- Visual Journalism Team
- BBC News
A massive eruption in Tonga on Saturday triggered a tsunami that spread across the Pacific in a matter of hours.
The waves hit Australia, New Zealand and Japan, as well as the west coast of North and South America.
An atmospheric shock wave has been detected around the world and a huge cloud of ash has covered the Pacific islands for thousands of kilometers.
Here’s what we know about why and how this ripple spread so widely and so violently.
Where is Tonga?
Tonga is made up of some 170 islands, many of them uninhabited, about 3,300 kilometers west of Australia.
The Hunga-Tonga-Hunga-Ha’apai volcano is located almost 65 kilometers from the capital.
On Saturday, the center of the volcano sank and disappeared into the sea.
Almost two hours later a devastating force occurred.
When the eruption was over, almost all of the volcano and the land around it had disappeared.
The eruption sent out a massive atmospheric shock wave, which traveled at 300 meters per second.
Changes in pressure were detected on the other side of the world, in Europe, 15 hours later.
The blast was heard across the Pacific, from Fiji to Alaska.
How fast did the tsunami spread?
Tsunami waves spread rapidly across the Pacific.
It took them less than 5 hours to get to New Zealand, and about 10 to get to Alaska.
Experts say the tsunami may have been caused by debris falling to the ocean floor and was driven by the pressure wave and its effect on the water surface.
The waves continued on Sunday and were still being reported in Australia on Monday.
Tsunami waves can be much more destructive than normal waves, even when they are not particularly high.
A normal wave can take 15 seconds to reach the shore and return to the sea.
Some of the tsunami waves in Australia were smaller than one meter but lasted almost 30 minutes.
They moved to the surface for 15 minutes, and it took another 15 minutes to come back up.
Why was the eruption so violent?
The exact reasons why this eruption was so violent are still being analyzed by experts.
Some believe that the speed with which the molten magma shot out of the volcano may have played a role.
When magma filled with volcanic gas is propelled through ocean water at high speeds, there is no chance for a layer of steam to cool it.
And this “fuel-coolant interaction” causes a massive chemical explosion, the researchers said.
Deeper waters may have suppressed it, but the volcano’s surface was only 150-200m underwater.
How is the situation on the ground at the moment?
Communications with Tonga have been largely destroyed, making it difficult to understand the scale of the damage.
Internet and phone communications are extremely limited and remote coastal areas are cut off.
The Red Cross said even satellite phones, which many aid agencies use, had poor reception from the ash cloud.
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The organization estimates that nearly 80,000 people may have been affected by the tsunami.
Dust from the volcano could contaminate water supplies, prompting locals to be warned to drink bottled water and wear masks.
The New Zealand government, which has been helping to establish the extent of the destruction, says the western coast of Tongatapu, Tonga’s main island, has suffered “significant damage”.
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Eddie is an Australian news reporter with over 9 years in the industry and has published on Forbes and tech crunch.