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An interdisciplinary research team led by scientists from Freie Universität Berlin and the Max Planck Institute for Meteorology has shown how deep lakes formed more than 9,500 years ago in the craters of the Tibesti Mountains and existed there for more than 5,000 years.

Regions known as large low shear velocity provinces—more memorably known as “big lower-mantle basal structures,” or BLOBs—have long been known to seismologists because seismic waves generated by earthquakes slow down when they pass through them.

One BLOB is under Africa, and the other sits below the Pacific Ocean. They are thousands of kilometers wide and may be more than a thousand kilometers high, containing up to 8% of Earth’s total volume.

The origin of the BLOBs is not certain, nor is it clear what they are made of. Many researchers think the BLOBs formed from subducting oceanic crust at ancient plate boundaries, while another hypothesis suggests they are remnants of the asteroid impact that threw up the material that became the Moon.

BLOBs are hotter than the surrounding mantle and perhaps compositionally distinct. While some research predicts they are denser than the mantle rock that houses them, other models have found the opposite.

Plume Factories

In the early 2000s, a group of scientists led by Trond Torsvik of the University of Oslo suspected a link between the BLOBs and volcanic activity at Earth’s surface. To test this theory, they mapped the location of large igneous provinces (LIPs) and kimberlites—diamond-bearing volcanic rocks that originate deep in Earth’s interior. The researchers then rewound the clock on these emplacements, restoring them to their position on Earth’s surface when the eruptions occurred.

The results, published in 2006, revealed that most of the eruptions occurred at the edges of one of the BLOBs. These findings supported the idea that large mantle plumes at BLOB edges hurl heat energy toward the surface and create LIPs. Activity at LIPs can trigger supervolcanoes, rip supercontinents apart, and release vast amounts of greenhouse gases. LIPs have even been implicated in some of Earth’s major mass extinctions.

The neat fit between eruptions and the position of the BLOBs, researchers claimed, showed that the BLOBs were immobile; tectonic plates moved relative to them, but the BLOBS themselves stayed where they were.

Not So Fast…

Nicolas Flament, a geophysicist and geodynamicist with the University of Wollongong (UOW) in Australia, said the idea of fixed BLOBs was initially attractive to researchers because it promised to fill a knowledge gap in the paleomagnetic history of Earth.

Geologists trace the movement of tectonic plates using paleomagnetic evidence, written by Earth’s magnetic field on volcanic rocks as they cool and solidify. These data can reveal the latitudinal position of an eruption on Earth’s surface, but they cannot reveal anything about longitude.

“Everything moves.”

If BLOBs are fixed in one spot, Flament said, ancient eruptions could be linked to the edges of the BLOBs, providing a much-needed reference for paleolongitude.

As a geodynamicist, however, Flament inhabits a world where, he said, “everything moves.” The concept of fixed BLOBs didn’t sit well with him. In 2022, he and some colleagues ran models that rewound Earth’s clock back a billion years. These models showed that the position of volcanic materials at the surface could be explained just as well if the BLOBs moved.

Flament and his team contend that subducting slabs disrupt the BLOBs, and they regularly break apart and remeld just like continents do at the surface. But by Flament’s own admission, there is a weakness in these findings. Like the Torsvik-led research, it “assumed that there was a link between the BLOBs and the eruptions…We didn’t actually check” to confirm that the link was there.

Bridging the Gap

Now a team led by UOW Ph.D. student Annalise Cucchiaro that includes Flament has shown through statistical modeling that large volcanic eruptions are, indeed, connected to the BLOBs. The team mapped volcanic deposits against billion-year reconstructions of mantle movement. The research was published in Communications Earth and Environment.

The scientists found a significant link between volcanic deposits and the mantle plumes that models predicted, “essentially filling that gap,” Flament said.

The researchers found no significant relationship between mantle paths and the BLOB edges, however—mantle plumes could originate from anywhere on the BLOB, not just the edge. As plumes rise through Earth’s interior, they encounter “mantle wind”—lateral movement of semisolid rock that may cause the plumes to tilt by as much as 5° from vertical. This tilting, the research showed, could account for many of the volcanic eruptions that were not directly over a BLOB.

The research also suggested that the BLOBs are slightly denser and less viscous than the surrounding mantle. Rather than being completely static, the BLOBs likely move around at a rate of about 1 centimeter per year.

Qian Yuan, a geophysicist with Texas A&M University who was not involved in the study, called the findings “very reasonable.” Yuan was the author of the asteroid origin theory of BLOB formation.

“The subducting slab is the strongest driving force of the manual convection,” he said, “so in all our models, we show the BLOBs will move around.”

Big Bottoms

Fred Richards, a geodynamicist at Imperial College London who was not involved in the study, has researched BLOBs extensively, looking for a model that accommodates everything known about them from seismological and geophysical data.

The UOW research, he said, adds to a growing body of evidence that the lower parts of the BLOBs are dense, but not too dense to prevent them from moving around. Linking a dense, viscous base to the eruption record, he said, is “something that hasn’t been clearly shown before.”

—Bill Morris, Science Writer

Citation: Morris, B. (2025), Blame it on the BLOBs, Eos, 106, https://doi.org/10.1029/2025EO250302. Published on 15 August 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Source: Geophysical Research Letters

Off the southern coast of Chile, three tectonic plates meet at a point known as the Chile Triple Junction. Two are oceanic plates, the Nazca and the Antarctic, which are separating in an active spreading center, creating a mid-ocean ridge between them. At the same time, both plates—spreading ridge included—are sliding into the mantle beneath a third plate, the South American. The Chile Triple Junction is the only place on Earth where an active spreading center is subducting under a continental plate.

Just to the east of the triple junction, beneath South America’s Patagonia region, a gap known as a slab window exists between the subducting oceanic plates. Caused by the subduction of the spreading center, the window exposes the overriding South American plate to hot mantle material from below.

Knowing the size and geometry of this opening is key for parsing out the area’s complex geology. However, limited offshore observations have left researchers unsure of where the slab window begins.

Recently, a new array of seismic stations deployed on the ocean floor off of Chile’s coast has boosted opportunities for observation. According to Azúa et al., the new seismic data help to pinpoint the beginning of the Patagonian slab window to just south of the Chile Triple Junction.

The seismic data captured shallow tectonic tremors, a type of “slow earthquake” that releases energy more gradually than conventional quakes—often over the course of several days. Slow earthquakes are increasingly being studied to enhance understanding of plate boundaries.

Using nearly 2 years’ worth of the new ocean bottom seismic data, the research team detected about 500 shallow tremors near the Chile Triple Junction. When they compared the locations of these tremors with the locations of previously detected conventional earthquakes, they noticed a distinct gap between where the two types of events occur.

The researchers interpret the gap in seismic activity as evidence of the youngest part of the Patagonian slab window, formed within the past 300,000 years.

Although further research will be needed to confirm and build on these findings, this work represents the first direct evidence of the offshore edge of this hole between the two subducting plates. (Geophysical Research Letters, https://doi.org/10.1029/2025GL115019, 2025)

—Sarah Stanley, Science Writer

Citation: Stanley, S. (2025), Finding the gap: Seismology offers slab window insights, Eos, 106, https://doi.org/10.1029/2025EO250299. Published on [DAY MONTH] 2025. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

In the face of growing global pressures, a new report from Securing Antarctica's Environmental Future (SAEF), including University of Adelaide researchers, highlights the opportunity to strengthen and future-proof Antarctic governance by responding to emerging conservation threats with coordinated, proactive measures.

SummaryCrashing ocean waves, or surf, have previously been identified as persistent generators of coherent infrasound signals from 0.5 to 20 Hz. Here, we demonstrate that infrasonic and seismic (seismo-acoustic) signals from surf are composed of repetitive transient events which can be detected and characterized using template matching. Using data collected from a series of field experiments designed to study seismo-acoustic surf signals in Santa Barbara, California, we show that source regions of these events can be constrained primarily to just offshore of a local coastal headland using a reverse-time-migration implementation on a small spatial scale (<5 km2). Our data include one continuously running infrasound sensor (September 2022–July 2023) to examine temporal signal evolution, complemented by several short-duration campaigns involving various infrasound arrays, co-located seismometers, and video recordings. Throughout varied oceanographic and atmospheric conditions, we detect up to tens of thousands of independent surf repeaters per day over the course of a year. The amplitudes of detected infrasound signals are correlated with offshore significant wave height and local wind speed. We identify coincident arrivals of seismic and infrasound signals with similar spectral characteristics, suggesting a linked source mechanism locally producing both the seismic and acoustic transient signals. Source regions estimated from array- and network-based methods correspond to the surf zone as seen in video footage, and the directions of selected transient signals align with the location of a rocky reef shelf nearshore. This work showcases the ability to extract near-real-time information about the coastal sea state from seismic and acoustic signal features.

SummaryCurrent geodetic velocities show that over half (up to 10 mm/yr) of Arabia-Eurasia shortening in the west is accommodated within a relatively narrow zone across the Kura basin of Azerbaijan, in which the most prominent active structure is the Kura fold-and-thrust belt, bordering the southern margin of the Greater Caucasus. The GNSS velocities furthermore suggest equivalent amounts of north-south right-lateral shear across the eastern Kura basin along the West Caspian fault zone that is accommodating relative motion between the Kura basin and the South Caspian basin. Although destructive historical earthquakes are known to have occurred, their spread is restricted geographically and their moment release accounts for only half of the accumulated deformation. These observations can be explained by incompleteness of the historical record, that the faults fail in rare larger earthquakes, or that they slip aseismically. To distinguish between these hypotheses we produce an InSAR velocity field using Sentinel-1 SAR data to image active tectonic deformation within the Kura basin of Azerbaijan. Tectonic signals are superimposed on those relating to non-tectonic processes, including widespread mud volcano inflation that highlights the important role of fluid flow within the basin sediments. We show aseismic creep occurs on two parallel faults of the West Caspian fault zone, and infer this also on the Kura Fold and Thrust Belt from sharp gradients in velocity indicating active fold growth. Recent paleoseismic studies of the faults imaged here indicate discrete slip events, and we speculate that the creep may be episodic, perhaps triggered by deeper earthquake events or by periods of enhanced fluid mobilisation. Together, the right-lateral and left-lateral faults appear to accommodate a large-scale expulsion of the Absheron region towards the South Caspian basin, perhaps driven by gravitational potential energy contrasts.

SummaryWhile global sea level rise is a major concern for ocean-connected coastal regions, inland seas such as the Black Sea exhibit water level changes primarily governed by regional hydrological and climatic factors. Understanding the drivers of water level variability in the Black Sea is essential due to its sensitivity to river inflow, evaporation, and limited connection to the global ocean. This study, for the first time, integrates satellite altimetry and satellite gravity data from 2003 to 2023 to analyze the long-term and seasonal variations in the Black Sea water levels, as well as local sea level variability and its driving factors. The results indicate that the sea level in the Black Sea experiences a positive trend of 1.04 ± 0.39 mm/yr. This comes, however, with a negative trend on a seasonal scale during autumn (–1.14 ± 0.27 mm/yr), which contrasts with the rising trends observed in other seasons. We found that the loading deformation induced by global mass redistribution contributes to 39 per cent of the Black Sea level trend, leading to an overestimation of actual climate-induced sea level change by 0.41 mm/yr. We further found that the reduction of precipitation and river inflow from surrounding basins leads to an increase in the salinity of the Black Sea, driving the decline in steric sea level. On the other hand, it has also increased the water mass of the Black Sea, compensating for the steric sea level drop.

Roughly two-thirds of all emissions of atmospheric methane—a highly potent greenhouse gas that is warming planet Earth—come from microbes that live in oxygen-free environments like wetlands, rice fields, landfills and the guts of cows.

Publication date: Available online 6 August 2025

Source: Advances in Space Research

Author(s): Jinrun Chen, Huan Huang, Xi Long, Leping Yang

Every human being leaves traces behind, and has done so for thousands of years. In a new study, a team led by lead author Dr. Yanming Ruan from MARUM—Center for Marine Environmental Sciences at the University of Bremen shows that human influence on soil erosion goes back much further than previously thought. Their findings have now been published in Geophysical Research Letters.

The aridity index is an invaluable tool used for estimating how dry (or how humid) a location is based on the precipitation and evapotranspiration occurring in the area. It is useful for predicting the severity of droughts, studying water availability changes due to climate change, and determining the allocation of water in resource planning.

USGS streamgages show flood conditions are now underway, with live cameras providing real-time views on the USGS HIVIS website. Glacier-caused flooding has become an annual threat since 2011, with record-breaking floods over the past two years that impacted more than 300 homes and threatened public safety.

Since the mid-1990s, the Greenland ice sheet has been losing mass, leaving only three floating tongues remaining. One of these, Nioghalvfjerdsbræ or the 79°N Glacier, is already showing the first signs of instability.

Using geochemical analyses of marine sediments, researchers have been able to quantitatively reconstruct the Atlantic Meridional Overturning Circulation over the past 12,000 years. The international research team, led by scientists from Heidelberg University and the University of Bern (Switzerland), is the first to calculate the large-scale circulation patterns of the Holocene. Their reconstruction shows that, while the AMOC experienced natural fluctuations over millennia, it remained stable for long periods of time.

Parts of Greater New Orleans are sinking by millimeters per year, increasing their vulnerability to floods and storm surges.

Flood protection infrastructure put in place in the months and years following Hurricane Katrina in 2005 could lose effectiveness more quickly than expected.

Though most of the city is stable, areas near the Louis Armstrong New Orleans International Airport, sections of flood protection walls, and certain industrial sites and wetlands are losing elevation, researchers reported in Science Advances earlier this summer. The rate and scale of these losses vary because rates of subsidence are affected by multiple factors, including groundwater pumping, wetland drainage, construction and urban development, and natural soil compaction.

Coupled with rising sea levels, the rapid subsidence could mean that without regular upgrades, flood protection infrastructure put in place in the months and years following Hurricane Katrina in 2005 could lose effectiveness more quickly than expected.

Spotting Subsidence from Above

As part of the new research, remote sensing expert Simone Fiaschi and his colleagues used interferometric synthetic aperture radar, or InSAR, to map subsidence across the city in 2002–2007 and 2016–2020. InSAR measures the distance between a satellite orbiting Earth and the planet’s surface. When averaged over measurements taken at different times, the satellite data can be used to detect millimeter-scale changes in elevation.

Knowing where and how quickly subsidence is occurring can clue scientists in to potential causes, said Fiaschi, who now works at the InSAR company TRE ALTAMIRA. “And that’s, of course, necessary if you want to intervene or…make adjustments to protect the city.”

During both periods, research showed that much of Greater New Orleans was stable, sinking or rising by less than 2 millimeters per year.

But a few hot spots revealed larger changes. For example, the area in and around the Louis Armstrong International Airport sank by up to 27 millimeters per year between 2016 and 2020, likely because of construction of a new terminal during that time.

Areas of concrete floodwall near the airport and along sections of the Mississippi River, built as part of the city’s $15 billion Hurricane and Storm Damage Risk Reduction System, also sank by more than 10 millimeters per year as the floodwalls settled.

Identifying Problem Areas

About half of New Orleans is already below sea level; even a small change in elevation raises the risk of flooding.

The city’s infrastructure may already be showing the effects of subsidence, said Krista Jankowski, a geoscientist at the consulting firm Arcadis who lives in New Orleans but did not participate in the new research. Filled potholes become artificial high spots as the land around them continues to sink, and fire hydrant collars that used to be level with surrounding lawns now sit several inches higher.

Wetlands within and beyond the floodwalls are sinking, too. Both natural erosion and human-driven water removal could be contributing to this subsidence.

“It’s an existential consideration for people who live in New Orleans.”

Other areas are even gaining elevation in response to human activity—or lack thereof. The Michoud neighborhood, in the city’s Ninth Ward, rose by up to 6 millimeters per year between 2016 and 2020. Until 2016, groundwater extraction by a local power plant caused Michoud to sink. But when the plant was decommissioned and pumping stopped in 2016, the water table started to recover and the land began to rebound. That finding showed that at least some of the subsidence can be fixed.

“I think that’s a nice aspect of the study, that it updates earlier studies and documents what parts have been fixed and what parts are still a problem,” said Tim Dixon, a geologist at the University of South Florida who was not involved in the new research.

Monitoring and managing subsidence is “an existential consideration for people who live in New Orleans,” Jankowski said. Having a better understanding of where subsidence is concentrated and how quickly those areas are sinking, she explained, will help “make sure we’re paying attention to places where there may be issues.”

—Skyler Ware (@skylerdware.bsky.social), Science Writer

Citation: Ware, S. (2025), Parts of New Orleans are sinking, Eos, 106, https://doi.org/10.1029/2025EO250300. Published on 14 August 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Earth and Space Science

Measurements of bathymetry, the underwater depth of the ocean floor, are typically done for shallow coastal waters from boats with echosounders or from aircraft using green-wavelength lidar. However, these methods can be expensive to field, hard to update, and cannot access all locations.

NASA’s Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) mission has introduced a new satellite-derived shallow water bathymetry product that will provide free, easy-to-access, and ready-to-use measurements for the world’s shallow coastal waters. This information is of value for navigational safety, in particular for measurements in very shallow water or close to shore where boats cannot safely operate. Scientists can also use the data to study coral reefs and near-shore aquatic habitats.

The shallow water bathymetry product is derived using data from the ICESat-2 green-wavelength Advanced Topographic Laser Altimeter System (ATLAS) lidar, which operates from an orbit about 500 kilometers above the Earth’s surface.

Parrish et al. [2025] present their results of the first processing of the ICESat-2 archive, providing bathymetric measurements from approximately 0.5 to 21.5 meters depth for 13.7 million kilometers of coastal waters. This initial data set has been validated against high accuracy airborne bathymetry data acquired over eight locations in the eastern United States and the Caribbean islands. The products will be regularly updated as ICESat-2 acquires new data, filling in areas not initially measured because of rough seas or cloud cover and updating earlier measurements over time.

 ​Citation: Parrish, C. E., Magruder, L. A., Perry, J., Holwill, M., Swinski, J. P., & Kief, K. (2025). Analysis and accuracy assessment of a new global nearshore ICESat-2 bathymetric data product. Earth and Space Science, 12, e2025EA004391. https://doi.org/10.1029/2025EA004391

—Cathleen Jones, Editor, Earth and Space Science

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Author(s): A. V. Bernatskiy, I. I. Draganov, N. A. Dyatko, I. V. Kochetov, V. V. Lagunov, and V. N. Ochkin

Experimental and numerical studies of the features of the spatial distribution of plasma parameters in a discharge not limited by walls were performed. A discharge supported by a hollow cathode in helium at low pressure was ignited in a chamber with dimensions much larger than the dimensions of the …

[Phys. Rev. E 112, 025204] Published Thu Aug 14, 2025

Author(s): Michael F. Zhang, Seth Davidovits, and Nathaniel J. Fisch

We study the amplification of isotropic, incompressible turbulence through multiple planar, collisional shocks, using analytical linear theory. There are two limiting cases we explore. The first assumes shocks occur rapidly in time such that the turbulence does not evolve between shocks. Whereas the…

[Phys. Rev. E 112, 025205] Published Thu Aug 14, 2025

Author(s): Feiyu Li, Seth Dorfman, and Xiangrong Fu

The parametric decay instability (PDI) of Alfvén waves—where a pump Alfvén wave decays into a backward-propagating child Alfvén wave and a forward ion acoustic wave—is a fundamental nonlinear wave-wave interaction and holds significant implications for space and laboratory plasmas. However, to date …

[Phys. Rev. E 112, 025206] Published Thu Aug 14, 2025

The Mediterranean Sea is particularly susceptible to marine heat waves—such as the record-breaking 2022 heat wave, which was characterized by anomalously high sea surface temperatures—due to the interplay of air-sea heat fluxes and local oceanographic processes, leading to significant impacts on marine ecosystems and coastal communities.