In March 2023, Southern California experienced heavy storms after almost 20 years of drought. Sixteen of these came from long, narrow regions of concentrated water vapor moving through the air, known as atmospheric rivers. During droughts, groundwater supplies up to 60% of the total water to the Greater Los Angeles area, so researchers think that stormwater from the 2023 events could have recharged groundwater reserves for future use. However, scientists lack adequate tools to assess how much groundwater is in the subsurface.

To overcome this challenge, researchers from California and Texas developed a new method to study deep groundwater. California gets a large number of earthquakes, so it has over 450 stations around the state to monitor the associated vibrations, referred to as seismic waves. To study how much the 2023 storm recharged the groundwater in the Greater Los Angeles area, the team used a tool called seismic-DI, which employs these seismic waves to estimate how much groundwater is stored at different depths. 

Seismic-DI works by measuring how fast seismic waves move through the Earth, known as their seismic velocity. The researchers explained that the Greater Los Angeles area is a very crowded city, so it produces an abundance of seismic waves. They measured changes in the seismic velocities of these underground waves to see where the groundwater is full of water, or saturated, versus partially full, or unsaturated. They used 20 years of these data to produce graphs that record changes in groundwater storage at different depths, known as hydrographs.

To validate the accuracy of seismic-DI, the researchers also compared their seismic hydrographs with groundwater thickness data from a NASA mission known as the Gravity Recovery and Climate Experiment, or GRACE. GRACE consists of 2 satellites that measure changes in Earth’s gravity, which reflect surface water and groundwater storage. Both their seismic hydrographs and the GRACE groundwater data demonstrated that the Greater Los Angeles region experienced an increase in groundwater storage from stormwater in the winter, and a reduction in groundwater storage during the dry summer. 

The team’s hydrographs showed that the 2023 storms saturated the Greater Los Angeles area groundwater down to 35 meters (114 feet), but it was abnormally dry at 200 meters (656 feet), and at a severe drought at 450 meters (1,476 feet). The GRACE data similarly demonstrated that the subsurface is in severe drought. Combined, these data indicated the 2023 storms helped the Greater Los Angeles area recover up to 90% of its groundwater at depths of 50 meters (164 feet) since the 2006-2022 drought. However, it recovered only about 40% at 75 meters (246 feet) and 20% to 30% at 100 meters (328 feet).

They concluded that the 2023 atmospheric river events recharged only shallow groundwater reserves in the Los Angeles area. As a result, they suggested future researchers consider deep groundwater reserves for a more complete assessment of total regional water deficits. While this study demonstrated that seismic-DI can successfully reveal spatial changes in groundwater and drought at depth, the team acknowledged that contributing factors like the amount, rate, and spatial variability of groundwater reserves remain targets of future work. 

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More than 90,000 tons of radioactive waste are stored on-site at nuclear power plants awaiting permanent disposal. Nuclear waste releases unstable forms of uranium and other elements, called radionuclides. Long-term exposure to radionuclides can cause cancer, so environmental safety regulations require that nuclear waste be made inaccessible for at least 1 million years. Thus, researchers are evaluating possible ways to store this waste permanently. 

One proposal is to store nuclear waste thousands of feet below ground in rock formations called deep geological repositories, or DGRs, to seal in radionuclides. Scientists can’t see into the future, so instead they look to the past to determine how well DRGs could work. A team of researchers from Canada recently analyzed uranium deposits that have existed for billions of years as an analog for how nuclear waste behaves deep underground.

Past researchers found that uranium deposits in ideal DGR conditions, with their protective casings intact, will stay contained for more than a billion years. However, these conditions require a stable geological environment. This team instead focused on uranium deposits in non-ideal conditions. They studied the Canadian Kiggavik uranium deposits, which occur in cracked bedrock approximately 500 meters (1,600 feet) below the surface. The team claimed these conditions are similar to DRGs with broken protective casings.

The team knew from previous work that most of the uranium minerals in the Kiggavik deposits are more than 274 million years old, but about 10% are less than 1 million years old. They found that these younger uranium minerals occurred alongside clay minerals surrounding the older uranium minerals and within open fractures. The researchers interpreted the older uranium as the source material of the younger uranium because of their proximity. They concluded that water must have infiltrated the deposits and interacted with older minerals, transporting uranium and forming new, younger minerals.

To determine the source of water infiltration, the researchers compared the chemistry of clay minerals formed alongside the younger uranium with modern snow in the Kiggavik region. They looked at the number of neutrons, or isotopes, in hydrogen atoms within the clay minerals, and found heavy values matching those of fresh water. These values indicated that snow or glacial meltwater was the source, rather than underlying bedrock or seawater. 

To determine when the water infiltrated over the last million years, the researchers used uranium-thorium dating to find when the radionuclides were mobilized. This dating method shows when uranium was removed from the original minerals by measuring how much its concentration was reduced by water infiltration. They found that the dates of these radionuclide mobilizations clustered into 5 separate water-infiltration events that occurred from 36 to 470 thousand years ago. 

Comparing these dates with existing climate records, the researchers found that the water infiltration events overlapped with periods when glaciers covered the ground surface. Normally, water can’t travel thousands of feet underground. But, like a hydraulic press, a glacier pushes water at its base downward. If the water encountered cracks in the ground, the pressure could inject it to the depth of the uranium deposit.

Next, the researchers wanted to measure how quickly radionuclides left the deposit. They measured the maximum distance between younger and older uranium minerals and used the age of the most recent water-infiltration event to estimate the fastest speed at which the radionuclides could have moved. They determined this maximum speed to be 0.0014 millimeters (0.000055 inches) per year. At that rate, they calculated it would take 360 million years for uranium radionuclides to travel 500 meters from a DGR at the same depth as the Kiggavik uranium deposits to the surface. This timescale far exceeds the necessary 1 million years for nuclear waste containment.

The team concluded that if glaciers were to return to Kiggavik, the uranium deposits wouldn’t experience substantial radionuclide movement, even in contact with glacial meltwater. Similarly, if a DGR has broken protective casings, radionuclides would be moving too slowly to reach the surface even if water leaked into it. They suggested their findings reduce constraints on viable DGR sites and could help ensure the long-term secure storage of nuclear waste.

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Waterfalls play an essential role in river development and landscape evolution. Researchers are particularly interested in how abrupt changes in the steepness of a river channel, also called knickpoints, develop. Knickpoints vary in size and can be as small as your index finger or as large as Niagara Falls. Researchers from Virginia hypothesized that waterfalls, a type of knickpoint, can influence erosion when a river channel is cut into solid rock, called bedrock. 

The researchers wondered whether fractures and other pre-existing weaknesses can influence how water removes rock slabs from a river channel, via an erosional process called plucking. Fractures can form in many different orientations, but the researchers focused on 3. Imagine a flat tabletop that represents a riverbed. Fractures that are parallel to the flat tabletop are called horizontal fractures. If you tip the table so the low end points downstream, that’s the direction of downstream-dipping fractures. If you tip the table so the low end points upstream, that’s the direction of upstream-dipping fractures. 

First, the researchers tested how fracture orientation changed erosion before an established knickpoint. They used a man-made channel, called a flume, to simulate a natural river system. To set up the experiment, they glued layers of small tiles about the size of an adult’s thumbnail to a plastic frame and put it in the flume. Then, they placed a layer of unglued tiles upstream of the knickpoint. 

To begin the experiment, the researchers incrementally increased the amount of water flowing through the flume every 5 minutes until they reached a maximum flow or all the loose tiles were “eroded.” They considered a tile to be “eroded” once it was transported over the knickpoint and downstream. The researchers measured the water depth at a fixed point upstream of the knickpoint, the number of tiles eroded through plucking, and the volume of water. They repeated this 8 times for each fracture orientation.

The team found differences in the amount and timing of erosion between the 3 orientations. In particular, they saw that erosion began at lower water speeds for horizontal beds than for tilted beds. Based on the observed erosion rates, they concluded that horizontal beds are the most susceptible to erosion, while upstream-dipping beds are the most resistant, and downstream-dipping beds fall between the 2. 

The researchers then tested how a knickpoint would develop and influence water flow if all of the tiles were unglued and free to move. They individually stacked almost 5,000 unglued tiles across the channel. Before starting the experiment, they filled the flume slowly with water to submerge all of the tiles without moving them. Then, they increased the water’s speed to start erosion. Instead of collecting measurements as they did in the first experiment, the researchers filmed this experiment and observed how the knickpoint shape changed and how plucking occurred. 

The researchers observed that the plucked tiles in this experiment formed piles downstream of the knickpoint in a process known as armoring. This armor of tiles, which represents loose rocks near a waterfall in a natural setting, prevents erosion of the underlying river bed. Only when the water transports the armor downstream can it erode the bedrock and develop a knickpoint.

Unlike the first experiment, researchers found no differences in erosion between fracture orientations in this experiment, but did observe differences in armoring. They found that upstream-dipping beds had the least armoring because water quickly transported piles of tiles near the waterfall downstream. Downstream-dipping beds had the most armoring, and their eroded tiles took longer to move downstream. 

The team concluded that waterfalls will erode at different rates based on their fracture orientation and armoring processes. The orientation of bedrock fractures also impacts the shape of the waterfall and the river channel around it. So the next time you see a large waterfall, consider that it may have started as a small fracture the size of your thumbnail.

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Don’t worry, it’s supposed to do that.

Prehistoric builders in Britain went to extraordinary lengths to create one of the country’s most striking ancient monuments. New research shows they intentionally transported enormous stones weighing more than 25 tonnes for at least 18 kilometers (11 miles) before raising them as the famous Devil’s Arrows, Britain’s tallest surviving prehistoric stone row. A study led [...]

Stonehenge is the most famous example of megalithic architecture across Britain and Ireland, but there are plenty of others, including Calanais, Newgrange, and Avebury, as well as the Devil's Arrows. The latter is Britain's tallest standing stone alignment, yet little is known about the provenance of its stones. Scientists have confirmed that the stones came from a site 18 kilometers (11 miles) away, transported by humans rather than glacial movement, according to a paper published in the Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

"Sites in southern England and Scotland receive considerable attention but monuments like the Devil's Arrows have remained comparatively understudied despite their significance," said co-author Jim Leary of the University of York. "We have now proved that Neolithic communities moved several 25-ton stones across Yorkshire, transforming a familiar site into an epic quest to create a sacred landscape."

Stonehenge has been the focus of recent chemical analyses identifying where all the stones that make up the structure came from, revealing that many originated in quarries a significant distance away. For instance, a 2019 study concluded that the 42 bluestones that make up the inner ring came all the way from western Wales. The outer layer of sarsen stones hails from much closer to home: Marlborough Downs, an area of round, grassy hills 25 to 30 km (17 miles) north of Stonehenge, which has the largest concentration of sarsen in the UK.

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Chang’e-6 samples suggest the Moon’s two very different sides may have formed when uneven heating drove magma from one hemisphere to the other. The Moon presents two dramatically different faces. Its Earth-facing hemisphere is rich in dark volcanic plains, while the farside is dominated by older highlands and a much thicker crust. New analyses of [...]

Drilling for electricity or geothermal energy is a common human-caused source of earthquakes. Drillers or engineers inject water into the earth to fracture underground rock through a process known as fracking. This allows scientists to produce clean energy almost anywhere on Earth by heating up water in the cracks using facilities called enhanced geothermal systems or EGS plants. However, fracking causes earthquakes, which are a major concern for people’s safety globally. Therefore, scientists are looking for new fracking methods that cause fewer earthquakes.

Fracking for EGS plants can trigger earthquakes by changing the pressure underground and adding stress to the surrounding rock. However, these earthquakes happen at pre-existing, naturally occurring cracks called faults, which are different from the newly formed, man-made cracks. Faults are naturally under pressure from the overlying rock and the surrounding earth since they reach deep underground. As pressure builds up over time, it eventually causes the rocks to shift along these faults and release energy in the form of earthquakes. 

During fracking, engineers use 4 different shut-in strategies to finish off water pumping. The standard industry strategy is called instant shut-in, where the injection pump is turned off immediately, but the water stays underground, causing the pressure to lower naturally. In a similar strategy, known as the tapered shut-in, engineers gradually reduce the water injection rate to zero instead of immediately turning it off. For the high-rate and low-rate extraction strategies, they pump the water back out after injection is complete, at different pump rates.

Recently, scientists aimed to mitigate the risk of earthquakes by testing these 4 shut-in strategies to determine which is most effective. They compared the shut-in strategies using crystalline basement rock with low porosity and permeability, meaning water couldn’t easily flow through it. Engineers use this same type of rock for EGS plants so they can control where the water flows. The scientists pumped water into the rock, then measured the pressure and stress levels where rocks began to move along faults, determining the point at which earthquakes would occur. 

The scientists applied high-rate and low-rate extraction methods to the rock and found that pressure and fault movements decreased. However, when they applied instant and tapered shut-in methods to the same rock, they increased the pressure and caused continuous fault slipping. They measured stress in the rock during these methods and found that high-rate extraction stabilized the fastest, while low-rate extraction stabilized more slowly. In contrast, instant shut-in continuously increased the pressure and slip, and tapered shut-in caused the highest stress of all.

The scientists also used a computer model to simulate what happened at an EGS site in South Korea, where earthquakes occurred after injections using the instant shut-in method. They set up the model using a rock with the same characteristics, injection wells, and faults as that site. Then, they simulated periods of injection based on the previous real-world events and modeled the effects of pressure and stress to determine if the earthquakes could have been prevented. 

The team used the model to compare how a site like this would respond to the instant shut-in method versus the other shut-in methods. They found that the tapered shut-in method increased pressure and stress in the rock, while the high-rate and low-rate methods both decreased pressure and stress. The high-rate method decreased pressure and stress more than the low-rate method. 

The scientists concluded that high-rate extraction is the most effective method for reducing the risks of post-injection earthquakes during EGS fracking in crystalline basement rock. Additionally, the scientists determined that the earthquakes in South Korea could have been prevented if engineers had used either the high-rate or low-rate extraction methods. They recommend using high-rate extraction to reduce earthquakes during EGS fracking, which would allow EGS plants to generate clean energy more safely.

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Since the formation of the Earth 4.2 billion years ago, hot rock from the interior of the planet has cooled off and developed crystals that accumulated over millions of years, forming surface rocks with a layered composition, referred to as continental crust. Geologic evidence of how continental crust formed comes from large, ancient crustal blocks, called cratons. Cratons have existed for billions of years and form the cores of continents. 

Scientists have shown that the upper 10 to 15 kilometers (6 to 9 miles) of continental crust contains high concentrations of elements like uranium and thorium that decay and release heat over time, referred to as radiogenic elements. However, the lower 20 kilometers (12 miles) of crust has very few radiogenic elements. The cause of this planetary-scale differentiation is highly questioned, as geoscientists don’t know what formation processes could produce this unique characteristic. 

Earlier researchers suggested that changes in the concentration of radiogenic elements could occur when tectonic plates collide. Plate collision induces temperatures in the lower crust high enough to melt minerals that contain uranium and thorium, like zircon and monazite. The newly melted minerals form magma, which then rises and crystallizes in the upper crust. To test whether this process formed the layered continental crust, researchers Andrew J. Smye and Peter B. Keleman incorporated geochemical data from studies worldwide into a mathematical model comparing how concentrations of radiogenic elements vary under different temperatures. 

The team separated their global analyses into 2 categories of rocks that were buried deep in the crust and subjected to intense pressures and temperatures, via a process known as metamorphism. The first category included rocks formed from the accumulation of eroded grains buried in the deep crust that are subjected to high pressures and temperatures, called metasedimentary rocks. The second category included rocks formed when magma rises from the deep Earth and solidifies before experiencing high pressures and temperatures, called metaigneous rocks.

The researchers analyzed 3 subcategories from each of the 2 types of deep-crustal rocks. The first was rocks that experienced no intense pressure or temperature, the second was rocks subjected to 650 to 900°C (about 1,200 to 1,650°F), and the third was rocks subjected to 900 to 1,100°C (about 1,650 to 2,000°F). The researchers modeled the geochemistry of the 3 rock types at different temperatures to determine whether ultra-high-temperature metamorphism could cause crustal differentiation of radiogenic elements.

Smye and Keleman found that monazite doesn’t melt in either metasedimentary or metaigneous rocks at temperatures below 900°C, as indicated by the relatively high thorium content in these deep-crustal rocks. Alternatively, they found that above 900°C, uranium and thorium concentrations decreased in metasedimentary rocks, suggesting that minerals like zircon and monazite were melting. The melted minerals enter magma and rise into the upper crust, leaving behind metasedimentary rocks depleted in radiogenic elements by around 0.10 ppm.  

The team concluded that the enrichment of uranium and thorium in the upper continental crust requires temperatures greater than 900°C to initiate the melting of zircon and monazite in the lower crust. Temperatures above 900°C are linked to the movement and collision of continental plates. This result suggests that evidence of Earth’s differentiation has been preserved for more than 3 billion years, spanning most of the planet’s geological history. Since stable continental crust formed, uranium and thorium enrichment in the upper crust has consistently recorded layering produced by ultra-high temperature metamorphism.

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Ocean Geology • Methane Hydrates • Gulf of Mexico Scientists mapped 70 seismic indicators of methane-hydrate stability beneath the northern Gulf of Mexico. Instead of following the neat pattern expected from pressure and temperature, the inferred boundaries wander by hundreds of meters — and researchers still cannot fully explain why. Conceptual cross-section of methane-hydrate stability […]

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A geologist reflects on the disaster and explains why rapid warming will make deadly glacial floods far more common.

© Jason Gulley for The New York Times

Since the 1850s, plowing and clear-cutting in modern agriculture have increased how fast soil erodes in the Upper Mississippi River Valley. Across the globe, farming strips soil up to 100 times faster than natural processes. It also removes farmable land and clogs waterways, threatening long-term environmental sustainability. However, scientists in the past have struggled to separate the effects of land-use changes from the transition out of the last ice age over the past 20,000 years. 

To determine whether current farming practices are sustainable, researchers from Minnesota recently measured the speed at which soil eroded during the ice age transition and compared it with modern agricultural erosion. They focused on the Trout Creek tributary of the Mississippi River. This tributary has 2 step-like formations, or terraces, on its bank that represent past floodplains before the river eroded to its current level. 

The oldest, upper terrace is about 14 meters (50 feet) above the lower terrace, which is about 8 meters (26 feet) above the modern floodplain. Scientists studying nearby areas have suggested that the terraces contain sediment from the last ice age, 20,000 years ago, referred to as the Last Glacial Maximum, to today. 

In the upper terrace, the researchers pushed an empty cylinder into the ground, like a straw into a layer cake, to collect a cylindrical sample of sediments about 4 centimeters (1.5 inches) wide and 6 meters (20 feet) deep, called a sediment core. They collected slices of this core from 2 meters (6 feet) and 6 meters (20 feet) to find the terrace’s age. 

Some grains in the sediment trap electrons while buried and release them when exposed to light. So the team shone light on the sediment slices to stimulate these electrons and measure the intensity of light emitted, known as their optically stimulated luminescence. Brighter light emissions indicate the sediment is older and was buried for a longer period of time. Using this method, they confirmed that the deep sediment slice was 22,000 years old, and the shallow sediment slice was 20,000 years old, dating the terrace back to the Last Glacial Maximum.

Next, the team drilled into the upper terrace with an auger to collect 25-centimeter (10-inch) wide plastic tubes of sediment. They pulled 4 samples from 0 to 2 meters (0 to 6 feet), and 1 sample from 6 meters (20 feet) deep. They explained that minerals in the sediment called quartz produce the radioactive form of the element beryllium, known as ¹⁰Be, when exposed to the Sun, so low ¹⁰Be means the sediment was buried quickly and had little sun exposure. The team measured the concentration of ¹⁰Be in each sediment sample and used an online calculator to estimate how quickly it eroded. The researchers calculated that during the Last Glacial Maximum, 0.073 millimeters (0.003 inches) of surface sediment were removed per year.

The researchers collected similar samples from the lower terrace and used optically stimulated luminescence to determine that it was between 22,000 and 14,000 years old. This terrace was the floodplain during the transition out of the Last Glacial Maximum, or deglacial period, where temperatures warmed and permafrost retreated. They measured the concentration of ¹⁰Be in samples from this terrace and determined that 0.049 millimeters (0.002 inches) of surface sediment were removed per year. 

Finally, the researchers measured ¹⁰Be in a sediment sample from the modern floodplain, deposited between 14,00 years ago and today. They found that the sediment had eroded 0.053 millimeters (0.002 inches) per year during that interval, at a rate slower than it had during the glacial period, but similar to the deglacial period. 

The researchers compared their findings to the average soil loss caused by modern agriculture, as reported by 4 previous scientists studying the area. They saw that modern farming removes an average of 0.60 millimeters (0.02 inches) of soil per year, which is 8 to 12 times greater than all the natural erosion rates they calculated. 

They concluded that the recent spike in soil loss from agriculture greatly exceeds that caused by the largest natural climate transition in recent Earth history. Human-driven erosion shows an upward “hockey stick” trend like the one seen in global temperatures, suggesting that similar trends could exist throughout Earth systems. The team concluded that modern agricultural practices aren’t currently sustainable. While measures like native plant reintroduction can help curb this trend, more research is required to determine how best to limit long-term erosion.

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Temperatures in the Arctic are increasing at a rate 4 times faster than the average global temperature. Scientists have documented the global effects of climate change, but there are still regions where these effects are less well known. This is the case for freshwater ecosystems in the Arctic.  

When the ground has been permanently frozen for 2 years, scientists call it permafrost. Permafrost contains soil, sand, rocks, and organic matter held together by ice. As temperatures rise, permafrost thaws, which can change groundwater flow paths. It can also alter a stream’s temperature, flow patterns, and nutrient loads by introducing new material from the permafrost.  

To determine how thawing permafrost affects Arctic ecosystems, scientists from the U.S. Geological Survey recently studied 10 headwater streams within the Brooks Range in the Noatak National Preserve of Alaska. The scientists studied streams with different amounts of permafrost and ice to test whether connections exist between permafrost, food webs, and populations of fish called the Dolly Varden and Arctic Graylings. They focused on these 2 species of fish because their migrations often indicate ecological shifts in the area.    

The scientists collected fish from the streams by temporarily stunning them, using a method called electrofishing, or by catching them in minnow traps. They manually identified each species they collected, then froze the fish and shipped them to a lab. Once in the lab, the scientists measured the length of each fish and used documented growth patterns to estimate its biomass. To calculate fish abundances, they divided their total biomass by the time spent electrofishing or trapping. Finally, they measured the energy density of each fish by burning it in a device called a bomb calorimeter. 

At each stream, the scientists took manual temperature measurements and deployed loggers that recorded the temperature every 15 minutes. They also deployed equipment at the bottom of each stream to record water pressure in 15-minute intervals and converted the data to depth, since pressure increases with depth. Then, they used wading rods to measure how much water was flowing through each stream at a given spot. 

They combined the depth and wading rod data to determine the flow rate of water in the streams over time. They used these data to identify unstable streams where water rose and fell rapidly. They also collected water samples from each stream and measured their nutrient concentrations, including dissolved organic carbon, nitrogen, and phosphorus, to determine water quality.   

Finally, they measured 2 types of smaller organisms that allow energy to flow through the food web to the fish, called microbial biofilms and macroinvertebrates. They used a hand-held device to estimate the types and amounts of biofilms, and nets to collect macroinvertebrates.

Once they had compiled these data, the team conducted a statistical analysis to compare the studied parameters and fish populations to the extent of permafrost in each area. They found that streams with more permafrost in the area had warmer temperatures, because the permafrost prevented water from infiltrating the soil to cool off. The streams with warmer temperatures, in turn, had lower abundances and biomass of Dolly Varden fish and Arctic Grayling with lower energy densities. They suggested that these results meant that the high temperatures had pushed the fish above their optimum temperature range. 

They also learned that the limited infiltration in permafrost areas caused rainfall to flow straight into the stream. This process created instability as the stream levels rose and fell rapidly. Fish in these unstable streams had lower energy densities, likely due to the harsher environment. 

Areas with greater permafrost also had higher concentrations of dissolved organic carbon and phosphorus, which stimulated the formation of biofilms at the bottom of the food chain. They noted that areas with more biofilms also had more macroinvertebrates and more Dolly Varden biomass. Since the Dolly Varden eats macroinvertebrates, this finding suggested that the lowest levels of the food web shape the health of species higher up. This is called the bottom-up effect, and means that areas with more biofilms and macroinvertebrates will likely have healthier and larger fish populations.  

The scientists explained that knowing how these factors influence Arctic fish populations can help researchers understand how thawing permafrost might affect Arctic ecosystems in the future. They anticipated that their data could help future researchers predict how these and other ecosystems will be impacted by changing landscape dynamics caused by global warming. 

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Have you ever experienced a severe weather event, like a hurricane or a tornado? Researchers have shown that climate change is causing such weather events to become more extreme and more frequent, destroying communities and infrastructure. To determine which areas are most at risk, researchers from Canada studied the environmental effects of a powerful flooding event that occurred in southwestern British Columbia (BC) in November 2021. 

They focused on a type of severe flooding event that is characteristic of the North American Pacific coastal region, called an atmospheric river. An atmospheric river occurs when a long, narrow vapor cloud flows toward land from the Pacific Ocean, causing heavy rainstorms. In November 2021, an atmospheric river in southwestern BC destroyed numerous regional highways, pipelines, power lines, and railways within its path. Over 18,000 people were evacuated due to flooding, and 6 people died. 

The team explained that before the storm, BC experienced a severe drought and an unprecedented heatwave, followed by widespread thunderstorm activity. In 2021, lightning and human activity caused nearly 1,000 wildfires, which led to the third-worst wildfire season ever recorded in BC, partially because trees grow back slowly in forests that have been cut down or harvested. Poor vegetation recovery makes harvested forests more vulnerable to wildfires than old-growth forests. The November atmospheric river occurred shortly after this wildfire season. 

To determine how the atmospheric river impacted southwestern BC, the researchers analyzed approximately 70,000 square kilometers (27,027 square miles) of affected area. They compared satellite images of southwestern BC from Google Earth, Sentinel, and Landsat taken before and after the event to detect changes in river channels and identify geohazards, like landslides and debris flows. They also used satellite images and Canadian government data to identify which forests had been harvested within the study area. The researchers then traversed the area to confirm their remote analyses. 

The researchers used a type of 3D remote sensing, called light detection and ranging, or lidar, to measure how the 2021 atmospheric river redistributed sediment in the Coquihalla and Coldwater River valleys. With the help of lidar, the researchers discovered that both rivers had severely unstable banks due to erosion from the flooding event. Along the Coquihalla River, approximately 53,000 cubic meters (1,871,677 cubic feet) of sediment were eroded, while nearly 50,000 cubic meters (1,765,733 cubic feet) of sediment were eroded along the Coldwater River. 

The researchers also found that hillslope geohazards increased the volume of sediment in both rivers. And in some cases, upstream areas with a history of forest harvesting and wildfires also affected stable banks downstream. For example, they identified debris flows on an unstable hillslope that triggered a landslide on a riverbank downstream. They observed that the river and stream channels shifted due to a sudden addition of sediment from hillslope geohazards and floodwater during the event.

In total, the researchers documented over 1,300 geohazards along 47 kilometers (about 30 miles) of the Coquihalla River and 19 kilometers (about 12 miles) of the Coldwater River and nearby creeks. Nearly half of the geohazards originated in an area with a history of wildfires or forest harvesting. Of the 155 geohazards at the Coquilhalla River, 43% occurred below forest harvesting resource roads, and of the 117 geohazards observed at the Coldwater River, 29% originated in areas with past wildfires.

The researchers suggested that their findings could help scientists predict where severe geohazards will occur during extreme weather events, since both watersheds had geohazards originating in harvested forests. Before 2000, clear-cutting was a widespread practice in BC, and the team’s results demonstrate that unsustainable harvesting practices like this can have lasting environmental impacts.

The researchers concluded that both forest harvesting and wildfires contributed to the severe impacts of the November 2021 atmospheric river, causing catastrophic landslides and debris flows to occur in traditionally dry regions. They suggested that more accurate risk assessments can better equip communities for severe weather events like this. While the next atmospheric river that lands in the Pacific coastal region may be worse than the last, this study can inform scientists and communities about which areas it might affect most.

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How special is Earth? It's one of those questions that runs through all of science, and here's a version of it most people have never thought about: why does our planet even have continents? A group of geologists now says the answer lies somewhere unexpected, in the shape of the Milky Way itself. Let's take a look.

Horseshoe crabs are marine animals more closely related to spiders than crabs. These animals have existed for more than 450 million years, and are sometimes called “living fossils” because they appear to have changed very little throughout their evolutionary history. However, horseshoe crabs have a poor fossil record, so this apparent lack of change could also be due to a lack of evidence, particularly when it comes to their reproduction. Scientists want to know: Are horseshoe crabs truly living fossils?

Modern horseshoe crabs reproduce by releasing hundreds of eggs and sperm into tidal waters, via a process called external fertilization. Until now, scientists have assumed that horseshoe crabs have always reproduced this way. But paleontologists have only found 3 fossil horseshoe crabs from the past 252 million years with their reproductive systems preserved, so this assumption is mainly based on an absence of evidence to the contrary. 

Scientists in the past interpreted the horseshoe crab’s long history of external fertilization as indicative of its evolutionary consistency. However, James Lamsdell and colleagues recently discovered a new fossil species of horseshoe crab in the 450 million-year-old Big Hill Formation in Michigan that challenges this assumption. 

To study the specimen, the scientists photographed it under 2 types of microscopes. The first type of microscope used polarized light to see structures in the fossil that may have blended into the rock, like putting on special glasses to see subtle textures. The second type of microscope used fluorescent light to reveal soft tissue in the fossil. Only some tissues, like ovarian tissue and preserved eggs, glow under fluorescence, so this method helped the team rule out non-biological structures, like bubbles, cracks, or minerals. 

The researchers found that their analytical techniques revealed remarkable details about the ancient horseshoe crab. One unique feature of the fossil was the shape of its exoskeleton. The fossil’s exoskeleton had a more shovel-like appearance than that of modern horseshoe crabs, which are less elongated and more round. It was also about 11 times smaller than a modern adult horseshoe crab. 

The researchers also discovered that the fossil preserved an intricate network of ovaries containing unfertilized eggs. This ovarian network lined the interior surface of the shell in a band of interconnected tubes, preserving both unfertilized eggs and developing eggs. They noted that the fossil eggs were all about 0.1 to 0.15 millimeters in diameter, about the same width as a human hair. This size consistency suggested that all the eggs developed at the same time, via a process called synchronous development. 

Since the fossil crab’s ovarian tubes contained developing eggs, it was an adult, meaning that the earliest adult horseshoe crabs were significantly smaller and shaped differently than modern adult horseshoe crabs. Despite their differences in size and shape, the fossil horseshoe crab’s reproductive system closely mirrored its modern one, in terms of its ovarian system and synchronous development of eggs. As in previous studies, it showed no evidence of internal fertilization.

The researchers concluded that the earliest horseshoe crabs also reproduced through external fertilization. This fossil horseshoe crab is more than 215 million years older than preexisting fossils preserving evidence of external fertilization, and suggests that the horseshoe crab’s mode of reproduction has been conserved for almost half a billion years!

However, the team’s findings reveal a more nuanced evolutionary history for the horseshoe crab than previously assumed. Although they’ve maintained the same reproductive system for almost half a billion years, the size and shape of their exoskeleton have changed. This discovery reveals that different parts of the horseshoe crab evolved at different rates. It seems that horseshoe crabs are not entirely the living fossils scientists once thought… while their bodies have evolved, their reproduction has endured.

The post Are horseshoe crabs truly “living fossils”? appeared first on Sciworthy.

Researchers used New Horizons images to identify evidence that liquid nitrogen may have flowed from beneath Pluto’s famous heart-shaped glacier. Dark markings across part of Pluto’s enormous heart-shaped glacier may record something unexpected beneath its frozen surface: liquid nitrogen moving upward and briefly flowing across the ice. Using observations from NASA’s New Horizons spacecraft, researchers [...]

Ireland’s iconic table mountain has a fascinating geological history.

Mount Toba was the biggest volcanic eruption in the last 2.6 million years, and some have suggested it nearly wiped out humanity. Around 74,000 years ago, a caldera on what is now Sumatra emptied thousands of cubic kilometers of magma in about two weeks, roughly a thousand times more than Mount Pinatubo spewed out in 1991. “People thought it might have caused massive cooling of the planet, and hence threatened the survival of our ancestors,” says Jinheum Park, a geoscientist at Johannes Gutenberg University in Mainz, Germany.

Park and his colleagues went looking for the records of that catastrophe in the mud taken from the bottom of a small crater lake on the Kenya-Tanzania border. They found instead that the effects of the Mount Toba eruption lasted under two years and amounted to perhaps half a degree of cooling.

Muddy calendars

Volcanic eruptions inject sulfur dioxide into the stratosphere, where it becomes a haze of tiny droplets that reflect sunlight back into space. Bigger eruptions eject more sulfur dioxide and, in principle, cause more cooling. But this trend stops working when the eruption exceeds a certain magnitude. “Bigger sulfate aerosols settle quickly, because they are heavier,” Park explains. This quick settling makes them less effective in scattering incoming solar radiation.

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