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Nicole SharpLa Grande Dune du PilatSouthwest of Bordeaux in France stands Europe’s tallest sand dune, La Grande Dune du Pilat. Some 2.7 kilometers long and over 100 meters high, this dune took shape here over thousands of years. It moves inland a few meters every year as winds blowing from the Atlantic push sand up its shallow seaward side to the dune’s crest. There, sand will avalanche down the steeper leeward side, advancing the dune little by little. The dune’s accumulation has not been steady; during cooler and drier times, sand has collected there, but it took warmer and wetter climes to grow the forests that have helped stabilize the soil and build the dune higher. Humanity has played a role as well, at times introducing new tree species to stabilize the dune. (Image credit: W. Liang; via <a href="https://earthobservatory.nasa.gov/images/154130/a-morphing-monument-of-sand?__readwiseLocation=" rel="nofollow noopener" target="_blank">NASA Earth Observatory</a>)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/aeolian-processes/" target="_blank">#aeolianProcesses</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/dunes/" target="_blank">#dunes</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/geophysics/" target="_blank">#geophysics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/sand-dunes/" target="_blank">#sandDunes</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a>

Nicole SharpPour-Over PhysicsFluids labs are filled with many a coffee drinker, and even those (like me) who don’t enjoy coffee, can find plenty of fascinating physics in their labmates’ mugs. Espresso has received the lion’s share of the research in recent years, but a <a href="https://doi.org/10.1063/5.0257924" rel="nofollow noopener" target="_blank">new study</a> looks at the unique characteristics of a pour-over coffee. In this technique, coffee grounds sit in a conical filter and a stream of hot water pours over the top of the grounds. Researchers found that the ideal pour creates a powerful mixing environment in a coffee-studded water layer that sits above a V-shaped bed of grains created by the falling water jet. The best mixing, they find, requires a pour height no greater than 50 centimeters (to prevent the jet from breaking into drops) but with enough height that the falling jet stirs up the grounds. You also want to pour slowly enough to give plenty of time for mixing, without letting the jet stick to the kettle’s spout, which (again) causes the jet to break up. That ideal pour extracts more coffee flavor from the grounds, allowing you to get the same strength of brew from fewer beans. As climate change makes coffee harder to grow, coffee drinkers will want every trick to stretch their supply. (Image credit: <a href="https://unsplash.com/photos/a-cup-of-coffee-with-a-dog-on-it-ygAeDaLKJe4" rel="nofollow noopener" target="_blank">S. Satora</a>; research credit: <a href="https://doi.org/10.1063/5.0257924" rel="nofollow noopener" target="_blank">E. Park et al.</a>; via <a href="https://arstechnica.com/science/2025/04/the-trick-to-making-great-pour-over-coffee-with-fewer-beans/?__readwiseLocation=" rel="nofollow noopener" target="_blank">Ars Technica</a>)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/coffee/" target="_blank">#coffee</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/jets/" target="_blank">#jets</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/mixing/" target="_blank">#mixing</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a>

Nicole SharpOn the Mechanics of Wet Sand <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/sandholes1.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/sandholes2.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/sandholes3.png" rel="nofollow noopener" target="_blank"></a> Sand is a critical component of many built environments. As most of us learn (via sand castle), adding just the right amount of water allows sand to be quite strong. But with too little water — or too much — sand is prone to collapse. For those of us outside the construction industry, we’re most likely to run into this problem on the beach while digging holes in the sand. In this Practical Engineering video, Grady explains the forces that stabilize and destabilize piled sand and where the dangers of excavation lie. (Video and image credit: Practical Engineering)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/civil-engineering/" target="_blank">#civilEngineering</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/geophysics/" target="_blank">#geophysics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material-2/" target="_blank">#granularMaterial_</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/infrastructure/" target="_blank">#infrastructure</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/shear/" target="_blank">#shear</a>

Nicole Sharp“Dispersion” <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp2.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp3.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp4.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp5.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp6.png" rel="nofollow noopener" target="_blank"></a> <a class="" href="https://fyfluiddynamics.com/wp-content/uploads/disp1.png" rel="nofollow noopener" target="_blank"></a> In “Dispersion,” particles spread under the influence of an unseen fluid. Like Roman de Giuli’s work, filmmaker Susi Sie creates macro images that look like ice floes, deserts, and river deltas viewed from above. This similarity of patterns at both large and small scales is a specialty of fluid physics. Just as artists use it to mimic larger flows, scientists use it to study planet-scale problems in the lab. (Video and image credit: <a href="https://www.susisie.de/" rel="nofollow noopener" target="_blank">S. Sie et al.</a>)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/dispersion/" target="_blank">#dispersion</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluids-as-art/" target="_blank">#fluidsAsArt</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-flow/" target="_blank">#granularFlow</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/particulates/" target="_blank">#particulates</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/reynolds-similarity/" target="_blank">#reynoldsSimilarity</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a>

Nicole SharpThawing Permafrost Primes SlumpsAs permafrost thaws on Arctic hillsides and shorelines, the land often deforms in a unique fashion, known as a slump. Formally known as mega retrogressive thaw slumps, these areas superficially resemble a landslide. They’re also prone to repeat performances: as many as 90% of Canada’s Arctic slumps recur in the same place as previous slumps. <a href="https://doi.org/10.1029/2023JF007556" rel="nofollow noopener" target="_blank">Researchers used</a> ground-penetrating radar and other tools to study the underground structure at slumps and found that several factors contribute to this repetitive cycle.Seawater soaking into the foot of a hilly shore can destabilize the permafrost, creating a slump. That changes the nearby ground cover, exposing more permafrost to warming; their measurements showed this warming could extend tens of meters underground, priming the area for future slumps. Similarly, the mudslides and narrow ravines that form on an active slump also shift away ground cover and warm the underlying permafrost. Together, these factors suggest that once a slump forms, more slumps will occur as the underlying permafrost warms. (Image credit: M. Krautblatter; research credit: <a href="https://doi.org/10.1029/2023JF007556" rel="nofollow noopener" target="_blank">M. Krautblatter et al.</a>; via <a href="https://eos.org/research-spotlights/down-in-the-slumps-tracing-erosion-cycles-in-arctic-permafrost" rel="nofollow noopener" target="_blank">Eos</a>)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/erosion/" target="_blank">#erosion</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/geophysics/" target="_blank">#geophysics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/slump/" target="_blank">#slump</a>

Nicole SharpPredicting Landslide SpeedsKnowing what speed a landslide will reach helps us predict how much damage they can cause. That speed depends on many factors: the steepness of the terrain, the sliding distance, the thickness of the flowing layer, and the type of grains making up the flow. <a href="https://doi.org/10.1103/PhysRevLett.134.028201?_gl=1*1cocu0i*_ga*Nzc0NDI4ODAxLjE2NzI4NTgxOTE.*_ga_ZS5V2B2DR1*MTczODAwMDU2My4xLjAuMTczODAwMDU2My4wLjAuMTAzMjUxODgwMA.." rel="nofollow noopener" target="_blank">Researchers found</a> that predictions from previous studies often underestimated the speeds reached by thicker flows. Through laboratory experiments with grains of different shapes, a team found that those models mistakenly assumed a fully-developed flow — in other words, one where the grains have reached a constant final speed. While spherical grains reach that state over a short sliding distance, that’s not the case for other grains.Instead, the team used their results to build a new predictive model for landslide speeds. This one still depends on incline angle and flow thickness, but it also uses a dynamical friction coefficient to describe the granular material and capture how the flow’s speed varies with distance down the incline. (Image credit: <a href="https://unsplash.com/photos/brown-and-gray-rocky-mountain-fsj6Ly_lqOs" rel="nofollow noopener" target="_blank">W. Hasselmann</a>; research credit: <a href="https://doi.org/10.1103/PhysRevLett.134.028201?_gl=1*xhbrcp*_ga*Nzc0NDI4ODAxLjE2NzI4NTgxOTE.*_ga_ZS5V2B2DR1*MTczODAwMDU2My4xLjAuMTczODAwMDU2My4wLjAuMTAzMjUxODgwMA.." rel="nofollow noopener" target="_blank">Y. Wu et al.</a>; via <a href="https://physics.aps.org/articles/v18/13?utm_campaign=weekly&utm_medium=email&utm_source=emailalert&__readwiseLocation=" rel="nofollow noopener" target="_blank">APS News</a>)<a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/avalanche/" target="_blank">#avalanche</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/fluid-dynamics/" target="_blank">#fluidDynamics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/geophysics/" target="_blank">#geophysics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-flow/" target="_blank">#granularFlow</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/granular-material/" target="_blank">#granularMaterial</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/landslide/" target="_blank">#landslide</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/physics/" target="_blank">#physics</a> <a rel="nofollow noopener" class="hashtag u-tag u-category" href="https://fyfluiddynamics.com/tagged/science/" target="_blank">#science</a>

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