FYFD

Tag: geophysics

  • The Underwater Effects of Volcanoes

    The Underwater Effects of Volcanoes

    Although volcanoes are typically located in or near the ocean, we’ve spent relatively little effort studying how eruptions affect the marine environment. A recent research voyage aimed to change that by studying the Patagonian Sea near the site of the 2008 Chaitén eruption. Marked by massive ashfalls that, when mixed with heavy rains, created huge mudslides, the 2008 eruption was the Chaitén volcano’s first in 9,000 years.

    The researchers mapped the seafloor near the volcano, finding massive dunes shaped by strong currents. Using a remotely operated vehicle, the team surveyed and sampled the seafloor, collecting sediments reaching back some 15,000 years. They also located ash from the 2008 eruption over 24 kilometers from the volcano. With their data, they hope to understand both how the recent eruption changed the marine environment as well as how older eruptions affected the area. (Image credits: volcano – USGS, dunes – Schmidt Ocean Institute; see also Schmidt Ocean Institute; via Ars Technica)

    Composite image showing the massive underwater dunes off the coast.
    Composite image showing the massive underwater dunes off the coast.

    P.S. – This Friday, January 24th from 12 to 1:30pm Eastern I’m moderating a panel discussion on the Traveling Gallery of Fluid Motion and how art and science can work together in public outreach. Register here to join. It’s free!

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  • Tracking Coastal Sediment Loss

    Tracking Coastal Sediment Loss

    Shorelines rely on an influx of sediment to counter what’s lost to erosion by waves and currents. But tracking that sediment flux is challenging in coastal regions where salt, waves, and storms batter delicate instruments. Instead, researchers have turned to remote sensing through high-resolution satellites like Landsat to monitor these areas. Researchers built an algorithm to analyze coastal imagery, validated with local sediment measurements; once built, they deployed it in a free tool that lets anyone build a 40-year timeline of a coastal area’s sediment history.

    Looking at thousands of sites around the world, the team found coastal sediment is on the decline, especially along sandy and muddy coastlines. Where has the sediment gone? It’s likely that human-built infrastructure — both on coasts and upstream along rivers — is disrupting the natural flow of sediments that would replenish these regions. (Image credit: NASA; research credit: W. Teng et al.; via Eos)

  • A New Mantle Viscosity Shift

    A New Mantle Viscosity Shift

    The rough picture of Earth’s interior — a crust, mantle, and core — is well-known, but the details of its inner structure are more difficult to pin down. A recent study analyzed seismic wave data with a machine learning algorithm to identify regions of the mantle where waves slowed down. These shifts in seismic wave speed occur in areas where the mantle’s viscosity changes; a higher viscosity makes waves travel slower.

    The team found seismic wave speed shifts at depths of 400 and 650 kilometers, corresponding to known viscosity changes. But they found shifts at 1050 and 1500 kilometers, as well — the first time anyone has shown a global viscosity shift at those depths. Their analysis suggests a higher viscosity in this mid-mantle transition zone, which could affect how tectonic plates, which rely on these slow mantle flows, move. (Image credit: NASA; research credit: K. O’Farrell and Y. Wang; via Eos)

  • Glacial Tributaries

    Glacial Tributaries

    Just as rivers have tributaries that feed their flow, small glaciers can flow as tributaries into larger ones. This astronaut photo shows Siachen Glacier and four of its tributaries coming together and continuing to flow from the top to the bottom of the image. The dark parallel lines running through the glaciers are moraines, where rocks and debris are carried along by the ice. Those seen here are medial moraines left by the joining of tributaries. When glaciers retreat, moraines are often left behind, strewn with sediment that ranges from the fine powder of glacial flour all the way to enormous boulders. (Image credit: NASA; via NASA Earth Observatory)

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  • A Magnetic Tsunami Warning

    A Magnetic Tsunami Warning

    Tsunamis are devastating natural disasters that can strike with little to no warning for coastlines. Often the first sign of major tsunami is a drop in the sea level as water flows out to join the incoming wave. But researchers have now shown that magnetic fields can signal a coming wave, too. Because seawater is electrically conductive, its movement affects local magnetic fields, and a tsunami’s signal is large enough to be discernible. One study found that the magnetic field level changes are detectable a full minute before visible changes in the sea level. One minute may not sound like much, but in an evacuation where seconds count, it could make a big difference in saving lives. (Image credit: Jiji Press/AFP/Getty Images; research credit: Z. Lin et al.; via Gizmodo)

  • Erie Algal Bloom

    Erie Algal Bloom

    Blue-green algae bloom in Lake Erie’s summer conditions. Unfortunately for those looking to spend summer on the water, the dominant organism in this bloom produces a toxin that “can cause liver damage, numbness, dizziness, and vomiting.” Bloom season can last from late June into October, depending on the how many nutrients get washed into the lake and when wind mixes the lake water in the fall. A new hyperspectral instrument aboard NASA’s PACE spacecraft will identify bloom species from space, helping scientists track, understand, and predict blooms like these. (Image credit: W. Liang; via NASA Earth Observatory)

  • Slushy Snow Affects Antarctic Ice Melt

    Slushy Snow Affects Antarctic Ice Melt

    More than a tenth of Antarctica’s ice projects out over the sea; this ice shelf preserves glacial ice that would otherwise fall into the Southern Ocean and raise global sea levels. But austral summers eat away at the ice, leaving meltwater collected in ponds (visible above in bright blue) and in harder-to-spot slush. Researchers taught a machine-learning algorithm to identify slush and ponds in satellite images, then used the algorithm to analyze nine years’ worth of imagery.

    The group found that slush makes up about 57% of the overall meltwater. It is also darker than pure snow, absorbing more sunlight and leading to more melting. Many climate models currently neglect slush, and the authors warn that, without it, models will underestimate how much the ice is melting and predict that the ice is more stable than it truly is. (Image credit: Copernicus Sentinel/R. Dell; research credit: R. Dell et al.; via Physics Today)

  • Underground Convection Thaws Permafrost Faster

    Underground Convection Thaws Permafrost Faster

    In recent years, Arctic permafrost has thawed at a surprisingly fast pace. Much of that is, of course, due to the rapid warming caused by climate change. But some of that phenomenon lives underground, where water’s unusual properties cause convection in gaps between rocks, sediment, and soil.

    Water is densest not as ice but as water. This is why ice cubes float in your glass. Water’s densest form is actually a liquid at 4 degrees Celsius. For water-logged Arctic soils, this means that the densest layer is not at the frozen depth but at a higher, shallower depth. This places a dense liquid-infused layer over a lighter one, a recipe for unstable convection.

    Illustration of underground convection and permafrost thaw. On the left: temperature and density of the water in Arctic soil varies with depth. The temperature decreases with depth, but because water is densest at 4 degrees Celsius, the density is greatest at a shallower depth than the freezing interface. As a result of this unstable configuration (dense water over less dense water), convection can occur (right side).
    Illustration of underground convection and permafrost thaw. On the left: temperature and density of the water in Arctic soil varies with depth. The temperature gets colder the deeper you go, but because water is densest at 4 degrees Celsius, the density is greatest at a shallower depth than the freezing interface. As a result of this unstable configuration (dense water over less dense water), convection can occur (right).

    In a recent numerical simulation, researchers found that this underground convection caused permafrost to thaw much more quickly than it would due to heat conduction alone. In fact, the effects appeared in as little as one month, so in a single summer, this convection could have a big effect on the thaw depth. (Image credit: top – Florence D., figure – M. Magnani et al.; research credit: M. Magnani et al.)

  • Origins of Salt Polygons

    Origins of Salt Polygons

    Around the world, dry salt lakes are crisscrossed by thousands of meter-wide salt polygons. Although they resemble crack patterns, these structures are actually the result of convection occurring in the salty groundwater beneath the soil. I have covered the physics previously, but this new article by several of the researchers gives a behind-the-scenes glimpse of the investigation itself and how they uncovered the true explanation. (Image credit: S. Liu, see also: Physics Today)

  • Trapped in a Taylor Column

    Trapped in a Taylor Column

    The world’s largest iceberg, A23a, is stuck. It’s not beached; there are a thousand meters or more of water beneath it. But thanks to a quirk of the Earth’s rotation, combined with underwater topology, A23a is stuck in place, spinning slowly for the foreseeable future. A23a is trapped in what’s known as a Taylor column, a rotating column of fluid that forms above submerged objects in a rotating flow. You can see the same dynamics in a simple tabletop tank.

    Pirie Bank sticks up from the seafloor, which sets up a stationary column of rotating water that iceberg A23a is now stuck in.
    Pirie Bank sticks up from the seafloor, which sets up a stationary column of rotating water that iceberg A23a is now stuck in.

    When a tank (or planet) is rotating steadily, there’s little variation in flow with depth. With an obstacle at the deepest layer — in this case, an underwater rise known as the Pirie Bank — water cannot pass through that lowest layer. And that deflection extends to all the layers above. The water above Pirie Bank just stays there, as if the entire column is an independent object. Caught inside this region, A23a will remain imprisoned there. How long will that last? There’s no way to know for sure, but a scientific buoy in another nearby Taylor column has been hanging out there for 4 years and counting. (Image credit: A23a – D. Fox/BAS, diagram – IBSCO/NASA; via BBC News; submitted by Anne R.)