Paris, Jan 17 (AFP\/APP):A rare volcano-triggered tsunami sparked by the eruption of Hunga Tonga-Hunga Ha’apai in Tonga could have been caused by shock waves or shifting underwater land, experts said Monday.<\/p>\n
“A volcanic-source tsunami event is rare but not unprecedented,” a post on the website for New Zealand’s geological hazard monitoring system GNS said Monday.<\/p>\n
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>\n
“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,” wrote Hanson.<\/p>\n
“This meant that the Saturday evening eruption initially occurred underwater and exploded through the ocean, causing a widespread tsunami,” he said.<\/p>\n
Two days after Hunga Tonga-Hunga Ha’apai’s massive explosion, the nation’s 100,000 population remained virtually cut off from the rest of the world with crippled communications and stalled emergency relief efforts.<\/p>\n
The volcano cloaked Tonga in a film of ash, sent a column of ash and gas 20 kilometres into the air and shock waves that could be seen from space rippling across the planet.<\/p>\n
It also triggered a Pacific-wide tsunami whose waves were strong enough to drown two women in Peru more than 10,000 kilometres (6,000 miles) away.<\/p>\n
– Ring of Fire –<\/p>\n
Hunga Tonga-Hunga Ha’apai is located in the so-called Ring of Fire, where a rift between shifting tectonic plates results in increased seismic activity.<\/p>\n
In a volcanic eruption, magma rising to the surface of the Earth’s crust causes volcanic gases to be released that then push their way out from underground, creating pressure.<\/p>\n
When the gases reach water it expands into water vapour, creating even more pressure.<\/p>\n
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>\n
“The tsunamis could have been triggered by shock waves propagating through water,” he commented on the Australian Science Media Centre.<\/p>\n
“But more likely largely by a landslide on the submarine part of the volcanic edifice triggered by the explosive eruption.”<\/p>\n
Yet another possibility is that the volcano’s special location just beneath the surface of the ocean could have made its effects worse.<\/p>\n
The volcano’s 1,800 metres of height is almost entirely submerged beneath the surface of the ocean, the edge of its crater forming an uninhabited island.<\/p>\n
“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,” Paris-based geologist Raphael Grandin told AFP.<\/p>\n
“But when it’s just under the surface, that’s when the tsunami risk is greatest,” he said.<\/p>\n
– Exceptionally loud eruption –<\/p>\n
People are reported to have heard Hunga Tonga-Hunga Ha’apai’s eruption as far away as Alaska, 9,000 kilometres from the source, which Grandin said is “exceptional”.<\/p>\n
“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,” he said.<\/p>\n
Experts also said that while the volcano could experience further activity, past research shows an eruption of Saturday’s scale probably only occurs every 1,000 years.<\/p>\n
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>\n","protected":false},"excerpt":{"rendered":"
Paris, Jan 17 (AFP\/APP):A rare volcano-triggered tsunami sparked by the eruption of Hunga Tonga-Hunga Ha’apai in Tonga could have been caused by shock waves or shifting underwater land, experts said Monday. “A volcanic-source tsunami event is rare but not unprecedented,” a post on the website […]<\/p>\n
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