On its face, the idea that sand and wind can come together to form massive mountainous dunes seems bizarre. But dunes — and their smaller cousins, ripples — are everywhere, not just on Earth but on other planetary bodies where fine particles and atmospheres interact. In this video, Joe Hanson gives a great overview of sand dynamics, beginning with what sand is, how it moves, and what it can ultimately form. It’s well worth a watch, even if you know a little about dunes already; I know I learned a thing or two! (Image and video credit: Be Smart)
A raft of particles floating on water has some natural cohesion from particle attraction and capillary action. But when the raft is pulled apart, what happens? Does it break cleanly in one spot? Does it stretch and deform? That’s what this video explores. It turns out that the speed you pull the raft at determines how it holds together. Every particle cluster has a preferred relaxation rate, and by choosing the pulling speed, you determine which relaxation rate — and therefore cluster size — can survive most effectively. (Image and video credit: K. Tô and S. Nagel)
In an ongoing series, Practical Engineering is looking at how civil engineers deal with sewage and wastewater. In this video, Grady looks at how wastewater gets treated to remove contaminants. Where possible, engineers use gravity to do this job, building infrastructure that slows the flow down and lets gravity make heavier particles settle out. Of course, sometimes gravity alone doesn’t act quickly enough, in which case engineers use a little extra help in the form of chemicals that can neutralize particles’ electric charge and help them clump together and settle faster. Check out the full video for a tour of how wastewater gets processed. (Image and video credit: Practical Engineering)
The green-blue plume on the left of this satellite image is an eruption from Kavachi, an underwater volcano in the Solomon Islands. Kavachi’s crest is currently estimated to lie 20 meters below the surface, with its base at a depth of 1.2 kilometers. Eruptions are quite common at the volcano, but that doesn’t stop wildlife — like hammerhead sharks! — from making the crater their home. Over the last century, Kavachi’s eruptions have repeatedly formed small islands at the surface, but they were quickly eroded away by wave action. (Image credit: J. Stevens/NASA/USGS; via NASA Earth Observatory)
In “Life and Chaos,” artists Roman Hill and Paul Mignot shot fluid flows live in a 1 cm x 1 cm square, then projected those images across 3,300 square meters. There’s something incredible about art on this immersive scale. It is literally impossible for any one visitor — or even the artists themselves — to experience the full piece; each person, by definition, can only take in a small part of the whole. That makes it all the more incredible to derive such a piece from a tiny, tiny canvas. As venues for this sort of immersive art spread, I can only imagine the amazing art we’ll see! (Image and video credit: R. Hill and P. Mignot)
With oceans warming, there’s more energy available to intensify hurricanes. And while our weather models have gotten better at predicting where hurricanes will go, they’re less good at predicting hurricane intensity, largely because capturing real data from storms is so difficult and dangerous. To address that shortfall, engineers build facilities like the one seen here, which simulates hurricane wind and water conditions so that scientists can study their interaction and better understand storm physics. Check out the full Be Smart video for a tour of the facility and a look at their work. (Image and video credit: Be Smart)
Bacteria like E. coliswim using flagella, helical filaments attached to biological motors on their bodies. By rotating the flagella, the bacterium generates thrust that propels it forward. Oddly, though, researchers observed decades ago that bacteria actually travel faster through complex fluids — like those with polymers or particles in them — than they do through simple fluids like water. A new study using colloids — small particles suspended in a liquid — shows why.
The researchers compared bacteria swimming through polymer-filled fluids and colloidal fluids and found strong overlap both qualitatively and quantitatively. They observed, for example, that bacteria swim in straighter lines — they wobble less — in complex fluids. The reason, according to the authors, is the hydrodynamic influence of the added materials. Essentially, when a bacterium swims near a colloid or piece of polymer, the particle exerts a torque on the microswimmer that reduces its wobble and enhances its speed. (Image credit: Cheng Research Group; research credit: S. Kamdar et al.; via Physics World)
Yellowstone National Park is filled with geysers, hot springs, and mudpots — all geophysical features driven by the underground movement of water heated by the underlying volcano. But what does that underground plumbing look like? To find out, a team of researchers flew a 25-m diameter electromagnetic loop over portions of the park; they used the electromagnetic feedback induced in the loop to roughly map the subsurface features of the park.
To their surprise, they found that deep hydrothermal vents in Yellowstone lie in discrete locations; previously, geologists assumed the vents were more widespread. With a better sense of what lies beneath, park officials will be able to build new infrastructure in areas better protected from one of the park’s biggest hazards: hydrothermal explosions caused by a buildup of pressure underground. (Image credits: top – I. Shturma, map – C. Finn et al.; research credit: C. Finn et al.; via Physics World)
Editor’s Note: This article was written and scheduled prior to the historic flooding in Yellowstone in June 2022.
Geophysical map of Yellowstone’s Upper Geyser Basin, including Old Faithful.
Rip currents — also known as rips — are a threat to beachgoers around the world, and, unfortunately, they’re often underestimated or misunderstood. As waves crash on the shore, water must find a path back out to sea, often through deeper channels that provide a break between the waves. These flow paths are rip currents, and they can form, shift, and intensify with little warning.
Over the years, researchers have found that efforts to educate beachgoers through signs, flags, and other methods once at the beach have done little to help visitors understand, avoid, or escape rips. Instead, it’s better to educate people long before the water is in sight. Since no one method is guaranteed success for escaping a rip, it’s better to learn to recognize and avoid these dangerous areas. Check out the video below for advice on spotting rips, and here’s a video showing rips from a surfer’s perspective, as well as one using dye flow visualization to mark a rip. Be safe and smart out there! (Image credit: P. Auitpol; video credit: Surf Life Saving Australia; via Hakai Magazine; submitted by Kam-Yung Soh)
Ferrofluids are made up of ferrous nanoparticles suspended in a carrier fluid like an oil. Under magnetic fields, they take on an array of shapes — from pointed spikes to elaborate labyrinths — depending on the field strength and what fluids they’re surrounded by. This photographic series by Linden Gledhill captures some of that fantastic variety, with ferrofluids that look like cells and nebulas in addition to mazes and tridents. See more of Gledhill’s work at his website and in previous posts. (Image credit: L. Gledhill)
