Feed aggregator

If astronomers have learned one lesson from 6,000 or so confirmed exoplanets, it’s to expect the unexpected. Even so, a giant planet orbiting a red dwarf star recently caught them by surprise. It is the largest planet relative to its host star yet discovered, and it defies the leading theory of giant-planet formation, according to a new study.

TOI-6894 b orbits an M dwarf star roughly one fifth the size and mass of the Sun—60% the mass of the next-smallest star with a giant planet. TOI-6894 b is the size of Saturn and half its mass. The planet is 40% the diameter of the host star, making it by far the highest planet-star size ratio yet seen.

“Because the star is so low mass, based on what we currently understand about planet formation and protoplanetary disks, we wouldn’t have expected it to be able to form a gas-giant planet,” said Edward Bryant, an astrophysicist at the University of Warwick in the U.K. and first author of the study, published in Nature Astronomy.

The planet was first detected by the Transiting Exoplanet Survey Satellite (TESS) in early 2020 and confirmed with additional observations over the following 3 years. TESS looks for the dip in a star’s brightness that occurs when a planet passes between it and Earth, blocking some of its light.

TESS, a planet-hunting space telescope, stares into space in this illustration. It has discovered more than 600 confirmed exoplanets, with thousands of candidate worlds awaiting confirmation. Credit: NASA Goddard Space Flight Center

Bryant and his colleagues scoured observations of 91,000 stars in the TESS catalog to determine the frequency of giant planets around low-mass red dwarfs, which are the smallest and faintest stars in the galaxy and the most common. They reported the discovery of several such planets in 2023.

The team’s new analysis shows that the transits of TOI-6894 b are record breakers, reducing the star’s brightness by 17% and hinting at how large the planet is relative to its star. The transits also show that it orbits every 3.37 days.

The follow-up observations with ground-based telescopes measured changes in the star’s radial velocity—back-and-forth “wobbles” in its motion caused by the planet’s gravitational pull that revealed the planet’s mass.

A Special Case?

The leading theory of giant planet formation, called core accretion, posits that such worlds form early in a star’s lifetime, when it is still encircled by a protoplanetary disk—a wide disk of gas and dust that comprises the raw building materials for planets. Heavier materials coalesce to form larger and larger bodies, eventually creating a core that can be several times the mass of Earth. When the core grows large enough, it gobbles up the surrounding gas, building a layered giant planet similar to Saturn or Jupiter.

“It’s a surprise to find a giant planet around such a tiny star because we just didn’t think there would be enough material there.”

“The total amount of heavy material in the disk determines how big of a core you can make,” said Joel Hartman, a research astronomer at Princeton University and a member of the study team. “It’s a surprise to find a giant planet around such a tiny star because we just didn’t think there would be enough material there.” Some studies, he added, have suggested that stars less than about one third the mass of the Sun should not be able to form giant planets at all.

“Theorists who model planet formation [with core accretion] are not able to create planets like TOI-6894 b,” said Emily Pass, an astrophysicist at the Massachusetts Institute of Technology who was not involved in the study. “So the question becomes, Are planets like TOI-6894 b special cases that formed in a different way, or does our entire model of giant planet formation need a revision?” Pass explained. “Understanding the occurrence rate of [such] planets will help test the various possibilities.”

Hinting at the Formation Mechanism

One possibility is a modified accretion mechanism, in which the growing planet hoovers up both heavy materials and gas simultaneously, forming a more mixed world.

“None of these theories can really explain this planet.”

Another possibility is direct collapse. “Instead of the core being built from the ground up, the disk fragments under its own self-gravity and directly collapses,” Bryant said. “If the disk becomes unstable in the right way, you can form giant planets around these low-mass stars. The problem is that some of the simulations predict that you would only form planets that are much, much more massive than Jupiter, which would be many times more massive than this planet. So none of these theories can really explain this planet. We’re really limited by our understanding of protoplanetary disks,” he said.

Hints of the planet’s formation mechanism may be found in its atmosphere, which is scheduled for study in the next year by the James Webb Space Telescope (JWST). As the planet passes in front of the star, starlight shining through the atmosphere will reveal its composition.

“We should be able to tell the difference in whether a planet formed from direct collapse versus core accretion by looking at the atmosphere’s metallicity,” which is the makeup of elements heavier than hydrogen and helium, Hartman said. “In the gravitational instability case, all the materials collapsed together, so the elements should all be mixed together. In the core accretion model, all the heavy elements should be in the core, with a gaseous envelope on top of it.”

Two charts compare (a) the mass and (b) size of many exoplanets to their host stars. TOI-6894 b, in purple, clearly stands out from the crowd. Credit: Bryant et al., 2025, https://doi.org/10.1038/s41550-025-02552-4, CC BY 4.0

Because of the large transit signal, TOI-6894 b should be “amenable” to additional ground-based studies, Hartman said, although none are currently planned. “We’ll wait and see what JWST tells us,” Bryant said.

—Damond Benningfield, Science Writer

Citation: Benningfield, D. (2025), A new exoplanet resets the scale, Eos, 106, https://doi.org/10.1029/2025EO250235. Published on 30 June 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.

An excellent new paper (Walden et al. 2025) examines the occurrence of accelerated movement in rock slope landslides in Alaska as adjacent glaciers melt.

The exceptional temperatures in recent days in both North America and Europe has once again highlighted the rate at which the climate is changing in response to anthropogenic increases in greenhouse gases. In most glaciated areas, retreat of the large ice masses is occurring. There has long been discussion of how the slopes adjacent to glaciers will respond to these changes.

There is a very good new open access paper (Walden et al. 2025) in the journal Natural Hazards and Earth System Sciences that examines this issue for eight landslides in southern coastal Alaska. These are large, rock slope failures in areas in which the adjacent glaciers are retreating rapidly. In some cases, the glacier has already retreated beyond the slope, leaving it bordering lakes or fjords. In other cases, the slope is still in contact with the ice, which is in retreat.

On of these landslides is at the actively retreating Barry Glacier – this is a very large rock slope failure, with an estimated volume of between 188 and 500 million cubic metres. This is a Google Earth image of the site in 1996:-

Google Earth image of the landslide at the Barry Glacier in Alaska in 1996.

And this is the same site in 2019:-

Google Earth image of the landslide at the Barry Glacier in Alaska in 2019.

And here is a slider to allow the images to be compared:-

Google Earth images.

The change in the glacier is, of course, startling, but the large rock slope landslide is also notable.

Walden et al. (2025) have used archive datasets extending back to the 1980s to examine these eight slopes as the glaciers below them changed. They found that six of the slopes have experienced a period of substantially increased rates of movement. In four sites, a pronounced acceleration was observed as the terminus of the glacier retreated past the landslide area. Two other sites showed rapid movement during a period of wet weather or as the glacier rapidly thinned. In two cases, the sites did not appear to undergo a change in behaviour.

This is illustrated by data from the Barry Glacier site. This is a part of Figure 4 from Walden et al. (2025), showing the measured landslide velocity (upper graph), the retreat of the terminus of the glacier (middle graph) and the change in thickness of the Barry glacier (lower graph). The pink shading shows onset of rapid movement. The slope underwent a really rapid phase of movement (over 20 metres per year) as the adjacent glacier thinned and the slope started to debuttress.

The behaviour of the rock slope at the Barry Glacier in Alaska. Part of Figure 4 from Walden at al. (2025).
Key parts of the original caption:
“Landslide and glacier evolution at the study sites. Row 1: landslide velocities from ITS-LIVE (black circles, with uncertainty estimates) and manual feature tracking (gray bars). Stars indicate the onset of slope-wide deformation, triangles stand for crack opening, and diamonds mean both deformation and crack opening. Row 2: terminus retreat (dark blue) and location of the landslide along the glacier centerline (light-blue shading). Row 3: glacier thickness change rates (purple) and absolute ice thickness (yellow; right-hand axis) below the landslide. … In all panels, light-red shading indicates the onset of landslide movement.

Large rock slopes are incredibly complex, and the ways in which they interact with their environment (including an adjacent glacier, but also rainfall, seismic forcing and suchlike) is also complex, so we would not expect them all to respond in the same way. But this study is important for two reasons.

First, it provides additional support for the notion that glacial debuttressing is an important element of the geomorphology of areas undergoing glacial retreat.

But second, large rock slope failures can be very hazardous, either through direct impact from the resulting rock avalanche or as a result of the generation of a localised displacement wave. This study once again highlights the need to monitor these types of slope better, to undertake hazard analyses and to ensure that local populations are prepared for the consequences of a rapid collapse event.

Reference

Walden, J., Jacquemart, M., Higman, B., Hugonnet, R., Manconi, A., and Farinotti, D. 2025. Landslide activation during deglaciation in a fjord-dominated landscape: observations from southern Alaska (1984–2022), Natural Hazards and Earth System Sciences, 25, 2045–2073, https://doi.org/10.5194/nhess-25-2045-2025.

Return to The Landslide Blog homepage Text © 2023. 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.

А.М. Быков

Огромное выделение энергии при вспышках сверхновых звёзд и наблюдения нетеплового радиоизлучения позволили В.Л. Гинзбургу и С.И. Сыроватскому более 60 лет назад обосновать гипотезу о ключевой роли сверхновых как источников основной компоненты галактических космических лучей. К настоящему моменту многоканальные наблюдения остатков сверхновых во всём диапазоне электромагнитных волн предоставили большой объём данных, подтвердивший факт ускорения протонов и электронов до энергий порядка 100 ТэВ. Остаются открытыми несколько вопросов, среди которых проблема происхождения и поиск источников наблюдаемых космических лучей высоких энергий в интервале от 100 ТэВ до 1000 ПэВ. Решение проблем эффективной конверсии кинетической энергии эжекты сверхновой, вращательной энергии пульсаров, а также анизотропных течений плазмы вокруг аккрецирующих чёрных дыр в популяцию релятивистских частиц требует кинетического моделирования нелинейных механизмов с широким динамическим диапазоном масштабов. Моделирование необходимо, чтобы определить максимальные энергии частиц, ускоряемых сверхальвеновскими течениями плазмы с вмороженными магнитными полями и бесстолкновительными ударными волнами. Задача сводится к выявлению физических механизмов сильного (сверхадиабатического) усиления магнитной турбулентности, необходимого для быстрого ускорения частиц механизмом Ферми. В обзоре представлены результаты кинетического моделирования и анализ нелинейных механизмов формирования сильной анизотропной магнитной турбулентности и спектров ускоренных частиц. Недавние наблюдения орбитальной обсерваторией IXPE (Imaging X-ray Polarimetry Explorer) поляризованного рентгеновского синхротронного излучения остатков сверхновых Тихо Браге, Кассиопея А, SN1006 и др. позволили с использованием нелинейных моделей заглянуть внутрь космических ускорителей частиц и понять механизмы модификации сильных ударных волн. Обсуждаются возможности ускорения ядер космических лучей мощными анизотропными истечениями плазмы в компактных релятивистских остатках коллапсировавших сверхновых звёзд. Молодые пульсары в двойных звёздных системах, а также аккрецирующие чёрные дыры — микроквазары могут ускорять ядра до энергий существенно выше ПэВ.

Hurricane Helene lasted only a few days in September 2024, but it altered the landscape of the Southeastern U.S. in profound ways that will affect the hazards local residents face far into the future.

A new study has revealed that small but mighty zooplankton—including copepods, krill, and salps—are key players in the Southern Ocean's ability to absorb and store carbon.

Parts of New Orleans and its surrounding wetlands are gradually sinking, and while most of the city remains stable, a new study from Tulane University researchers suggests that sections of the region's $15 billion post-Katrina flood protection system may need regular upgrades to outpace long-term land subsidence.

A new study challenges recent claims about dramatic "greening" in Antarctica and how this conflicts with decades of field-based ecological knowledge. The new opinion article, "Is Antarctica Greening?" published in Global Change Biology, responds directly to recent high-profile studies that asserted unprecedented ecological transformations based on remote sensing data.

A global study has revealed that mineral-associated organic matter (MAOM) serves as the most stable long-term reservoir of carbon across diverse ecosystems, providing new insights into how carbon moves and stabilizes in soils.

The morning of 23 July 2024 was like most summer mornings in Yellowstone National Park. Cars vied for parking spaces, bison lounged in meadows, and tourists strolled along boardwalks taking in sights of bubbling springs and spouting plumes of water and steam. All were unaware of the pressure that had built underneath Black Diamond Pool, a thermal spring in Wyoming’s Biscuit Basin about 3.5 kilometers northwest of famed Old Faithful Geyser.

Suddenly, just before 10:00 a.m., jets of muddy, rock-laden water and steam shot from the turbid depths of the pool, building into bursts as high as 400–600 feet (~120–180 meters) that showered the surrounding area and boardwalk with rocks and mud. Water from the pool surged toward the nearby Firehole River, carrying boulders and debris, and a steam plume was visible from kilometers away.

A still image taken from a video shot by a Yellowstone visitor shows the 23 July 2024 hydrothermal explosion at Black Diamond Pool. Credit: Juliet Su

Fifty-five seconds after the explosion began, it was over. Left behind was a roughly 1-square-kilometer debris field, as well as many stunned onlookers, fresh from scrambling away from the unexpected outburst and wondering what had just happened.

Safety was the paramount concern in the immediate aftermath of the event. But scientists also mobilized quickly to monitor for additional activity and to collect timely observations that could help piece together why the explosion happened. On a longer timescale, federal, state, and academic organizations are working together to better understand the dynamics and triggers of hydrothermal explosions to recognize warning signs of future events before they occur.

What Are Hydrothermal Explosions?

Hydrothermal explosions, like the July 2024 event at Black Diamond Pool (Figure 1), occur in many volcanic-hydrothermal areas around the world. When a pressurized hot water reservoir instantaneously decompresses, superheated water violently flashes to steam that has enough energy to break surrounding rock [Muffler et al., 1971; Thiéry and Mercury, 2009; Browne and Lawless, 2001; Montanaro et al., 2022].

Fig. 1. This helicopter image taken 23 July 2024 shows Biscuit Basin, with major hydrothermal features labeled. The debris field from the hydrothermal explosion is the area covered with gray sediment around Black Diamond Pool. The inset map shows the location of Biscuit Basin within Yellowstone National Park. Credit: Photo by Joe Bueter, National Park Service

Such explosions exist on a continuum from large, destructive events to smaller geyser eruptions that routinely spew water and steam into the air. Geysers are caused by constrictions in hydrothermal plumbing systems that temporarily trap boiling water and steam until the pressure is high enough for the water to erupt. Hydrothermal explosions, on the other hand, occur less frequently. They are primed by the gradual pressure increase in a confined system, followed by rapid decompression caused either by rupturing of a hydrothermal seal or by an external event like a landslide or earthquake. Large geyser eruptions can destroy geysers’ plumbing systems and throw rock and mud like hydrothermal explosions, and small, spontaneously reoccurring hydrothermal explosions may arguably be more consistent with geyser activity.

In Yellowstone National Park, at least 18 massive hydrothermal explosions have formed craters ranging from 300 to 2,500 meters across.

In Yellowstone National Park, the occurrence of hydrothermal explosions has been recognized for decades. Since the end of the most recent glaciation roughly 14,000 years ago, at least 18 massive hydrothermal explosions have formed craters ranging from 300 to 2,500 meters across, the largest of which—formed about 13,800 years ago—is the biggest explosion crater on Earth [Muffler et al., 1971; Morgan et al., 2009; Christiansen et al., 2007].

More than 2 dozen hydrothermal explosions have been documented within Yellowstone National Park since its founding in 1872 [Christiansen et al., 2007]. One of the best-observed events prior to 2024 was the explosion of Porkchop Geyser in Norris Geyser Basin on 5 September 1989 [Fournier et al., 1991]. That event—witnessed by nine people, none of whom were injured—threw small rocks and debris 60 meters from the vent and left a crater more than 10 meters wide.

Smaller hydrothermal explosions occur more frequently than larger ones (maybe as often as annually), but they usually go unwitnessed because they occur in the backcountry, at night, or during winter months. Hydrothermally active areas around the world sometimes show signs of instability or increases in temperature prior to an explosion; however, there are no known universal precursory signals upon which forecasts can be based.

Keeping Watch over Yellowstone’s Activity

The lack of knowledge about hydrothermal explosion occurrence rates, precursory signals, and triggers motivated the Yellowstone Volcano Observatory (YVO), a consortium of nine federal, state, and academic organizations, to include hydrothermal processes and hazards in its recently developed hazards monitoring plan [Yellowstone Volcano Observatory, 2022]. The plan includes the installation of broadband seismic, infrasound, thermal, and deformation sensors within geyser basins to better detect anomalous hydrothermal activity and investigate the potential to forecast hazardous events.

A prototype hydrothermal monitoring station, installed in Norris Geyser Basin in 2023, immediately paid dividends. The station clearly detected infrasound signals from nearby geyser eruptions and a small hydrothermal explosion that occurred on 15 April 2024—the first hydrothermal explosion in Yellowstone National Park to be documented by instrumental monitoring [Poland et al., 2025].

Yellowstone Volcano Observatory’s volcano monitoring network barely detected the explosion, even though it was big enough to destroy a section of boardwalk adjacent to Black Diamond Pool.

However, no hydrothermal monitoring station was installed at Biscuit Basin in July 2024, and YVO’s volcano monitoring network barely detected the explosion, even though it was big enough to destroy a section of boardwalk adjacent to Black Diamond Pool. The destructive event—thankfully, no injuries resulted—emphasizes the importance of expanded monitoring in geyser basins of Yellowstone National Park. It also highlights the risk posed by even small explosions that occur when people are nearby.

Much remains unknown about the processes leading to hydrothermal explosions and how best to safeguard the more than 4 million visitors to Yellowstone National Park every year from this underappreciated hazard [e.g., Montanaro et al., 2022]. The goal of postexplosion scientific investigations is to develop understanding that will enable better monitoring, detection, and, potentially, forecasting of future dangerous hydrothermal events.

Black Diamond Pool’s Explosive Past and Present

Explosive activity has recurred sporadically at Black Diamond Pool over its roughly 120-year life. Broken, angular rocks from previous explosions that were cemented back together before being ejected on 23 July 2024 provide evidence of this repeated explosive activity.

According to early geologic maps and photographs, Black Diamond Pool did not exist before 1902. It likely formed dramatically from a hydrothermal explosion sometime between then and 1912. Documents preserved in the Yellowstone National Park archives reference a few short periods of explosive activity that enlarged the new pool and formed two additional springs.

Black Diamond Pool (larger pool at top right) and Black Opal Pool (smaller pool at center left) are seen in this aerial photo taken in 1959 (left). A small hydrothermal explosion occurred at Black Diamond Pool in 2009 (right). Credit: left: Yellowstone Heritage & Research Center photo 35734, Public Domain; right: Wade Johnson, EarthScope

The area was quiet after 1960 until a series of short explosive events of varying intensity (though none approaching the scale of the July 2024 event) reinitiated in 2006. The frequent activity ceased by early 2013, and only three isolated events were reported between then and July 2024.

The 23 July hydrothermal explosion—which occurred during the park’s busiest month—stunned tourists, National Park Service (NPS) officials, and the scientific community. Visitation numbers had peaked a few days earlier, and on the day of the explosion, cameras recorded 209 visitors to Biscuit Basin by 9:00 a.m. Within minutes of the approximately 10:00 a.m. event, law enforcement rangers arrived on the scene and quickly closed the basin to the public to prevent injuries should explosive activity continue.

YVO’s initial response primarily involved communicating to the public and emergency managers about the cause of the event and the potential for additional activity. Observatory scientists also fielded numerous media inquiries.

Coordination of the scientific response began in parallel with these communications activities. YVO scientists and experienced collaborators from other institutions deployed to the field within hours to days to install monitoring equipment and gather time-sensitive data using a variety of approaches.

Fanning Out in Biscuit Basin

Working near an unstable, potentially explosive pool in the immediate aftermath of the explosion was an exercise in situational awareness.

Working near an unstable, potentially explosive pool in the immediate aftermath of the explosion was an exercise in situational awareness, but the extensive training and experience of the scientists involved helped to ensure their safety.

Field teams worked in pairs, with one person keeping an eye out for signs of an ensuing explosion while the other collected data. High-temperature areas surrounding the pool suggested the presence of boiling water or steam underneath a thin crust where the ground could easily collapse or another explosion could break out. Near the pool edge, slippery mud and overhangs that could crumble unexpectedly into the pool also posed particular hazards.

The field teams also knew that newly unsealed hydrothermal systems can emit higher-than-normal amounts of hazardous gases. Thankfully, blowing winds following the explosion diluted potentially dangerous concentrations as well as the strong perfume of acid, sulfur, and hydrocarbons, helping the teams get on with their work.

Geology and Mapping. Hydrothermal explosions leave behind debris fields that can be used to discern many properties of the explosions [Breard et al., 2014]. For example, the size and distribution of ballistic blocks around the vent provide clues about the energy of the explosion. This information also enables calculations of ballistic vulnerability—the probability of a human fatality at any given location around the vent in the event of another explosion of similar size. In addition, rocks excavated from the preexisting subsurface hydrothermal system are useful for understanding the pressure and temperature conditions before the explosion and how sealed the system was.

A field team working near Black Diamond Pool on 28 July 2024 collects location and lithology data for ballistic rocks thrown by the 23 July hydrothermal explosion (left). National Park Service (NPS) employees fly an uncrewed aerial vehicle over the 23 July explosion debris field to image the deposits on 25 July (right). Credit: Photos taken under National Park Service Milestones research permit 1016-9 by Lauren Harrison, Colorado State University

Field teams from Colorado State University, NPS, and the University of California, Berkeley documented the sizes, distribution, and lithology of ballistic blocks thrown by the explosion to begin piecing together what the underlying hydrothermal system looked like before and during the explosion. NPS also used an uncrewed aerial vehicle to collect thermal and structure-from-motion imagery of the deposits and the surrounding area. These images helped identify areas with elevated temperatures and quantify the volume of material ejected by the 23 July explosion.

Dense seismic networks, which can sense the vibrations of bubbles and the brecciation of rock, are powerful tools for resolving subsurface hydrothermal plumbing and detecting small explosions.

Near-Surface Geophysics. Dense seismic networks, which can sense the vibrations of bubbles and the brecciation of rock, are powerful tools for resolving subsurface hydrothermal plumbing, detecting small explosions, and helping scientists assess hazards from ongoing activity.

To record seismic signals in the aftermath of the explosion at Black Diamond Pool, the University of Utah deployed a temporary array of 33 seismometers around the pool by 26 July, and the instruments recorded for about 2 months. Four infrasound microphones were also deployed roughly 300 meters northwest of the pool from 19 August to 18 October. These data will be processed to pinpoint and explore signals from geyser activity and subsequent small hydrothermal explosions in Biscuit Basin.

A temporary seismometer deployed and photographed on 26 July 2024 sits near Black Diamond Pool (left). Another temporary seismometer deployed after the 23 July event—and seen here on 16 October—is partially buried in fine sediment following several small explosions at Black Diamond Pool (right). Credit: Photos taken under National Park Service Milestones research permit 1016-9 by Jamie Farrell, University of Utah

Several weeks after the explosion, field teams from the University of Wyoming and NPS collected nuclear magnetic resonance (NMR), electrical resistivity (ER), and transient electromagnetics (TEM) datasets. NMR data provide estimates of the volume and location of water stored in the subsurface, including in confining, low-permeability zones. ER, which measures resistivity encountered by electrical currents, is ideal for identifying water-saturated subsurface pathways, as hydrothermal waters contain dissolved salts and are electrically conductive. TEM uses pulses of electric current to induce electric and magnetic fields underground. How fast these fields decay is another indication of variations in subsurface resistivity.

Together these techniques paint 3D views of hydrothermal fluids and lithological contrasts in the subsurface—important information for understanding the conditions and characterizing hazard potential in the postexplosion Black Diamond Pool system.

Water and Gas Chemistry. Gas emissions and water chemistry data were collected after the 23 July explosion by the U.S. Geological Survey (USGS), Montana Technological University, and the University of Wyoming to help probe underground processes.

An NPS employee prepares to sample water from Black Diamond Pool on 23 July 2024. The long pole is used for safely dipping sample bottles into the center of the pool, where the hottest water indicates locations of primary thermal water vents. Credit: Photo taken under National Park Service Milestones research permit 1016-9 by Mara Reed, University of California, Berkeley

Gridded measurements of carbon dioxide gas efflux, for example, provide information on spatial variations in diffuse gas fluxes at the surface that can be used to map subsurface gas pathways. Simultaneous measurements of isotopes of the short-lived radioactive gas radon in the same samples used for carbon dioxide measurements can help identify the sources of emissions and timescales of gas movement.

The chemical composition of the water in Black Diamond Pool is important because the solubility of different chemical species depends on the temperature at which water and rocks react. Critically, silica solubility decreases with decreasing temperature, and as hydrothermal waters cool, amorphous (noncrystalline) silica precipitates in subsurface flow paths [Fournier, 1985].

Past analyses of water chemistry at Black Diamond Pool have indicated that water and rocks there react at lower temperatures compared with systems farther south in Upper Geyser Basin, including at Old Faithful [Price et al., 2024]. These lower temperatures are more favorable for silica precipitation and may contribute to sealing flow paths and building pressure for hydrothermal explosions in Biscuit Basin.

Early Insights into the 2024 Explosion

The data collected following the explosion of Black Diamond Pool on 23 July 2024 are still being analyzed to provide a detailed account of the conditions preceding and following the event. However, some preliminary insights are available from the initial observations.

Many indicators point to the explosion being caused by self-sealing in the hydrothermal system.

Many indicators point to the explosion being caused by self-sealing in the hydrothermal system, with the result that increases in subsurface pressure eventually overcame the strength of the sealing rocks—a common mechanism for hydrothermal explosions globally [Morgan et al., 2009; Montanaro et al., 2022]. The lack of a strong earthquake nearby, either before or during the explosion, indicates it was not seismically triggered.

Furthermore, some of the ejected debris—namely, minimally altered, high-porosity, and high-permeability conglomerates and sandstones—likely contained much of the liquid water that flashed to steam and powered the explosion (Figure 2). On the other hand, completely silicified and intensely altered low-permeability rocks also found in the debris field likely constituted the seal that contained the pent-up pressure before the explosion.

Fig. 2. Ballistic rocks thrown by the 23 July 2024 hydrothermal explosion show variation in their degree of alteration, porosity, and permeability. An unaltered, obsidian-rich, cross-bedded sandstone (left) has high porosity and permeability, whereas a gravel lag within a sandstone is highly altered and silicified and has low porosity and permeability (right). These samples were collected under National Park Service Milestones research permit 1016-9. Click image for larger version. Credit: Phillip Kondracki, Colorado State University

The initial analyses of the seismic and infrasound data, as well as observations from scientists and passing visitors, indicate that small explosions at Black Diamond Pool have continued since 23 July 2024 through to the present, posing an ongoing hazard. Some of these explosions have been accompanied by water surges flowing east into the nearby Firehole River and have been large enough to carry seismic instruments several meters downhill and partially bury others in fine sediment. Two witnessed events were observed to throw water, mud, and small rocks 20–30 feet (6–9 meters) into the air. A webcam installed in mid-May 2025 to better document activity at Black Diamond Pool captured a similar small eruption on 31 May 2025.

Better Science for Better Response

New hazard maps and recent geophysical investigations will guide the National Park Service’s response to ensure public safety within Biscuit Basin.

The scientific response to the 23 July 2024 hydrothermal explosion has focused on improving understanding of the event to inform strategies that can be used to detect, and potentially forecast, similar future explosions. New hazard maps and recent geophysical investigations will guide NPS’s response to ensure public safety within Biscuit Basin, helping to address specific questions such as when the basin can be reopened, whether walkways must be relocated, and what the short-term probability of another large explosive event at Black Diamond Pool is. Scientific investigation will also guide YVO’s efforts to deploy targeted monitoring to other hydrothermal areas in Yellowstone National Park.

Hydrothermal explosions in Yellowstone National Park are an underappreciated hazard, and a pressing need exists to better understand where, why, and how often they happen. Filling these knowledge gaps requires multidisciplinary studies that consortia like YVO and its collaborators are well suited to undertake. Ultimately, improved monitoring of hydrothermal hazards will aid risk assessment and mitigation and help park officials and visitors avoid dangerous situations in Biscuit Basin, elsewhere in Yellowstone National Park, and at hydrothermal systems worldwide.

Acknowledgments

We especially thank Jamie Farrell, who assisted with preparation of this article and led the deployment of temporary seismometers and infrasound arrays in Biscuit Basin after the July 2024 explosion. We also acknowledge the many people involved in event response, scientific investigation, and management and policy decisions associated with the 23 July 2024 explosion of Black Diamond Pool. Scientists and personnel from USGS, NPS, Colorado State University, the University of Utah, the University of Wyoming, and Montana Technological University who have contributed include Phillip Kondracki, Alex Hammerstrom, Kiernan Folz-Donahue, Elle Blom, Blaine McCleskey, Sara Peek, Shaul Hurwitz, Steven Rice, Carrie Guiles, Jaclyn Mcllwain, Hillary Robinson, Andy Parkinson, Lexi Peterson, Lisa Morgan, Pat Shanks, Greg Vaughan, Jen Lewicki, Alycia Cox, Michael Loya, Andrew Miller, Katie Copeland, Kallen Snow, and Adaeze Ugwu. We thank Shaul Hurwitz and Patrick Muffler for constructive reviews. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. government.

References

Breard, E. C. P., et al. (2014), Using the spatial distribution and lithology of ballistic blocks to interpret eruption sequence and dynamics: August 6 2012 Upper Te Maari eruption, New Zealand, J. Volcanol. Geotherm. Res., 286, 373–386, https://doi.org/10.1016/j.jvolgeores.2014.03.006.

Browne, P. R. L., and J. V. Lawless (2001), Characteristics of hydrothermal eruptions, with examples from New Zealand and elsewhere, Earth Sci. Rev., 52(4), 299–331, https://doi.org/10.1016/S0012-8252(00)00030-1.

Christiansen, R. L., et al. (2007), Preliminary assessment of volcanic and hydrothermal hazards in Yellowstone National Park and vicinity, U.S. Geol. Surv. Open File Rep., 2007-1071, 94 pp., https://pubs.usgs.gov/of/2007/1071/.

Fournier, R. O. (1985), The behavior of silica in hydrothermal solutions, in Geology and Geochemistry of Epithermal Systems, Rev. Econ. Geol., vol. 2, edited by B. R. Berger, P. M. Bethke, and J. M. Robertson, pp. 45–61, Soc. of Econ. Geol., Littleton, Colo., https://doi.org/10.5382/Rev.02.03.

Fournier, R. O., et al. (1991), Conditions leading to a recent small hydrothermal explosion at Yellowstone National Park, Geol. Soc. Am. Bull., 103(8), 1,114–1,120, https://doi.org/10.1130/0016-7606(1991)103%3C1114:CLTARS%3E2.3.CO;2.

Montanaro, C., et al. (2022), Phreatic and hydrothermal eruptions: From overlooked to looking over, Bull. Volcanol., 84(6), 64, https://doi.org/10.1007/s00445-022-01571-7.

Morgan, L. A., W. C. P. Shanks III, and K. L. Pierce (2009), Hydrothermal processes above the Yellowstone magma chamber: Large hydrothermal systems and large hydrothermal explosions, Spec. Pap. Geol. Soc. Am., 459, https://doi.org/10.1130/2009.2459(01).

Muffler, L. J. P., D. E. White, and A. H. Truesdell (1971), Hydrothermal explosion craters in Yellowstone National Park, Geol. Soc. Am. Bull., 82(3), 723–740, https://doi.org/10.1130/0016-7606(1971)82[723:heciyn]2.0.co;2.

Poland, M. P., et al. (2025), The first instrumentally detected hydrothermal explosion in Yellowstone National Park, Geophys. Res. Lett., 52(11), e2025GL115850, https://doi.org/10.1029/2025GL115850.

Price, M. B., et al. (2024), Historic water chemistry data for thermal features, streams, and rivers in the Yellowstone National Park area, 1883–2021, data release, U.S. Geol. Surv., Reston, Va., https://doi.org/10.5066/P9KSEVI1.

Thiéry, R., and L. Mercury (2009), Explosive properties of water in volcanic and hydrothermal systems, J. Geophys. Res. Solid Earth, 114(B5), B05205, https://doi.org/10.1029/2008JB005742.

Yellowstone Volcano Observatory (2022), Volcano and earthquake monitoring plan for the Yellowstone Caldera system, 2022–2032, U.S. Geol. Surv. Sci. Invest. Rep., 2022-5032, 23 pp., https://doi.org/10.3133/sir20225032.

Author Information

Lauren Harrison (lauren.n.harrison@colostate.edu), Colorado State University, Fort Collins; Michael Poland, Yellowstone Volcano Observatory, U.S. Geological Survey, Vancouver, Wash.; Mara Reed, University of California, Berkeley; Ken Sims, University of Wyoming, Laramie; and Jefferson D. G. Hungerford, National Park Service, Mammoth, Wyo.

Citation: Harrison, L., M. Poland, M. Reed, K. Sims, and J. D. G. Hungerford (2025), Hydrothermal hazards on display in Yellowstone National Park, Eos, 106, https://doi.org/10.1029/2025EO250233. Published on 27 June 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.

SummaryFirst-arrival traveltime tomography (FATT) is a widely used method for characterizing near-surface velocity structures in geotechnical engineering and resource exploration. We introduce an improved version of FATT, named first-arrival adjoint tomography (FAAT), which involves the joint inversion of first-arrival absolute traveltimes and differential traveltimes. Unlike absolute traveltimes, differential traveltimes, derived from common sources or receivers, offer heightened sensitivity to fine-scale structures near the receivers or sources, respectively. This dual sensitivity makes FAAT particularly effective in imaging highly heterogeneous media. However, the proximity of rays associated with differential traveltimes can lead to the instability of the inversion. To overcome this challenge, we simultaneously incorporate absolute traveltimes and differential traveltimes to update the velocity model. This approach improves the stability of the inversion process, leading to improved resolution of inverted results. We specifically employ the fast-sweeping method to solve the factored eikonal equation, providing robust solutions in models with complex geological structures. Furthermore, we address the inverse problem by computing the gradient of data misfit using the efficient adjoint-state method. Through numerical testing, we validate the effectiveness of FAAT in comparison to that using only absolute or differential traveltimes. Finally, we apply the proposed FAAT method to near-surface site characterization at Bishan-AMK Park in Singapore. Compared with FATT and validated against borehole data, FAAT demonstrates its ability to establish more reliable velocity models, revealing finer details and substantially improving geological interpretation.

SUMMARYNumerical models are a powerful tool for understanding and predicting the impact of landslide-generated tsunamis. We use here the HySEA code which incorporates a multilayer structure and non-hydrostatic pressure to simulate the tsunami generated by a potential submarine landslide located offshore of the Mayotte island. The island is surrounded by a lagoon and steep slopes weakened by the 2018 seismo-volcanic crisis. The influence of the input parameters and of the model assumptions is shown to change by a factor 2 the predicted maximum water free surface elevation, velocity and maximum inundation depth. This demonstrates the need of using numerical models for building local scaling laws to relate tsunami and landslide properties. Our results highlight the necessity of incorporating high-resolution bathymetry, in-depth variations through multilayer modeling and relevant landslide rheology to accurately predict tsunami impact. In case of strong topography variations as in Mayotte, using 4 layers seems to be a good compromise between accuracy and computational cost. Accounting for these effects would enable to refine hazard maps by identifying safe and high-risk coastal zones and to improve wave arrival time estimates, thus reducing tsunami-related risks in regions like Mayotte.

SummaryUnder compression in the brittle regime, rocks fail as fracture interaction, propagation and coalescence produce a process zone of high strains that forms the nucleus of the fault that eventually traverses the rock core. Early analyses suggested that this process zone extends through relatively intact rock close to the peak stress, and that the deformation that develops earlier in loading does not guide the location of this process zone. Here, we assess the predictability of the location of the process zone in triaxial compression experiments on Darley Dale sandstone. We develop supervised machine learning models to predict whether a particular location in the rock core will eventually host high shear and dilative strain, and thus eventually reside within the process zone. We calculate the local incremental strain tensors throughout the rock cores using digital volume correlation of X-ray tomograms captured during the experiments. We find that the models produce accuracies of 0.73 on average, indicating that it is possible to predict the location of the process zone using observations of the strain field preceding macroscopic failure. The average accuracy increases to 0.84 when the data are restricted to later in the experiment because the strain field becomes more similar to the final strain field that hosts the process zone. The models primarily rely on the shear strain field to predict the location of the process zone, likely because it is more spatially persistent than the dilative strain. The local neighborhood of the strain field is helpful for predicting whether a location will eventually host the process zone only when the data are restricted to one experiment. When the data includes several experiments, the models primarily rely on global statistics of the strain fields. The varying correlation lengths of the dilative and shear strain field of different experiments help explain this result.

AbstractActive tectonic movements and surface deformation are observed in the eastern Tibetan Plateau. Understanding variations in crustal thickness and the deep Moho interface is crucial for elucidating the expansion of the Tibetan Plateau. This study utilizes InSAR to derive vertical surface deformation and applies loading corrections based on Green's function method. Additionally, satellite gravity data are used to separate hydrological and tectonic signals to infer changes in the Moho interface. Our results indicate that the regionally averaged loading effects, estimated using localized Green's functions (LGF), account for approximately 16.5 per cent of the InSAR-derived vertical displacement field. This contribution exhibits significant spatial variability, exceeding 100 per cent in regions with strong hydrological activity. The loading calculation is highly sensitive to Earth model: the relative difference between the load displacement obtained using the local Green's function and that obtained with an average Green's function reaches 48.2 per cent. After applying loading corrections, a more accurate Moho uplift rate of –8.2 ± 3.1 mm/a is obtained. The findings support the conclusion that the Moho interface rises in the southern region of the study area, with crustal thinning, while the Moho surface sinks in the northern region, with crustal thickening.

body {background-color: #D2D1D5;} Research & Developments is a blog for brief updates that provide context for the flurry of news that impacts science and scientists today.

It’s a bird! It’s a plane! It’s… a bolide!

People in Georgia, Tennessee, and the Carolinas reported sightings of a fireball overhead on Thursday afternoon, 26 June. It is unclear whether it was a meteor or space junk entering Earth’s atmosphere. Meteors can exceed one meter in size and are referred to as bolides when they explode in the atmosphere.

VIDEO | This was just sent to me taken from a dash camera on I-85 SB in Upstate South Carolina pic.twitter.com/49PvNsorAK

— Cody Alcorn (@CodyAlcorn) June 26, 2025

Sometimes, meteorite pieces can be recovered on the ground after such an event. In this case, they may need to be fished out of the foundation of a home. One fragment was reported to have struck a roof in Henry County, Georgia, according to Atlanta news station 11 Alive.

 
Related

•  Rare ‘bolide’ fireball falls from sky, sightings reported across metro Atlanta and broader Southeast
•  American Meteor Society
 

Mike Hankey, operations manager of the American Meteor Society, told 11 Alive that the organization received more than 100 reports of fireball sightings within 2 hours. Most reported said the sighting occurred between 12:25 and 12:40 p.m. EDT.

He explained that bolides can enter the atmosphere at speeds of up to 50,000 miles (80,000 kilometers) per hour, but slow to hundreds of miles per hour as they near Earth’s surface.

“You don’t want to get hit by one,” he clarified. (We at Eos tend to agree.) “It can cause a lot of harm, damages. They’ll go through multiple floors of a home, oftentimes.”

The bolide was bright enough that it was captured briefly by NOAA’s GOES-19 satellite, around the border of Virginia and North Carolina.

There have been many reports of a #fireball streaking across the southeastern U.S. this afternoon! The Geostationary Lightning Mapper (#GLM) on @NOAA's #GOES satellites can occasionally detect these bright meteors (aka #bolides) when they pass through the atmosphere.

See the… pic.twitter.com/SeODhBdYiK

— NOAA Satellites (@NOAASatellites) June 26, 2025

NASA Jet Propulsion Laboratory’s Center for Near Earth Object Studies (CNEOS) fireballs database reports that this marks the 20th fireball detected by U.S. government sensors this year. However, the Geostationary Lightning Mapper aboard the NOAA-operated GOES East and GOES West satellites detected nearly 700 this year. In April, another bolide made headlines when it flew over Mexico City.

@matthewcappucci

WOW! A fireball METEOR just EXPLODED over Georgia and South Carolina! Shards/meteorites may be found near/south of Atlanta. In SC and GA, some folks reported a sonic boom. Did you see or hear it!? #meteor #georgia #atlanta #southcarolina #meteorite #meteoroid #fireball #weather #science #space #astronomy

♬ original sound – Capooch

According to the Swinburne University of Technology, about 5,000 bolides fall to Earth each year, but very few are observed, in large part because so many of them enter the atmosphere over the ocean.

—Emily Dieckman (@emfurd.bsky.social), Associate Editor

These updates are made possible through information from the scientific community. Do you have a story idea about science or scientists? We’re listening! Send us a tip at eos@agu.org. 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.

NOAA and its research partners are forecasting a mild to moderate harmful algal bloom (HAB) in western Lake Erie this summer. This year's bloom is expected to measure 3 on the HAB severity index, with a potential range of 2–4.

When an extreme weather event occurs, the probability or risk of other events can often increase, leading to what researchers call "cascading" hazards.

Scientists have identified what could be the oldest rocks on Earth from a rock formation in Canada.

At this year's Living Planet Symposium, attendees heard how ESA's Next Generation Gravity Mission could provide the first opportunity to directly track a vital ocean circulation system that warms our planet—but is now weakening, risking a possible collapse with far-reaching consequences.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: AGU Advances

Deep earthquakes are still a mystery that has been debated for a long time, but no consensus has been made so far. They originate at depths of 500 to 700 kilometers where there are extreme pressure and temperature conditions that should prevent the failure mechanisms that generate shallow earthquakes. Despite decades of observations and various proposed theories, a coherent mechanism that accounts for deep earthquake magnitudes has yet to be identified.

Jia et al. [2025] present an unprecedented analysis of 40 deep earthquakes worldwide with large magnitudes. They find that most of them are governed by a common mechanism facilitated by shear thermal runaway, ultimately allowing earthquakes to grow larger and release more energy. This explanation applies to deep earthquakes across diverse environments, from the coldest slabs such as Tonga, to the warmest, including those beneath South America.

Citation: Jia, Z., Fan, W., Mao, W., Shearer, P. M., & May, D. A. (2025). Dual mechanism transition controls rupture development of large deep earthquakes. AGU Advances, 6, e2025AV001701. https://doi.org/10.1029/2025AV001701

—Alberto Montanari, Editor-in-Chief, AGU Advances

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.

Scientists for the first time have detected a slow slip earthquake in motion during the act of releasing tectonic pressure on a major fault zone at the bottom of the ocean.