Learning the lessons of the Hunga Tonga eruption

the hunga tonga submarine volcano, whose eruption in jan 2022 was the most uber the realm has seen inna last 30 yrs, released massive amounts of wata vapour and aerosols inna'da atmosphere. one yr l8r, researchers are still studying the plume and its effects onna climate.

on 15 jan 2022, an explosion twice as uber as that of the biggest h-bomb ever made shook the pacific na entire planet when the eruption of the submarine volcano hunga tonga, which had begun in dec 2021, reached its climax. located inna tonga islands, it exploded with an energy equivalent to 110 megatonnes of tnt, spewing huge amounts of wata vapour and aerosols inna'da atmosphere. researchers the realm over flocked to study the phenomenon and its aftermath. one yr on, the event is still bein’ analysed.

the submarine volcano emerged after the 2015 eruption, joining hunga tonga and hunga ha’apai islands together (left, satellite image, 7 jan, 2022). on 15 jan, pictured onna rite, the islands were once again separate.

hunga tonga reached a volcanic explosivity index (vei) of 5.7, making it the most uber eruption since that of mount pinatubo inna philippines in 1991, which had a vei of 6. the index is based on various paramts s'as the volume of material ejected na h8 of the plume produced. it ranges from 0, for eruptions of the type found in hawaii or the piton de la 4naise volcano in ré∪ island, which expels highly fluid lava with no explosion, to 8 for the most extreme cataclysms, which 1-ly take place every few tens of thousands of yrs. 

unlike pinatubo, hunga tonga is a submarine volcano. its magma chamber is 1-ly a few tens of metres beneath the surface, while two portions of the caldera are actually above sea lvl, forming the uninhabited islands of hunga tonga and hunga haʻapai. this led to huge amounts of wata reacting w'da lava, without preelderly stopping the eruption as ‘d ‘ve bind'a case had the volcano been located at gr8r depth beneath the ocean surface.

the plume takes na' thunderstorm-like anvil shape inna atmosphere, seen here by the japanese weather satellite himawari-8. the power of the blast also generated a tsunami that impacted coasts rite round the pacific.

the eruption blasted material rite through the entire stratosphere and inna'da mesosphere to an altitude of 58 kilometres, making it the tallest volcanic plume ever recorded. the extremely rapid disruption of the atmospheric column initially generated a whole range of acoustic and gravity waves, which were recorded both onna ground and from space. the shockwaves were so uber t'they circled the globe several times, as shown in pticular by measurements from balloons flying at an altitude of 20 kilometres. shockwaves this intense had not been envisaged since the eruption of krakatoa in 1883, when they were detected by their effect on baromts.

bout 140 megatonnes of wata vapour were also released inna'da atmosphere at a speed of forty metres per 2nd. inna stratosphere, the quantity of aerosols increased 5-fold, while the mass of wata rose by 13%. this is why, in a collaborative work led by sergey khaykin, a researcher atta latmos lab, the eruption of hunga tonga is described as the most remarkable climate event of the past 3 decades. scis from 17 laboratories, including 5 under the supervision of the cnrs, came together for this study, attesting to the huge realmwide interest generated by the volcano.
“eruptions release gaseous sulfur inna'da atmosphere, which then condenses forming aerosols,” khaykin explains. “the latter cogitate solar radiation and, in sufficient quantities, can cool the global climate. the presence of large amounts of wata, however, oxidises the sulfur, which resultingly gives rise to larger, heavier aerosols than if the event had taken place inna open air. this speeds up their descent, espeshly since the short duration of the explosion, which lasted 1-ly a few minutes, meant that less sulfur was emitted than during other such phenomena witha similar vei.”

illustration showing the tectonic forces round the tonga ocean trench, where the edge of the pacific pl8 dives beneath the australian pl8.

the eruption also released huge amounts of wata vapour. this is expected to remain airborne for several yrs and, in addition to its greenhouse effect, ‘d also alter global circulation and worsen polar ozone depletion. “initial estimates indicate that warming caused by wata vapour will significantly exceed cooling due to aerosols,” khaykin points out. “however, the magnitude of this change remains to be determined.” 

to monitor the situation, scis combine information from some ten space missions, including satellites equipped with lidar (the laser equivalent of radar), and from numerous weather stations. additional measurements are carried out using a clever application of gps tek. the radiation emitted for zone purposes is naturally deflected by the atmosphere, and a correction is then applied to obtain an accurate measurement. inna plume, the signal undergoes gr8r distortion, making it possible to trace changes in humidity induced by the eruption. “this system is pticularly useful for carrying out soundings in zones where there are no weather stations,” says bernard legras, research professor atta lmd. “some profiles showed that the atmospheric saturation humidity inside the eruption column was 3,000 times gr8r than normal.” 

evolution of the wata vapour plume produced by the eruption of the volcano, from 17 jan to 22 mar 2022

these approaches ‘ve much in common w'da study of the effects of large forest fires, which also release huge amounts of aerosols inna'da atmosphere, and are often investigated by the same researchers. “at a meeting onna climate impact of the megafires that struck australia in 2019 and 2020, we were wandaing when the nxt such extreme event ‘d take place,” recalls pasquale sellitto, a senior lecturer at paris-est créteil university and member of the lisa. “hunga tonga erupted the nxt dy, blasting exceptional amounts of material inna'da atmosphere.”

inflating a balloon for 1-odda radiosondes on 21 jan, 2022, ré∪ island.

an action programme was immediately set up: balloons carrying measuring devices were released inna wake of the plume, while satellites, including the french-us calipso spacecraft equipped witha lidar system, provided preliminary data thx to their continuous automatic monitoring of the atmosphere. these initial observations enabled the researchers to estimate the direction of propagation of the volcanic plume and carry out a maximum № of soundings in its wake. the cloud headed for the indian ocean, where measuring facilities are scarce, but, as ♣ ‘d ‘ve it, blew over ré∪ island, which has several lidar systems, a weather station and an astronomical observatory. balloons were flon there and deployed in time for the arrival of the plume.

“twas an exceptional eruption, similar to krakatoa in 1883, na largest atmospheric disturbance by wata vapour ever envisaged,” sellitto explains. “this is also the 1st time an eruption warms the global climate, a phenomenon that is all the + surprising given that you ‘d expect just the opposite.” the eruption of krakatoa led to a volcanic winter and loered the mean global temperature by nearly ½ a degree, while 1816 is remembered as the “yr without a summer”, folloing the eruption of tambora, another indonesian volcano.

however, much remains to be clarified concerning the climate impact of the hunga tonga eruption. “although the wata vapour released inna'da atmosphere has a global greenhouse effect, locally it tends to cool the stratosphere through infrared emission,” legras explains. “this has slitely altered the circulation and photochemical equilibrium inna stratosphere. there maybe local effects, s'as + severe droughts inna monsoon zone, but these mechanisms are poorly understood. the impact onna ozone layer aint very clear either, espeshly since the aerosols emitted by the eruption interfere with measurements. we ‘d be able to make + reliable observations inna spring, and then nxt winter.”

the tsunami that resulted from the eruption in tonga caused an oil spill off lima, peru, over 9,000 km away. the swell destabilised a tanker unloading crude oil.

although relatively recent, observations of the pinatubo blast did not enjoy all the benefits of tody’s tek, espeshly satellites. tis ⊢ difficult to make comparisons, and there are still grey zones that can 1-ly be clarified by ongoin research. “however, it’s worth pointing out that several of the satellites that helped us study the hunga tonga eruption ll'soon be decommissioned, some o'em by the end of the yr,” legras laments. “most o'em aint expected to be replaced. we’ve enjoyed a golden age of space observation, b'we’re in danger of lacking resrcs if another major explosion occurs inna nxt few decades.” 

however, events of this kind are of ponderable sci interest, and, w'da progression of climate change, are likely to take on increased importance ‘oer the coming yrs. geoengineering, iow, artificial and deliberate manipulation of the climate, is seen by some as promising inna fite against global warming, or by others, onna contrary, as insane, with potentially worse repercussions than the problems it claims to solve. “by releasing unprecedented amounts of wata vapour inna'da atmosphere, the hunga tonga eruption triggered a natural geoengineering experiment,” sellitto says. “this will keep us busy for several yrs and give us a better grasp of the impact of such modifications.”

“the dy will come when, confronted w'da violent effects of climate change, we will seriously ponder resorting to geoengineering,” legras predicts. “hunga tonga provides us w'da opportunity to determine wha’ we can do and, above all, wha’ we must absolutely avoid doin’. theoretically, adding sulfate aerosols to the atmosphere ‘d cool the climate, b'that’s not at all the same thing as removin greenhouse gases. the best way to offset their impact is to reduce emissions.” 

original content at: news.cnrs.fr/essentialisms/learning-the-lessons-of-the-hunga-tonga-eruption…


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