Surfer and photographer Tim McKenna lives in the village of Teahupo’o on Tahiti’s southeastern coast. The area’s shallow coral reef system creates some of the world’s biggest barreling waves, which attract surfers from around the world. McKenna captures the majestic power of these surges in these black-and-white photographs; you can find more of his work on his website and Instagram. (Image credit: T. McKenna; via Colossal)
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)
Like most microswimmers, these Synura uvella algae use cilia to swim. Cilia are tiny, hair-like appendages that flap to produce thrust. Even under a microscope, the cilia are hard to see because they are so thin and move quickly in and out of the microscope’s narrow focus. A cilia’s stroke is always asymmetric — no simple back-and-forth motions for them — because, at the algae’s scale, symmetric motion won’t move you anywhere. This is a peculiar feature of small swimmers in viscous fluids. At the human scale, we can mimic the same physics by mixing and unmixing fluids like corn syrup. (Video and image credit: L. Cesteros; via Nikon Small World in Motion)
Viscous fingers form when a low-viscosity fluid is pumped into a narrow, viscous-fluid-filled gap. The branching pattern that forms depends on the ratio of the two viscosities, among other factors. To better understand what goes on inside these fingers, researchers carefully alternated injecting dyed and undyed fluid. This creates a pattern of concentric rings that deform as the fingers spread.
In this particular study, the initial fluid and injected fluids are miscible, meaning that they can mix into one another. In modeling their experiments, the team found that this mixing created stratification — i.e., layers of fluids with different densities — in the narrow gap between their plates. The stratification’s effects were large enough that the model required a correction term for them; that’s a bit surprising because we’d usually expect that the tiny third-dimension of the gap would be too small to matter! (Image and research credit: S. Gowan et al.)
It’s wild that we’re still discovering new weather phenomena, but the gigantic jets seen here were only identified in 2002. This uncommon type of lightning shoots up from the tops of thunderstorms into the ionosphere. The video/image above was caught by cameras normally used to monitor meteors. The jets themselves are red in color, a result of the electrical discharge interacting with nitrogen in the atmosphere. (Video and image credits: b/w – Caribbean Astronomy Society, color – F. Lucena; via Gizmodo)
When a drop settles gently against a pool of the same liquid, it will coalesce. The process is not always a complete one, though; sometimes a smaller droplet breaks away and remains behind (to eventually do its own settling and coalescence). When this happens, it’s known as partial coalescence.
Here, researchers investigate ways to tune partial coalescence, specifically to produce more than a single droplet. To do so, they add surfactants to the oil layer surrounding their water droplet. The surfactants make the rebounding column of water skinnier, which triggers the Rayleigh-Plateau instability that’s necessary to break the column into more than one droplet. (Image and video credit: T. Dong and P. Angeli)
Pour the Greek liquor ouzo into water, and your glass will billow with a milky, white cloud, formed from tiny oil droplets. The drink’s unusual dynamics come from the interactions of three ingredients: water, oil, and ethanol. Ethanol is able to dissolve in both water and oil, but water and oil themselves do not mix.
In this video, researchers explore the turbulent effects of pouring ouzo into water. In particular, pouring from the top creates a fountain-like effect, due to a tug-of-war between the ouzo’s momentum and its buoyancy. Momentum wants the ouzo to push down into the water, and buoyancy tries to lift it back up. For an extra neat effect, they also show what happens when the ouzo is confined to a 2D plane and what happens when momentum and buoyancy act together instead of oppositely. (Image and video credit: Y. Lee et al.)
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.
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.)
For bridges, deep-sea platforms, and marine wind turbines, engineers have to build secure foundations able to withstand extremely heavy loads. Just how do they do this? One technique — driven piles — is as simple as driving poles into the ground. This is the method medieval engineers used to establish the city of Venice, but the origins of the technique are lost to history. Driving piles compacts the ground around and beneath the foundation, enabling it to withstand far greater loads.
In some applications, hammering piles just isn’t practical. Drilling piles is another common technique. In this method, the drilled hole is reinforced with an outer casing, then concrete is pumped in to harden. Drilled piles will work even underwater, as long as the concrete gets pumped in from the bottom. Then it can push water up and out of the casing without absorbing enough water to change its properties. (Video and image credit: Practical Engineering)
