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July 30, 2025

Séisme au Kamtchatka : que sait-on de l’un des dix plus puissants tremblements de terre jamais enregistrés ?

Source: The Conversation – France in French (2) – By Dee Ninis, Earthquake Scientist, Monash University

Mercredi 30 juillet vers 11 h 30 heure locale, un séisme de magnitude 8,8 a frappé la côte de la péninsule du Kamtchatka à l’extrême est de la Russie. La région est le siège d’une activité sismique depuis plusieurs mois, et des dizaines de répliques ont déjà eu lieu autour de ce séisme. Des alertes au tsunami ont été lancées rapidement tout autour du Pacifique – et certaines ont déjà pu être levées.

Avec une profondeur d’environ 20 kilomètres, ce puissant séisme, qui figure parmi les dix plus forts jamais enregistrés et le plus important au monde depuis 2011, a causé des dégâts matériels et fait des blessés dans la plus grande ville voisine, Petropavlovsk-Kamtchatski, située à seulement 119 kilomètres de l’épicentre.

Des alertes au tsunami et des évacuations ont été déclenchées en Russie, au Japon et à Hawaï, et des avis ont été émis pour les Philippines, l’Indonésie et même la Nouvelle-Zélande et le Pérou.

Toute la région du Pacifique est très exposée à des séismes puissants et aux tsunamis qui en résultent, car elle est située dans la « ceinture de feu », une zone d’activité sismique et volcanique intense. Les dix séismes les plus puissants jamais enregistrés dans l’histoire moderne se sont tous produits dans la ceinture de feu.

Voici pourquoi la tectonique des plaques rend cette partie du monde si instable.

Pourquoi le Kamtchatka est-il touché par des séismes aussi violents ?

Au large de la péninsule du Kamtchatka se trouve la fosse des Kouriles, une frontière tectonique où la plaque Pacifique est poussée sous la plaque d’Okhotsk.

Alors que les plaques tectoniques se déplacent continuellement les unes par rapport aux autres, l’interface entre les plaques tectoniques est souvent « bloquée ». La tension liée au mouvement des plaques s’accumule jusqu’à dépasser la résistance de l’interface, puis se libère sous la forme d’une rupture soudaine : un séisme.

En raison de la grande superficie de l’interface aux frontières des plaques, tant en longueur qu’en profondeur, la rupture peut s’étendre sur de vastes zones à la frontière des plaques. Cela donne lieu à certains des séismes les plus importants et potentiellement les plus destructeurs au monde.

Un autre facteur qui influe sur la fréquence et l’intensité des séismes dans les zones de subduction est la vitesse à laquelle les deux plaques se déplacent l’une par rapport à l’autre.

Dans le cas du Kamtchatka, la plaque Pacifique se déplace à environ 75 millimètres par an par rapport à la plaque d’Okhotsk. Il s’agit d’une vitesse relativement élevée pour des plaques tectoniques, ce qui explique que les séismes y sont plus fréquents que dans d’autres zones de subduction. En 1952, un séisme de magnitude 9,0 s’est produit dans la même zone de subduction, à environ 30 kilomètres seulement du séisme de magnitude 8,8 d’aujourd’hui.

Parmi les autres exemples de séismes à la frontière d’une plaque en subduction, on peut citer le séisme de magnitude 9,1 qui a frappé la région de Tohoku au Japon en 2011 et le séisme de magnitude 9,3 qui a frappé Sumatra et les îles Andaman en Indonésie le 26 décembre 2004. Ces deux séismes ont débuté à une profondeur relativement faible et ont provoqué une rupture de la limite des plaques jusqu’à la surface.

Ils ont soulevé un côté du fond marin par rapport à l’autre, déplaçant toute la colonne d’eau de l’océan située au-dessus et provoquant des tsunamis dévastateurs. Dans le cas du séisme de Sumatra, la rupture du fond marin s’est produite sur une longueur d’environ 1 400 kilomètres.

Que va-t-il se passer maintenant ?

Au moment où nous écrivons ces lignes, environ six heures après le séisme, 35 répliques d’une magnitude supérieure à 5,0 ont déjà été enregistrées, selon le service de surveillance sismique états-unien (l’United States Geological Survey, USGS).

Les répliques se produisent lorsque les tensions dans la croûte terrestre se redistribuent après le séisme principal. Elles sont souvent d’une magnitude inférieure d’un point à celle du séisme principal. Dans le cas du séisme d’aujourd’hui, cela signifie que des répliques d’une magnitude supérieure à 7,5 sont possibles.

Pour un séisme de cette ampleur, les répliques peuvent se poursuivre pendant des semaines, voire des mois, mais leur magnitude et leur fréquence diminuent généralement avec le temps.

Le séisme d’aujourd’hui a également provoqué un tsunami qui a déjà touché les communautés côtières de la péninsule du Kamtchatka, des îles Kouriles, et d’Hokkaido au Japon.

Au cours des prochaines heures, le tsunami se propagera à travers le Pacifique, atteignant Hawaï environ six heures après le séisme et se poursuivant jusqu’au Chili et au Pérou. [ndlt : à l’heure où nous effectuons cette traduction, les alertes à Hawaï ont été réduites, et annulées aux Philippines. Les vagues ont atteint la côte ouest des États-Unis, jusqu’à un mètre de hauteur en Californie et dans l’Oregon.]

Les spécialistes des tsunamis continueront d’affiner leurs modèles des effets du tsunami au fur et à mesure de sa propagation, et les autorités de la protection civile fourniront des conseils faisant autorité sur les effets locaux attendus.

Quelles leçons peut-on tirer de ce séisme pour d’autres régions du monde ?

Heureusement, les séismes d’une telle ampleur sont rares. Cependant, leurs effets au niveau local et à l’échelle mondiale peuvent être dévastateurs.

Outre sa magnitude, plusieurs aspects du séisme qui a frappé le Kamtchatka aujourd’hui en feront un sujet de recherche particulièrement important.

Par exemple, la région a connu une activité sismique très intense ces derniers mois et un séisme de magnitude 7,4 s’est produit le 20 juillet. L’influence de cette activité antérieure sur la localisation et le moment du séisme d’aujourd’hui sera un élément crucial de ces recherches.

Tout comme le Kamtchatka et le nord du Japon, la Nouvelle-Zélande est située au-dessus d’une zone de subduction, et même de deux zones de subduction. La plus grande, la zone de subduction de Hikurangi, s’étend au large de la côte est de l’île du Nord.

D’après les caractéristiques de cette interface tectonique et les archives géologiques des séismes passés, la zone de subduction de Hikurangi est susceptible de produire des séismes de magnitude 9. Cela ne s’est jamais produit dans l’histoire, mais si cela arrivait, cela provoquerait un tsunami.

La menace d’un séisme majeur dans une zone de subduction n’est jamais écartée. Le séisme qui s’est produit aujourd’hui au Kamtchatka est un rappel important pour tous ceux qui vivent dans des zones sismiques de rester prudents et de tenir compte des avertissements des autorités de protection civile.

Dee Ninis travaille au Seismology Research Centre, est vice-présidente de l’Australian Earthquake Engineering Society et membre du comité de la Geological Society of Australia – Victoria Division.

John Townend reçoit des financements des fonds Marsden et Catalyst de la Royal Society Te Apārangi, de la Natural Hazards Commission Toka Tū Ake et du ministère néo-zélandais des Entreprises, de l’Innovation et de l’Emploi. Il est ancien président et directeur de la Seismological Society of America ainsi que président de la New Zealand Geophysical Society.

– ref. Séisme au Kamtchatka : que sait-on de l’un des dix plus puissants tremblements de terre jamais enregistrés ? – https://theconversation.com/seisme-au-kamtchatka-que-sait-on-de-lun-des-dix-plus-puissants-tremblements-de-terre-jamais-enregistres-262251

July 30, 2025

More than 50% of Detroit students regularly miss class – and schools alone can’t solve the problem

Source: The Conversation – USA – By Jeremy Singer, Assistant Professor of Education, Wayne State University

Nobody learns in an empty classroom. Jeffrey Basinger/Newsday RM via Getty Images

Thousands of K-12 students in Detroit consistently miss days of school.

Chronic absenteeism is defined as missing at least 10% of school days – or 18 in a 180-day academic year. In Detroit, chronic absenteeism rose during the COVID-19 pandemic and remains a persistent challenge.

To encourage attendance, the Detroit Public Schools Community District is getting creative. This past year, Michigan’s largest school district awarded US$200 gift cards to nearly 5,000 high schoolers for attending all their classes during a two-week period, and Superintendent Nikolai Vitti also floated the idea of providing bikes to help students get to class. Some district students lack access to reliable transportation.

To understand the consequences of kids regularly missing school, The Conversation U.S. spoke with Sarah Lenhoff, associate professor of education at Wayne State University and director of the Detroit Partnership for Education Equity & Research, an education-focused research collaborative, and Jeremy Singer, an assistant professor of education at Wayne State University. Lenhoff and Singer wrote a book published in March about the socioeconomic drivers of chronic absenteeism in K-12 schools and how policymakers and communities, not just educators, can help.

Is chronic absenteeism the same as truancy?

No. Truancy is how schools have thought about and dealt with student attendance problems since the early days of public education in the United States in the 19th century and is still defined in state law across the country. It focuses on “unexcused” absences and compliance with mandatory school attendance laws. By contrast, chronic absenteeism includes any absence – whether “excused” or “unexcused” – because each absence can be consequential for student learning and development.

Chronic absenteeism is usually defined as missing 10% or more school days. The 10% threshold is somewhat arbitrary, since researchers know that the consequences of missing school accumulate with each day missed. But the specific definition of chronic absenteeism has been solidified in research and by policymakers. Most states now include a measure of chronic absenteeism in their education accountability systems.

How big of a problem is chronic absenteeism in Detroit’s K-12 public schools?

Detroit has among the highest chronic absenteeism rates in the country: more than 50% in recent school years. Prior to the pandemic, the average rate of chronic absenteeism nationwide was about 15%, and it was around 24% in 2024.

In one of our prior studies, we found Detroit’s chronic absenteeism rate was much higher than other major cities – even others with high absenteeism rates such as Milwaukee or Philadelphia.

This is related to the depth of social and economic inequalities that Detroit families face. Compared to other major cities, Detroit has higher rates of poverty, unemployment and crime. It has worse public health conditions. And even its winters are some of the coldest of major U.S. cities. All of these factors make it harder for kids to attend school.

Rates of chronic absenteeism spiked in Detroit during the COVID-19 pandemic, as they did statewide. The Detroit Public Schools Community District has come close to returning to its pre-pandemic levels of absenteeism. The rates were 66% in the 2023-24 school year compared to 62% in the school year right before the pandemic began, 2018-19.

Detroit’s charter schools have struggled more to bring down their chronic absenteeism rates post-pandemic, but the numbers are lower overall – 54% in the 2023-24 school year compared to 36% in 2018-19.

A Black woman wearing a red T-shirt and sunglasses holds up a sign reading 'OUR FIGHT FOR DETROIT KIDS' — A school social worker from Noble Elementary-Middle School protests outside Detroit Public Schools headquarters.
Bill Pugliano/Getty Images

How does missing school affect students?

The connection between attendance and achievement is clear: Students who miss more school on average score worse on reading and math tests. As early as pre-K, being chronically absent is linked to lower levels of school readiness, both academically and behaviorally. By high school, students who miss more school tend to earn lower grades and GPAs and are less likely to graduate.

And it’s not just the absent students who are affected. When more kids in a class miss school regularly, that is associated with lower overall test scores and worse measures of skills such as executive functioning for other students in that class.

Does chronic absenteeism vary by family income or other factors?

Rates of chronic absenteeism are much higher among students from low-income families. In these cases, absenteeism is often driven by factors outside a student’s control such as unstable housing, unreliable transportation, health issues, lack of access to child care, or parents who work nontraditional hours. These challenges make it harder for students to get to school consistently, even when families are deeply committed to education.

School-based factors also influence attendance. Students are more likely to be chronically absent in schools with weaker relationships with families or a less positive school culture. However, even schools with strong practices may struggle if they serve communities facing deep socioeconomic hardship.

Ultimately, we don’t view chronic absenteeism as an issue of student motivation or family values. Rather, we see it as an issue related to the unequal conditions that shape students’ lives.

Does punishing absent kids or their parents work?

Many schools have suspended students for absences, or threatened their parents with fines or jail time. In some cases, families have lost social services due to their children’s chronic absenteeism.

Research shows these strategies are not only ineffective, they can make the problem worse.

For example, we found that when schools respond with punishment instead of support, they often alienate the very students and families who are already struggling to stay connected. Harsh responses can deepen mistrust between families and schools. When absences are treated as a personal failing caused by a lack of motivation or irresponsibility rather than symptoms of deeper challenges, students and parents may disengage further.

Instead, educators might ask: What’s getting in the way of consistent attendance, and how can we help? That shift from blame to understanding can help improve attendance.

What can policymakers, school districts and community organizations do to reduce chronic absenteeism?

Chronic absenteeism is a societal issue, not just a school problem. In other words, we need to recognize that chronic absenteeism is not a problem that schools can solve alone. While educators work to improve conditions within schools, policymakers and community leaders can take responsibility for the broader factors that influence attendance.

This could look like investing more resources and fostering collaboration across sectors such as health care, housing, transportation and social services to better support students and their families. Community organizations can play a role too, offering wraparound services such as mental health care, access to transportation, and after-school programming, all of which can support families. In the meantime, educators can focus on what they can control: strengthening communication with families, building supportive relationships and helping families connect with existing services that can remove attendance barriers.

Sarah Lenhoff receives funding from the Skillman Foundation, the Joyce Foundation, the Kresge Foundation, the William T. Grant Foundation, the American Institutes for Research, and the Urban Institute.

Jeremy Singer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. More than 50% of Detroit students regularly miss class – and schools alone can’t solve the problem – https://theconversation.com/more-than-50-of-detroit-students-regularly-miss-class-and-schools-alone-cant-solve-the-problem-260773

July 30, 2025

From the Green party to Corbyn’s new launch – is it time Westminster took joint leaders more seriously?

Source: The Conversation – UK – By Stefan Stern, Visiting Professor of Management Practice, Bayes Business School, City St George’s, University of London

Are two heads better than one? This is a question that members of the Green party will be asking themselves over the summer as they take part in the election of a new leader … or leaders.

Former co-leader Carla Denyer MP announced in May that she would not be standing again. Her co-leader, Adrian Ramsay MP, is now joined on the prospective leadership ticket by another Green MP, Ellie Chowns. (It is a Green party rule that where there is a joint leadership the job holders must be of different genders.)

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They are being challenged by Zack Polanski, currently deputy leader of the party and a member of the London Assembly, who has positioned himself not merely as a solo candidate but also as a rather more radical one. While his politics have little in common with those of Reform party leader Nigel Farage, Polanksi has suggested the Greens could learn from his approach.

The contest presents us with an intriguing conundrum – or even a paradox. In the real world – that is, away from Westminster – expecting a single human being to display all the qualities and attributes required to lead a complicated business or organisation is rightly seen as unrealistic. Leadership is a team activity, to be carried out collectively.

This is one reason why it’s so troubling to see excessive pay packets being delivered to bosses who should not be taking all the credit for the success of a business.

Of course, the leadership provided by the ultimate boss matters, but good corporate governance involves testing the suggestions and instincts of the chief executive with the ideas of other senior executives or directors. This is known, perhaps rather euphemistically on occasion, as “challenge”.

But in Westminster politics a rather more traditional (we could say old-fashioned) view of leadership prevails. Here the orthodoxy holds that something called “strong leadership” stems mainly from a dominant single figure who is firmly in charge.

This belief is based in part on the mythology which surrounds the leadership of Margaret Thatcher, the “Iron Lady” who supposedly never took a step back (although she did), and who dismissed “wets” and “moaning minnies” who expressed doubt about her policy choices. Tony Blair in turn paid homage to this mythology, famously once declaring: “I’ve got no reverse gear”.

In Westminster changing your mind, even in the light of new evidence, is invariably labelled a U-turn, and is considered to be bad. This is also how the British media frames their actions.

So here is the Green party’s conundrum: against this backdrop, they would arguably get better media coverage and perhaps win more support from voters if they installed a single leader in the more conventional way. This is the case that could be made for Polanski.

But at the same time, the Greens are not meant to be just like all the other parties. They have a different view of the world, so why should they conform to the other people’s view of what leadership looks like?

Behind every strong leader

Successful businesses have often been led by double acts. Behind some swaggering CEOs there is often a cautious and competent chief financial officer making sure the numbers add up.

When the Granada media group was growing to a dominant market position in the 1990s, its CEO, Gerry Robinson, got most of the attention but his trusted managing director, Charles Allen, was an equally important, if less prominent, figure. Berkshire Hathway, one of the world’s most successful investment vehicles, has been led by the well-known Warren Buffett for decades, but for most of that time he had his old but less famous friend Charlie Munger at his side (Munger died in 2023).

Westminster’s latest prototype party, the alliance of independent pro-Gaza MPs, is also considering a joint leadership structure with former Labour MPs Zarah Sultana and Jeremy Corbyn at the helm. The difficulty here is that it is not yet clear exactly how the two figures would share their leadership duties. The much-discussed launch is planned for later this year.

Voting for the new Green party leader(s) will take place through all of August, with the result declared on September 2. We will see if the arguments in favour of a more conventional leadership structure (albeit with more radical policies and tone) prevail over the less conventional structure (but with a steadier political approach).

Either way, the Greens will continue to provide an alternative voice and approach in our still developing multiparty era. And maybe that’s a good thing too. When you look around the world at some other self-styled “strong leaders” – Trump, Putin, Netanyahu, to name but three – a break from having similar aspiring “strong leaders” at Westminster might be welcome.

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Stefan Stern does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. From the Green party to Corbyn’s new launch – is it time Westminster took joint leaders more seriously? – https://theconversation.com/from-the-green-party-to-corbyns-new-launch-is-it-time-westminster-took-joint-leaders-more-seriously-262058

July 30, 2025

The Assassin: Keeley Hawes drama is a milestone for menopause on screen

Source: The Conversation – UK – By Beth Johnson, Professor of Television & Media Studies, University of Leeds

Keeley Hawes’s new Channel 4 and Prime Video drama, The Assassin, introduces a premise that feels both bold and overdue. It follows Julie (Hawes), a menopausal woman, overlooked and emotionally stalled, who worked as a hitwoman in her youth and unexpectedly comes out of retirement to return to the profession.

It’s pulpy, stylised and laced with dark humour. But beneath the genre trappings lies something more striking – a cultural pivot in how menopause and midlife womanhood is being written and visualised on British television.

Historically, menopause has been television’s silent transition. Onscreen, it was something female characters either didn’t have, didn’t talk about, or, when acknowledged, were mocked for. Sitcoms of the 1980s and 1990s, such as Birds of a Feather or Absolutely Fabulous, played menopausal symptoms for laughs.

In drama, menopause tended to arrive invisibly: women stopped being protagonists, were subtly phased out of storylines, or returned only as wives, mothers, or medical cases.

Television has always been shaped by industry ideas about youth, sex appeal and marketability – ideas that left little room for midlife women unless confined to supporting roles – or contained within the domestic, ensemble structures of soap operas.

While shows like New Tricks (2003), Last Tango in Halifax (2012) and Call the Midwife (2012) gradually shifted the dial, menopause itself remained offscreen: considered either too niche, too biological, or too awkward to dramatise.

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What The Assassin offers is not just a menopausal character, but midlife as premise. Rather than sidelining her life stage, the show lets its rhythms – emotional turbulence, internal chaos, flickers of disorientation, flashes of wit and a deep, simmering strength – seep into the storytelling itself.

The story ties her hormonal shifts to emotional volatility, a sense of personal invisibility, fractured family life and existential grief. And then she snaps. But it’s not collapse; it’s re-ignition. She becomes lethal — not in spite of midlife, but because of it.

I research the way midlife female protagonists are presented in British television drama. I’ve recently written about Russell T. Davies’ work in particular, arguing that his dramas (such as It’s a Sin, 2021, and Nolly, 2023) reclaim neglected figures by placing their emotional complexity and cultural marginalisation at the centre.

Nolly offered a compelling reappraisal of Noele Gordon (played by Helena Bonham Carter), the soap star unceremoniously dumped from her own show – a decision now widely understood to be rooted in sexism and ageism. Davies refused to let her disappear quietly, instead making her menopause-era strength and defiance the dramatic core of his show.

The trailer for The Assasain.

Similarly, my work with Professor Kristyn Gorton on Sally Wainwright’s series Happy Valley (2014) explores how Catherine Cawood (played by Sarah Lancashire) embodies emotional realism, grief, rage and midlife fatigue – not as flaws, but as substance. These female characters don’t just react to events; they are the story. Their emotions are not incidental but generative, propelling the narrative, shaping its tone and demanding audience recognition.

The Assassin fits this trajectory. It joins a growing body of British TV that blends genre hybridity with emotional and political resonance. Like Killing Eve (2018) or I Hate Suzie (2020), it uses the structure of the thriller to think critically about gender, ageing and identity.

The menopausal hitwoman is, of course, a metaphor as much as a plot. She is rage personified: a woman no longer governed by the social niceties that often temper female representation. She’s also funny, erratic and uncontained.

A menopausal reckoning

Importantly, The Assassin doesn’t simply celebrate her transformation. It stages it as messy, uncomfortable and morally complex. This is menopause not as a redemptive arc but as a reckoning, with a body that’s changing, a past that won’t stay buried, and a society that prefers women neat, young and silent.

There’s still work to do. British television remains far more comfortable exploring middle-aged male protagonists than women in the same life stage. But what’s changing, and what I frequently explore in my research, is the tone and ambition with which female midlife is now being scripted. Where menopause was once a punchline or absence, it’s becoming a story. And not just any story, but one shaped by genre, irony, feeling and risk.

Thanks to its long-form, visual medium, television can explore the ordinary in ways that resonate deeply, from the exhaustion of grief to the frustration of being dismissed. Menopause, long under-explored, offers rich dramatic territory: emotional volatility, bodily transformation, the redefinition of self. What The Assassin understands is that these aren’t signs of decline. They’re tools of narrative power.

By giving us a menopausal character who is central, subversive and narratively in control, The Assassin signals a broader shift. It reminds us that midlife is not an endpoint, but a site of potential – for drama, for comedy and for cultural critique. British television is, at last, beginning to give menopause the storylines it deserves.

Beth Johnson does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. The Assassin: Keeley Hawes drama is a milestone for menopause on screen – https://theconversation.com/the-assassin-keeley-hawes-drama-is-a-milestone-for-menopause-on-screen-262101

July 30, 2025

UK and France pledges won’t stop Netanyahu bombing Gaza – but Donald Trump or Israel’s military could

Source: The Conversation – UK – By Paul Rogers, Professor of Peace Studies, University of Bradford

Keir Starmer says unless there’s a ceasefire and a peace process leading to a two-state solution, Britain will recognise the state of Palestine at the UN in September. The UK prime minister is following a similar, alebit unconditional, pledge from the French president, Emmanuel Macron.

They are reacting to what Starmer referred to as the “intolerable situation” in Gaza. In Scotland, Donald Trump has also complained at the humanitarian catastrophe of people starving in Gaza, saying: “We’ve got to get the kids fed.”

Does this mean western politicians are finally prepared to act? Quite possibly. Will it have any discernible effect on Benjamin Netanyahu? Doubtful.

Trump still appears to trust Netanyahu to feed the people of Gaza, or so he told reporters as he flew back from his weekend of “golf buggy diplomacy” on July 29. And as long as the US president supports Netanyahu, the Israeli prime minister can act with few restraints.

True, the vigorous international reaction to the food crisis in Gaza has finally had some effect. But the Israeli response so far has been largely symbolic.

It has comprised air drops of aid by Israel and the United Arab Emirates, and some “tactical” or “humanitarian” pauses in the assault in parts of the Gaza Strip to allow for the delivery of aid. Air drops are good for publicity, but the amount of aid they actually deliver is very small and hugely expensive.

How did we get to this point? The current phase of the conflict started in mid-March, when the Israeli government began blocking all aid to Gaza.

That lasted two months until some shipments were allowed. In recent weeks, an average of about 70 trucks a day have crossed the border. But the reality is 500-600 trucks a day are required to support and restore heath to 2 million people.

Meanwhile, more than 1,000 Palestinians have been killed – mostly shot – since May while trying to get food at one of the four overcrowded distribution sites run by the private, US-backed Gaza Humanitarian Foundation (GHF). Before being replaed by the GHF system, UN agencies ran 400 distribution points across the territory.

What the daily pauses in some areas, which began on July 27, actually represent is far from clear, given that fighting continues in much of the Strip. There is little sign that Netanyahu’s government wants an early end to the war. From its perspective, there can only be peace when all the hostages are returned and Hamas has been destroyed.

But Hamas is proving far more resolute than expected. Its survival is little short of remarkable given the huge force the Israelis have used to try and destroy it.

The usual Israeli military priority in dealing with an insurgency is to follow what is known colloquially as the “Dahiya doctrine”. If an insurgency cannot be handled without serious casualties, then the Israel Defense Forces (IDF) directs its operations at civilian infrastructure and the general population to undermine support for the insurgents.

The tactic is so called because it was developed as a way of dealing with a Hezbollah stronghold in the Dahiya suburb of west Beirut in 1982. The reduction of much of Gaza to ruins is taking the doctrine to extremes, yet it is failing – Hamas is still there.

This is reportedly common knowledge in IDF circles, but rarely admitted in public. A notable exception is the senior retired IDF officer, Major-General Itzhak Brik.

Brik’s publicised view is that Hamas has already replaced its thousands of casualties with new recruits. They may not be trained in the conventional sense, but they have learnt their craft while surviving in a war zone and seeing so many of their friends and family killed and wounded.

No end in sight

Israel’s demands may be that it will end the war if Hamas surrenders and disarms, then goes into exile. The problem with this is Hamas doesn’t think Israel would end the war.

Instead, it believes Gaza would be forcibly cleared and resettled, and the occupied West Bank would see a huge increase in settlers. In this scenario, a two-state solution would be a pipe dream, and Israel would be the regional superpower able to rise to any future challenge.

So, is there any prospect of Israel being forced to compromise, to accept a UN-monitored ceasefire and seek a negotiated settlement? External political pressure is certainly rising, especially the potential formal recognition of the state of Palestine by the UK and France.

But in both cases, the conditions for the road to peace are such that they are effectively non-starters. Macron envisages a “demilitarised Palestine” living alongside Israel. Starmer has called for Hamas to disarm and play no role in the future governance of Palestinians. Neither plan has the slightest chance of getting off the ground.

In any case, without Trump’s full backing it would still mean little. Economic and social sanctions by a state or group will have little impact because there will always be states or organisations sufficiently supportive of Israel to bypass them.

We are left with two possible routes to a settlement. One is that Trump is sufficiently motivated to insist Netanyahu negotiates.

That is unlikely, unless the US president somehow gets the idea that his own reputation is being damaged. Even then, the influence of the Israel lobby in the US, especially the support for Israel of tens of millions of Christian Zionists, is formidable.

The other route to a peace deal is if the war is becoming problematic for the Israeli military. If more of the IDF’s top brass recognise that this war, right from the start, was always going to be unwinnable, this might yet move the conflict in the direction of a settlement.

Paul Rogers does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. UK and France pledges won’t stop Netanyahu bombing Gaza – but Donald Trump or Israel’s military could – https://theconversation.com/uk-and-france-pledges-wont-stop-netanyahu-bombing-gaza-but-donald-trump-or-israels-military-could-262131

July 30, 2025

Viral ‘kettlebell challenge’ could do you more harm than good – here’s why

Source: The Conversation – UK – By Jen Wilson, Senior Exercise and Health Practitioner, Nottingham Trent University

The challenge may sound like a quick and easy way to get fit, but it may actually be the least effective way of adding kettlebells to your workouts. Tongpool Piasupun/ Shutterstock

The “100 kettlebell swings a day” challenge is the latest viral fitness endeavour on social media. The challenge is simple: pick up a kettlebell and do 100 swings (bringing the kettlebell from between your legs and using your core and glutes to swing it up to chest or shoulder height) every day. These can be done either in one stint, or broken up throughout the day.

Proponents of the challenge say it leads to fat loss, improved muscle mass and a stronger posterior chain (glutes, back and hamstrings) – all in a short daily session.

At first glance, it sounds like a time-efficient, no-fuss approach to getting fitter with minimal equipment. But while there’s some merit in consistency, this type of challenge often ignores fundamental principles of exercise and training – and could even do more harm than good.

Here’s a few reasons why it might be best to skip the kettlebell challenge – and what you can try instead.

1. It’s not personalised to you

One of the biggest flaws in the 100 kettlebell swings challenge is that it treats everyone the same, regardless of experience level, injury history, mobility or training goals. What’s manageable for an advanced athlete could cause problems for a beginner with poor hip mobility or lower back issues.

Daily, high-rep dynamic movements which use explosive power, such as kettlebell swings, require good technique, good posture and body awareness. Without that, you’re simply reinforcing poor movement patterns. Worse, you could be inviting injury when such movements are done repeatedly.

Effective training should be personalised – or at least adapted to your movement abilities and fitness requirements in order to have the most impact.

2. No room for progress

The human body adapts quickly. If you do the same 100 reps with the same amount of weight every single day, the challenge becomes less effective over time. That initial burn you felt in week one? It’ll be gone by week three.

In well-designed training programmes, there’s a principle called “progressive overload”. This involves gradually increasing stress on the body, either through the amount of weight you’re lifting, the number of repetitions you do of an exercise, the number of sets you complete or the complexity of your movements.

The 100-swing challenge skips this entirely. This means you’ll probably hit a plateau fairly quickly.

3. Risk of injury

Doing 100 swings every day, especially without rest or proper technique, can lead to injuries such as muscle strains or joint pain in the back and shoulders.

Too much repetitive movement, insufficient recovery time and inexperience can also lead to an increased risk of an overuse injury – a condition caused by repeated stress on muscles, joints or tissues. This often results in pain, swelling, or stiffness and could potentially mean taking weeks or even months off from working out to fully recover.

Picking up this challenge might be appealing but it also ticks a lot of boxes for overuse injury.

4. It undermines recovery

Recovery between workouts is not optional. In fact, it’s where the actual adaptation happens. Training breaks the body down, while recovery builds it back stronger.

Kettlebell swings, especially if performed explosively and with heavier loads, place stress on your central nervous system. Doing them every single day without rest days, mobility work (such as stretching) or variation can lead to chronic fatigue, poor sleep, nagging injuries and even reduced performance in other areas of training.

A group of young, fit people perform kettlebell swings in a gym. — This daily challenge doesn’t leave the body enough time for integral recovery.
wavebreakmedia/ Shutterstock

If you’ve started the challenge and find you’re constantly sore, tight or worn down, the challenge may be doing more harm than good.

5. It’s a one-dimensional solution

Fitness isn’t just about repetition. True strength and conditioning involves a variety of movements, such as pushing, pulling, squatting, rotating and stabilising.

The 100-swing challenge trains only one plane of motion and one movement pattern. While that’s better than nothing, it’s nowhere near comprehensive. Moreover, doing the same task over and over can become mindless. You’re not necessarily getting stronger or fitter – you’re just going through the motions.

A smarter way to use kettlebells

In fairness, the challenge does have some value in the right context. For beginners who need structure, it can help establish a daily habit. It requires minimal equipment, little space and can raise heart rate, build endurance and activate the posterior chain.

But for it to be sustainable and effective, a few things must be in place:

Your form must be solid
The kettlebell weight must be appropriate for your fitness level
You should vary the volume or intensity over time
You should include rest days
It should be part of a broader training plan – not your only form of training

If you enjoy kettlebell swings, there are more intelligent and safer ways to include them in your training than doing 100 reps every day.

Try incorporating swings into interval sessions, circuits or strength workouts with varied repetitions and loads. Instead of doing 100 swings alone, aim for 100 total reps using a mix of exercises, such as goblet squats, rows and presses. This approach not only keeps things more balanced, but also reduces the risk of injury from overuse and gives different muscle groups time to recover .

The “100 kettlebell swings a day” challenge might sound appealing in its simplicity, but simple doesn’t always mean smart. Without personalisation, progression and recovery, it can quickly turn into a repetitive grind that risks doing more harm than good.

Yes, training should be challenging, but it should also be strategic. Your body deserves more than just a checkbox of daily repetitions – it needs the right moves done the right way.

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

– ref. Viral ‘kettlebell challenge’ could do you more harm than good – here’s why – https://theconversation.com/viral-kettlebell-challenge-could-do-you-more-harm-than-good-heres-why-260010

July 30, 2025

Why do corporations act against the public interest? We may have the answers (it’s not just greed)

Source: The Conversation – UK – By Stephen R. Buzdugan, Senior Lecturer in International Business, Manchester Metropolitan University

For the past two years, Tesla has been embroiled in a bitter dispute with the Swedish labour union IF Metall. It is of a scale that the union hasn’t witnessed since the 1930s.

At the heart of the dispute is Tesla’s refusal to sign a collective bargaining agreement. This is a pillar of the “Swedish model” of labour relations, which is prized by Sweden’s citizens due to its perceived contribution to social wellbeing and shared prosperity.

Instead, Tesla has opted to circumvent striking union workers and bring its cars into the country using non-unionised labour and labour from neighbouring countries. Tesla’s actions to undermine a system that Sweden strongly supports are what we call “anti-societal”. That is, they might be said to undermine democratic norms and the broader public interest.

More broadly, it isn’t unusual to see corporations acting in ways that negatively affect the public interest, with effects such as environmental degradation, poor working conditions or violations of anti-trust laws. Multinational corporations are often in the news for violating or avoiding government regulations and working behind the scenes to influence regulation to their advantage.

Among many examples is the Volkswagen group’s “Dieselgate” emissions scandal. The German carmaker cheated on vehicle tests to make diesel cars seem less polluting than they were in reality. The company later acknowledged it had “screwed up” and breached customers’ trust.

And it is believed that oil and gas giant Exxon had evidence in the 1970s that fossil fuels contribute to climate change, but mounted a a campaign of disinformation in order to stifle regulation of their products. (In 2021, Exxon CEO Darren Woods told US politicians that the company “does not spread disinformation regarding climate change”.)

These examples raise the question of why corporations engage in activities against the public interest. Yet browse through any standard textbook used in a university business or management course, and you will struggle to find answers.

Instead, for several decades the standard viewpoint has been that multinational corporations are mainly economic entities without any particular interest in doing either harm or good. Any anti-societal corporate behaviour has typically been chalked up to a few “bad apples”.

The fact that corporations have political power and systematically use it in their interests in ways that harm society has been largely left out of the picture.

Our recent research shows that the underlying nature of the global economy can influence any corporation to behave anti-societally. We argue that under certain circumstances, a corporation like Tesla might face a threat that compromises its market position, assets or even its existence.

IF Metall, for example, poses a significant threat to Tesla’s business model. If the Swedish trade union wins this dispute it could strengthen the bargaining position of trade unions across Europe. In this case, a corporation like Tesla will exert its power to protect itself. But this often comes with negative consequences for society.

We call this the “self-preservation perspective” of the multinational corporation. It illuminates the ways in which corporations use political power to their advantage, often to society’s cost.

The balance of power

The self-preservation perspective can help people to understand how corporate political power should be challenged through both regulation and activism. Trade union action, for instance, can act as a powerful political force to balance corporate power.

The idea of “self-preservation” comes from international relations theory and an overlooked argument by the late Harvard economist John Kenneth Galbraith .These suggest that any organisation – a nation state or a multinational corporation – will seek primarily to preserve itself in the face of threats.

We apply the idea of self-preservation to modern multinational corporations that seek to survive in a global economy marked by fierce competition and complex regulation.

This perspective predicts that, when faced with a regulatory threat, a multinational corporation will weigh up four strategic options.

First, it may try to influence the regulation through sometimes ethically questionable political activities. Second, it may consider avoiding or ignoring the regulation by exploiting loopholes or by taking strategic legal action. Third, it can decide to comply with the regulation. And last, it can think about exiting the market altogether.

We predict that the corporation’s choice depends on its relative level of political power and resources, as well as the profitability of the market it is operating in. However, it also depends on how powerful it is in relation to governments, trade unions and non-governmental organisations (NGOs).

MOT documentation showing volkswagen emission details — Volkswagen tried to cheat its way around emissions regulation.
SGM/Shutterstock

If government enforcement or societal pressure are very strong, this may steer a corporation toward adapting to the regulation, rather than more negative influencing or avoiding behaviour. One example is Apple’s recent changes to its App Store rules in Europe, to comply with the European Union’s Digital Markets Act.

In the case of Tesla versus the Swedish union, Tesla has exerted its power to avoid regulation. In doing so it has considered the scale of the threat to its business model across Europe and its perceived power relative to the trade union. This possibly stems from Tesla’s strong ties to the technology sector, where engagement with unions is often seen as an unnecessary threat to innovation.

If Tesla’s avoidance strategy succeeds, it would effectively dissolve the Swedish model, creating a system that’s less secure for workers. From our self-preservation perspective, IF Metall’s success in the dispute will depend on how well – and how widely – the unions, government and citizens can galvanise opposition. By balancing corporate power in this way, societies might hope to protect their interests against the might of multinational giants.

David Freund receives funding from Handelsbanken Research Foundation.

Ulf Holm receives funding from Handelsbanken’s Research Foundations.

Stephen R. Buzdugan does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

– ref. Why do corporations act against the public interest? We may have the answers (it’s not just greed) – https://theconversation.com/why-do-corporations-act-against-the-public-interest-we-may-have-the-answers-its-not-just-greed-261866

July 30, 2025

El precio de la sumisión: España paga la debilidad de Bruselas ante EE. UU.

Source: The Conversation – (in Spanish) – By Armando Alvares Garcia Júnior, Professor de Direito Internacional e Relações Internacionais, UNIR – Universidad Internacional de La Rioja

El sector del aceite de oliva será uno de los más afectados por el acuerdo. BearFotos/Shutterstock

El acuerdo comercial firmado entre Estados Unidos y la Unión Europea, lejos de representar un éxito diplomático para Bruselas, revela la profunda crisis de liderazgo y de visión estratégica de la Comisión Europea. Bajo la presión de la Administración Trump, la UE ha cedido en aspectos fundamentales, consolidando una relación profundamente desigual que erosiona tanto la competitividad como la soberanía de los Estados miembros.

España se convierte, una vez más, en un ejemplo paradigmático de los costes de una negociación mal gestionada y de la desconexión de las élites europeas respecto a los intereses reales de sus ciudadanos y sectores productivos.

El corazón del pacto, sellado en Turnberry (Escocia) el domingo 27 de julio de 2025, es la imposición de un arancel general del 15 % a las exportaciones europeas a Estados Unidos. Este nivel, muy por encima del 1,4 % medio vigente antes de la escalada comercial abierta oficialmente por la Casa Blanca el 2 de abril de 2025, constituye una penalización directa a la industria, la agricultura y la tecnología europea, y no encuentra correspondencia en las importaciones de productos estadounidenses, que quedan libres de cualquier restricción equivalente.

La Comisión, en lugar de defender con firmeza el principio de reciprocidad, ha preferido instalarse en el “mal menor”, justificando su decisión en la supuesta amenaza de una guerra comercial abierta que, según Bruselas, traería consecuencias devastadoras para el empleo y el crecimiento.

Esta postura resignada transmite una preocupante falta de ambición y debilita la posición negociadora de la UE ante futuras rondas con Washington u otros bloques.

Un golpe al tejido productivo español

En España, el acuerdo golpea de manera directa al tejido productivo más dinámico y estratégico. El sector agroalimentario, con el aceite de oliva y el vino a la cabeza, verá encarecidos sus productos en el mercado estadounidense, con riesgo real de pérdida de cuota y cierre de empresas exportadoras.

Organizaciones empresariales como la Federación Española de Industrias de Alimentación y Bebidas han calificado la medida de “imposición injusta y desequilibrada”, alertando del peligro que supone para miles de empleos y para el equilibrio de la balanza comercial.

España, que ya mantiene un déficit comercial con EE. UU., pierde cualquier capacidad de compensar este golpe a través de otros mercados, en un contexto global marcado por el proteccionismo y la rivalidad de potencias.

Golpe al vino y al aceite de oliva

La industria vinícola calcula que el nuevo arancel puede reducir las ventas en Estados Unidos hasta un 10 %, justo cuando la competencia internacional es más intensa y el margen de maniobra para pequeñas y medianas empresas es mínimo.

El sector del aceite de oliva, del que España es líder mundial, se enfrenta a un escenario similar: más de mil millones de euros en exportaciones en juego y ningún mecanismo de apoyo efectivo por parte de Bruselas, a pesar de su esperpéntico documento de autobombo.

El pacto va mucho más allá del simple intercambio de bienes. La Comisión Europea ha aceptado un compromiso masivo de compras de energía estadounidense –gas natural, petróleo y combustible nuclear– por valor de 640 000 millones de euros en el periodo 2025-2028. Esta decisión, presentada como un paso hacia la independencia de las materias primas rusas, en realidad supone una transferencia de dependencia y una renuncia explícita a la diversificación de proveedores.

La Comisión tampoco ha defendido la industria de defensa europea, comprometiendo inversiones y adquisiciones de armamento estadounidense sin transparencia ni debate democrático real sobre los términos y la conveniencia estratégica de estas compras.

Críticas y desconfianza de los ciudadanos

El acuerdo ha desatado críticas en todo el continente, no solo entre los países más afectados, sino también en los principales aliados de Bruselas. La tibieza de la defensa institucional, la falta de transparencia y el desdén por los intereses de la industria europea están alimentando la creciente desconfianza de los ciudadanos y reforzando el escepticismo ante el proyecto comunitario.

Las justificaciones de la Comisión, basadas en evitar una guerra comercial a cualquier precio, no resisten el análisis cuando el coste real es una pérdida sostenida de autonomía, empleo y capacidad de influencia.

La gestión de este acuerdo evidencia las carencias de la actual Comisión Europea en materia de liderazgo, defensa de intereses estratégicos y conexión con las necesidades reales de la economía europea.

La renuncia a exigir reciprocidad, el sacrificio de sectores clave y la aceptación de una nueva dependencia –energética y militar– confirman un retroceso preocupante. España, como otros Estados miembros, paga un precio alto por la resignación de Bruselas, y el conjunto del continente enfrenta el riesgo de una década perdida en autonomía y competitividad si no se recupera la ambición y la firmeza en la defensa de sus intereses.

Armando Alvares Garcia Júnior no recibe salario, ni ejerce labores de consultoría, ni posee acciones, ni recibe financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y ha declarado carecer de vínculos relevantes más allá del cargo académico citado.

– ref. El precio de la sumisión: España paga la debilidad de Bruselas ante EE. UU. – https://theconversation.com/el-precio-de-la-sumision-espana-paga-la-debilidad-de-bruselas-ante-ee-uu-262172

July 30, 2025

El terremoto de Kamchatka figura entre los diez más fuertes jamás registrados: esto es lo que tienen en común

Source: The Conversation – (in Spanish) – By Dee Ninis, Earthquake Scientist, Monash University

El terremoto de magnitud 8,8 que sacudió la costa de la península de Kamchatka, en el extremo oriental de Rusia, es uno de los diez más fuertes de la historia y el mayor del mundo desde 2011. Este seísmo ha causado daños en edificios y heridos en la ciudad más grande cercana, Petropávlovsk-Kamchatski, a solo 119 kilómetros del epicentro.

Las alertas de tsunami y las evacuaciones han resonado en Rusia, Japón y Hawái, y se han emitido avisos para Filipinas, Indonesia y lugares tan lejanos como Nueva Zelanda y Perú.

La región del Pacífico es muy propensa a sufrir terremotos de gran intensidad y los tsunamis que estos provocan, ya que se encuentra en el llamado Cinturón de Fuego, una zona de elevada actividad sísmica y volcánica. Los diez terremotos más potentes registrados en la historia moderna se produjeron en esa región.

He aquí por qué la estructura subyacente de nuestro planeta hace que esta parte del mundo sea tan inestable.

¿Por qué se producen terremotos tan fuertes en Kamchatka?

Justo frente a la costa de la península de Kamchatka se encuentra la fosa de Kuril-Kamchatka, un límite de placas tectónicas donde la placa del Pacífico empuja bajo la placa de Okhotsk.

Mientras que las placas tectónicas se mueven continuamente unas respecto a otras, la interconexión entre ellas suele estar “atascada”. La tensión se acumula hasta que supera la resistencia de dicha zona de contacto, momento en el que se libera en forma de ruptura repentina: se produce un terremoto.

Debido a las grandes extensiones de los puntos de contacto en los límites de las placas, tanto en longitud como en profundidad, la ruptura puede abarcar grandes áreas. Esto da lugar a algunos de los terremotos más grandes y potencialmente destructivos de la Tierra.

Otro factor que influye en la frecuencia y la magnitud de los terremotos en las zonas de subducción es la velocidad a la que se mueven las dos placas entre sí.

En el caso de Kamchatka, la placa del Pacífico se mueve a aproximadamente 75 milímetros por año con respecto a la de Okhotsk. Se trata de una velocidad relativamente alta para los estándares tectónicos, lo que provoca que los grandes terremotos sean más frecuentes aquí que en otras zonas de subducción. En 1952, se produjo un terremoto de magnitud 9,0 en la misma zona de subducción, a solo unos 30 kilómetros del terremoto de magnitud 8,8 producido hoy.

Otros ejemplos de terremotos en límites de placas de subducción son el terremoto de magnitud 9,1 de Tohoku-Oki (Japón) de 2011 y el terremoto de magnitud 9,3 de Sumatra-Andaman Indonesia, ocurrido en 2004. Ambos se iniciaron a una profundidad relativamente baja y rompieron el límite de la placa hasta la superficie.

Elevaron un lado del lecho marino con respecto al otro, desplazando el océano que se encontraba sobre él y provocando devastadores tsunamis. En el caso del terremoto del 26 de diciembre de 2004, la ruptura del lecho marino se produjo a lo largo de unos 1400 km.

¿Qué es probable que suceda a continuación?

En el momento de redactar este artículo, aproximadamente seis horas después del terremoto, ya se han producido 35 réplicas de magnitud superior a 5,0, según el Servicio Geológico de los Estados Unidos.

Las réplicas se producen cuando la tensión dentro de la corteza terrestre se redistribuye tras el terremoto principal. A menudo son de una magnitud inferior a la del seísmo principal. En el caso del terremoto de hoy, eso significa que son posibles réplicas de magnitud superior a 7,5.

En un terremoto de esta magnitud, las réplicas pueden continuar durante semanas o meses, pero normalmente disminuyen en magnitud y frecuencia con el tiempo.

El seísmo de hoy también ha provocado un tsunami que ya ha afectado a las comunidades costeras de la península de Kamchatka, las islas Kuriles y Hokkaido, en Japón.

En las próximas horas, ese tsunami se propagará por el Pacífico, llegando a Hawái aproximadamente seis horas después del terremoto y continuando hasta Chile y Perú.

Los científicos especializados en tsunamis seguirán perfeccionando sus modelos de sus efectos a medida que se propague, y las autoridades de defensa civil proporcionarán información oficial sobre los efectos locales previstos.

¿Qué lecciones se pueden extraer de este terremoto para otras partes del mundo?

Afortunadamente, terremotos tan grandes como el de hoy son poco frecuentes. Sin embargo, sus efectos a nivel local y en todo el mundo pueden ser devastadores.

Aparte de su magnitud, varios aspectos del terremoto de hoy en Kamchatka lo convertirán en un foco de investigación especialmente importante.

Por ejemplo, la zona ha sido muy activa sísmicamente en los últimos meses, y el 20 de julio se produjo un terremoto de magnitud 7,4. La forma en que esta actividad previa ha afectado a la ubicación y el momento del evento de hoy será un aspecto crucial de la investigación.

Al igual que Kamchatka y el norte de Japón, Nueva Zelanda también se encuentra sobre una zona de subducción; de hecho, sobre dos zonas de subducción. La mayor de ellas, la zona de subducción de Hikurangi, se extiende mar adentro a lo largo de la costa este de la isla Norte.

Según las características de estos puntos de contacto entre placas y los registros geológicos de terremotos pasados, es probable que la zona de subducción de Hikurangi sea capaz de producir terremotos de magnitud 9. No lo ha hecho en tiempos históricos, pero si ocurriera, provocaría un tsunami.

La amenaza de un gran terremoto en la zona de subducción nunca desaparece. El terremoto de hoy en Kamchatka es un importante recordatorio para todos los que viven en zonas propensas a los terremotos de que deben mantenerse a salvo y prestar atención a las advertencias de las autoridades de defensa civil.

Dee Ninis trabaja en el Centro de Investigación Sismológica, es Vicepresidenta de la Sociedad Australiana de Ingeniería Sísmica y miembro del Comité de la Sociedad Geológica de Australia – División Victoria.

John Townend recibe financiación de los fondos Marsden y Catalyst de la Royal Society Te Apārangi, de la Comisión de Riesgos Naturales Toka Tū Ake y del Ministerio de Empresa, Innovación y Empleo de Nueva Zelanda. Ha sido presidente y director de la Sociedad Sismológica de América y presidente de la Sociedad Geofísica de Nueva Zelanda.

– ref. El terremoto de Kamchatka figura entre los diez más fuertes jamás registrados: esto es lo que tienen en común – https://theconversation.com/el-terremoto-de-kamchatka-figura-entre-los-diez-mas-fuertes-jamas-registrados-esto-es-lo-que-tienen-en-comun-262245

July 30, 2025

Tsunamis: qué altura pueden alcanzar las olas como las generadas por el terremoto en Rusia

Source: The Conversation – (in Spanish) – By José Luis González Fernández, Profesor Ayudante Doctor Didáctica de las Matemáticas, Universidad de Castilla-La Mancha

Grandes olas en la playa de Garrapata (California) Gustavo Gerdel/Wikimedia commons, CC BY-SA

Las olas han fascinado a la humanidad desde tiempos inmemoriales, tanto por su belleza como por su fuerza destructiva. Hoy, esa dualidad se manifiesta con crudeza tras el terremoto de magnitud 8,8 en Rusia, que ha desatado alertas de tsunami en todo el Pacífico y ha obligado a evacuar a millones de personas. Este tipo de fenómenos nos recuerda que, más allá de su estética, las olas pueden convertirse en fuerzas implacables de la naturaleza.

La ola de un terremoto

El terremoto más potente jamás registrado (terremoto de Valdivia, Chile, 1960) liberó la energía equivalente a 20 000 bombas atómicas de Hiroshima. Tal energía podría provocar un tsunami de solo 4,55 metros de altura en alta mar, pero que podría ascender hasta 1,7 kilómetros en costa. El aumento se debe al llamado efecto shoaling o asomeramiento: las olas aumentan de tamaño al acercarse a la costa.

Sin embargo, el tamaño real fue muchísimo menor (unos 10 metros) ya que el terremoto se produjo en tierra firme y no toda la energía fue a parar a una sola ola. Eso no quiere decir que no fuera destructor: el tsunami atravesó el océano Pacífico, causando la muerte de más de 2 000 personas en Chile, Perú, Hawái y Japón.

Animación de The Pacific Tsunami Warning Center (PTWC) muestra cómo se propagó por el océano Pacífico el tsunami que generó el terremoto de Chile y llegó a Japón.

Donde el viento y la física chocan

En condiciones normales, la mayoría de las olas están generadas por viento. Tienen un ciclo de formación, crecimiento y rompimiento que depende de la velocidad, alcance y duración del viento y la profundidad del agua. Sin embargo, incluso en condiciones óptimas, las olas no pueden crecer indefinidamente.

La física establece una proporción límite entre la altura de una ola y su longitud de onda: cuando esa relación supera 1/7, la ola se vuelve inestable y rompe. Es decir, la cresta se desploma hacia adelante porque ya no puede sostenerse.

Además, hay otro factor clave: la profundidad del agua. A medida que una ola se acerca a la costa, el fondo marino frena su base mientras la cresta sigue avanzando, lo que hace que la onda se incline y eventualmente rompa. En aguas poco profundas, una ola no puede tener una altura mayor a aproximadamente 0,88 veces la profundidad local. Así, en una playa donde el agua tiene 3 metros de profundidad, la ola máxima teórica que podría romper sería de unos 2,64 metros. Este límite es observable y verificable, y se utiliza frecuentemente en ingeniería costera y en predicción de oleajes.

Ambos fenómenos establecen algunos de los límites fundamentales a la altura de las olas en el mar.

Gigantes inesperados: la ola Draupner

Ahora bien, hay ocasiones en que el océano parece desafiar estas reglas. Las llamadas olas extremas o rogue waves (olas monstruo) son eventos poco frecuentes pero muy reales, en los que una ola de tamaño descomunal aparece sin aviso, duplicando o triplicando la altura típica del oleaje circundante.

Una de las más conocidas fue registrada en 1995 por una plataforma petrolera en el mar del Norte: la ola Draupner, que alcanzó los 25,6 metros de altura. Este evento confirmó lo que hasta entonces muchos consideraban un mito marinero. Desde entonces, varios estudios han demostrado que estas olas extremas pueden formarse por la combinación constructiva de múltiples olas, la interacción con corrientes oceánicas, o fenómenos aún en estudio. Sin embargo, en la práctica, su altura no suele superar los 30 metros en mar abierto.

Recreación de la ola Draupner para un documental de la BBC.

Cuando la Tierra crea olas: 520 metros de altura

Más allá de lo que el viento puede generar, existen olas de origen geológico conocidas como megatsunamis. Estas olas se producen por deslizamientos de tierra, colapsos de glaciares o impactos de meteoritos, que desplazan una enorme cantidad de agua de forma repentina.

Un caso dramático ocurrió en la Bahía de Lituya, en Alaska, en 1958. Un sismo de 7,8 grados en la Escala de Richter provocó el desprendimiento de una montaña. Más de 30 millones de metros cúbicos de tierra y piedras cayeron en bloque al agua, desde una altura de 900 metros. El colapso provocó una ola que alcanzó una altura estimada de 524 metros.

fiordo con montañas y lago que muestran donde se desprendión una montaña — Esquema que muestra dónde se produjo el desprendimiento de la montaña que provocó el megatsunami en la bahía de Lituya (Alaska).
Wikimedia commons, CC BY

Este fenómeno, aunque real, fue muy distinto de las olas comunes puesto que no se produjo en el océano. Sólo afectó al fiordo.

La energía necesaria para formar algo similar en mar abierto es tan colosal que solo podría producirse por eventos extraordinarios, como el impacto de un gran asteroide en el océano.

El tamaño de un megatsunami

¿Existe entonces un límite físico al tamaño de un megatsunami? Es difícil responder con exactitud. Pero podemos hacer una estimación sencilla si nos centramos sólo en la energía asociada.

Imaginemos una única “ola” que se desplaza (también llamada solitón u ola solitaria) generada por un terremoto o el impacto de un meteorito. Por simplicidad, obviaremos la fricción, el flujo turbulento y otros factores complejos. La altura que puede alcanzar dependerá de su energía cinética y potencial. Si además conocemos algunos parámetros, como su anchura o velocidad, podremos estimar un valor.

Por tanto, vamos a introducir los datos correspondientes a algunos de los mayores fenómenos creadores de tsunamis conocidos. Así, veremos qué alturas máximas son físicamente posibles. No obstante, es importante tener en mente que sobreestiman los límites reales y muy probablemente nunca sean alcanzados.

La caída de un meteorito

Por otro lado, el meteorito más energético del que tenemos conocimiento, (Chicxulub), conocido popularmente por poner fin a los dinosaurios, liberó la energía equivalente a 67 000 millones de bombas de Hiroshima. Tanta energía podría haber generado una ola de no más de 16 kilómetros en costa, si bien en la literatura se estima que “sólo” habría alcanzado en torno a entre 1 y 3 kilómetros de altura.

No hay olas infinitas

Las olas no pueden crecer indefinidamente. Su altura está limitada por factores como la longitud de onda, la profundidad del agua y la energía disponible.

En mar abierto, las olas generadas por viento difícilmente superan los 30 metros. Más allá de eso, entramos en el terreno de los tsunamis y megatsunamis, que pueden generar olas de cientos de metros, pero dependen de procesos geológicos violentos y muy raros.

En cualquier caso, en la práctica, existe un límite razonable a la altura de las olas que el mar puede ofrecernos.

Podemos ir a la playa sin miedo, siempre, claro, que no vivamos, en estos momentos, en la costa afectada por el efecto del terremoto en Rusia.

Las personas firmantes no son asalariadas, ni consultoras, ni poseen acciones, ni reciben financiación de ninguna compañía u organización que pueda obtener beneficio de este artículo, y han declarado carecer de vínculos relevantes más allá del cargo académico citado anteriormente.

– ref. Tsunamis: qué altura pueden alcanzar las olas como las generadas por el terremoto en Rusia – https://theconversation.com/tsunamis-que-altura-pueden-alcanzar-las-olas-como-las-generadas-por-el-terremoto-en-rusia-260535