eclecticca)

  • Inside Avalanches

    Inside Avalanches

    Avalanches have traditionally been difficult to model and predict because of their complex nature. In the case of a slab avalanche, the sort often triggered by a lone skier or hiker, there is a layer of dense, cohesive snow atop a layer of weaker, porous snow. The presence of the skier can destabilize that inner layer, causing a fracture known as an anticrack to propagate through the slab. Eventually, it collapses under the weight of the overlying snow and an avalanche occurs.

    What makes this so complicated is that the snow behaves as both a solid – during the initial fracturing – and as a fluid – during the flow of the avalanche. Researchers are making progress, though, using new models capable of simulating the full event (shown above) by leveraging techniques developed and used in computer animation for films. That’s right – the physics-based animation used in films like Frozen is helping researchers understand and predict actual avalanche physics! (Image and research credit: J. Gaume et al.; via Penn Engineering; submitted by Kam-Yung Soh)

  • Titan’s Dust Storms

    Titan’s Dust Storms

    Earth and Mars are well-known for their dust storms, but a new source of extraterrestrial dust storms is joining them: Saturn’s moon Titan. Titan already shares unusual similarities to Earth: it is the only other place known to currently have stable liquid bodies at its surface. On Earth, water makes up our lakes and oceans; on Titan, it’s methane.

    The evidence that Titan may also have dust storms dates from several Cassini flybys in 2009 and 2010. Cassini observed short-lived infrared bright spots in a dune-covered equatorial region. After considering several other possible sources for these temporary bright spots, researchers concluded that the most likely explanation was dust clouds suspended by high winds. This suggests that the dune fields on Titan are still actively changing, just like those on Earth and Mars! (Image credit: artist’s concept for Titan dust storm – NASA/ESA/IPGP/Labex UnivEarthS/University Paris Diderot; research credit: S. Rodriguez et al.; submitted by jpshoer)

  • Icy Penitentes

    Icy Penitentes

    At high, dry altitudes, fields of snow transform into rows of narrow, blade-like formations as tall as 2 meters. Known as penitentes – due to their similarity to kneeling worshipers – these surreal snow sculptures form primarily due to solar reflection. Surrounded by dry air and intense sunlight, the snow tends to sublimate directly into water vapor rather than melt into water. This turns an initially flat snowfield into one randomly dotted with little depressions. The curved surface of those depressions helps reflect incoming sunlight, causing the indentations to grow deeper and deeper over time. Although the high Andes are best known for their penitentes, they form elsewhere as well. Recent work has even identified them on Pluto! (Image credit: G. Hüdepohl; research credit: M. Betterton)

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    Tornadoes, Fire, and Ice

    It’s time for another look at breaking fluid dynamics research with the latest FYFD/JFM video! This time around, we tackle some geophysical fluid dynamics, like listening to the sounds newborn tornadoes make below the range of human hearing; studying how melting ice affects burning oil spills; and how salt sinking from sea ice affects the ocean circulation. Check out the full video below for much more! If you’ve missed any of the previous videos in the series, you can check them out here. (Image and video credit: T. Crawford and N. Sharp)

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    Waves Below the Surface

    Even a seemingly calm ocean can have a lot going on beneath the surface. Many layers of water at different temperatures and salinities make up the ocean. Both of those variables affect density, and one stable orientation for the layers is with lighter layers sitting atop denser ones. Any motion underwater can disturb the interface between those two layers, creating internal waves like the ones in this demo. In the actual ocean, these internal waves can be enormous – 800 meters or more in height! In regions like the Strait of Gibraltar where flowing tides encounter underwater topography, large internal waves are a daily occurrence. Internal waves can also show up in the atmosphere and are sometimes visible as long striped clouds. (Video and image credit: Cal Poly)

  • Kilauea’s Lava Lake

    Kilauea’s Lava Lake

    Hawaii’s Kilauea Volcano continues to erupt, sending magma flowing through multiple fissures. The U.S. Geological Survey has sounded a warning, however, that the volcano could erupt more explosively. Hot spot volcanoes like Hawaii’s generally have more basaltic lava, which has a lower viscosity than more silica-rich magmas like those seen on continental plates. That makes Hawaii’s volcanoes less prone to explosive detonations like the 1980 Mt. St. Helens eruption. With less viscous lava, there’s less likelihood of plugging a magma chamber and causing a deadly buildup of pressure from toxic gases.

    But that doesn’t mean that there’s no risk. In particular, officials are concerned by the rapid draining of a lava lake near Kilauea’s summit. As illustrated below, if the lava level drops below the water table, that increases the likelihood of steam forming in the underground chambers through which lava flows. The rapid drainage has destabilized the walls around the lava lake, causing frequent rockfalls into the chamber. If those were to plug part of the chamber and cause a steam buildup, then there could be an explosive eruption that releases the pressure. To be clear: even if this were to happen, it would be nothing like the explosiveness of Mt. St. Helens. But it would include violent expulsions of rock and widespread ash-fall. (Image credits: USGS, source; via Gizmodo)

  • Crevasses

    Crevasses

    Glacial ice is constantly flowing but at speeds we don’t notice by eye. That doesn’t mean there aren’t signs, though! Crevasses, narrow fractures in the ice that may be tens of meters deep, are a sign of those flows. Crevasses form in areas where the ice is under high stress. That could be a spot where the ice is flowing down a steeper incline or a place where multiple ice flows merge. Researchers can even use ice-penetrating radar to locate buried crevasses deep inside the ice. These are remnants of past flow conditions and provide hints at how the ice flows have changed over time. Crevasses are also a path for meltwater to penetrate deep into the ice, which can change slip conditions at the base of the glacier and increase both flow and melt rates. (Image credit: NASA/Digital Mapping Survey; via NASA Earth Observatory)

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    Mediterranean Currents

    Ocean currents play a major role in the weather and climate of our planet. This video shows a simulation of the surface ocean currents in the Mediterranean and Atlantic over an 11-month period. Each second corresponds to 2.75 days. You’ll see many swirling eddies in the Mediterranean and more flow along the coastlines in the Atlantic. One observation worth noting: near the end of the video, you’ll notice that flow through the Strait of Dover between England and France changes its direction, flowing back and forth depending on tidal forces. In contrast, flow through the Strait of Gibraltar is always into the Mediterranean (within the timescale of the simulation, at least). This net in-flow to the Mediterranean is due in part to the warm waters there evaporating at a higher rate than the cooler Atlantic. (Video credit: NASA; via Flow Viz; h/t to Ralph L)