#“Ontong Java”

[johniac]

SciTech Chronicles. . . . . .May 10th, 2025

[seabattical]

(via tackingoutrigger.com Hans Klaar)

[astroimages]

A TERRA ESTÁ RACHANDO? NÃOOOOO!!! VAMOS EXPLICAR!!!

SPACE TODAY NO TEATRO: "MARTE, NOSSO PRÓXIMO DESTINO?" 13 DE ABRIL | 16:00 | TEATRO GAZETA - SP INGRESSOS: https://bileto.sympla.com.br/event/103209 VISITE A NOVA SPACE TODAY STORE E ADQUIRA A SUA COLEÇÃO EM HOMENAGEM AOS 10 ANOS DE INTERESTELAR!!! https://www.spacetodaystore.com.br/kit-10-anos-interestelar-com-4-camisetas-preta Neste vídeo, apresentamos uma nova perspectiva sobre a teoria das placas tectônicas: tradicionalmente, acreditava-se que as placas oceânicas são rígidas até alcançarem o limite convergente, mas pesquisas recentes mostram que áreas como os platôs Ontong Java, Shatsky, Hess e Manihiki podem sofrer intensa deformação antes mesmo de chegarem à trincheira de subducção. Você vai entender o que são os platôs oceânicos – regiões onde a crosta do fundo do mar é anormalmente espessa – e descobrir por que eles parecem ser mais suscetíveis a fraturas, falhas normais e até episódios de vulcanismo tardio, mesmo distantes das margens de placas. O termo “sin-drift” descreve exatamente esse fenômeno de deformação acontecendo enquanto o platô ainda “deriva” rumo à subducção, desafiando o paradigma de que as tensões tectônicas só se manifestam nas bordas. O segredo desse processo pode estar numa espécie de “polia de subducção”, em que a força de tração do slab em subducção (slab pull) é transmitida por centenas, às vezes milhares, de quilômetros, gerando tensão suficiente para romper a crosta mais frágil de um platô oceânico. Evidências sísmicas, geológicas e petrológicas confirmam que falhas e magmatismo nas profundezas do Pacífico são correlatos diretos dessa interação à distância. No vídeo, abordamos os estudos de perfis sísmicos, modelos numéricos e exemplos de campo que comprovam o surgimento de grandes falhas, bacias e episódios vulcânicos sincrônicos com a viagem dessas placas. Tais descobertas são importantes para a compreensão global da dinâmica terrestre, pois mostram que a rigidez das placas oceânicas não é tão absoluta quanto se pensava. Por fim, discutimos como essas ideias se encaixam em um contexto astronômico e planetário: a maneira pela qual o interior de um planeta se reorganiza tectonicamente é uma das chaves para entender sua história evolutiva e até sua habitabilidade. Portanto, conhecer detalhadamente os processos de formação e deformação dos platôs oceânicos da Terra nos ajuda a compreender mundos distantes, onde processos semelhantes podem estar em ação. Aprofunde-se nesse tema surpreendente e compartilhe com quem ama ciência e geologia! Acompanhe o vídeo para entender de perto a teoria, as evidências e as implicações de descobrir que as placas oceânicas não são tão imóveis quanto acreditávamos. #earth #life #universe APRESENTAÇÃO: Sérgio Sacani • X: @spacetoday1 • Instagram: @spacetoday1 MARKETING & CONTEÚDO Beattriz Gonçalves • Instagram: @soubiagoncalves • LinkedIn: /in/beattrizgoncalves PRODUÇÃO: Gabriela Augusta • Instagram: @gabiaugusta_ EDIÇÃO: Alexandre Ziolkowski • Instagram: @thealexandrez FOTOGRAFIA: Caroline Oliveira • Instagram: @carolineoliveirafotos DESIGNER: Nina Soraya • Instagram: @nina.zayit

[travelella]

The Pacific Ocean

The largest ocean - covering more than 30% of Earth.

About 15 times the size of the US; covers about 28% of the global surface; almost equal to the total land area of the world

It touches the west coast border of the Americas along with East Asia and Australia.

The equator divides the Pacific Ocean into two separate parts – the North Pacific Ocean and the South Pacific Ocean.

Pacific means “peaceful” in Latin.

Total area: 168.723 million sq km

Coastline: 135,663 km

Ocean volume: 669.88 million cu km

Lowest Point: Challenger Deep in the Mariana Trench - 10,924 m

Mean Depth: -4,080 m

Percent of World Ocean total volume: 50.1%

Includes Arafura Sea, Bali Sea, Banda Sea, Bering Sea, Bering Strait, Celebes Sea, Coral Sea, East China Sea, Flores Sea, Gulf of Alaska, Gulf of Thailand, Gulf of Tonkin, Java Sea, Philippine Sea, Sea of Japan, Sea of Okhotsk, Solomon Sea, South China Sea, Sulu Sea, Tasman Sea, and other tributary water bodies.

Continental Slope: Where the ocean bottom drops off more rapidly until it meets the deep-sea floor (abyssal plain) at about 3,200 m (10,500 ft) water depth. These waters are characterized by cold temperatures, low light conditions, and very high pressures.

Pribilof Canyon

Zhemchug Canyon - deepest submarine canyon

Abyssal Plains: at depths of over 3,000 m (10,000 ft) and covering 70% of the ocean floor, are the largest habitat on earth. Sunlight does not penetrate to the sea floor, making these deep, dark ecosystems less productive than those along the continental shelf. Despite their name, these “plains” are not uniformly flat; they are interrupted by features like hills, valleys, and seamounts. 

Aleutian Basin

Central Pacific Basin

Northeast Pacific Basin

Northwest Pacific Basin

Philippine Basin

Southwest Pacific Basin

Tasman Basin

Mid-Ocean Ridge: Rising up from the abyssal plain, is an underwater mountain range, over 64,000 km (40,000 mi) long, rising to an average depth of 2,400 m (8,000 ft.) Form at divergent plate boundaries where two tectonic plates are moving apart and new crust is created by magma pushing up from the mantle. Tracing their way around the global ocean, this system of underwater volcanoes forms the longest mountain range on Earth.

East Pacific Rise

Pacific-Antarctic Ridge

Undersea Terrain Features: The Abyssal Plain is commonly interrupted by a variety of commonly named undersea terrain features including seamounts, guyots, ridges, and plateaus. Seamounts are submarine mountains at least 1,000 m (3,300 ft) high formed from individual volcanoes on the ocean floor. They are distinct from the plate-boundary volcanic system of the mid-ocean ridges, because seamounts tend to be circular or conical. A circular collapse caldera is often centered at the summit, evidence of a magma chamber within the volcano. Flat topped seamounts are known as guyots. Long chains of seamounts are often fed by "hot spots" in the deep mantle. These hot spots are associated with stationary plumes of molten rock rising from deep within the Earth's mantle. These hot spot plumes melt through the overlying tectonic plate as it moves and supplies magma to the active volcanic island at the end of the chain of volcanic islands and seamounts. An undersea ridge is an elongated elevation of varying complexity and size, generally having steep sides. An undersea plateau is a large, relatively flat elevation that is higher than the surrounding relief with one or more relatively steep sides. Although submerged, these features can reach close to sea level. 

Caroline Seamounts

East Mariana Ridge

Emperor Seamount Chain

Hawaiian Ridge

Lord Howe Seamount Chain

Louisville Ridge

Kapingamarangi (Ontong-Java) Rise; note - largest submarine plateau

Macclesfield Bank

Marshall Seamounts

Magellan Seamounts

Mid-Pacific Seamounts

Reed Tablemount

Shatsky Rise; note - third largest submarine plateau

Tonga-Kermadec Ridge

Ocean Trenches: The deepest parts of the ocean floor and are created by the process of subduction. Trenches form along convergent boundaries where tectonic plates are moving toward each other, and one plate sinks (is subducted) under another. The location where the sinking of a plate occurs is called a subduction zone. Subduction can occur when oceanic crust collides with and sinks under (subducts) continental crust resulting in volcanic, seismic, and mountain-building processes. Subduction can also occur in the convergence of two oceanic plates where one will sink under the other and in the process create a deep ocean trench. Subduction processes in oceanic-oceanic plate convergence also result in the formation of volcanoes. Over millions of years, the erupted lava and volcanic debris pile up on the ocean floor until a submarine volcano rises above sea level to form a volcanic island. Such volcanoes are typically strung out in chains called island arcs. As the name implies, volcanic island arcs, which closely parallel the trenches, are generally curved.

Aleutian Trench

Chile Trench

Izu-Ogasawara Trench

Japan Trench

Kermadec Trench

Kuril-Kamchatka Trench

Manus Trench

Mariana Trench; note - deepest ocean trench

Middle America Trench

Nansei-Shoto Trench

Palau Trench

Philippine Trench

Peru-Chile Trench

South New Hebrides Trench

Tonga Trench

Yap Trench

Atolls: The remains of dormant volcanic islands. In warm tropical oceans, coral colonies establish themselves on the margins of the island. Then, over time, the high elevation of the island collapses and erodes away to sea level leaving behind an outline of the island in the form of the fringing coral reef. The resulting low island is typified by the coral reef surrounding a low elevation of sand and coral above sea level with an interior shallow lagoon. Often times the remaining dry land is broken into a ring of islets. Some lagoons can be hundreds of square kilometers. It may take as long as 300,000 years for an atoll formation to occur. Guyots are submerged atoll structures, which explains why they are flat topped seamounts. 

Federated States of Micronesia

French Polynesia

Kiribati

Marshall Islands

Midway Island

Tonga

Tuvalu

US Pacific Island Wildlife Refuges

Vanuatu

Wake Island

------------------------------------------------------------------

Ocean Zones: The Ocean is divided into three zones based on depth and light level. Although some sea creatures depend on light to live, others can do without it. Sunlight entering the water may travel about 1,000 m into the oceans under the right conditions, but there is rarely any significant light beyond 200 m.

The upper 200 m (656 ft) of the ocean is called the euphotic, or "sunlight," zone. This zone contains the vast majority of commercial fisheries and is home to many protected marine mammals and sea turtles. Only a small amount of light penetrates beyond this depth.

The zone between 200 m (656 ft) and 1,000 m (3,280 ft) is usually referred to as the "twilight" zone, but is officially the dysphotic zone. In this zone, the intensity of light rapidly dissipates as depth increases. Such a minuscule amount of light penetrates beyond a depth of 200 m that photosynthesis is no longer possible.

The aphotic, or "midnight," zone exists in depths below 1,000 m (3,280 ft). Sunlight does not penetrate to these depths and the zone is bathed in darkness.

------------------------------------------------------------------

Natural Resources: oil and gas fields, polymetallic nodules, sand and gravel aggregates, placer deposits, fish

Natural Hazards: surrounded by a zone of violent volcanic and earthquake activity sometimes referred to as the "Pacific Ring of Fire"; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire; 80% of tsunamis, caused by volcanic or seismic events, occur within the "Pacific Ring of Fire"; subject to tropical cyclones (typhoons) in southeast and east Asia from May to December (most frequent from July to October); tropical cyclones (hurricanes) may form south of Mexico and strike Central America and Mexico from June to October (most common in August and September); cyclical El Nino/La Nina phenomenon occurs in the equatorial Pacific, influencing weather in the Western Hemisphere and the western Pacific; ships subject to superstructure icing in extreme north from October to May; persistent fog in the northern Pacific can be a maritime hazard from June to December

Enviornmental - Current Issues: Pollution from land- and sea-based sources (such as sewage, nutrient runoff from agriculture, plastic pollution, and toxic waste); habitat destruction; over-fishing; climate change leading to sea level rise, ocean acidification, and warming; endangered marine species include the dugong, sea lion, sea otter, seals, turtles, and whales; oil pollution in Philippine Sea and South China Sea

Major Seaport(s): Bangkok (Thailand), Hong Kong (China), Kao-hsiung (Taiwan), Los Angeles (US), Manila (Philippines), Busan (South Korea), San Francisco (US), Seattle (US), Shanghai (China), Singapore, Sydney (Australia), Vladivostok (Russia), Wellington (NZ), Yokohama (Japan)

[earthstory]

The giant plateau If you look at this bathymetric image showing the depth of the seafloor in the Western Pacific Ocean, one spot stands out more than any other. On this map I’ve marked it with the initials OJP – the Ontong-Java Plateau.

The Ontong-Java Plateau is a monster. It covers an area of about 1,900,000 square kilometers – larger than the state of Alaska. It sits entirely beneath the ocean, typically about 1.5 to 3 kilometers beneath the ocean surface and about 2-3 kilometers above the surrounding ocean floor. It is so big and massive that as it rode along the Pacific Plate it ran into a subduction zone and would not go down. There is now an extinct subduction zone to the southwest of the plateau and subduction zones are developing on the other side of the Solomon Islands to take up the stress. The Ontong-Java Plateau is a gigantic volcanic feature. Scientists drilled samples and found that it is a gigantic pile of basaltic lava that erupted rapidly around 120 million years ago. Most of the volume of the plateau was erupted within a short space of only a couple million years, maybe even less (it’s hard to tell the difference between 121 and 122 million year old rocks using the techniques that date basaltic igneous rocks). The size of the plateau as seen today though, is only part of the story of this monster. A plateau this size was expected to sit much higher up and have even have volcanoes above the ocean waters, but drilling efforts at the highest part of the plateau in its western side only found rocks that erupted underwater. However, about a decade ago geologists realized something else – there were 2 other plateaus in the Pacific with the exact same age, the Manihiki Plateau in the open Pacific and the Hikurangi Plateau currently running into New Zealand (both marked on the map). These 2 plateaus have also been drilled and have not only the same age as the Ontong-Java Plateau, they match in other chemical details as well. In 2005 a plate tectonic reconstruction was created showing that these 3 large provinces could have originally formed together and rifted apart shortly after their creation. Their shapes even fit together – the Manihiki plateau has a western ridge that fits well into a gap in the eastern Ontong-Java plateau. In that case, the original center of the Ontong-Java would be in the now-disrupted eastern portion of the plateau. When scientists drilled in that area, they found volcanic rocks erupted above the Pacific Ocean and even hit pieces of buried trees. The hypothesis accurately predicted the geology of the plateau and now most scientists agree that these 3 plateaus once hooked together as a true monster. Within the space of a couple million years a huge amount of lava poured out onto the Pacific Ocean floor. It piled up so high that large islands formed in the middle. After the eruptions finished, its mass was so great that gravity pulled it apart, creating faults and rift zones in the part that was formerly the center. This outpouring of lava at its largest covered about 1% of the surface area of the entire planet – almost the size of Australia today. These gigantic eruptions have happened at various points in geologic history and produce areas we call “large igneous provinces” or LIPs. Although none that we know of are the size of the Ontong-Java plateau, many have similar properties – huge outpourings of basaltic lava forming within the space of 1-2 million years. The most likely explanation for the formation of LIPs is a plume of extra-hot material rising through the mantle. When it hits the surface, it would melt like crazy, rapidly producing a huge outpouring of lava as the heat is removed. That outpouring of lava would bring all sorts of new elements to the Earth’s surface, including metals, nutrients that life can use, and gases that can be toxic to life. Some LIPs, like those in Siberia, have been proposed as explanations for large mass extinctions on Earth. However, the Ontong-Java Plateau is by far the largest LIP on Earth and it is not associated with a mass extinction, maybe suggesting that the link between mass extinctions and volcanic provinces is more complicated. For example, the LIP in Siberia might have been especially deadly due to interaction with a coal layer, while the Ontong-Java plateau’s effects might have been minimized due to erupting mostly under water rather than at the surface. Regardless of the lack of an Ontong-Java mass extinction, this feature is still an amazing monster. No other LIP compares to it in size, and it’s big enough to reshape the plate tectonic patterns in the Pacific Ocean. -JBB Image credit: http://bit.ly/1Kr4PLP References: http://bit.ly/1U59oOU http://bit.ly/1JuX0Vc http://bit.ly/1HsSJzm http://bit.ly/1BUWXza

[accuratepicuresofanthropologists]

Hot off the scanner, four studies of Ian Hogbin from Anthropology in Oceania: "from left to right, Ontong Java, 1927, Wage 1934, Busman 1944, Sydney 1967

[plokoonsdisapprovingeyebrows]

because it still absolutely blows my tiny lil mind:

there is a very large basaltic oceanic plateau just north of the Solomon Islands, the Ontong Java Plateau. It is 1.8 million square km in area, or about the same size as Alaska.

there is another very large basaltic oceanic plateau in the Cook Islands, the Manihiki Plateau. It covers 770,000 square km, more or less the same size as Turkey.

there is a slightly smaller basaltic oceanic plateau currently jammed halfway through a subduction zone on the east coast of New Zealand, the Hikurangi Plateau. It currently covers about 400,000 square km, which is not quite as large as Iraq. However, it may have been up to twice that size before it started being jammed into the bowels of the Earth by tectonics.

There is some pretty decent evidence that all three of these plateaus were formed together in one colossal mega-plateau, 120 million years ago. 

[plokoonsdisapprovingeyebrows]

“once”

*laughs*

The Siberian Traps aren’t even the largest large igneous province out there (although they are, indeed, very large). Try the Central Atlantic Magmatic Province for size, or Ontong Java Nui. We have a list of dozens of LIPs going back over a billion years, and yeah, they do have a tendency to coincide with mass extinction events. The Siberian Traps are something of an outlier in terms of severity; the theory is that they erupted in a region of the crust that was full of some very volatile hydrocarbons and the resulting injection of gases into the atmosphere was much worse than it otherwise would have been.

I also feel like I should point out that LIPs take a very long time to erupt. Tens of millions of years, usually, although by definition there needs to be a ‘main pulse’ of magma emplaced in less than 5 million years. It’s not all coming to the surface at once in a magmatic hell-world, it would be slower. 

Venus has LOCKED tectonic plates??? How does that work? How are they even counted as individual plates if it’s the tectonic equivalent of Pangea?

it's not so much that Venus's tectonic plates are locked, it's more that it never had them in the first place!

which is a major surprise, actually, because Venus is the most Earth-like of the other planets in our solar system.

surprise?

"what," you may say, flailing in consternation, "about Mars?? why are we trying to colonize Mars if Venus is more Earth-like???"

and it's a good question! Venus IS technically more Earth-like in the sense that it's right next door, is a solid 80% the size of Earth, and has both a working atmosphere and a liquid mantle composed of molten rock, BUT- it's also important to note that Venus is the hottest planet in the solar system and it rains boiling sulfuric acid at almost all times! our first probes to the damn place actually melted. MELTED.

this is what Hell looks like.

BUT ANYWAY so Venus is the planet in our solar system that's the MOST physically similar to Earth, our dear mother who does not rain boiling sulfuric acid on our heads hardly at all ever, so it's kind of a shock that its geology is COMPLETELY FUCKING DIFFERENT.

see, Earth's outer crust is broken up into a series of mind-breakingly-massive tectonic plates that sort of skid around on top of the liquid mantle, slowly drifting in different directions driven by Earth's rotation and bonking into each other randomly like a 300-million-year-long Pinball tournament!

but on Venus, the entire outer crust is a single solid piece sitting on top of the liquid mantle, like the peel of an orange.

though not as good for you. because of the whole Boiling Acid thing.

and contrary to what you might think, this actually makes Venus a VERY VIOLENT place! the outer crust twists and deforms slightly as the liquid mantle spins under it, like a water balloon being flung repeatedly against a wall by a small child, but all of that force can't really be dispersed because the crust is a single solid piece of rigid rock!

so what happens is that this force builds and builds and BUILDS until Venus can't take the strain anymore and has a very volcanic tantrum about it.

unlike the rest of the solar system, the surface of Venus is made of relatively new and entirely volcanic rock- because the entire planet is basically having a planet-wide eruption event at all times, with multiple huge volcanos just spewing gigantic amounts of liquid rock everywhere like it's their damn job, to the point where Venus is just getting resurfaced like a McDonalds parking lot every epoch or so.

aren't you glad Earth doesn't do this? I am SO glad Earth doesn't do this.

(much, anyway)

uh anyway that's why we're trying to colonize Mars instead, and why plate tectonics are a GOOD thing! thanks for coming to my TED talk bye

[earthstory]

The Emperor’s Head Our modern thinking behind hotspots is that they are generated by mantle plumes. A huge plume of extra warm mantle rises up to the surface, triggering formation of a large igneous province – a huge pile of igneous rocks somewhere on the surface. That is followed by a long chain of volcanoes, produced by warm mantle continuing to rise up the pipe formed by the plume.

The best established example of this sequence on Earth is the Hawaiian-Emperor seamount chain, a chain of volcanoes starting at Hawaii and extending all the way to the Kamchatka Peninsula, where the chain ends at a subduction zone. Thus, although Hawaii is an extremely well-developed chain of hotspot volcanoes, it is missing one thing – the plume head! Hawaii’s large igneous province isn’t there – either it was subducted, or something is very different about the Hawaiian chain and we don’t understand plume formation at all. A new paper purports to answer this question. Using seismic waves that head through the Earth and powerful supercomputers, scientists are able to detect pieces of material that went down subduction zones, and as data and computers improve they can find these pieces even if they’re now deep inside the planet. 800 kilometers deep beneath the Kamchatka Peninsula, there is a 1000-kilometer wide piece of crust that appears extra thick – a group of authors from several US universities and led by a scientist from Michigan State just proposed that this section of thickened crust represents the Hawaiian plume head. It would have been subducted between 20-30 million years ago, to reach the current depth. While this hypothesis is interesting, it is difficult to test. We’ll never drill down that deep to actually sample this stuff, and the thickened crust could also be related to interaction between the subducted plate and boundaries in the mantle. To confirm this hypothesis, scientists will somehow need to either find pieces of this plateau that stuck to Kamchatka and can be firmly tied to its formation, or come up with a full model for plate motion that includes this plateau. Interestingly, the bend in the Hawaiian-Emperor chain would have happened before this proposed plateau was subducted, so somehow the hypothesis requires that it hit Kamchatka and went down fairly easily, which is the opposite behavior of many other subducted oceanic plateaus. For example, the massive Ontong-Java plateau hit a subduction zone in the Southwestern Pacific and was so large that it shut down the subduction zone entirely, causing a new set of faults to form on the opposite side of Papua New Guinea, so somehow this plateau went down far easier. -JBB Original paper: https://science.sciencemag.org/content/370/6519/983

[plokoonsdisapprovingeyebrows]

red lines are active subduction zones. purple are inactive former subduction zones. bright blue is the outline of the zealandia continental limits. green dots are the Tasmantid and Lord Howe volcanic chains. 

haven’t added the spreading centers bc it’s hard to tell where they are exactly but there are two in the north fiji basin (between fiji and vanuatu) and two in the lau basin (the triangular bit between fiji and tonga.

fun fact! the inactive subduction zone that terminates in the solomon islands was probably bunged up by the ontong-java plateau! some shit is just way too big to subduct XD

who wants a cool geology fact? i found out some shit about plate tectonics around fiji and its making me feral skdhdj

[solomonherald]

Heightening of Quarantine Stations for Western and Choiseul Province commences

Construction work to heighten quarantine and isolation facilities for Western and Choiseul Province have commenced this week-thanks to Community Access and Urban Services Enhancement (CAUSE).National Disaster Council in a statement announced that CAUSE has been awarded the contracts to fast-track the readiness of the quarantine buildings for border communities under special arrangements by government through Ministry of Finance and Treasury, Ministry of Infrastructure Development, World Bank and Honiara City Council.“The upgrade work is mainly to repurpose those identified existing infrastructures at Nusatupe, Noro Lodge and Taro station as directed by government infrastructure architect teams and World Health Organization to a liveable standard.“The heightening construction is expected to be completed in the next three weeks,” the statement said.The Government is currently stepping up its multi-sectoral agency response and preparedness activities in Shortland Islands, Choiseul and the Malaita Outer Islands.The surge of positive cases in neighbouring Papua New Guinea and community transmission into Bougainville calls for a greater step-up- extension of the Western boundary emergency zone to cover northern most of Choiseul and Malaita’s Ontong Java Atolls. Read the full article

[sciencebulletin]

World's largest 'lava lamp bubble' under NZ

Seismic wave-speeds have revealed part of an ancient volcanic "superplume" beneath New Zealand, highlighting connections between the Earth's deep interior and the surface we live on. Research by Te Herenga Waka–Victoria University of Wellington geophysicists Professor Tim Stern and Associate Professor Simon Lamb, together with colleagues, indicates that the North Island sits on part of the "largest volcanic outpouring" on Earth, created by an upwelling in the Earth's deep interior. That event happened about 120 million years ago when a giant plume of hot rock detached itself from the core-mantle boundary, about 3000 km below the Earth's surface, and rose rapidly to the surface as a superplume. A paper on the findings of Professor Stern and Associate Professor Lamb, both from the School of Geography, Environment and Earth Sciences, has been published today in the leading United States journal Science Advances. Professor Stern says the ancient superplume connected the Earth's deep interior with the planet's surface. "In the 1970s, geophysicists proposed that the Earth's mantle was undergoing a churning motion, rather like a lava lamp, and hot blobs of buoyant rock rose up as plumes from as far as the Earth's core. "Melting of this rock near the surface could then be the cause of prolific volcanism, such as that observed in Iceland or Hawaii. "Even larger volcanic outpourings have happened in the geological past, of which the biggest known occurred in the southwestern Pacific in the Cretaceous Period during the time of the dinosaurs, forming a continent-sized underwater volcanic plateau. "Subsequently, the motion of the tectonic plates broke up this plateau, and one fragment– today forming the Hikurangi Plateau—drifted away to the south, and now underlies the North Island and also the shallow ocean offshore." Professor Stern and colleagues studied the speed of seismic waves (vibrations) through these rock layers to determine their origins and features. "The key observation in the new study is that seismic pressure 'P' waves–effectively soundwaves—triggered by either earthquakes or man-made explosions travel through the mantle rocks beneath the Hikurangi Plateau much faster than are observed beneath most of the sea floor, reaching speeds of 9 kilometers a second," he says. "A peculiar feature of these high speeds is that they are equally high for seismic vibrations traveling in all horizontal directions, but much lower for those vibrations traveling vertically upwards." That difference between vertical and horizontal speed allowed Professor Stern and Associate Professor Lamb to match the Hikurangi Plateau rocks with those of the Manihiki Plateau north of Samoa and the Ontong-Java Plateau north of the Solomon Islands, which have the same speed characteristics. That showed they were all part of the same superplume. "The extraordinary thing is that all these plateaux were once connected, making up the largest volcanic outpouring on the planet in a region over 2000 km across." Associate Professor Lamb says it came as a surprise that the "flow predicted for a giant mushroom-shaped superplume head would produce in mantle rocks exactly these very high speeds and this peculiar speed distribution". "The associated volcanic activity may have played an important role in Earth history, influencing the planet's climate and also the evolution of life by triggering mass extinctions. "It is an intriguing thought that New Zealand now sits on top of what was once such a powerful force in the Earth." Professor Stern says the geological community had been close to rejecting the idea of plumes altogether. "Direct evidence for their existence has been elusive. But, with this study, we now have both hard evidence that such plume activity did indeed occur and also a fingerprint method to detect fragments of the largest plumes of all–superplumes–rising up from near the Earth's core." Provided by: Victoria University of Wellington More information: Tim Stern et al. High mantle seismic P-wave speeds as a signature for gravitational spreading of superplumes. Science Advances (2020). DOI: 10.1126/sciadv.aba7118 Image Credit: Victoria University of Wellington Read the full article