A warm summer in 2022 has resulted in record melting on Svalbard. Located halfway between the Norwegian mainland and the North Pole, more than half of Svalbard is normally covered in ice. But with glaciers in retreat and firn — a surface layer of compressed porous snow — melting, pale blue ice is getting direct exposure to the sun and warm air temperatures. The result has been melting 3.5 times larger than the average melt between 1981 and 2010. Look closely and you’ll find deep blue meltwater ponds dotting the ice, too. The run-off of meltwater has likely carried extra sediment into the surrounding waters, accounting for some of the paler water colors along the coast. (Image credit: J. Stevens/USGS; via NASA Earth Observatory)
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Landslide-Triggered Tsunamis
After the 2018 Anak Krakatoa eruption, a tsunami that ricocheted through the surrounding waters, killing hundreds on nearby islands. The source of that tsunami was a small landslide. Once the air cleared and researchers could assess how much material slid into the ocean, they were shocked that such a small volume created so much destruction.
Now new efforts are revealing the linkage between landslides and the waves they make. Researchers released glass beads into a tank of water, observing the waves that form as the beads run out. Depending on the relative initial height of the beads compared to the water depth, they observed three different kinds of waves. Not only that, they were able to connect the granular mechanics of the landslide to the hydrodynamic formation of waves, allowing predictions of the waves that will form for a given landslide.
Currently, the predictive model isn’t sophisticated enough to handle a geometry as complex as that of the Anak Krakatoa landslide, but it’s an important step toward understanding — and potentially mitigating the damage of — future oceanside landslides. (Image and research credit: W. Sarlin et al.; via APS Physics; submitted by Kam-Yung Soh)
Fire Ant Rafts
When you run into a fire ant, you’re in for a bad day. But if you run into a colony-sized raft of fire ants, well, that’s going to be a very bad day. These insects evolved to survive Amazonian floods, and that prowess has helped them spread far from their original homes. When waters start rushing into their home, the ants set out on a rescue mission, pulling their young out. The ants lash themselves and the youngsters together with their own bodies and form a floating raft. Thanks to the hydrophobic hairs on the larvae and ants, they trap a layer of air near their bodies. This helps them breathe, even if they’re on the bottom of the raft. Learn lots more about fire ants, including how they act as fluid, over here. (Image and video credit: Deep Look)
A Comet’s Tail Swept Away
On Christmas Day 2021, Comet Leonard put on a show in our skies. Though the comet was a pale streak to the naked eye, photographer Gerald Rhemann caught a striking event: the moment part of the comet’s tail disconnected from its body. The solar wind swept the comet’s gas and dust away. Though I’ve talked about the fluid dynamics of comets before, this image is the most stunning example I’ve seen. It’s no wonder that it won the top prize at the Astronomy Photographer of the Year competition. (Image credit: G. Rhemann; via Colossal; see also APOTY)
Aerosols and Instruments
Although COVID has disrupted all of our lives, orchestras saw particular disruption, as little was known about how instruments spread aerosol droplets. In this recent study, a team looked at many wind instruments, as played by professional musicians, for the aerosol load and air flow each instrument creates. They found that, on the whole, wind instruments — like flutes, clarinets, trumpets, and others — create aerosol loads comparable to normal speech. The air flow from each instrument comes primarily from the bell (for brass instruments) or tone holes (for woodwinds) and has a much lower velocity than coughing or sneezing. As a result, the flow decays away to the background air-flow after about 2 meters. (Image credit: trumpet – E. Awuy, trombone – Q. Brosseau et al.; research credit: Q. Brosseau et al.)
As a musician plays a scale on their trombone, flow from the bell is revealed through artificial fog and laser illumination. 
Free Contact Lines
How a simple drop of water sits on a surface is a strangely complicated question. The answer depends on the droplet’s size, its chemistry, the roughness of the surface, and what kind of material it’s sitting on. Vetting the mathematical models that describe these behaviors is especially difficult since droplets often get stuck, or “pinned,” along their contact line where water, air, and surface meet.
To get around this issue, researchers sent their experiment to the International Space Station, asking astronauts to run the tests for them. Without gravity‘s influence squishing drops, the astronauts could use much larger droplets than they could on Earth. Larger drops are less likely to get pinned by a stray surface defect, so on the space station, astronauts could place droplets on a vibrating platform and observe their contact line freely moving as the drop changed shape. Under these conditions, the experiment tested many surfaces with different wetting characteristics, thereby gathering data to test models we cannot easily confirm on Earth. (Image and research credit: J. McCraney et al.; via APS Physics)
Dripping Glaze on Ceramics
Candy-colored glaze oozes down the sides of Brian Giniewski’s Drippy Pots. These mugs seem like a great way to the start the day with a little happy, fluidsy action! (Image credit: B. Giniewski; via Colossal)
Rising Through Turbulence
Plankton — microscopic creatures with often limited swimming abilities — can face daily journeys of hundreds of vertical meters in the ocean. That’s a daunting prospect for any tiny swimmer. A new mathematical model suggests that plankton can have an easier time of it, though, by riding turbulent currents.
The researchers modeled an individual planktar (singular of plankton) capable of sensing nearby velocity gradients and rotating its body to control its swimming direction. With this simple set of controls, their simulated planktar was able to “surf” turbulent currents, covering vertical distances at twice its normal swimming speed despite its curvy path.
Currently, there’s no direct experimental evidence that plankton do this, but it does seem to make sense of experimenters’ observations. With the model’s results to guide them, experimentalists are looking for microswimmers actively orienting themselves based on turbulence. (Image credit: top – B. de Kort, illustration – R. Monthiller et al.; research credit: R. Monthiller et al.; via APS Physics)
How Gas Pump Nozzles Work
Ever wonder how a gas pump shuts off when the tank is full? You might guess that there’s a sophisticated electronic sensor hidden in there. But there isn’t! Gas pumps use an entirely mechanical technique to sense a full tank and shut off flow, as Steve Mould demonstrates in this video.
There are two key components — one fluid mechanical and one based on mechanical linkages — inside the handle. The part that senses a full tank is a Venturi tube, shown in Image 2. The top section of the Venturi tube contains a constriction, where (incompressible) flow is forced to speed up. That increase in speed creates a drop in pressure, which is reflected by the movement of the water in the curved tube below the constriction.
Notice that when there’s no flow through the top tube, the water level is equal on either side of the lower, curved tube. That means that the outside air pressure (connected to the short arm) equals the pressure in the constriction (connected to the long arm). When air is flowing through the constriction, the water level shifts. The water in the short arm gets pushed down while the water in the long arm gets sucked up. That change means that the air pressure outside the tube is now higher than pressure in the constriction.
I’ll let Steve explain what that means for the gas pump! (Image and video credit: S. Mould)
Flowers Through a Hazy Veil
A smoke-like haze obscures colorful bouquets in these photographs from artist Robert Peek. To achieve the effect, Peek submerges his subjects underwater with white dye that sinks due to its greater density. The wakes traced by the dye are impressively laminar, so the dye must drift rather slowly past each petal. The overall effect is beautifully dream-like. You can find more of Peek’s work on Behance and Instagram. (Image credit: R. Peek; via Colossal)