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Shock waves, landslides may have caused 'rare' volcano tsunami: experts

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Agence France-Presse

<div class="embed-wrap"><figure data-feedback="fb:likes,fb:comments"><img alt="An eruption occurs at the underwater volcano Hunga Tonga-Hunga Ha" apai="" off="" January="" in="" this="" screen="" grab="" obtained="" from="" a="" social="" media="" video.="" Video="" recorded="" Tonga="" Geological="" Services="" via="" src="https://sa.kapamilya.com/absnews/abscbnnews/media/2022/reuters/01/18/tonga.jpg"/><figcaption>An eruption occurs at the underwater volcano Hunga Tonga-Hunga Ha&#x27;apai off Tonga, January 14, 2022 in this screen grab obtained from a social media video. Video recorded January 14, 2022. <em>Tonga Geological Services via Reuters</em></figcaption></figure></div><p>A rare volcano-triggered tsunami sparked by the eruption of Hunga Tonga-Hunga Ha&#x27;apai in Tonga could have been caused by shock waves or shifting underwater land, experts said Monday.</p><p>&quot;A volcanic-source tsunami event is rare but not unprecedented,&quot; a post on the website for New Zealand&#x27;s geological hazard monitoring system GNS said Monday.</p><p>GNS Tsunami Duty Officer Jonathan Hanson said it probably occurred in part thanks to a previous eruption of the same volcano one day earlier.</p><p>&quot;It is likely that the earlier 14 January eruption blew away part of the volcano above water, so water flowed into the extremely hot vent,&quot; wrote Hanson. </p><ul class="op-related-articles">	<li><a href="https://news.abs-cbn.com/overseas/01/18/22/tsunami-caused-by-tonga-volcano-eruption-stumps-experts">Tsunami caused by Tonga volcano eruption stumps Japan weather experts</a></li></ul><p>&quot;This meant that the Saturday evening eruption initially occurred underwater and exploded through the ocean, causing a widespread tsunami,&quot; he said.</p><ul class="op-related-articles">	<li><a href="https://news.abs-cbn.com/overseas/01/16/22/tonga-volcano-causes-significant-damage-but-no-deaths-ardern">Tonga volcano causes &#x27;significant&#x27; damage but no deaths: NZ prime minister</a></li></ul><p>Two days after Hunga Tonga-Hunga Ha&#x27;apai&#x27;s massive explosion, the nation&#x27;s 100,000 population remained virtually cut off from the rest of the world with crippled communications and stalled emergency relief efforts.</p><p>The volcano cloaked Tonga in a film of ash, sent a column of ash and gas 20 kilometers into the air and shock waves that could be seen from space rippling across the planet. </p><p>It also triggered a Pacific-wide tsunami whose waves were strong enough to drown two women in Peru more than 10,000 kilometers away.</p><div><strong>- Ring of Fire -</strong></div><p>Hunga Tonga-Hunga Ha&#x27;apai is located in the so-called Ring of Fire, where a rift between shifting tectonic plates results in increased seismic activity.</p><p>In a volcanic eruption, magma rising to the surface of the Earth&#x27;s crust causes volcanic gases to be released that then push their way out from underground, creating pressure.</p><p>When the gases reach water it expands into water vapor, creating even more pressure.</p><p>Volcano expert Ray Cas of Monash University in Australia said he suspected the intensity of the explosion suggested a large amount of gas had risen into the vent.</p><p>&quot;The tsunamis could have been triggered by shock waves propagating through water,&quot; he commented on the Australian Science Media Centre.</p><p>&quot;But more likely largely by a landslide on the submarine part of the volcanic edifice triggered by the explosive eruption.&quot;</p><p>Yet another possibility is that the volcano&#x27;s special location just beneath the surface of the ocean could have made its effects worse.</p><p>The volcano&#x27;s 1,800 meters of height is almost entirely submerged beneath the surface of the ocean, the edge of its crater forming an uninhabited island.</p><p>&quot;When eruptions happen deep in the ocean, the water tends to muffle the activity. When it happens in the air, the risks are concentrated to the immediate area,&quot; Paris-based geologist Raphael Grandin told AFP.</p><ul class="op-related-articles">	<li><a href="https://news.abs-cbn.com/overseas/01/16/22/tsunami-reaches-japan-3-meter-waves-possible-jma">Tsunami reaches Japan, 3-meter waves possible: meteorological agency</a></li></ul><p>&quot;But when it&#x27;s just under the surface, that&#x27;s when the tsunami risk is greatest,&quot; he said.</p><ul class="op-related-articles">	<li><a href="https://news.abs-cbn.com/overseas/01/16/22/volcano-triggers-tonga-tsunami-alerts-from-japan-to-us">Volcano triggers Tonga tsunami, alerts from Japan to US</a></li></ul><div><strong>- Exceptionally loud eruption -</strong></div><p>People are reported to have heard Hunga Tonga-Hunga Ha&#x27;apai&#x27;s eruption as far away as Alaska, 9,000 kilometers from the source, which Grandin said is &quot;exceptional&quot;.</p><p>&quot;As far as I know the last explosion that was audible at that distance was caused by the Krakatoa volcano in Indonesia in 1883 -- it killed 36,000 people,&quot; he said.</p><p>Experts also said that while the volcano could experience further activity, past research shows an eruption of Saturday&#x27;s scale probably only occurs every 1,000 years.</p><p>Scientists who commented on the phenomenon said they would know more about how it took place once communication with the Pacific nation of some 170 islands could be restored.</p><div><strong>RELATED VIDEO</strong></div><figure class="op-interactive"><iframe allow="autoplay; fullscreen" frameBorder="0" height="100%" id="ivsplayer01" scrolling="no" src="https://player.ivideosmart.com/ivsplayer/v4/dist/html/iframe-src.html?iframeid=ivsplayer01&amp;key=e8c22c015ca9eafa76f1e3edfa03c603&amp;spid=3001339&amp;vid=1896215" width="100%"></iframe></figure><div class="iwantbar">Watch more in <a href="//www.iwantv.com.ph/">iWantv</a> or <a href="//tfc.tv/">TFC.tv</a></div>

GNS Tsunami Duty Officer Jonathan Hanson said it probably occurred in part thanks to a previous eruption of the same volcano one day earlier.