Why was the tsunami not that bad? Ask Russia

By James C. Pearce

One of the strongest earthquakes ever recorded, it brought little damage. The catastrophe many feared would engulf the Pacific never came to be. The evacuations were, thankfully, an overreaction.

More unusually, the Russian press was straightforward and open with what had just occurred and The Kremlin likewise.

So what happened and is this so unusual?  The magnitude 8.8 quake struck at 8:24 a.m. local time off Petropavlovsk-Kamchatsky in the Kamchatka peninsula. It was one of the 10 largest ever recorded, according to the USGS.

The Kamchatka Peninsula is remote and sparsely populated, but it lies in the "Pacific ring of fire," consisting of Russia, Japan and China. It is called this because of the high number of earthquakes and volcanoes that occur in this ring region of the north Pacific (or Northeast Asia for our pedantic readers).

The quakes that do occur in Kamchatka are among the strongest in the world. Just off the coast of the Kamchatka Peninsula, the Pacific plate is moving northwest at about 8 cm (3 in) per year. This is only about twice the rate that human fingernails grow, but it is fast by tectonic standards. There, it comes into contact with another, smaller plate called the Okhotsk microplate.

The Pacific plate is oceanic, which means it has dense rocks and wants to sink beneath the less dense microplate. As the Pacific plate sinks toward the centre of the Earth, it heats up and begins to melt, effectively disappearing.

But this process is not always plain sailing. Often, the plates can get stuck as they move past each other, and the overriding plate is dragged downwards. This friction can build up over thousands of years, but can then be released in just a couple of minutes. This is known as a ‘megathrust earthquake’ and is exactly what happened.

When the quake hit, Russian authorities said a tsunami hit and flooded the port town of Severo-Kurilsk, while local media said a wave of between three and four meters high was recorded in the Elizovsky district of Kamchatka.

Videos posted on Russian social media appeared to show buildings in the town submerged in seawater.

One of the more popular images shown was that of a kindergarten building missing its facade, which had been completely ripped off. On top of that came a video of surgeons continuing to perform the surgery as the earthquake continued. The patient was unharmed, and the surgery was successful.

Authorities said the population of around 2,000 people was evacuated.

The quake injured several people in Russia, state media reported, but none of them seriously.

Authorities in Russia's Sakhalin region declared a state of emergency in the northern Kuril Islands, where tsunami waves have damaged buildings and caused flooding. The mayor of the islands said that "everyone" there had fled to safety.

Warnings of aftershocks of up to 7.5 magnitude were issued and at least six aftershocks further rattled the region, including one of 6.9 magnitude and another listed at 6.3. Kamchatka’s volcanoes began erupting soon after. First was the Klyuchevskoy volcano.

The volcano exhibited Strombolian activity, releasing ash and producing lava flows. Authorities warned that ash plumes may reach altitudes of up to 10 kilometres above sea level.

Other volcanoes in the region were also active. Shiveluch and Bezymianny were undergoing extrusive-explosive eruptions, with ash emissions of up to 8 km.

Karymsky continued its summit eruption, also with ash clouds potentially reaching up to 8 kilometres high. Increased seismic activity, suggesting a possible explosive eruption, with ash columns potentially rising as high as 6 kilometres.

Emergency responders issued a strong advisory, asking the public to avoid approaching within 10 kilometres of the summit areas of any of these volcanoes.

The earthquake's epicenter is roughly the same as the powerful 9.0 quake in 1952, which resulted in a destructive, Pacific-wide tsunami, according to the USGS. Why, then, were things not just as bad for the Pacific region despite all the warnings across five continents? 

The sudden movement of a megathrust earthquake can displace water above the plates, which can then travel to the coastline as a tsunami. In the deep ocean, a tsunami can travel at more than 500mph (800km/h), about as fast as a passenger airplane. Here, the distance between waves is very long and the waves aren't very high, rarely more than a metre.

Yet, as a tsunami enters shallow water near land, it slows down, often to about 20 to 30mph. The distance between waves shortens, and waves grow in height, which can effectively create a wall of water near the coast.

It is not guaranteed that a very strong earthquake will lead to a particularly tall tsunami reaching far inland and in this case, that is exactly what happened.

That may explain why the Russian press and Kremlin were quite open and forthcoming. Russia’s remotest region got the worst of it, and it was not all that bad. When the Kremlin has nothing to explain, it doesn’t bother trying.

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