FYFD

Tag: geophysics

  • 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)

  • Upcoming Webcast

    Upcoming Webcast

    This weekend I’ll be holding my second live webcast for FYFD patrons. This month we’ll be focusing on the subject of planetary science, one of the coolest applications out there for fluid dynamics. My guests will be Keri Bean, a NASA JPL mission operations engineer and atmospheric scientist, and Professor Geoffrey Collins, a geologist at Wheaton College in Massachusetts. Keri has worked on all the recent Martian missions, including Mars Curiosity and the Phoenix Lander. She currently works on operations for the Dawn mission to Ceres. Geoff studies the geophysics of icy planets and moons like Pluto and Titan. He was part of the Galileo and Cassini missions to Jupiter and Saturn and is currently part of the team working on a future mission to Europa.

  • Martian Viscous Flow

    Martian Viscous Flow

    These images from the Mars Reconnaissance Orbiter show what are called viscous flow features. They are the Martian equivalent of glacial flow. Such features are typically found in Mars’ mid-latitudes.

    Ground-penetrating radar studies of Mars have shown that some of these features contain water ice covered in a protective layer of rock and dust, making them true glaciers. Another study of similar Martian surface features found that their slope was consistent with what could be produced by a ~10 m thick layer of ice and dust flowing superplastically over a timescale equal to the estimated age of the surface features. Superplastic flow occurs when solid matter is deformed well beyond its usual breaking point and is one of the common regimes for glacial ice flow on Earth. (Image credit: NASA/JPL/U. of Arizona; via beautifulmars)

  • Pyroclastic Flow

    Pyroclastic Flow

    Major volcanic eruptions can be accompanied by pyroclastic flows, a mixture of rock and hot gases capable of burying entire cities, as happened in Pompeii when Mt. Vesuvius erupted in 79 C.E. For even larger eruptions, such as the one at Peach Spring Caldera some 18.8 million years ago, the pyroclastic flow can be powerful enough to move half-meter-sized blocks of rock more than 150 km from the epicenter. Through observations of these deposits, experiments like the one above, and modeling, researchers were able to deduce that the Peach Spring pyroclastic flow must have been quite dense and flowed at speeds between 5 – 20 m/s for 2.5 – 10 hours! Dense, relatively slow-moving pyroclastic flows can pick up large rocks (simulated in the experiment with large metal beads) both through shear and because their speed generates low pressure that lifts the rocks so that they get swept along by the current. (Image credit: O. Roche et al., source)

  • Glaciers in Motion

    Glaciers in Motion

    To the naked eye, glaciers don’t appear to move much, but appearances can be deceiving. Like avalanches and turbidity currents, glaciers flow under the influence of gravity. They typically move at speeds around 1 meter per day, but some glaciers, like those shown above in Pakistan’s Central Karakorum National Park, can briefly surge to speeds a thousand times higher than their usual. The animation above shows 25 years worth of Landsat satellite imagery, enabling one to more easily observe the motion of these slow giants. Try picking out a feature along one of the glaciers and watch it move year-by-year. The glaciers just right of the image centerline are some of the best!  (Image credit: J. Allen; via NASA Earth Observatory; submitted by Vince D)

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  • Underwater Landslides

    Underwater Landslides

    Turbidity currents are a gravity-driven, sediment-laden flow, like a landslide or avalanche that occurs underwater. They are extremely turbulent flows with a well-defined leading edge, called a head. Turbidity currents are often triggered by earthquakes, which shake loose sediments previously deposited in underwater mountains and canyons. Once suspended, these sediments make the fluid denser than surrounding water, causing the turbidity current to flow downhill until its energy is expended and its sediment settles to form a turbidite deposit. By sampling cores from the seafloor, scientists studying turbidites can determine when and where magnitude 8+ earthquakes have occurred over the past 12,000+ years!  (Video credit: A. Teijen et al.; submitted by Simon H.)

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    How the Grand Canyon Formed

    The Grand Canyon is a monument to the power of water, air, and time. In this video from It’s Okay To Be Smart, Joe Hanson describes the formation of the Grand Canyon – from the ancient oceans that created its many layers to the tectonic upthrusts that eventually created the Colorado River that continues to cut through the Canyon’s rocks today. Fluid dynamics play a major role in the geology of the Grand Canyon, whether it’s in the mantle convection that helps drive plate tectonics or the sedimentation that builds and erodes rock layers.   (Video credit: It’s Okay To Be Smart)

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    Calbuco

    Filmmaker Martin Heck captured incredible timelapse footage of the Chilean volcano Calbuco erupting earlier this year. Fluid dynamics on these enormous geophysical scales is always awe-inducing. In the beginning, clouds bob gently and flow around the landscape. Then the volcano erupts, and the towering ash cloud of the eruption roils with turbulence, displaying eddies with length scales from hundreds of meters down to centimeters. And when the hot ash has risen and cooled, it forms a cap that spreads horizontally. Nature is a wonderful demonstrator of fluid dynamics, but what always amazes me is how very alike flows are whether they are confined to a laboratory or take up an entire planet. (Video credit: M. Heck; via It’s Okay To Be Smart)

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    Convection from a Heat Source

    Convection is a major driver in many flows in nature. In this film, the UCLA Spinlab demonstrates buoyant convection caused by a local heat source. They deposit dye on a submerged, continuously heated plate, then observe as the dye slowly rises with the heated (lower density) fluid. The surface forms a cap for the rising dye, which then spreads horizontally. Qualitatively similar flows can be seen in nature over volcanic eruptions or in thunderstorms when clouds reach the troposphere or a capping inversion. Be sure to check out the rest of the Spinlab’s videos. (Video credit: UCLA Spinlab; submitted by Jon B.)