FYFD

Tag: geology

  • Prehistoric Seiche

    Prehistoric Seiche

    Sixty-six million years ago, a meteorite impact in modern-day Mexico wiped out the dinosaurs and most other living species of the time. To call the event catastrophic feels like an understatement. At the site of impact, rocks and animals were vaporized. Further away, molten rock condensed into glass beads that form a geological layer found around the world.

    Still further away, in what is now North Dakota and was then the bank of a freshwater river, scientists have discovered a deposit full of saltwater fish, sharks, and rays that would have lived in the vast inland sea (A) that stretched northward from Texas. The meteorite’s impact pushed these creatures kilometers upstream against the river’s natural flow.

    One possible explanation for the inundation is a tsunami. But geological evidence indicates the deposit took place within 15 minutes to two hours of the impact, when glass beads were still raining down. To travel the 3,000 km from the point of impact would take a tsunami on the order of 18 hours – far too long.

    Instead, the deposit is likely the result of a seiche (pronounced “saysh”) – a type of standing wave that occurs in an enclosed or partially enclosed body of water. If you imagine water sloshing in a cup or a tub, that’s essentially what a seiche is, but this was on a much larger scale. (For an example, check out this insane footage of an earthquake-induced seiche in a swimming pool.)

    What set the seiche to sloshing are the seismic waves triggered by the meteorite impact. They would have reached this site 6-13 minutes after the impact and triggered waves on the order of 10m. As the waves drove up the riverways, they carried dead and dying sea creatures with them, leaving them stranded on the riverbank until scientists uncovered them tens of millions of years later. (Image and research credit: R. DePalma et al.; via The Conversation; submitted by Kam-Yung Soh)

  • Forming a Waterfall

    Forming a Waterfall

    Many factors can affect a waterfall’s formation – changes in bedrock structure, tectonic shifts, and glacial motion, to name a few. But a new study suggests that some waterfalls may be self-forming. Using a lab-scale experiment, researchers created a homogeneous “bedrock” out of polyurethane foam, which they eroded with a combination of constant water flow and particulates. Even without external perturbations, the flow carved out a series of steps.

    As a pool deepened, particles built up inside, armoring the bed against further erosion. But further downstream, the chute continued to erode, steepening the area between them until a waterfall formed. On the timescale of the experiment, the waterfalls lasted only 20 minutes or so, but that’s equivalent to up to 10,000 years in geological time. (Image credit: M. Huey; research credit: J. Scheingross et al.; via EOS News; submitted by Kam-Yung Soh)

  • Magma Mixing

    Magma Mixing

    Magmas typically consist of a mixture of molten liquid, bubbles, and solid crystals. As they mix, those crystals can sink from one viscous layer into another. To investigate this sort of process, researchers studied solid particles sinking across an interface between two viscous liquids. This is what we see above. One fluid is clear; the other is dyed red, and gravity points toward the left so the particles fall from right to left.

    What happens when the particle reaches the interface between fluids depends on three main factors: the gravitational force acting on the particle, the surface tension at the interface, and the ratio of the viscosities of the two fluids. The researchers observed two main outcomes. In one (top), the particle slows at the interface and breaks through slowly, its surface wetted by the second fluid so that it drags little to none of the previous fluid with it. The researchers named this the film drainage mode. It tends to occur when the viscosity ratio between fluids is large.

    The second method, shown in the bottom image, is the tailing mode. As the particle approaches, the interface deforms. A thick layer of the first fluid coats the particle even as it pass through, forming a tail that destabilizes behind the falling particle. This mode occurs when the viscosity ratio is small or the gravitational force is large compared to the surface tension. (Image and research credit: P. Jarvis et al.)

  • Landslide Lubrication

    Landslide Lubrication

    In 2008, an 8.2 magnitude earthquake in China caused the enormous Daguangbao landslide, which loosed over one cubic kilometer of rocks and debris. That material rushed down the mountainside, running more than 4 kilometers before coming to a stop. A new study uses field measurements and laboratory experiments to explain how the landslide could run so far from its source.

    The researchers found that friction between the sliding material and the stable rock heated that layer to over 850 degrees Celsius, hot enough to start decomposing the dolomite in the fall. That vaporized carbon dioxide out of the rock, which helped lower the friction. Simultaneously, the high temperatures and high pressures within in the landslide caused recrystallization in the falling rocks; this created a viscous layer that helped lubricate the slide. The team estimated that the two mechanisms working in tandem enabled the landslide to reach an estimated 60 m/s. (Image and research credit: W. Hu et al.; via Nature; submitted by Kam-Yung Soh)

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    Even Mountains Flow

    Over about 5 months of 2018, the summit of Mount Kilauea slowly collapsed as the volcano erupted. Seen in timelapse, it’s a remarkable reminder of the ancient Greek philosopher Heraclitus’s observation, “Everything flows.” All things change, so given enough time, just about everything can flow.

    Fluid dynamicists actually capture this concept in a dimensionless ratio known as the Deborah number. Named for a Biblical prophet who states, “The mountains flow before the Lord,” the Deborah number is defined as the ratio between the time needed for a material to respond applied stress and the time over which the process is observed. In practice, a lower Deborah number indicates a more fluid-like material while a higher one represents more solid-like behavior.

    Be sure to check out the full video. There’s some spectacular lava flow footage near the end – definitely a small Deborah number! (Video and image credit: USGS via Science; research credit: C. Neal et al.)

  • Forming an Oxbow

    Forming an Oxbow

    Without human intervention, meandering rivers become more sinuous over time. This is driven by the flow around a river bend, which tends to push sediment from the outer bank of the curve to the inner, making the bend more pronounced. Eventually, loops in the river can pinch off and form a separate oxbow lake, as seen in the animation above and video below.

    By studying many photo sequences like this one, researchers have concluded that how quickly a river bend meanders depends on its curvature. In general, the higher the curvature, the faster the river bend will migrate. When rivers deviate from this rule of thumb, it’s typically because part of a river bank is tougher to erode than other sections. (Image and video credit: Z. Sylvester/Geolounge; research credit: Z. Sylvester; via Landsat; submitted by Aatish B.)

  • Lava Bomb

    Lava Bomb

    What you see above is a homemade lava bomb. To systematically study what happens when groundwater meets lava, scientists melted basalt and created their own meter-scale explosion-on-demand. Inside the container, they can inject water and observe the resulting dynamics.

    Beneath the lava, the water forms what scientists call a domain. Thanks to the Leidenfrost effect, it can be protected from direct contact with the lava by a thin vapor layer that boils off it. If the water domain is large enough, buoyancy will pull it upward through the lava. Whether the water maintains a spherical shape or begins to distort and break up into smaller domains depends on the speed of its rise.

    At some point, though, either naturally or through an external trigger (like the sledgehammer you see above), the water and lava can contact, resulting in explosive vaporization of the water and an explosion. What’s visible at the surface depends on the depth at which the explosion takes place. Scientists are eager to characterize these variations, which will help them better predict the explosive danger of eruptions like Kilauea and Eyjafjallajökull. (Image and research credit: I. Sonder et al.; video credit: NYTimes; submitted by Kam-Yung Soh)

  • Ricequakes

    Ricequakes

    Rockfill dams, sinkholes, ice shelves, and other geological features often consist of brittle, porous materials that are partially submerged. Over time, pressure and chemical reactions with the fluid around them can cause these structures to collapse, but it can take many, many years. 

    To study the physics behind this, researchers have turned to a new model: puffed rice cereal. Like their counterparts in nature, puffed rice grains contain micropores that slowly soften and get crushed after being wetted. Researchers filled their test container with puffed rice and put it under pressure to give the whole stack a constant stress. Then they injected milk in the bottom section of the container. After an immediate collapse in the wet material (lower left), the remaining grains collapsed slowly in a series of “ricequakes”. 

    As the micropores compacted, the cereal let out audible cracks that corresponded with the motion of a crushing wavefront (lower right). The time between ricequakes increased linearly and depended on pore size. The relationship was so consistent, researchers found, that they could predict how long the puffed rice stack had been wet simply by listening to the time between crackles! Experiments like these offer scientists an exciting chance to understand geological physics that would otherwise take up to millions of years to observe. (Image and research credit: I. Einav and F. Guillard; via Physics World; submitted by Kam-Yung Soh)

  • Namibia From Above

    Namibia From Above

    From above, we see an all-new perspective on the flows of air and water that shape our world. Although they look like abstract art, these aerial photographs of Namibia by Leah Kennedy show rippling dunes and spreading fingers of water. Linear dunes like these grow when the prevailing winds are always from the same direction. Over time, rivers meander, always seeking new drainage paths. Patterns like these are probably driven by periodic flooding. (Image credit: L. Kennedy; via Colossal)

  • Watery Veins

    Watery Veins

    Glacial river veins wend and meander through these aerial photographs of Iceland by photographer Stas Bartnikas. Rivers naturally change their course over time, but here seasonal melts and the slow grinding of glaciers adds further chaos to the scene. Captured from above, these landscapes show the scars of past flows. (Image credit: S. Bartnikas; via Colossal)