The clear plastic disks use to study clogging appear rather plain — at least until you look at them through polarizers. Then the disks light up with a web of lines that reveal the unseen forces between the particles. In this video, researchers use this trick to explore how spontaneous clogs occur. If particles jam together into an arch, that bridge can be strong enough to hold the weight of all the particles above it, bringing the flow to a halt. Some arches aren’t strong enough to hold for long; they can break in moments. Other more stable arches persist. By watching the flow through polarizers and carefully tracking the ebb and flow of the forces between particles, researchers can predict which clogs will have staying power. (Video credit: B. McMillan et al.)
In a cave, mineral-rich water drips from the ceiling, spreading ions used to build stalagmites. A recent study considers how the depth of a pool affects the droplet’s splash and how material from the droplet spreads. The authors found several scenarios that vary widely depending on pool depth.
A droplet falling into a shallow pool creates a splash that quickly breaks up into droplets. This flings the red droplet material in many directions.
A drop falling into a shallow pool had a splash that quickly broke up into droplets (above). By dyeing the pool green and the droplet red, they could track where the droplet’s material wound up. The spray of small droplets carried fluid far, but the main point of impact had a strong concentration of the drop’s fluid.
With a deeper pool, the drop’s impact creates a thick crown splash that collapses in on itself. The drop’s fluid is quickly mixed into the pool.
In contrast, a deeper pool sent up a thick-walled splash crown that collapsed in on itself. This droplet’s material saw lots of mixing with the pool, but only near the point of impact. From their work, the authors concluded that models of stalagmite growth should incorporate pool depth in order to capture how minerals actually concentrate and move. (Image credit: cave – H. Roberson, others – J. Parmentier et al.; research credit: J. Parmentier et al.; via APS Physics; submitted by Kam-Yung Soh)
The Earth’s interior is almost entirely inaccessible to humanity, so how do we know what it consists of? As explained in this video, our knowledge of the planet’s interior is based on measuring waves sent out by earthquakes and nuclear blasts. Both produce two kinds of waves — pressure waves (P-waves) and shear waves (S-waves) that travel through the earth and get picked up by seismometers. Scientists noticed that pressure waves travel through the center of the planet while shear waves — which get dissipated in liquids — do not. This led them to conclude that part of Earth’s interior is a liquid. The idea of a solid inner core came from observations of pressure waves scattering in a way that only made sense if they’d hit something solid. (Video and image credit: Science)
For the first time, scientists have found evidence of deep, fast-flowing ancient rivers on Mars. After examining images taken recently by the Perseverance rover in Jezero Crater, fluvial experts have spotted familiar signs of turbulent river flow. The mosaic above shows an area nicknamed “Shrinkle Haven,” where curved bands of rock mark the landscape. Although scientists are confident that a powerful river deposited these rocks, they’re still debating whether that river was a meandering one like the Mississippi or a braided river like the Platte.
Nicknamed “Pinestand,” this hill’s sedimentary layers were likely formed by a deep, fast-moving river.
In another area, known as “Pinestand,” scientists spotted hills as high as 20 meters tall with clear sedimentary layers. Like Shrinkle Haven’s rock bands, formations like this are most often associated with a large, fast-flowing river. (Image credits: NASA/JPL-Caltech/ASU/MSSS; via Gizmodo; see also NASA JPL)
Few volcanoes are as well-studied as those of the Big Island of Hawai’i. With a host of seismic monitors and frequent eruptions, scientists know the near-surface region of Hawai’i well. But a recent study looked at nearly 200,000 seismic events after the 2018 collapse of Kilauea’s crater and found hints of what goes on much deeper.
Mapping out earthquakes beneath the island revealed a cluster of activity near a village named Pahala. These earthquakes took place 36 to 43 kilometers below the surface and seem to be connected to magma filling a sill complex there. From that deep reservoir, the team was also able to map seismic activity leading upwards to both Kilauea and Mauna Loa volcanoes. Despite the 34 kilometers between those two volcanoes, they appear to be fed through the same web of magma! (Image credit: top – USGS, illustration – J. Wilding et al.; research credit: J. Wilding et al.; via Physics Today)
This cartoon illustrates the web of magma linking Kilauea and Mauna Loa deep underground.
In their natural state, rivers are variable in their course, shifting and meandering. Sometimes they deposit sediment, and sometimes they erode it. In this video, Grady from Practical Engineering digs into the principles behind these changes. With help from Emriver‘s stream tables, which demonstrate years of changes in a river over minutes, Grady shows how changing the sediment load, flow rate, and other factors in a river affect its course. (Video credit: Practical Engineering)
Around the world, salt playas are criss-crossed with meter-sized polygons formed by ridges of salt. The origins of these structures — and the reason for their consistency across different regions of the world — have been unclear, but a new study shows that salt polygons form due to convection happening in the soil underground.
Through a combination of numerical modeling, simulation, lab-scale experiment, and field work, the team revealed the mechanism underlying salt polygons. Areas that form polygons have much greater rates of evaporation than precipitation, and, as water evaporates, these areas draw groundwater from nearby. Salt gets carried with this groundwater.
With strong evaporation, the lake bed forms a highly-concentrated layer of salty water near the surface. Convection cells form, with some regions drawing less saline water upward, while denser, saltier water sinks in other areas. The subsurface convection lines up exactly with the surface structures. The interior regions of polygons are areas where less salty water rises, and salt instead concentrates along the edges of polygons, where saltier water sinks below the surface while evaporation draws solid salt to the surface.
This snapshot shows a numerical simulation of the subsurface convection and surface evaporation that lead to salt polygon formation. Low salinity areas are yellow, while high salinity ones are black. At the surface, blue regions have the maximum upward flow and red regions have the maximum downward flow. The dark, highly saline fingers under the surface align to the red areas on the surface, indicating areas where salty water is sinking.
It’s a beautiful result that matches the size, shape, and development time observed for salt polygons in the real world. The team even excavated below salt polygons in Death Valley to confirm that the salt content below ground matched their model’s patterns. Since salt playas are a major source for dust and aerosols that affect climate, their work will be an important factor in future climate modelling. (Image credit: feature – T. Nevidoma, simulation – J. Lasser et al.; research credit: J. Lasser et al.; via APS Physics; submitted by Kam-Yung Soh)
Lava spurts from the Fagradalsfjall volcano in Iceland in this award-winning photo by Riten Dharia. It’s always bizarre to see molten rock flowing in fountains and rivers because it’s so unlike our daily experiences. Some deeply buried areas of the Earth, including the outer part of the core, are often described as liquid rock, which brings to mind lava. But that’s not, in fact, what those regions are like. If you were to visit Earth’s outer core in some super-submersible, you would not find a sea of lava. Instead, you would find yourself surrounded by what seemed to be solid rock. That’s not to say that the outer core is solid — just that it flows on geological timescales that are far longer than any human’s lifetime! (Image credit: R. Dharia; via Gizmodo)
This pale green plume signals the activities of Kaitoku, an underwater seamount near Japan. Periodic activity picked up there in August 2022 and continued into the new year. The rising plume likely consists of superheated acidic seawater mixed with particulates, sulfur, and rock fragments. Underwater volcanoes like this one are thought to account for up to 80 percent of our planet’s volcanic activity. (Image credit: L. Dauphin; via NASA Earth Observatory)
Though we often think of the Earth as changing slowly, some events are so catastrophic that they change the landscape irrevocably. Some 15,000 years ago, a massive lake covered what is now Missoula, Montana. Dammed in by a 2,000-foot-tall wall of glacial ice, this lake contained more water than Lakes Ontario and Erie combined. But when the ice dam broke, the lake drained in days, sending a deluge across the Pacific Northwest.
The floodwaters carved new canyons and waterfalls, left massive ripples in the landscape, and deposited rocks from thousands of kilometers away as they raged their way to the sea. It was one of the most massive floods the Earth has ever seen. And, incredibly, it happened over and over as the lake refilled and broke again. Check out this Be Smart video for even more of this incredible story. (Image and video credit: Be Smart)
